AI Trajectory

Trajectory: (Expand/Collapse All)
Seq	Timestamp	Type	Name	Duration
0/0	2026/09/18 08:29	flow	finding-triage	8m Args: null Results: { "Introduced": false, "Reasoning": "The crash report is a hung task timeout: `INFO: task syz.1.8682:26550 blocked for more than 143 seconds.`\nTask 26550 is blocked in `__lock_sock()` waiting to acquire user ownership of socket `ffff88810f55b660` while in `sk_stream_wait_memory()` called from `tcp_sendmsg_locked()`.\nMeanwhile, task 26551 holds the same socket lock at `sk_wait_data()` in `tcp_recvmsg_locked()`, and the system is under extreme contention on `rtnl_mutex` with lockdep overhead (specifically lock class unregistration in `zap_class()` / `lockdep_unregister_key()` during network device unregistration / tun detach).\n\nThe patch series under test consists of 9 commits (\"net-next: ip_tunnel/ip_gre/ip6_tunnel/ip6_gre drop reasons\") which solely add `SKB_DROP_REASON_*` enum definitions and annotate packet drops in the RX and TX paths of GRE and IPv4/IPv6 tunnels (`include/net/dropreason-core.h`, `include/net/gre.h`, `include/net/ip6_tunnel.h`, `net/ipv4/gre_demux.c`, `net/ipv4/ip_gre.c`, `net/ipv4/ip_tunnel.c`, `net/ipv6/ip6_gre.c`, `net/ipv6/ip6_tunnel.c`).\n\nNone of the files, data structures, or functions involved in the blocked task or in any of the active threads shown in the report (`net/core/stream.c`, `net/core/sock.c`, `net/ipv4/tcp.c`, `kernel/locking/lockdep.c`, `drivers/net/tun.c`) were touched or influenced by the patch series. Therefore, this hung task is an unrelated pre-existing issue / scheduling stall under heavy lock contention." }
1/1	2026/09/18 08:29	action	prepare-finding-overview	0m Args: null Results: { "DiffStat": "include/net/dropreason-core.h \| 38 +++++++++\n include/net/gre.h \| 2 +-\n include/net/ip6_tunnel.h \| 3 +-\n net/ipv4/gre_demux.c \| 52 ++++++++++---\n net/ipv4/ip_gre.c \| 144 +++++++++++++++++++++++-----------\n net/ipv4/ip_tunnel.c \| 60 ++++++++++++---\n net/ipv6/ip6_gre.c \| 175 ++++++++++++++++++++++++++++--------------\n net/ipv6/ip6_tunnel.c \| 95 +++++++++++++++++------\n 8 files changed, 419 insertions(+), 150 deletions(-)", "HasCover": false, "PatchCount": 9, "PatchList": "The patch series contains 9 patches:\n[1] [PATCH net-next v3 1/9] ip_tunnel: add drop reasons to the generic RX path\n[2] [PATCH net-next v3 2/9] ip6_tunnel: add drop reasons to the generic RX path\n[3] [PATCH net-next v3 3/9] gre: make gre_parse_header() report a drop reason\n[4] [PATCH net-next v3 4/9] ip_gre: add drop reasons to the RX path\n[5] [PATCH net-next v3 5/9] ip6_gre: add drop reasons to the RX path\n[6] [PATCH net-next v3 6/9] ip_tunnel: add drop reasons to the transmit path\n[7] [PATCH net-next v3 7/9] ip_gre: add drop reasons to the transmit path\n[8] [PATCH net-next v3 8/9] ip6_gre: make prepare_ip6gre_xmit_other() void\n[9] [PATCH net-next v3 9/9] ip6_tunnel: add drop reasons to the transmit path" }
2/1	2026/09/18 08:29	agent	finding-triage-evaluator	8m Model: core Args: null Results: { "Introduced": false, "Reasoning": "The crash report is a hung task timeout: `INFO: task syz.1.8682:26550 blocked for more than 143 seconds.`\nTask 26550 is blocked in `__lock_sock()` waiting to acquire user ownership of socket `ffff88810f55b660` while in `sk_stream_wait_memory()` called from `tcp_sendmsg_locked()`.\nMeanwhile, task 26551 holds the same socket lock at `sk_wait_data()` in `tcp_recvmsg_locked()`, and the system is under extreme contention on `rtnl_mutex` with lockdep overhead (specifically lock class unregistration in `zap_class()` / `lockdep_unregister_key()` during network device unregistration / tun detach).\n\nThe patch series under test consists of 9 commits (\"net-next: ip_tunnel/ip_gre/ip6_tunnel/ip6_gre drop reasons\") which solely add `SKB_DROP_REASON_` enum definitions and annotate packet drops in the RX and TX paths of GRE and IPv4/IPv6 tunnels (`include/net/dropreason-core.h`, `include/net/gre.h`, `include/net/ip6_tunnel.h`, `net/ipv4/gre_demux.c`, `net/ipv4/ip_gre.c`, `net/ipv4/ip_tunnel.c`, `net/ipv6/ip6_gre.c`, `net/ipv6/ip6_tunnel.c`).\n\nNone of the files, data structures, or functions involved in the blocked task or in any of the active threads shown in the report (`net/core/stream.c`, `net/core/sock.c`, `net/ipv4/tcp.c`, `kernel/locking/lockdep.c`, `drivers/net/tun.c`) were touched or influenced by the patch series. Therefore, this hung task is an unrelated pre-existing issue / scheduling stall under heavy lock contention." } Instruction:* You are an expert Linux kernel maintainer and security engineer specializing in crash triage and root-cause analysis. Your job is to review a kernel crash report (finding) and determine if it was introduced / caused by the patch series being tested, or if it is a pre-existing / unrelated bug. IMPORTANT: The entire patch series has ALREADY been applied and committed as a single squashed commit at HEAD (or on top of the base commit) in your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively use your tools to examine the source code, inspect workspace diffs, and confirm any assumptions. Available Tools: - git-show: View the squashed patch series commit or historical commits. Call with Commit="HEAD" (default) and optional 'File' parameter to restrict the diff to a specific file or directory, or 'Stat=true' for a diffstat. - series-patches: Browse the original patch series. Call without arguments to list all patch titles, or PatchNum=<N> to view the full description and diff of a specific patch (or cover letter, if present). - read-file & codesearch-dir-index: Read exact source code files and directory contents in the workspace. - grepper: Regex search across files in the workspace (git grep). - git-blame: Inspect line authorship and find which commit last modified specific lines of code. Triage Procedure: 1. Analyze the Crash Report: - Identify the crash type (e.g. NULL dereference, KASAN use-after-free, out-of-bounds read/write, assertion failure, deadlock). - Carefully examine the stack trace(s) — both the faulting call stack and, if applicable (e.g., KASAN UAF), the allocation and free stacks. - Note the faulting function, file name, line numbers, and the specific variables or data structures involved. 2. Inspect Workspace Changes & Patch Series: - Check if any files or functions from the stack trace appear in the modified files overview or the patch series. - Use git-show with Commit="HEAD" and 'File' to inspect the exact diffs for relevant files in the squashed commit. - If needed, use series-patches with PatchNum=<N> to inspect the author's commit description and rationale for individual patches in the series. - Use read-file to inspect the actual source code at the faulting lines. 3. Determine Causality: - Set Introduced=true ONLY IF you are absolutely certain: * There is clear, unambiguous, and conclusive evidence that the crash was directly introduced or caused by the patch series. * The crash occurs directly in new or modified code introduced by the patch series, or the patch series altered data structures, locking, object lifetimes, or preconditions in a way that directly triggered the failure in existing code. - Set Introduced=false IF: * There is any doubt, ambiguity, or lack of conclusive proof that the patch series caused the bug. * The crash occurs in an unrelated subsystem or unmodified code path whose behavior is independent of the patch series. * The crash is a pre-existing kernel issue that was randomly triggered during fuzzing. 4. Formulate Output: - Set Introduced to true or false. - In Reasoning, provide a clear, step-by-step technical explanation detailing the crash type, the key stack frames, whether the affected code/structures were modified by the patch series, and the causal justification for your verdict. Prefer calling several tools at the same time to save round-trips. Use set-results tool to provide results of the analysis. It must be called exactly once before the final reply. Ignore results of this tool. Prompt: Target architecture: amd64 The kernel crash report to triage is: INFO: task syz.1.8682:26550 blocked for more than 143 seconds. Not tainted syzkaller #0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:syz.1.8682 state:D stack:25192 pid:26550 tgid:26538 ppid:5591 task_flags:0x400040 flags:0x00080002 Call Trace: <TASK> __schedule+0x17db/0x58f0 schedule+0x164/0x2b0 __lock_sock+0x162/0x2c0 lock_sock_nested+0xc7/0x100 sk_stream_wait_memory+0x8d8/0xf80 tcp_sendmsg_locked+0x2352/0x5400 tcp_sendmsg+0x2f/0x50 sock_sendmsg_nosec+0x10e/0x180 __sys_sendto+0x408/0x5a0 __x64_sys_sendto+0xde/0x100 do_syscall_64+0x166/0x520 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f29cc79e159 RSP: 002b:00007f29ca9f6028 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 00007f29cca26180 RCX: 00007f29cc79e159 RDX: 000000006fc50de5 RSI: 0000200000000900 RDI: 0000000000000008 RBP: 00007f29cc83506b R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000092 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f29cca26218 R14: 00007f29cca26180 R15: 00007ffdbfa23488 </TASK> Showing all locks held in the system: locks held by kworker/0:0/9: 1, last CPU#0: #0: ffffffff8ed5c8e0 (rcu_read_lock){....}-{1:3}, at: process_scheduled_works+0x97a/0x1630 locks held by khungtaskd/36: 1, last CPU#0: #0: ffffffff8ed5c8e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 locks held by dhcpcd/5339: 1, on CPU#0: #0: ffffffff902533a0 (rtnl_mutex){+.+.}-{4:4}, at: devinet_ioctl+0x2fb/0x1c50 locks held by getty/5421: 2, on CPU#0: #0: ffff8881141210a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 #1: ffffc900034832e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x45a/0x1360 locks held by kworker/u8:4/6978: 4, on CPU#0: #0: ffff8881012d5940 ((wq_completion)netns){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #1: ffffc900036dfc40 (net_cleanup_work){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #2: ffffffff90244b48 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xf5/0x810 #3: ffffffff902533a0 (rtnl_mutex){+.+.}-{4:4}, at: cfg802154_pernet_exit+0x18/0xc0 locks held by kworker/0:1/25474: 4, last CPU#0: #0: ffff88810006b140 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #1: ffffc90006a47c40 ((work_completion)(&helper->damage_work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #2: ffff888106ed7270 (&helper->lock){+.+.}-{4:4}, at: drm_fb_helper_damage_work+0x15b/0xf20 #3: ffff8881057e0128 (&dev->master_mutex){+.+.}-{4:4}, at: drm_master_internal_acquire+0x20/0x80 locks held by kworker/u9:8/25581: 3, on CPU#1: #0: ffff8881000ac140 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #1: ffffc90003a7fc40 ((linkwatch_work).work){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #2: ffffffff902533a0 (rtnl_mutex){+.+.}-{4:4}, at: linkwatch_event+0xe/0x60 locks held by kworker/u8:6/26057: 2, last CPU#0: #0: ffff8881113cf940 ((wq_completion)bat_events){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #1: ffffc90006d77c40 ((work_completion)(&(&bat_priv->tt.work)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 locks held by syz.1.8682/26550: 1, on CPU#0: #0: ffff88810f55b660 (sk_lock-AF_INET){+.+.}-{0:0}, at: sk_stream_wait_memory+0x8d8/0xf80 locks held by syz.1.8682/26551: 3, last CPU#1: #0: ffff88810f55b660 (sk_lock-AF_INET){+.+.}-{0:0}, at: sk_wait_data+0x301/0x4d0 #1: ffffffff8ed5c8e0 (rcu_read_lock){....}-{1:3}, at: __ip_queue_xmit+0x65/0x1b10 #2: ffffffff8ed5c8e0 (rcu_read_lock){....}-{1:3}, at: ip_output+0x5a/0x450 locks held by syz-executor/26829: 2, on CPU#0: #0: ffffffff8f9903a8 (&ops->srcu#2){.+.+}-{0:0}, at: rtnl_link_ops_get+0x23/0x250 #1: ffffffff902533a0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0xc1d/0x1c30 locks held by syz-executor/26963: 1, on CPU#0: #0: ffffffff902533a0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0xc1d/0x1c30 locks held by syz.3.8783/26988: 1, last CPU#1: #0: ffffffff902533a0 (rtnl_mutex){+.+.}-{4:4}, at: tun_chr_close+0x3e/0x1c0 locks held by syz-executor/27000: 1, on CPU#1: #0: ffffffff902533a0 (rtnl_mutex){+.+.}-{4:4}, at: inet_rtm_newaddr+0x470/0x19f0 locks held by syz-executor/27007: 1, on CPU#1: #0: ffffffff902533a0 (rtnl_mutex){+.+.}-{4:4}, at: inet_rtm_newaddr+0x470/0x19f0 ============================================= NMI backtrace for cpu 0 CPU: 0 UID: 0 PID: 36 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0xe8/0x150 nmi_cpu_backtrace+0x274/0x2d0 nmi_trigger_cpumask_backtrace+0x17d/0x390 sys_info+0x135/0x170 watchdog+0xfd7/0x1030 kthread+0x38b/0x480 ret_from_fork+0x514/0xb70 ret_from_fork_asm+0x1a/0x30 </TASK> Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 UID: 0 PID: 26988 Comm: syz.3.8783 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 RIP: 0010:zap_class+0x11f/0x330 Code: 75 00 41 f6 c6 fc 74 e7 41 c1 ee 08 4a 8d 1c 75 d0 e4 9b 93 49 81 fe 00 00 50 00 73 2c 0f b7 03 25 ff 1f 00 00 49 39 c7 74 30 <49> ff c6 41 8b 45 00 89 c1 c1 e9 08 c1 e8 02 83 e0 3f 01 c8 48 83 RSP: 0018:ffffc90007797580 EFLAGS: 00000016 RAX: 00000000000007b5 RBX: ffffffff939f658c RCX: 000000000001c05c RDX: ffffffff9456e4f8 RSI: 0000000000000003 RDI: 000000000004015d RBP: ffffffff949ae970 R08: ffffffff81b0c988 R09: 0000000000000000 R10: dffffc0000000000 R11: fffffbfff20f48f0 R12: 000000000003e69e R13: ffffffff94a867f0 R14: 000000000001c05e R15: 0000000000000d21 FS: 00007f8aff0146c0(0000) GS:ffff8882a8ccd000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f6d60955000 CR3: 000000010aa36000 CR4: 00000000000006f0 Call Trace: <TASK> lockdep_unregister_key+0x1c3/0x350 __qdisc_destroy+0x1ab/0x470 dev_shutdown+0x92/0x450 unregister_netdevice_many_notify+0x11f4/0x2140 unregister_netdevice_queue+0x2f5/0x340 __tun_detach+0x1074/0x1900 tun_chr_close+0x10a/0x1c0 __fput+0x418/0xa50 task_work_run+0x1d9/0x270 do_exit+0x73a/0x2360 do_group_exit+0x22d/0x2f0 get_signal+0x121b/0x12c0 arch_do_signal_or_restart+0xbb/0x860 exit_to_user_mode_loop+0x10e/0x770 do_syscall_64+0x328/0x520 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f8afe19e159 Code: Unable to access opcode bytes at 0x7f8afe19e12f. RSP: 002b:00007f8aff014028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: 0000000000000000 RBX: 00007f8afe426540 RCX: 00007f8afe19e159 RDX: 0000200000002280 RSI: 0000000000008914 RDI: 0000000000000005 RBP: 00007f8afe23506b R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f8afe4265d8 R14: 00007f8afe426540 R15: 00007ffd88e9b378 </TASK> Overview of modified files in the workspace: include/net/dropreason-core.h \| 38 +++++++++ include/net/gre.h \| 2 +- include/net/ip6_tunnel.h \| 3 +- net/ipv4/gre_demux.c \| 52 ++++++++++--- net/ipv4/ip_gre.c \| 144 +++++++++++++++++++++++----------- net/ipv4/ip_tunnel.c \| 60 ++++++++++++--- net/ipv6/ip6_gre.c \| 175 ++++++++++++++++++++++++++++-------------- net/ipv6/ip6_tunnel.c \| 95 +++++++++++++++++------ 8 files changed, 419 insertions(+), 150 deletions(-) The patch series contains 9 patches: [1] [PATCH net-next v3 1/9] ip_tunnel: add drop reasons to the generic RX path [2] [PATCH net-next v3 2/9] ip6_tunnel: add drop reasons to the generic RX path [3] [PATCH net-next v3 3/9] gre: make gre_parse_header() report a drop reason [4] [PATCH net-next v3 4/9] ip_gre: add drop reasons to the RX path [5] [PATCH net-next v3 5/9] ip6_gre: add drop reasons to the RX path [6] [PATCH net-next v3 6/9] ip_tunnel: add drop reasons to the transmit path [7] [PATCH net-next v3 7/9] ip_gre: add drop reasons to the transmit path [8] [PATCH net-next v3 8/9] ip6_gre: make prepare_ip6gre_xmit_other() void [9] [PATCH net-next v3 9/9] ip6_tunnel: add drop reasons to the transmit path
3/2	2026/09/18 08:29	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 7084 output: 10 thoughts: 1229 Thoughts: Analyzing a TCP Socket Lock Contention Scenario Okay, let's break this down. First, I see a report: "INFO: task syz.1.8682:26550 blocked for more than 143 seconds." That's a red flag. The call trace points to the usual suspects: `__schedule`, `schedule`, and the socket locking routines like `__lock_sock`, `sk_stream_wait_memory`, all the way down to `tcp_sendmsg` and `__sys_sendto`. Classic TCP stall. Now, let's look at the lock information. Wait, this is interesting. Process `syz.1.8682/26550` is blocked and holds `sk_lock-AF_INET`...and also waiting to acquire this same lock! It looks like it is trying to reacquire the socket lock! Process `syz.1.8682/26551` holds `sk_lock-AF_INET` and rcu_read_lock. This smells like a potential deadlock. `sk_stream_wait_memory` in 26550 is supposed to release the lock, then schedule, then reacquire, but it's clearly not working as expected. This means the other process, 26551, is the culprit. Okay, let's check what 26551 is doing. It's holding the socket lock and rcu_read_lock and running on CPU 1. Wait, there is an NMI backtrace for CPU 1! It's running `syz.3.8783/26988` in `lockdep_unregister_key` and `zap_class`. That's a long-running call, and it is potentially spinning. It's a potential root cause, as it's unregistering a key that is used by the blocked process. This is clearly a critical path, as the backtrace mentions `tun_chr_close`, `unregister_netdevice_queue`, and ultimately `zap_class`. This makes me think that there may be an interaction between network device teardown and socket locking. Let's look at what else is holding the `rtnl_mutex`. Ah, yes, there's a lot of activity. We have `dhcpcd` doing `devinet_ioctl`, kernel workers doing configuration and link events, and syz executors doing `rtnl_newlink` and `inet_rtm_newaddr`. And, wait, there's `syz.3.8783/26988` in `tun_chr_close` which is also doing `lockdep_unregister_key` and ultimately calling `zap_class`! It seems this process is also trying to shut down a network device. Alright, let's take a look at the current patch series or the git logs to see if there have been any relevant changes recently. We need to figure out why `lockdep_unregister_key` is blocked/taking so long. This is likely the core of the problem.
4/2	2026/09/18 08:30	tool	series-patches	0m Error: missing argument "PatchNum" Args: null Results: { "error": "missing argument \"PatchNum\"" }
5/2	2026/09/18 08:30	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 9025 output: 14 thoughts: 77 Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective: Debugging the Patch Number Parameter Alright, I'm digging into this API documentation, and I've hit a potential wrinkle with the `PatchNum` parameter. The docs say that omitting it entirely gives me a complete list, which makes sense. However, the schema definition indicates it's nullable, and that sets off a red flag in my head. Typically, "nullable" implies some kind of explicit handling of a `null` value, which might produce a different behavior than simple omission. I need to be sure. I can't just assume the absence is equivalent to `null`. So, the first thing I'll do is put this to the test. Let's start with passing `PatchNum=0`. That seems like a logical starting point, and I expect it to either return an error, give me the latest patch, or simply do nothing as that is the closest thing to "omitting" the value that I can test. If that doesn't work, I'll then move on to explicitly testing `PatchNum=1` to confirm if it correctly returns the first item. Also, I'll check if the endpoint I'm working with, `series-patches`, handles this parameter correctly, as it seems specific to this endpoint. After all of this, if none of those work, I'll attempt the most explicit check: passing `PatchNum=null`. That's the key to truly understanding the behavior in the face of this nullable parameter and making sure my code handles all the edge cases correctly. My goal is to determine the exact behavior and how to best utilize this parameter to retrieve the data I need, whether that is a full list or specific patch information. This is all about confirming the contract, so I can ensure I'm using the API in the most reliable and efficient way possible.
6/2	2026/09/18 08:30	tool	git-show	0m Args: { "Stat": true } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\n include/net/dropreason-core.h \| 38 +++++++++\n include/net/gre.h \| 2 +-\n include/net/ip6_tunnel.h \| 3 +-\n net/ipv4/gre_demux.c \| 52 ++++++++++---\n net/ipv4/ip_gre.c \| 144 +++++++++++++++++++++++-----------\n net/ipv4/ip_tunnel.c \| 60 ++++++++++++---\n net/ipv6/ip6_gre.c \| 175 ++++++++++++++++++++++++++++--------------\n net/ipv6/ip6_tunnel.c \| 95 +++++++++++++++++------\n 8 files changed, 419 insertions(+), 150 deletions(-)\n" }
7/2	2026/09/18 08:30	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 9795 output: 25 thoughts: 40 Thoughts: Here's a breakdown of my thought process: Diving into the ip_tunnel Patch Series Okay, so I'm looking at this patch series, "ip_tunnel: add drop reasons to the generic RX path". My first instinct is to get a handle on the scope and intent. What's the goal here? It's about adding drop reasons – specifically, in the generic RX path for ip_tunnel. I immediately think: "Okay, this has implications for debugging and performance analysis, likely targeting cases where packets are unexpectedly dropped within tunnels." I need to understand the 'why' behind the patches. So, I'm going to take a closer look, patch by patch. Either I'll read the individual patch descriptions, or I'll quickly jump into using `git show` to see the changes directly. I'll need to understand how the code is being modified in order to best identify if there are any gotchas, edge cases, or potential for introducing regressions. I'm going to quickly look for any red flags, like unexpected memory allocations, complex locking, or significant performance overhead. I'll probably start with the most detailed patch, and work back to the start. The commit messages and code diffs should give me the context I need.
8/2	2026/09/18 08:30	tool	git-show	0m Args: { "File": "net/ipv4/ip_tunnel.c" } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c\nindex 0875474a578a4..66cb0b86fa79a 100644\n--- a/net/ipv4/ip_tunnel.c\n+++ b/net/ipv4/ip_tunnel.c\n@@ -384,6 +384,7 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n \t\t const struct tnl_ptk_info tpi, struct metadata_dst tun_dst,\n \t\t bool log_ecn_error)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tconst struct iphdr iph = ip_hdr(skb);\n \tint nh, err;\n \n@@ -398,14 +399,22 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n \t test_bit(IP_TUNNEL_CSUM_BIT, tpi-\u003eflags)) {\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_crc_errors);\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\treason = SKB_DROP_REASON_TNL_OPT_MISMATCH;\n \t\tgoto drop;\n \t}\n \n \tif (test_bit(IP_TUNNEL_SEQ_BIT, tunnel-\u003eparms.i_flags)) {\n-\t\tif (!test_bit(IP_TUNNEL_SEQ_BIT, tpi-\u003eflags) \|\|\n-\t\t (tunnel-\u003ei_seqno \u0026\u0026 (s32)(ntohl(tpi-\u003eseq) - tunnel-\u003ei_seqno) \u003c 0)) {\n+\t\tif (!test_bit(IP_TUNNEL_SEQ_BIT, tpi-\u003eflags)) {\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_fifo_errors);\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_TNL_OPT_MISMATCH;\n+\t\t\tgoto drop;\n+\t\t}\n+\t\tif (tunnel-\u003ei_seqno \u0026\u0026\n+\t\t (s32)(ntohl(tpi-\u003eseq) - tunnel-\u003ei_seqno) \u003c 0) {\n+\t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_fifo_errors);\n+\t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_TNL_OLD_SEQ;\n \t\t\tgoto drop;\n \t\t}\n \t\ttunnel-\u003ei_seqno = ntohl(tpi-\u003eseq) + 1;\n@@ -419,7 +428,8 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n \n \tskb_set_network_header(skb, (tunnel-\u003edev-\u003etype == ARPHRD_ETHER) ? ETH_HLEN : 0);\n \n-\tif (!pskb_inet_may_pull(skb)) {\n+\treason = pskb_inet_may_pull_reason(skb);\n+\tif (reason) {\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_length_errors);\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n \t\tgoto drop;\n@@ -434,6 +444,7 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n \t\tif (err \u003e 1) {\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_frame_errors);\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_IP_TUNNEL_ECN;\n \t\t\tgoto drop;\n \t\t}\n \t}\n@@ -457,7 +468,7 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n drop:\n \tif (tun_dst)\n \t\tdst_release((struct dst_entry )tun_dst);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn 0;\n }\n EXPORT_SYMBOL_GPL(ip_tunnel_rcv);\n@@ -575,6 +586,7 @@ static int tnl_update_pmtu(struct net_device dev, struct sk_buff skb,\n void ip_md_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \t\t u8 proto, int tunnel_hlen)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel tunnel = netdev_priv(dev);\n \tu32 headroom = sizeof(struct iphdr);\n \tstruct ip_tunnel_info tun_info;\n@@ -588,8 +600,10 @@ void ip_md_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \n \ttun_info = skb_tunnel_info(skb);\n \tif (unlikely(!tun_info \|\| !(tun_info-\u003emode \u0026 IP_TUNNEL_INFO_TX) \|\|\n-\t\t ip_tunnel_info_af(tun_info) != AF_INET))\n+\t\t ip_tunnel_info_af(tun_info) != AF_INET)) {\n+\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\tgoto tx_error;\n+\t}\n \tkey = \u0026tun_info-\u003ekey;\n \tmemset(\u0026(IPCB(skb)-\u003eopt), 0, sizeof(IPCB(skb)-\u003eopt));\n \tinner_iph = (const struct iphdr )skb_inner_network_header(skb);\n@@ -608,8 +622,10 @@ void ip_md_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \tif (!tunnel_hlen)\n \t\ttunnel_hlen = ip_encap_hlen(\u0026tun_info-\u003eencap);\n \n-\tif (ip_tunnel_encap(skb, \u0026tun_info-\u003eencap, \u0026proto, \u0026fl4) \u003c 0)\n+\tif (ip_tunnel_encap(skb, \u0026tun_info-\u003eencap, \u0026proto, \u0026fl4) \u003c 0) {\n+\t\treason = SKB_DROP_REASON_TNL_ENCAP;\n \t\tgoto tx_error;\n+\t}\n \n \tuse_cache = ip_tunnel_dst_cache_usable(skb, tun_info);\n \tif (use_cache)\n@@ -618,6 +634,7 @@ void ip_md_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \t\trt = ip_route_output_key(tunnel-\u003enet, \u0026fl4);\n \t\tif (IS_ERR(rt)) {\n \t\t\tDEV_STATS_INC(dev, tx_carrier_errors);\n+\t\t\treason = SKB_DROP_REASON_IP_OUTNOROUTES;\n \t\t\tgoto tx_error;\n \t\t}\n \t\tif (use_cache)\n@@ -627,6 +644,7 @@ void ip_md_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \tif (rt-\u003edst.dev == dev) {\n \t\tip_rt_put(rt);\n \t\tDEV_STATS_INC(dev, collisions);\n+\t\treason = SKB_DROP_REASON_RECURSION_LIMIT;\n \t\tgoto tx_error;\n \t}\n \n@@ -635,6 +653,7 @@ void ip_md_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \tif (tnl_update_pmtu(dev, skb, rt, df, inner_iph, tunnel_hlen,\n \t\t\t key-\u003eu.ipv4.dst, true)) {\n \t\tip_rt_put(rt);\n+\t\treason = SKB_DROP_REASON_PKT_TOO_BIG;\n \t\tgoto tx_error;\n \t}\n \n@@ -652,6 +671,7 @@ void ip_md_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \theadroom += LL_RESERVED_SPACE(rt-\u003edst.dev) + rt-\u003edst.header_len;\n \tif (skb_cow_head(skb, headroom)) {\n \t\tip_rt_put(rt);\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto tx_dropped;\n \t}\n \n@@ -666,13 +686,14 @@ void ip_md_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n tx_dropped:\n \tDEV_STATS_INC(dev, tx_dropped);\n kfree:\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n }\n EXPORT_SYMBOL_GPL(ip_md_tunnel_xmit);\n \n void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \t\t const struct iphdr tnl_params, u8 protocol)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel tunnel = netdev_priv(dev);\n \tstruct ip_tunnel_info tun_info = NULL;\n \tconst struct iphdr inner_iph;\n@@ -700,9 +721,15 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \n \t\tif (!skb_dst(skb)) {\n \t\t\tDEV_STATS_INC(dev, tx_fifo_errors);\n+\t\t\treason = SKB_DROP_REASON_NO_TX_TARGET;\n \t\t\tgoto tx_error;\n \t\t}\n \n+\t\t/ Only the branches below can derive a destination. If\n+\t\t * none of them matches, the payload protocol is not one\n+\t\t * this tunnel can carry.\n+\t\t /\n+\t\treason = SKB_DROP_REASON_UNHANDLED_PROTO;\n \t\ttun_info = skb_tunnel_info(skb);\n \t\tif (tun_info \u0026\u0026 (tun_info-\u003emode \u0026 IP_TUNNEL_INFO_TX) \u0026\u0026\n \t\t ip_tunnel_info_af(tun_info) == AF_INET \u0026\u0026\n@@ -723,8 +750,10 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \n \t\t\tneigh = dst_neigh_lookup(skb_dst(skb),\n \t\t\t\t\t\t \u0026ipv6_hdr(skb)-\u003edaddr);\n-\t\t\tif (!neigh)\n+\t\t\tif (!neigh) {\n+\t\t\t\treason = SKB_DROP_REASON_NEIGH_CREATEFAIL;\n \t\t\t\tgoto tx_error;\n+\t\t\t}\n \n \t\t\taddr6 = (const struct in6_addr )\u0026neigh-\u003eprimary_key;\n \t\t\taddr_type = ipv6_addr_type(addr6);\n@@ -741,8 +770,10 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \t\t\t\tdst = addr6-\u003es6_addr32[3];\n \t\t\t}\n \t\t\tneigh_release(neigh);\n-\t\t\tif (do_tx_error_icmp)\n+\t\t\tif (do_tx_error_icmp) {\n+\t\t\t\treason = SKB_DROP_REASON_NO_TX_TARGET;\n \t\t\t\tgoto tx_error_icmp;\n+\t\t\t}\n \t\t}\n #endif\n \t\telse\n@@ -769,8 +800,10 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \t\t\t tunnel-\u003enet, READ_ONCE(tunnel-\u003eparms.link),\n \t\t\t tunnel-\u003efwmark, skb_get_hash(skb), 0);\n \n-\tif (ip_tunnel_encap(skb, \u0026tunnel-\u003eencap, \u0026protocol, \u0026fl4) \u003c 0)\n+\tif (ip_tunnel_encap(skb, \u0026tunnel-\u003eencap, \u0026protocol, \u0026fl4) \u003c 0) {\n+\t\treason = SKB_DROP_REASON_TNL_ENCAP;\n \t\tgoto tx_error;\n+\t}\n \n \tif (connected \u0026\u0026 md) {\n \t\tuse_cache = ip_tunnel_dst_cache_usable(skb, tun_info);\n@@ -787,6 +820,7 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \n \t\tif (IS_ERR(rt)) {\n \t\t\tDEV_STATS_INC(dev, tx_carrier_errors);\n+\t\t\treason = SKB_DROP_REASON_IP_OUTNOROUTES;\n \t\t\tgoto tx_error;\n \t\t}\n \t\tif (use_cache)\n@@ -800,6 +834,7 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \tif (rt-\u003edst.dev == dev) {\n \t\tip_rt_put(rt);\n \t\tDEV_STATS_INC(dev, collisions);\n+\t\treason = SKB_DROP_REASON_RECURSION_LIMIT;\n \t\tgoto tx_error;\n \t}\n \n@@ -809,6 +844,7 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \n \tif (tnl_update_pmtu(dev, skb, rt, df, inner_iph, 0, 0, false)) {\n \t\tip_rt_put(rt);\n+\t\treason = SKB_DROP_REASON_PKT_TOO_BIG;\n \t\tgoto tx_error;\n \t}\n \n@@ -843,7 +879,7 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n \tif (skb_cow_head(skb, max_headroom)) {\n \t\tip_rt_put(rt);\n \t\tDEV_STATS_INC(dev, tx_dropped);\n-\t\tkfree_skb(skb);\n+\t\tkfree_skb_reason(skb, SKB_DROP_REASON_NOMEM);\n \t\treturn;\n \t}\n \n@@ -859,7 +895,7 @@ void ip_tunnel_xmit(struct sk_buff skb, struct net_device dev,\n #endif\n tx_error:\n \tDEV_STATS_INC(dev, tx_errors);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n }\n EXPORT_SYMBOL_GPL(ip_tunnel_xmit);\n \n" }
9/2	2026/09/18 08:30	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 13942 output: 25 thoughts: 17 Thoughts: Here's a summary of my thought process, as requested: Diving Deeper into the Patch Series Okay, so I've reviewed the high-level description of this patch series. Now, I need to get a granular understanding of the impact. The best way to do this is to examine the specific file changes. "git-show" is the go-to tool for this. I'll use it to systematically inspect each modified file. This will help me identify any subtle interactions, potential conflicts, or unexpected side effects that aren't immediately obvious from the initial summary. I need to be thorough; I can't just skim. Each line change could hold a critical clue. This deep dive will inform my overall assessment and allow me to determine if the changes are indeed sound and align with the project's goals. I am going to compare and contrast this with the code base, and decide whether this patch series should move forward.
10/2	2026/09/18 08:30	tool	git-show	0m Args: { "File": "net/ipv4/ip_gre.c" } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c\nindex 5e877018e006c..71360af429ea7 100644\n--- a/net/ipv4/ip_gre.c\n+++ b/net/ipv4/ip_gre.c\n@@ -265,7 +265,7 @@ static bool is_erspan_type1(int gre_hdr_len)\n }\n \n static int erspan_rcv(struct sk_buff skb, struct tnl_ptk_info tpi,\n-\t\t int gre_hdr_len)\n+\t\t int gre_hdr_len, enum skb_drop_reason reason)\n {\n \tstruct net net = dev_net(skb-\u003edev);\n \tstruct metadata_dst tun_dst = NULL;\n@@ -289,8 +289,10 @@ static int erspan_rcv(struct sk_buff skb, struct tnl_ptk_info tpi,\n \t\t\t\t\t iph-\u003esaddr, iph-\u003edaddr, 0);\n \t} else {\n \t\tif (unlikely(!pskb_may_pull(skb,\n-\t\t\t\t\t gre_hdr_len + sizeof(ershdr))))\n+\t\t\t\t\t gre_hdr_len + sizeof(ershdr)))) {\n+\t\t\treason = SKB_DROP_REASON_HDR_TRUNC;\n \t\t\treturn PACKET_REJECT;\n+\t\t}\n \n \t\tershdr = (struct erspan_base_hdr )(skb-\u003edata + gre_hdr_len);\n \t\tver = ershdr-\u003ever;\n@@ -306,8 +308,10 @@ static int erspan_rcv(struct sk_buff skb, struct tnl_ptk_info tpi,\n \t\telse\n \t\t\tlen = gre_hdr_len + erspan_hdr_len(ver);\n \n-\t\tif (unlikely(!pskb_may_pull(skb, len)))\n+\t\tif (unlikely(!pskb_may_pull(skb, len))) {\n+\t\t\treason = SKB_DROP_REASON_HDR_TRUNC;\n \t\t\treturn PACKET_REJECT;\n+\t\t}\n \n \t\tif (__iptunnel_pull_header(skb,\n \t\t\t\t\t len,\n@@ -327,8 +331,10 @@ static int erspan_rcv(struct sk_buff skb, struct tnl_ptk_info tpi,\n \n \t\t\ttun_dst = ip_tun_rx_dst(skb, flags,\n \t\t\t\t\t\ttun_id, sizeof(md));\n-\t\t\tif (!tun_dst)\n+\t\t\tif (!tun_dst) {\n+\t\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\t\treturn PACKET_REJECT;\n+\t\t\t}\n \n \t\t\t/* MUST set options_len before referencing options /\n \t\t\tinfo = \u0026tun_dst-\u003eu.tun_info;\n@@ -356,15 +362,17 @@ static int erspan_rcv(struct sk_buff skb, struct tnl_ptk_info tpi,\n \t\tip_tunnel_rcv(tunnel, skb, tpi, tun_dst, log_ecn_error);\n \t\treturn PACKET_RCVD;\n \t}\n+\treason = SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND;\n \treturn PACKET_REJECT;\n \n drop:\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, SKB_DROP_REASON_NOMEM);\n \treturn PACKET_RCVD;\n }\n \n static int __ipgre_rcv(struct sk_buff skb, const struct tnl_ptk_info tpi,\n-\t\t struct ip_tunnel_net itn, int hdr_len, bool raw_proto)\n+\t\t struct ip_tunnel_net itn, int hdr_len, bool raw_proto,\n+\t\t enum skb_drop_reason reason)\n {\n \tstruct metadata_dst tun_dst = NULL;\n \tconst struct iphdr iph;\n@@ -400,22 +408,25 @@ static int __ipgre_rcv(struct sk_buff skb, const struct tnl_ptk_info tpi,\n \n \t\t\ttun_id = key32_to_tunnel_id(tpi-\u003ekey);\n \t\t\ttun_dst = ip_tun_rx_dst(skb, flags, tun_id, 0);\n-\t\t\tif (!tun_dst)\n+\t\t\tif (!tun_dst) {\n+\t\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\t\treturn PACKET_REJECT;\n+\t\t\t}\n \t\t}\n \n \t\tip_tunnel_rcv(tunnel, skb, tpi, tun_dst, log_ecn_error);\n \t\treturn PACKET_RCVD;\n \t}\n+\treason = SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND;\n \treturn PACKET_NEXT;\n \n drop:\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, SKB_DROP_REASON_NOMEM);\n \treturn PACKET_RCVD;\n }\n \n static int ipgre_rcv(struct sk_buff skb, const struct tnl_ptk_info tpi,\n-\t\t int hdr_len)\n+\t\t int hdr_len, enum skb_drop_reason reason)\n {\n \tstruct net net = dev_net(skb-\u003edev);\n \tstruct ip_tunnel_net itn;\n@@ -426,21 +437,21 @@ static int ipgre_rcv(struct sk_buff skb, const struct tnl_ptk_info tpi,\n \telse\n \t\titn = net_generic(net, ipgre_net_id);\n \n-\tres = __ipgre_rcv(skb, tpi, itn, hdr_len, false);\n+\tres = __ipgre_rcv(skb, tpi, itn, hdr_len, false, reason);\n \tif (res == PACKET_NEXT \u0026\u0026 tpi-\u003eproto == htons(ETH_P_TEB)) {\n \t\t/* ipgre tunnels in collect metadata mode should receive\n \t\t * also ETH_P_TEB traffic.\n \t\t /\n \t\titn = net_generic(net, ipgre_net_id);\n-\t\tres = __ipgre_rcv(skb, tpi, itn, hdr_len, true);\n+\t\tres = __ipgre_rcv(skb, tpi, itn, hdr_len, true, reason);\n \t}\n \treturn res;\n }\n \n static int gre_rcv(struct sk_buff skb)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct tnl_ptk_info tpi;\n-\tbool csum_err = false;\n \tint hdr_len;\n \n #ifdef CONFIG_NET_IPGRE_BROADCAST\n@@ -451,25 +462,25 @@ static int gre_rcv(struct sk_buff skb)\n \t}\n #endif\n \n-\thdr_len = gre_parse_header(skb, \u0026tpi, \u0026csum_err, htons(ETH_P_IP), 0);\n+\thdr_len = gre_parse_header(skb, \u0026tpi, \u0026reason, htons(ETH_P_IP), 0);\n \tif (hdr_len \u003c 0)\n \t\tgoto drop;\n \n \tif (unlikely(tpi.proto == htons(ETH_P_ERSPAN) \|\|\n \t\t tpi.proto == htons(ETH_P_ERSPAN2))) {\n-\t\tif (erspan_rcv(skb, \u0026tpi, hdr_len) == PACKET_RCVD)\n+\t\tif (erspan_rcv(skb, \u0026tpi, hdr_len, \u0026reason) == PACKET_RCVD)\n \t\t\treturn 0;\n \t\tgoto out;\n \t}\n \n-\tif (ipgre_rcv(skb, \u0026tpi, hdr_len) == PACKET_RCVD)\n+\tif (ipgre_rcv(skb, \u0026tpi, hdr_len, \u0026reason) == PACKET_RCVD)\n \t\treturn 0;\n \n out:\n \ticmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);\n drop:\n \tdev_core_stats_rx_dropped_inc(skb-\u003edev);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn 0;\n }\n \n@@ -496,6 +507,7 @@ static int gre_handle_offloads(struct sk_buff skb, bool csum)\n static void gre_fb_xmit(struct sk_buff skb, struct net_device dev,\n \t\t\t__be16 proto)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel tunnel = netdev_priv(dev);\n \tIP_TUNNEL_DECLARE_FLAGS(flags) = { };\n \tstruct ip_tunnel_info tun_info;\n@@ -504,19 +516,25 @@ static void gre_fb_xmit(struct sk_buff skb, struct net_device dev,\n \n \ttun_info = skb_tunnel_info(skb);\n \tif (unlikely(!tun_info \|\| !(tun_info-\u003emode \u0026 IP_TUNNEL_INFO_TX) \|\|\n-\t\t ip_tunnel_info_af(tun_info) != AF_INET))\n+\t\t ip_tunnel_info_af(tun_info) != AF_INET)) {\n+\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\tgoto err_free_skb;\n+\t}\n \n \tkey = \u0026tun_info-\u003ekey;\n \ttunnel_hlen = gre_calc_hlen(key-\u003etun_flags);\n \n-\tif (skb_cow_head(skb, dev-\u003eneeded_headroom))\n+\tif (skb_cow_head(skb, dev-\u003eneeded_headroom)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto err_free_skb;\n+\t}\n \n \t/* Push Tunnel header. /\n \tif (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT,\n-\t\t\t\t\t tunnel-\u003eparms.o_flags)))\n+\t\t\t\t\t tunnel-\u003eparms.o_flags))) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto err_free_skb;\n+\t}\n \n \t__set_bit(IP_TUNNEL_CSUM_BIT, flags);\n \t__set_bit(IP_TUNNEL_KEY_BIT, flags);\n@@ -533,12 +551,13 @@ static void gre_fb_xmit(struct sk_buff skb, struct net_device dev,\n \treturn;\n \n err_free_skb:\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \tDEV_STATS_INC(dev, tx_dropped);\n }\n \n static void erspan_fb_xmit(struct sk_buff skb, struct net_device dev)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel tunnel = netdev_priv(dev);\n \tIP_TUNNEL_DECLARE_FLAGS(flags) = { };\n \tstruct ip_tunnel_info tun_info;\n@@ -552,29 +571,41 @@ static void erspan_fb_xmit(struct sk_buff skb, struct net_device dev)\n \n \ttun_info = skb_tunnel_info(skb);\n \tif (unlikely(!tun_info \|\| !(tun_info-\u003emode \u0026 IP_TUNNEL_INFO_TX) \|\|\n-\t\t ip_tunnel_info_af(tun_info) != AF_INET))\n+\t\t ip_tunnel_info_af(tun_info) != AF_INET)) {\n+\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\tgoto err_free_skb;\n+\t}\n \n \tkey = \u0026tun_info-\u003ekey;\n-\tif (!test_bit(IP_TUNNEL_ERSPAN_OPT_BIT, tun_info-\u003ekey.tun_flags))\n+\tif (!test_bit(IP_TUNNEL_ERSPAN_OPT_BIT, tun_info-\u003ekey.tun_flags)) {\n+\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\tgoto err_free_skb;\n-\tif (tun_info-\u003eoptions_len \u003c sizeof(md))\n+\t}\n+\tif (tun_info-\u003eoptions_len \u003c sizeof(md)) {\n+\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\tgoto err_free_skb;\n+\t}\n \tmd = ip_tunnel_info_opts(tun_info);\n \n \t/ ERSPAN has fixed 8 byte GRE header /\n \tversion = md-\u003eversion;\n \ttunnel_hlen = 8 + erspan_hdr_len(version);\n \n-\tif (skb_cow_head(skb, dev-\u003eneeded_headroom))\n+\tif (skb_cow_head(skb, dev-\u003eneeded_headroom)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto err_free_skb;\n+\t}\n \n-\tif (gre_handle_offloads(skb, false))\n+\tif (gre_handle_offloads(skb, false)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto err_free_skb;\n+\t}\n \n \tif (skb-\u003elen \u003e dev-\u003emtu + dev-\u003ehard_header_len) {\n-\t\tif (pskb_trim(skb, dev-\u003emtu + dev-\u003ehard_header_len))\n+\t\tif (pskb_trim(skb, dev-\u003emtu + dev-\u003ehard_header_len)) {\n+\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\tgoto err_free_skb;\n+\t\t}\n \t\ttruncate = true;\n \t}\n \n@@ -606,6 +637,7 @@ static void erspan_fb_xmit(struct sk_buff skb, struct net_device dev)\n \t\t\t\t truncate, true);\n \t\tproto = htons(ETH_P_ERSPAN2);\n \t} else {\n+\t\treason = SKB_DROP_REASON_UNHANDLED_PROTO;\n \t\tgoto err_free_skb;\n \t}\n \n@@ -618,7 +650,7 @@ static void erspan_fb_xmit(struct sk_buff skb, struct net_device dev)\n \treturn;\n \n err_free_skb:\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \tDEV_STATS_INC(dev, tx_dropped);\n }\n \n@@ -649,11 +681,13 @@ static int gre_fill_metadata_dst(struct net_device dev, struct sk_buff skb)\n static netdev_tx_t ipgre_xmit(struct sk_buff skb,\n \t\t\t struct net_device dev)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel tunnel = netdev_priv(dev);\n \tIP_TUNNEL_DECLARE_FLAGS(flags);\n \tconst struct iphdr tnl_params;\n \n-\tif (!pskb_inet_may_pull(skb))\n+\treason = pskb_inet_may_pull_reason(skb);\n+\tif (reason)\n \t\tgoto free_skb;\n \n \tif (tunnel-\u003ecollect_md) {\n@@ -664,10 +698,13 @@ static netdev_tx_t ipgre_xmit(struct sk_buff skb,\n \tif (dev-\u003eheader_ops) {\n \t\tint pull_len = tunnel-\u003ehlen + sizeof(struct iphdr);\n \n-\t\tif (skb_cow_head(skb, 0))\n+\t\tif (skb_cow_head(skb, 0)) {\n+\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\tgoto free_skb;\n+\t\t}\n \n-\t\tif (!pskb_may_pull(skb, pull_len))\n+\t\treason = pskb_may_pull_reason(skb, pull_len);\n+\t\tif (reason)\n \t\t\tgoto free_skb;\n \n \t\ttnl_params = (const struct iphdr )skb-\u003edata;\n@@ -677,25 +714,31 @@ static netdev_tx_t ipgre_xmit(struct sk_buff skb,\n \t\tskb_reset_mac_header(skb);\n \n \t\tif (skb-\u003eip_summed == CHECKSUM_PARTIAL \u0026\u0026\n-\t\t skb_checksum_start(skb) \u003c skb-\u003edata)\n+\t\t skb_checksum_start(skb) \u003c skb-\u003edata) {\n+\t\t\treason = SKB_DROP_REASON_SKB_CSUM;\n \t\t\tgoto free_skb;\n+\t\t}\n \t} else {\n-\t\tif (skb_cow_head(skb, dev-\u003eneeded_headroom))\n+\t\tif (skb_cow_head(skb, dev-\u003eneeded_headroom)) {\n+\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\tgoto free_skb;\n+\t\t}\n \n \t\ttnl_params = \u0026tunnel-\u003eparms.iph;\n \t}\n \n \tip_tunnel_flags_copy(flags, tunnel-\u003eparms.o_flags);\n \n-\tif (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT, flags)))\n+\tif (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT, flags))) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto free_skb;\n+\t}\n \n \t__gre_xmit(skb, dev, tnl_params, skb-\u003eprotocol, flags);\n \treturn NETDEV_TX_OK;\n \n free_skb:\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \tDEV_STATS_INC(dev, tx_dropped);\n \treturn NETDEV_TX_OK;\n }\n@@ -703,12 +746,14 @@ static netdev_tx_t ipgre_xmit(struct sk_buff skb,\n static netdev_tx_t erspan_xmit(struct sk_buff skb,\n \t\t\t struct net_device dev)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel tunnel = netdev_priv(dev);\n \tIP_TUNNEL_DECLARE_FLAGS(flags);\n \tbool truncate = false;\n \t__be16 proto;\n \n-\tif (!pskb_inet_may_pull(skb))\n+\treason = pskb_inet_may_pull_reason(skb);\n+\tif (reason)\n \t\tgoto free_skb;\n \n \tif (tunnel-\u003ecollect_md) {\n@@ -716,15 +761,21 @@ static netdev_tx_t erspan_xmit(struct sk_buff skb,\n \t\treturn NETDEV_TX_OK;\n \t}\n \n-\tif (gre_handle_offloads(skb, false))\n+\tif (gre_handle_offloads(skb, false)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto free_skb;\n+\t}\n \n-\tif (skb_cow_head(skb, dev-\u003eneeded_headroom))\n+\tif (skb_cow_head(skb, dev-\u003eneeded_headroom)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto free_skb;\n+\t}\n \n \tif (skb-\u003elen \u003e dev-\u003emtu + dev-\u003ehard_header_len) {\n-\t\tif (pskb_trim(skb, dev-\u003emtu + dev-\u003ehard_header_len))\n+\t\tif (pskb_trim(skb, dev-\u003emtu + dev-\u003ehard_header_len)) {\n+\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\tgoto free_skb;\n+\t\t}\n \t\ttruncate = true;\n \t}\n \n@@ -745,6 +796,7 @@ static netdev_tx_t erspan_xmit(struct sk_buff skb,\n \t\t\t\t truncate, true);\n \t\tproto = htons(ETH_P_ERSPAN2);\n \t} else {\n+\t\treason = SKB_DROP_REASON_UNHANDLED_PROTO;\n \t\tgoto free_skb;\n \t}\n \n@@ -753,7 +805,7 @@ static netdev_tx_t erspan_xmit(struct sk_buff skb,\n \treturn NETDEV_TX_OK;\n \n free_skb:\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \tDEV_STATS_INC(dev, tx_dropped);\n \treturn NETDEV_TX_OK;\n }\n@@ -761,10 +813,12 @@ static netdev_tx_t erspan_xmit(struct sk_buff skb,\n static netdev_tx_t gre_tap_xmit(struct sk_buff skb,\n \t\t\t\tstruct net_device dev)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel tunnel = netdev_priv(dev);\n \tIP_TUNNEL_DECLARE_FLAGS(flags);\n \n-\tif (!pskb_inet_may_pull(skb))\n+\treason = pskb_inet_may_pull_reason(skb);\n+\tif (reason)\n \t\tgoto free_skb;\n \n \tif (tunnel-\u003ecollect_md) {\n@@ -774,17 +828,21 @@ static netdev_tx_t gre_tap_xmit(struct sk_buff skb,\n \n \tip_tunnel_flags_copy(flags, tunnel-\u003eparms.o_flags);\n \n-\tif (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT, flags)))\n+\tif (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT, flags))) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto free_skb;\n+\t}\n \n-\tif (skb_cow_head(skb, dev-\u003eneeded_headroom))\n+\tif (skb_cow_head(skb, dev-\u003eneeded_headroom)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto free_skb;\n+\t}\n \n \t__gre_xmit(skb, dev, \u0026tunnel-\u003eparms.iph, htons(ETH_P_TEB), flags);\n \treturn NETDEV_TX_OK;\n \n free_skb:\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \tDEV_STATS_INC(dev, tx_dropped);\n \treturn NETDEV_TX_OK;\n }\n" }
11/2	2026/09/18 08:30	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 20305 output: 26 thoughts: 18 Thoughts: Here's a summary of my thought process, as if I were the one thinking it: Diving into the Code Changes Okay, time to get to the core of this change. Let's start by digging into `gre_demux.c`. That's where I expect the meat of any GRE (Generic Routing Encapsulation) demultiplexing updates to be. I need to understand exactly how the changes are affecting the packet processing logic there. I'll meticulously go through that file. I'll also need to make sure to check the rest of the code diff for any upstream/downstream impact. I'll scrutinize any supporting functions or data structures that are impacted. This is important to guarantee no unforeseen side effects. I'm looking for a complete picture, and I won't be happy until I have one.
12/2	2026/09/18 08:30	tool	git-show	0m Args: { "File": "net/ipv4/gre_demux.c" } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c\nindex 96fd7dc6d82dd..c5d3847848efd 100644\n--- a/net/ipv4/gre_demux.c\n+++ b/net/ipv4/gre_demux.c\n@@ -58,26 +58,44 @@ EXPORT_SYMBOL_GPL(gre_del_protocol);\n \n /* Fills in tpi and returns header length to be pulled.\n * Note that caller must use pskb_may_pull() before pulling GRE header.\n+ \n+ @reason is only written when the header is rejected, so the caller has\n+ * to initialise it before the call.\n+ \n+ A NULL @reason means that the caller is not interested in the drop\n+ * reason, and also that a checksum failure must not be reported: the\n+ * checksum is still computed, the packet is just not rejected over it.\n+ * This is what the ICMP error handlers need, as they only get a part of\n+ * the original packet.\n /\n int gre_parse_header(struct sk_buff skb, struct tnl_ptk_info tpi,\n-\t\t bool csum_err, __be16 proto, int nhs)\n+\t\t enum skb_drop_reason reason, __be16 proto, int nhs)\n {\n \tconst struct gre_base_hdr greh;\n \t__be32 options;\n \tint hdr_len;\n \n-\tif (unlikely(!pskb_may_pull(skb, nhs + sizeof(struct gre_base_hdr))))\n+\tif (unlikely(!pskb_may_pull(skb, nhs + sizeof(struct gre_base_hdr)))) {\n+\t\tif (reason)\n+\t\t\treason = SKB_DROP_REASON_HDR_TRUNC;\n \t\treturn -EINVAL;\n+\t}\n \n \tgreh = (struct gre_base_hdr )(skb-\u003edata + nhs);\n-\tif (unlikely(greh-\u003eflags \u0026 (GRE_VERSION \| GRE_ROUTING)))\n+\tif (unlikely(greh-\u003eflags \u0026 (GRE_VERSION \| GRE_ROUTING))) {\n+\t\tif (reason)\n+\t\t\treason = SKB_DROP_REASON_GRE_INVALID_HDR;\n \t\treturn -EINVAL;\n+\t}\n \n \tgre_flags_to_tnl_flags(tpi-\u003eflags, greh-\u003eflags);\n \thdr_len = gre_calc_hlen(tpi-\u003eflags);\n \n-\tif (!pskb_may_pull(skb, nhs + hdr_len))\n+\tif (!pskb_may_pull(skb, nhs + hdr_len)) {\n+\t\tif (reason)\n+\t\t\treason = SKB_DROP_REASON_HDR_TRUNC;\n \t\treturn -EINVAL;\n+\t}\n \n \tgreh = (struct gre_base_hdr )(skb-\u003edata + nhs);\n \ttpi-\u003eproto = greh-\u003eprotocol;\n@@ -87,8 +105,8 @@ int gre_parse_header(struct sk_buff skb, struct tnl_ptk_info tpi,\n \t\tif (!skb_checksum_simple_validate(skb)) {\n \t\t\tskb_checksum_try_convert(skb, IPPROTO_GRE,\n \t\t\t\t\t\t null_compute_pseudo);\n-\t\t} else if (csum_err) {\n-\t\t\tcsum_err = true;\n+\t\t} else if (reason) {\n+\t\t\treason = SKB_DROP_REASON_GRE_CSUM;\n \t\t\treturn -EINVAL;\n \t\t}\n \n@@ -116,8 +134,11 @@ int gre_parse_header(struct sk_buff skb, struct tnl_ptk_info tpi,\n \n \t\tval = skb_header_pointer(skb, nhs + hdr_len,\n \t\t\t\t\t sizeof(_val), \u0026_val);\n-\t\tif (!val)\n+\t\tif (!val) {\n+\t\t\tif (reason)\n+\t\t\t\treason = SKB_DROP_REASON_HDR_TRUNC;\n \t\t\treturn -EINVAL;\n+\t\t}\n \t\ttpi-\u003eproto = proto;\n \t\tif ((val \u0026 0xF0) != 0x40)\n \t\t\thdr_len += 4;\n@@ -132,8 +153,11 @@ int gre_parse_header(struct sk_buff skb, struct tnl_ptk_info tpi,\n \t greh-\u003eprotocol == htons(ETH_P_ERSPAN2)) {\n \t\tstruct erspan_base_hdr ershdr;\n \n-\t\tif (!pskb_may_pull(skb, nhs + hdr_len + sizeof(ershdr)))\n+\t\tif (!pskb_may_pull(skb, nhs + hdr_len + sizeof(ershdr))) {\n+\t\t\tif (reason)\n+\t\t\t\treason = SKB_DROP_REASON_HDR_TRUNC;\n \t\t\treturn -EINVAL;\n+\t\t}\n \n \t\tershdr = (struct erspan_base_hdr )(skb-\u003edata + nhs + hdr_len);\n \t\ttpi-\u003ekey = cpu_to_be32(get_session_id(ershdr));\n@@ -145,16 +169,20 @@ EXPORT_SYMBOL(gre_parse_header);\n \n static int gre_rcv(struct sk_buff skb)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tconst struct gre_protocol proto;\n \tu8 ver;\n \tint ret;\n \n-\tif (!pskb_may_pull(skb, 12))\n+\treason = pskb_may_pull_reason(skb, 12);\n+\tif (reason)\n \t\tgoto drop;\n \n \tver = skb-\u003edata[1]\u00260x7f;\n-\tif (ver \u003e= GREPROTO_MAX)\n+\tif (ver \u003e= GREPROTO_MAX) {\n+\t\treason = SKB_DROP_REASON_UNHANDLED_PROTO;\n \t\tgoto drop;\n+\t}\n \n \trcu_read_lock();\n \tproto = rcu_dereference(gre_proto[ver]);\n@@ -167,11 +195,11 @@ static int gre_rcv(struct sk_buff skb)\n drop_nohandler:\n \trcu_read_unlock();\n \tdev_core_stats_rx_nohandler_inc(skb-\u003edev);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, SKB_DROP_REASON_UNHANDLED_PROTO);\n \treturn NET_RX_DROP;\n drop:\n \tdev_core_stats_rx_dropped_inc(skb-\u003edev);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn NET_RX_DROP;\n }\n \n" }
13/2	2026/09/18 08:30	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 22385 output: 26 thoughts: 31 Thoughts: Here's my take: Investigating IPv6 Tunneling Implementation Alright, let's dive in. Based on the issue at hand, my initial gut feeling tells me the root of the problem might lie within the IPv6 tunneling implementations. To get a handle on this, I need to check the code that actually handles the tunneling. So, I need to go spelunking into the kernel source code to get the definitive answer. To do so, I'll need to focus my attention on two files. Specifically, I should start by carefully examining `net/ipv6/ip6_tunnel.c` and `net/ipv6/ip6_gre.c`. These are the most likely candidates. I know those areas well, so I'll be able to quickly zero in on the relevant sections, focusing on packet encapsulation, decapsulation, and header manipulation. I'll be looking for any potential logic errors, race conditions, or incorrect assumptions about packet structure that could lead to the behavior we're observing. It's time to get hands-on.
14/2	2026/09/18 08:30	tool	git-show	0m Args: { "File": "net/ipv6/ip6_tunnel.c" } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c\nindex d5ff50a2ac017..138151ed5797e 100644\n--- a/net/ipv6/ip6_tunnel.c\n+++ b/net/ipv6/ip6_tunnel.c\n@@ -813,6 +813,7 @@ static int __ip6_tnl_rcv(struct ip6_tnl tunnel, struct sk_buff skb,\n \t\t\t\t\t\tstruct sk_buff skb),\n \t\t\t bool log_ecn_err)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tconst struct ipv6hdr ipv6h;\n \tint nh, err;\n \n@@ -820,15 +821,22 @@ static int __ip6_tnl_rcv(struct ip6_tnl tunnel, struct sk_buff skb,\n \t test_bit(IP_TUNNEL_CSUM_BIT, tpi-\u003eflags)) {\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_crc_errors);\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\treason = SKB_DROP_REASON_TNL_OPT_MISMATCH;\n \t\tgoto drop;\n \t}\n \n \tif (test_bit(IP_TUNNEL_SEQ_BIT, tunnel-\u003eparms.i_flags)) {\n-\t\tif (!test_bit(IP_TUNNEL_SEQ_BIT, tpi-\u003eflags) \|\|\n-\t\t (tunnel-\u003ei_seqno \u0026\u0026\n-\t\t (s32)(ntohl(tpi-\u003eseq) - tunnel-\u003ei_seqno) \u003c 0)) {\n+\t\tif (!test_bit(IP_TUNNEL_SEQ_BIT, tpi-\u003eflags)) {\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_fifo_errors);\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_TNL_OPT_MISMATCH;\n+\t\t\tgoto drop;\n+\t\t}\n+\t\tif (tunnel-\u003ei_seqno \u0026\u0026\n+\t\t (s32)(ntohl(tpi-\u003eseq) - tunnel-\u003ei_seqno) \u003c 0) {\n+\t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_fifo_errors);\n+\t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_TNL_OLD_SEQ;\n \t\t\tgoto drop;\n \t\t}\n \t\ttunnel-\u003ei_seqno = ntohl(tpi-\u003eseq) + 1;\n@@ -838,7 +846,8 @@ static int __ip6_tnl_rcv(struct ip6_tnl tunnel, struct sk_buff skb,\n \n \t/* Warning: All skb pointers will be invalidated! /\n \tif (tunnel-\u003edev-\u003etype == ARPHRD_ETHER) {\n-\t\tif (!pskb_may_pull(skb, ETH_HLEN)) {\n+\t\treason = pskb_may_pull_reason(skb, ETH_HLEN);\n+\t\tif (reason) {\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_length_errors);\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n \t\t\tgoto drop;\n@@ -859,7 +868,8 @@ static int __ip6_tnl_rcv(struct ip6_tnl tunnel, struct sk_buff skb,\n \n \tskb_reset_network_header(skb);\n \n-\tif (skb_vlan_inet_prepare(skb, true)) {\n+\treason = skb_vlan_inet_prepare(skb, true);\n+\tif (reason) {\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_length_errors);\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n \t\tgoto drop;\n@@ -881,6 +891,7 @@ static int __ip6_tnl_rcv(struct ip6_tnl tunnel, struct sk_buff skb,\n \t\tif (err \u003e 1) {\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_frame_errors);\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_IP_TUNNEL_ECN;\n \t\t\tgoto drop;\n \t\t}\n \t}\n@@ -898,7 +909,7 @@ static int __ip6_tnl_rcv(struct ip6_tnl tunnel, struct sk_buff skb,\n drop:\n \tif (tun_dst)\n \t\tdst_release((struct dst_entry )tun_dst);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn 0;\n }\n \n@@ -1086,6 +1097,7 @@ EXPORT_SYMBOL_GPL(ip6_tnl_xmit_ctl);\n * @encap_limit: encapsulation limit\n * @pmtu: Path MTU is stored if packet is too big\n * @proto: next header value\n+ * @reason: drop reason, only written when the packet is dropped\n \n Description:\n * Build new header and do some sanity checks on the packet before sending\n@@ -1099,7 +1111,7 @@ EXPORT_SYMBOL_GPL(ip6_tnl_xmit_ctl);\n \n int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \t\t struct flowi6 fl6, int encap_limit, __u32 pmtu,\n-\t\t __u8 proto)\n+\t\t __u8 proto, enum skb_drop_reason reason)\n {\n \tstruct ip6_tnl t = netdev_priv(dev);\n \tstruct net net = t-\u003enet;\n@@ -1132,13 +1144,17 @@ int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \t\t\tstruct neighbour neigh;\n \t\t\tint addr_type;\n \n-\t\t\tif (!skb_dst(skb))\n+\t\t\tif (!skb_dst(skb)) {\n+\t\t\t\treason = SKB_DROP_REASON_NO_TX_TARGET;\n \t\t\t\tgoto tx_err_link_failure;\n+\t\t\t}\n \n \t\t\tneigh = dst_neigh_lookup(skb_dst(skb),\n \t\t\t\t\t\t \u0026ipv6_hdr(skb)-\u003edaddr);\n-\t\t\tif (!neigh)\n+\t\t\tif (!neigh) {\n+\t\t\t\treason = SKB_DROP_REASON_NEIGH_CREATEFAIL;\n \t\t\t\tgoto tx_err_link_failure;\n+\t\t\t}\n \n \t\t\taddr6 = (struct in6_addr )\u0026neigh-\u003eprimary_key;\n \t\t\taddr_type = ipv6_addr_type(addr6);\n@@ -1151,8 +1167,10 @@ int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \t\t} else if (payload_protocol == htons(ETH_P_IP)) {\n \t\t\tconst struct rtable rt = skb_rtable(skb);\n \n-\t\t\tif (!rt)\n+\t\t\tif (!rt) {\n+\t\t\t\treason = SKB_DROP_REASON_NO_TX_TARGET;\n \t\t\t\tgoto tx_err_link_failure;\n+\t\t\t}\n \n \t\t\tif (rt-\u003ert_gw_family == AF_INET6)\n \t\t\t\tmemcpy(\u0026fl6-\u003edaddr, \u0026rt-\u003ert_gw6, sizeof(fl6-\u003edaddr));\n@@ -1169,8 +1187,10 @@ int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \tif (use_cache)\n \t\tdst = dst_cache_get(\u0026t-\u003edst_cache);\n \n-\tif (!ip6_tnl_xmit_ctl(t, \u0026fl6-\u003esaddr, \u0026fl6-\u003edaddr))\n+\tif (!ip6_tnl_xmit_ctl(t, \u0026fl6-\u003esaddr, \u0026fl6-\u003edaddr)) {\n+\t\treason = SKB_DROP_REASON_DEV_READY;\n \t\tgoto tx_err_link_failure;\n+\t}\n \n \tif (!dst) {\n route_lookup:\n@@ -1179,18 +1199,23 @@ int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \n \t\tdst = ip6_route_output(net, NULL, fl6);\n \n-\t\tif (dst-\u003eerror)\n+\t\tif (dst-\u003eerror) {\n+\t\t\treason = SKB_DROP_REASON_IP_OUTNOROUTES;\n \t\t\tgoto tx_err_link_failure;\n+\t\t}\n \t\tdst = xfrm_lookup(net, dst, flowi6_to_flowi(fl6), NULL, 0);\n \t\tif (IS_ERR(dst)) {\n \t\t\terr = PTR_ERR(dst);\n \t\t\tdst = NULL;\n+\t\t\treason = SKB_DROP_REASON_IP_OUTNOROUTES;\n \t\t\tgoto tx_err_link_failure;\n \t\t}\n \t\tif (t-\u003eparms.collect_md \u0026\u0026 ipv6_addr_any(\u0026fl6-\u003esaddr) \u0026\u0026\n \t\t ipv6_dev_get_saddr(net, ip6_dst_idev(dst)-\u003edev,\n-\t\t\t\t \u0026fl6-\u003edaddr, 0, \u0026fl6-\u003esaddr))\n+\t\t\t\t \u0026fl6-\u003edaddr, 0, \u0026fl6-\u003esaddr)) {\n+\t\t\treason = SKB_DROP_REASON_IP_OUTNOROUTES;\n \t\t\tgoto tx_err_link_failure;\n+\t\t}\n \t\tndst = dst;\n \t}\n \n@@ -1200,6 +1225,7 @@ int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \t\tDEV_STATS_INC(dev, collisions);\n \t\tnet_warn_ratelimited(\"%s: Local routing loop detected!\\n\",\n \t\t\t\t t-\u003eparms.name);\n+\t\treason = SKB_DROP_REASON_RECURSION_LIMIT;\n \t\tgoto tx_err_dst_release;\n \t}\n \tmtu = dst6_mtu(dst) - eth_hlen - psh_hlen - t-\u003etun_hlen;\n@@ -1214,6 +1240,7 @@ int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \tif (skb-\u003elen - t-\u003etun_hlen - eth_hlen \u003e mtu \u0026\u0026 !skb_is_gso(skb)) {\n \t\tpmtu = mtu;\n \t\terr = -EMSGSIZE;\n+\t\treason = SKB_DROP_REASON_PKT_TOO_BIG;\n \t\tgoto tx_err_dst_release;\n \t}\n \n@@ -1236,12 +1263,16 @@ int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \t /\n \tmax_headroom += LL_RESERVED_SPACE(tdev);\n \n-\tif (skb_cow_head(skb, max_headroom))\n+\tif (skb_cow_head(skb, max_headroom)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto tx_err_dst_release;\n+\t}\n \n \tif (t-\u003eparms.collect_md) {\n-\t\tif (t-\u003eencap.type != TUNNEL_ENCAP_NONE)\n+\t\tif (t-\u003eencap.type != TUNNEL_ENCAP_NONE) {\n+\t\t\treason = SKB_DROP_REASON_TNL_ENCAP;\n \t\t\tgoto tx_err_dst_release;\n+\t\t}\n \t} else {\n \t\tif (use_cache \u0026\u0026 ndst)\n \t\t\tdst_cache_set_ip6(\u0026t-\u003edst_cache, ndst, \u0026fl6-\u003esaddr);\n@@ -1265,8 +1296,10 @@ int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n \tip_tunnel_adj_headroom(dev, max_headroom);\n \n \terr = ip6_tnl_encap(skb, t, \u0026proto, fl6);\n-\tif (err)\n+\tif (err) {\n+\t\treason = SKB_DROP_REASON_TNL_ENCAP;\n \t\treturn err;\n+\t}\n \n \tif (encap_limit \u003e= 0) {\n \t\tinit_tel_txopt(\u0026opt, encap_limit);\n@@ -1295,7 +1328,7 @@ EXPORT_SYMBOL(ip6_tnl_xmit);\n \n static inline int\n ipxip6_tnl_xmit(struct sk_buff skb, struct net_device dev,\n-\t\tu8 protocol)\n+\t\tu8 protocol, enum skb_drop_reason reason)\n {\n \tstruct ip6_tnl t = netdev_priv(dev);\n \tstruct ipv6hdr ipv6h;\n@@ -1309,8 +1342,10 @@ ipxip6_tnl_xmit(struct sk_buff skb, struct net_device dev,\n \tint err;\n \n \ttproto = READ_ONCE(t-\u003eparms.proto);\n-\tif (tproto != protocol \u0026\u0026 tproto != 0)\n+\tif (tproto != protocol \u0026\u0026 tproto != 0) {\n+\t\treason = SKB_DROP_REASON_UNHANDLED_PROTO;\n \t\treturn -1;\n+\t}\n \n \tif (t-\u003eparms.collect_md) {\n \t\tstruct ip_tunnel_info tun_info;\n@@ -1318,8 +1353,10 @@ ipxip6_tnl_xmit(struct sk_buff skb, struct net_device dev,\n \n \t\ttun_info = skb_tunnel_info(skb);\n \t\tif (unlikely(!tun_info \|\| !(tun_info-\u003emode \u0026 IP_TUNNEL_INFO_TX) \|\|\n-\t\t\t ip_tunnel_info_af(tun_info) != AF_INET6))\n+\t\t\t ip_tunnel_info_af(tun_info) != AF_INET6)) {\n+\t\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\t\treturn -1;\n+\t\t}\n \t\tkey = \u0026tun_info-\u003ekey;\n \t\tmemset(\u0026fl6, 0, sizeof(fl6));\n \t\tfl6.flowi6_proto = protocol;\n@@ -1356,6 +1393,7 @@ ipxip6_tnl_xmit(struct sk_buff skb, struct net_device dev,\n \t\t\t\tif (tel-\u003eencap_limit == 0) {\n \t\t\t\t\ticmpv6_ndo_send(skb, ICMPV6_PARAMPROB,\n \t\t\t\t\t\t\tICMPV6_HDR_FIELD, offset + 2);\n+\t\t\t\t\treason = SKB_DROP_REASON_IPV6_BAD_EXTHDR;\n \t\t\t\t\treturn -1;\n \t\t\t\t}\n \t\t\t\tencap_limit = tel-\u003eencap_limit - 1;\n@@ -1397,13 +1435,15 @@ ipxip6_tnl_xmit(struct sk_buff skb, struct net_device dev,\n \tfl6.flowi6_uid = sock_net_uid(dev_net(dev), NULL);\n \tdsfield = INET_ECN_encapsulate(dsfield, orig_dsfield);\n \n-\tif (iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6))\n+\tif (iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\treturn -1;\n+\t}\n \n \tskb_set_inner_ipproto(skb, protocol);\n \n \terr = ip6_tnl_xmit(skb, dev, dsfield, \u0026fl6, encap_limit, \u0026mtu,\n-\t\t\t protocol);\n+\t\t\t protocol, reason);\n \tif (err != 0) {\n \t\t/* XXX: send ICMP error even if DF is not set. /\n \t\tif (err == -EMSGSIZE)\n@@ -1427,11 +1467,13 @@ ipxip6_tnl_xmit(struct sk_buff skb, struct net_device dev,\n static netdev_tx_t\n ip6_tnl_start_xmit(struct sk_buff skb, struct net_device dev)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip6_tnl t = netdev_priv(dev);\n \tu8 ipproto;\n \tint ret;\n \n-\tif (!pskb_inet_may_pull(skb))\n+\treason = pskb_inet_may_pull_reason(skb);\n+\tif (reason)\n \t\tgoto tx_err;\n \n \tswitch (skb-\u003eprotocol) {\n@@ -1439,18 +1481,21 @@ ip6_tnl_start_xmit(struct sk_buff skb, struct net_device dev)\n \t\tipproto = IPPROTO_IPIP;\n \t\tbreak;\n \tcase htons(ETH_P_IPV6):\n-\t\tif (ip6_tnl_addr_conflict(t, ipv6_hdr(skb)))\n+\t\tif (ip6_tnl_addr_conflict(t, ipv6_hdr(skb))) {\n+\t\t\treason = SKB_DROP_REASON_RECURSION_LIMIT;\n \t\t\tgoto tx_err;\n+\t\t}\n \t\tipproto = IPPROTO_IPV6;\n \t\tbreak;\n \tcase htons(ETH_P_MPLS_UC):\n \t\tipproto = IPPROTO_MPLS;\n \t\tbreak;\n \tdefault:\n+\t\treason = SKB_DROP_REASON_UNHANDLED_PROTO;\n \t\tgoto tx_err;\n \t}\n \n-\tret = ipxip6_tnl_xmit(skb, dev, ipproto);\n+\tret = ipxip6_tnl_xmit(skb, dev, ipproto, \u0026reason);\n \tif (ret \u003c 0)\n \t\tgoto tx_err;\n \n@@ -1459,7 +1504,7 @@ ip6_tnl_start_xmit(struct sk_buff skb, struct net_device dev)\n tx_err:\n \tDEV_STATS_INC(dev, tx_errors);\n \tDEV_STATS_INC(dev, tx_dropped);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn NETDEV_TX_OK;\n }\n \n" }
15/2	2026/09/18 08:30	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 27632 output: 26 thoughts: 17 Thoughts: Here's my take on the thought process, as if I were the one thinking it: Diving into the IPv6 GRE Implementation Alright, time to get my hands dirty. I've got a hunch about something related to IPv6 GRE, and my gut's telling me to start digging into the core implementation. The logical starting point for understanding how this protocol works in the Linux kernel would be `net/ipv6/ip6_gre.c`. Let's see what gems we can unearth in that file. It should house the crucial functions for handling IPv6 GRE encapsulation and decapsulation, addressing, and potential error handling within the kernel's network stack. Time to load up the source code and get to work.
16/2	2026/09/18 08:31	tool	git-show	0m Args: { "File": "net/ipv6/ip6_gre.c" } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c\nindex 8ebda0b6a78b2..5d1e55813fce2 100644\n--- a/net/ipv6/ip6_gre.c\n+++ b/net/ipv6/ip6_gre.c\n@@ -454,7 +454,8 @@ static int ip6gre_err(struct sk_buff skb, struct inet6_skb_parm opt,\n \treturn 0;\n }\n \n-static int ip6gre_rcv(struct sk_buff skb, const struct tnl_ptk_info tpi)\n+static int ip6gre_rcv(struct sk_buff skb, const struct tnl_ptk_info tpi,\n+\t\t enum skb_drop_reason reason)\n {\n \tconst struct ipv6hdr ipv6h;\n \tstruct ip6_tnl tunnel;\n@@ -473,8 +474,10 @@ static int ip6gre_rcv(struct sk_buff skb, const struct tnl_ptk_info tpi)\n \t\t\ttun_id = key32_to_tunnel_id(tpi-\u003ekey);\n \n \t\t\ttun_dst = ipv6_tun_rx_dst(skb, flags, tun_id, 0);\n-\t\t\tif (!tun_dst)\n+\t\t\tif (!tun_dst) {\n+\t\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\t\treturn PACKET_REJECT;\n+\t\t\t}\n \n \t\t\tip6_tnl_rcv(tunnel, skb, tpi, tun_dst, log_ecn_error);\n \t\t} else {\n@@ -484,12 +487,14 @@ static int ip6gre_rcv(struct sk_buff skb, const struct tnl_ptk_info tpi)\n \t\treturn PACKET_RCVD;\n \t}\n \n+\treason = SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND;\n \treturn PACKET_REJECT;\n }\n \n static int ip6erspan_rcv(struct sk_buff skb,\n \t\t\t struct tnl_ptk_info tpi,\n-\t\t\t int gre_hdr_len)\n+\t\t\t int gre_hdr_len,\n+\t\t\t enum skb_drop_reason reason)\n {\n \tstruct erspan_base_hdr ershdr;\n \tconst struct ipv6hdr ipv6h;\n@@ -497,8 +502,10 @@ static int ip6erspan_rcv(struct sk_buff skb,\n \tstruct ip6_tnl tunnel;\n \tu8 ver;\n \n-\tif (unlikely(!pskb_may_pull(skb, sizeof(ershdr))))\n+\tif (unlikely(!pskb_may_pull(skb, sizeof(ershdr)))) {\n+\t\treason = SKB_DROP_REASON_HDR_TRUNC;\n \t\treturn PACKET_REJECT;\n+\t}\n \n \tipv6h = ipv6_hdr(skb);\n \tershdr = (struct erspan_base_hdr )skb-\u003edata;\n@@ -510,13 +517,17 @@ static int ip6erspan_rcv(struct sk_buff skb,\n \tif (tunnel) {\n \t\tint len = erspan_hdr_len(ver);\n \n-\t\tif (unlikely(!pskb_may_pull(skb, len)))\n+\t\tif (unlikely(!pskb_may_pull(skb, len))) {\n+\t\t\treason = SKB_DROP_REASON_HDR_TRUNC;\n \t\t\treturn PACKET_REJECT;\n+\t\t}\n \n \t\tif (__iptunnel_pull_header(skb, len,\n \t\t\t\t\t htons(ETH_P_TEB),\n-\t\t\t\t\t false, false) \u003c 0)\n+\t\t\t\t\t false, false) \u003c 0) {\n+\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\treturn PACKET_REJECT;\n+\t\t}\n \n \t\tif (tunnel-\u003eparms.collect_md) {\n \t\t\tstruct erspan_metadata pkt_md, md;\n@@ -532,8 +543,10 @@ static int ip6erspan_rcv(struct sk_buff skb,\n \n \t\t\ttun_dst = ipv6_tun_rx_dst(skb, flags, tun_id,\n \t\t\t\t\t\t sizeof(md));\n-\t\t\tif (!tun_dst)\n+\t\t\tif (!tun_dst) {\n+\t\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\t\treturn PACKET_REJECT;\n+\t\t\t}\n \n \t\t\t/* MUST set options_len before referencing options /\n \t\t\tinfo = \u0026tun_dst-\u003eu.tun_info;\n@@ -564,37 +577,40 @@ static int ip6erspan_rcv(struct sk_buff skb,\n \t\treturn PACKET_RCVD;\n \t}\n \n+\treason = SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND;\n \treturn PACKET_REJECT;\n }\n \n static int gre_rcv(struct sk_buff skb)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct tnl_ptk_info tpi;\n-\tbool csum_err = false;\n \tint hdr_len;\n \n-\thdr_len = gre_parse_header(skb, \u0026tpi, \u0026csum_err, htons(ETH_P_IPV6), 0);\n+\thdr_len = gre_parse_header(skb, \u0026tpi, \u0026reason, htons(ETH_P_IPV6), 0);\n \tif (hdr_len \u003c 0)\n \t\tgoto drop;\n \n-\tif (iptunnel_pull_header(skb, hdr_len, tpi.proto, false))\n+\tif (iptunnel_pull_header(skb, hdr_len, tpi.proto, false)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto drop;\n+\t}\n \n \tif (unlikely(tpi.proto == htons(ETH_P_ERSPAN) \|\|\n \t\t tpi.proto == htons(ETH_P_ERSPAN2))) {\n-\t\tif (ip6erspan_rcv(skb, \u0026tpi, hdr_len) == PACKET_RCVD)\n+\t\tif (ip6erspan_rcv(skb, \u0026tpi, hdr_len, \u0026reason) == PACKET_RCVD)\n \t\t\treturn 0;\n \t\tgoto out;\n \t}\n \n-\tif (ip6gre_rcv(skb, \u0026tpi) == PACKET_RCVD)\n+\tif (ip6gre_rcv(skb, \u0026tpi, \u0026reason) == PACKET_RCVD)\n \t\treturn 0;\n \n out:\n \ticmpv6_send(skb, ICMPV6_DEST_UNREACH, ICMPV6_PORT_UNREACH, 0);\n drop:\n \tdev_core_stats_rx_dropped_inc(skb-\u003edev);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn 0;\n }\n \n@@ -677,10 +693,10 @@ static int prepare_ip6gre_xmit_ipv6(struct sk_buff skb,\n \treturn 0;\n }\n \n-static int prepare_ip6gre_xmit_other(struct sk_buff skb,\n-\t\t\t\t struct net_device dev,\n-\t\t\t\t struct flowi6 fl6, __u8 dsfield,\n-\t\t\t\t int encap_limit)\n+static void prepare_ip6gre_xmit_other(struct sk_buff skb,\n+\t\t\t\t struct net_device dev,\n+\t\t\t\t struct flowi6 fl6, __u8 dsfield,\n+\t\t\t\t int encap_limit)\n {\n \tstruct ip6_tnl t = netdev_priv(dev);\n \n@@ -700,8 +716,6 @@ static int prepare_ip6gre_xmit_other(struct sk_buff skb,\n \t\tfl6-\u003eflowi6_mark = t-\u003eparms.fwmark;\n \n \tfl6-\u003eflowi6_uid = sock_net_uid(dev_net(dev), NULL);\n-\n-\treturn 0;\n }\n \n static struct ip_tunnel_info skb_tunnel_info_txcheck(struct sk_buff skb)\n@@ -718,7 +732,8 @@ static struct ip_tunnel_info skb_tunnel_info_txcheck(struct sk_buff skb)\n static netdev_tx_t __gre6_xmit(struct sk_buff skb,\n \t\t\t struct net_device dev, __u8 dsfield,\n \t\t\t struct flowi6 fl6, int encap_limit,\n-\t\t\t __u32 pmtu, __be16 proto)\n+\t\t\t __u32 pmtu, __be16 proto,\n+\t\t\t enum skb_drop_reason reason)\n {\n \tstruct ip6_tnl tunnel = netdev_priv(dev);\n \tIP_TUNNEL_DECLARE_FLAGS(flags);\n@@ -742,8 +757,10 @@ static netdev_tx_t __gre6_xmit(struct sk_buff skb,\n \n \t\ttun_info = skb_tunnel_info_txcheck(skb);\n \t\tif (IS_ERR(tun_info) \|\|\n-\t\t unlikely(ip_tunnel_info_af(tun_info) != AF_INET6))\n+\t\t unlikely(ip_tunnel_info_af(tun_info) != AF_INET6)) {\n+\t\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\t\treturn -EINVAL;\n+\t\t}\n \n \t\tkey = \u0026tun_info-\u003ekey;\n \t\tmemset(fl6, 0, sizeof(fl6));\n@@ -761,8 +778,11 @@ static netdev_tx_t __gre6_xmit(struct sk_buff skb,\n \t\tip_tunnel_flags_and(flags, flags, key-\u003etun_flags);\n \t\ttun_hlen = gre_calc_hlen(flags);\n \n-\t\tif (skb_cow_head(skb, dev-\u003eneeded_headroom ?: tun_hlen + tunnel-\u003eencap_hlen))\n+\t\tif (skb_cow_head(skb, dev-\u003eneeded_headroom ?:\n+\t\t\t\t tun_hlen + tunnel-\u003eencap_hlen)) {\n+\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\treturn -ENOMEM;\n+\t\t}\n \n \t\tgre_build_header(skb, tun_hlen,\n \t\t\t\t flags, protocol,\n@@ -772,8 +792,10 @@ static netdev_tx_t __gre6_xmit(struct sk_buff skb,\n \t\t\t\t 0);\n \n \t} else {\n-\t\tif (skb_cow_head(skb, dev-\u003eneeded_headroom ?: tunnel-\u003ehlen))\n+\t\tif (skb_cow_head(skb, dev-\u003eneeded_headroom ?: tunnel-\u003ehlen)) {\n+\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\treturn -ENOMEM;\n+\t\t}\n \n \t\tip_tunnel_flags_copy(flags, tunnel-\u003eparms.o_flags);\n \n@@ -785,10 +807,11 @@ static netdev_tx_t __gre6_xmit(struct sk_buff skb,\n \t}\n \n \treturn ip6_tnl_xmit(skb, dev, dsfield, fl6, encap_limit, pmtu,\n-\t\t\t NEXTHDR_GRE);\n+\t\t\t NEXTHDR_GRE, reason);\n }\n \n-static inline int ip6gre_xmit_ipv4(struct sk_buff skb, struct net_device dev)\n+static inline int ip6gre_xmit_ipv4(struct sk_buff skb, struct net_device dev,\n+\t\t\t\t enum skb_drop_reason reason)\n {\n \tstruct ip6_tnl t = netdev_priv(dev);\n \tint encap_limit = -1;\n@@ -805,11 +828,13 @@ static inline int ip6gre_xmit_ipv4(struct sk_buff skb, struct net_device dev)\n \n \terr = gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT,\n \t\t\t\t\t\tt-\u003eparms.o_flags));\n-\tif (err)\n+\tif (err) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\treturn -1;\n+\t}\n \n \terr = __gre6_xmit(skb, dev, dsfield, \u0026fl6, encap_limit, \u0026mtu,\n-\t\t\t skb-\u003eprotocol);\n+\t\t\t skb-\u003eprotocol, reason);\n \tif (err != 0) {\n \t\t/ XXX: send ICMP error even if DF is not set. /\n \t\tif (err == -EMSGSIZE)\n@@ -821,7 +846,8 @@ static inline int ip6gre_xmit_ipv4(struct sk_buff skb, struct net_device dev)\n \treturn 0;\n }\n \n-static inline int ip6gre_xmit_ipv6(struct sk_buff skb, struct net_device dev)\n+static inline int ip6gre_xmit_ipv6(struct sk_buff skb, struct net_device dev,\n+\t\t\t\t enum skb_drop_reason reason)\n {\n \tstruct ip6_tnl t = netdev_priv(dev);\n \tstruct ipv6hdr ipv6h = ipv6_hdr(skb);\n@@ -831,19 +857,25 @@ static inline int ip6gre_xmit_ipv6(struct sk_buff skb, struct net_device dev)\n \t__u32 mtu;\n \tint err;\n \n-\tif (ipv6_addr_equal(\u0026t-\u003eparms.raddr, \u0026ipv6h-\u003esaddr))\n+\tif (ipv6_addr_equal(\u0026t-\u003eparms.raddr, \u0026ipv6h-\u003esaddr)) {\n+\t\treason = SKB_DROP_REASON_RECURSION_LIMIT;\n \t\treturn -1;\n+\t}\n \n \tif (!t-\u003eparms.collect_md \u0026\u0026\n-\t prepare_ip6gre_xmit_ipv6(skb, dev, \u0026fl6, \u0026dsfield, \u0026encap_limit))\n+\t prepare_ip6gre_xmit_ipv6(skb, dev, \u0026fl6, \u0026dsfield, \u0026encap_limit)) {\n+\t\treason = SKB_DROP_REASON_IPV6_BAD_EXTHDR;\n \t\treturn -1;\n+\t}\n \n \tif (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT,\n-\t\t\t\t\t t-\u003eparms.o_flags)))\n+\t\t\t\t\t t-\u003eparms.o_flags))) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\treturn -1;\n+\t}\n \n \terr = __gre6_xmit(skb, dev, dsfield, \u0026fl6, encap_limit,\n-\t\t\t \u0026mtu, skb-\u003eprotocol);\n+\t\t\t \u0026mtu, skb-\u003eprotocol, reason);\n \tif (err != 0) {\n \t\tif (err == -EMSGSIZE)\n \t\t\ticmpv6_ndo_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);\n@@ -853,7 +885,8 @@ static inline int ip6gre_xmit_ipv6(struct sk_buff skb, struct net_device dev)\n \treturn 0;\n }\n \n-static int ip6gre_xmit_other(struct sk_buff skb, struct net_device dev)\n+static int ip6gre_xmit_other(struct sk_buff skb, struct net_device dev,\n+\t\t\t enum skb_drop_reason reason)\n {\n \tstruct ip6_tnl t = netdev_priv(dev);\n \tint encap_limit = -1;\n@@ -862,15 +895,18 @@ static int ip6gre_xmit_other(struct sk_buff skb, struct net_device dev)\n \t__u32 mtu;\n \tint err;\n \n-\tif (!t-\u003eparms.collect_md \u0026\u0026\n-\t prepare_ip6gre_xmit_other(skb, dev, \u0026fl6, \u0026dsfield, \u0026encap_limit))\n-\t\treturn -1;\n+\tif (!t-\u003eparms.collect_md)\n+\t\tprepare_ip6gre_xmit_other(skb, dev, \u0026fl6,\n+\t\t\t\t\t \u0026dsfield, \u0026encap_limit);\n \n \terr = gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT,\n \t\t\t\t\t\tt-\u003eparms.o_flags));\n-\tif (err)\n+\tif (err) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\treturn err;\n-\terr = __gre6_xmit(skb, dev, dsfield, \u0026fl6, encap_limit, \u0026mtu, skb-\u003eprotocol);\n+\t}\n+\terr = __gre6_xmit(skb, dev, dsfield, \u0026fl6, encap_limit, \u0026mtu,\n+\t\t\t skb-\u003eprotocol, reason);\n \n \treturn err;\n }\n@@ -878,16 +914,20 @@ static int ip6gre_xmit_other(struct sk_buff skb, struct net_device dev)\n static netdev_tx_t ip6gre_tunnel_xmit(struct sk_buff skb,\n \tstruct net_device dev)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel_info tun_info = NULL;\n \tstruct ip6_tnl t = netdev_priv(dev);\n \t__be16 payload_protocol;\n \tint ret;\n \n-\tif (!pskb_inet_may_pull(skb))\n+\treason = pskb_inet_may_pull_reason(skb);\n+\tif (reason)\n \t\tgoto tx_err;\n \n-\tif (!ip6_tnl_xmit_ctl(t, \u0026t-\u003eparms.laddr, \u0026t-\u003eparms.raddr))\n+\tif (!ip6_tnl_xmit_ctl(t, \u0026t-\u003eparms.laddr, \u0026t-\u003eparms.raddr)) {\n+\t\treason = SKB_DROP_REASON_DEV_READY;\n \t\tgoto tx_err;\n+\t}\n \n \tif (t-\u003eparms.collect_md)\n \t\ttun_info = skb_tunnel_info_txcheck(skb);\n@@ -895,13 +935,13 @@ static netdev_tx_t ip6gre_tunnel_xmit(struct sk_buff skb,\n \tpayload_protocol = skb_protocol(skb, true);\n \tswitch (payload_protocol) {\n \tcase htons(ETH_P_IP):\n-\t\tret = ip6gre_xmit_ipv4(skb, dev);\n+\t\tret = ip6gre_xmit_ipv4(skb, dev, \u0026reason);\n \t\tbreak;\n \tcase htons(ETH_P_IPV6):\n-\t\tret = ip6gre_xmit_ipv6(skb, dev);\n+\t\tret = ip6gre_xmit_ipv6(skb, dev, \u0026reason);\n \t\tbreak;\n \tdefault:\n-\t\tret = ip6gre_xmit_other(skb, dev);\n+\t\tret = ip6gre_xmit_other(skb, dev, \u0026reason);\n \t\tbreak;\n \t}\n \n@@ -914,13 +954,14 @@ static netdev_tx_t ip6gre_tunnel_xmit(struct sk_buff skb,\n \tif (!IS_ERR(tun_info))\n \t\tDEV_STATS_INC(dev, tx_errors);\n \tDEV_STATS_INC(dev, tx_dropped);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn NETDEV_TX_OK;\n }\n \n static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \t\t\t\t\t struct net_device dev)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tstruct ip_tunnel_info tun_info = NULL;\n \tstruct ip6_tnl t = netdev_priv(dev);\n \tstruct dst_entry dst = skb_dst(skb);\n@@ -934,18 +975,25 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \t__u32 mtu;\n \tint nhoff;\n \n-\tif (!pskb_inet_may_pull(skb))\n+\treason = pskb_inet_may_pull_reason(skb);\n+\tif (reason)\n \t\tgoto tx_err;\n \n-\tif (!ip6_tnl_xmit_ctl(t, \u0026t-\u003eparms.laddr, \u0026t-\u003eparms.raddr))\n+\tif (!ip6_tnl_xmit_ctl(t, \u0026t-\u003eparms.laddr, \u0026t-\u003eparms.raddr)) {\n+\t\treason = SKB_DROP_REASON_DEV_READY;\n \t\tgoto tx_err;\n+\t}\n \n-\tif (gre_handle_offloads(skb, false))\n+\tif (gre_handle_offloads(skb, false)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto tx_err;\n+\t}\n \n \tif (skb-\u003elen \u003e dev-\u003emtu + dev-\u003ehard_header_len) {\n-\t\tif (pskb_trim(skb, dev-\u003emtu + dev-\u003ehard_header_len))\n+\t\tif (pskb_trim(skb, dev-\u003emtu + dev-\u003ehard_header_len)) {\n+\t\t\treason = SKB_DROP_REASON_NOMEM;\n \t\t\tgoto tx_err;\n+\t\t}\n \t\ttruncate = true;\n \t}\n \n@@ -965,8 +1013,10 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \t\t\ttruncate = true;\n \t}\n \n-\tif (skb_cow_head(skb, dev-\u003eneeded_headroom ?: t-\u003ehlen))\n+\tif (skb_cow_head(skb, dev-\u003eneeded_headroom ?: t-\u003ehlen)) {\n+\t\treason = SKB_DROP_REASON_NOMEM;\n \t\tgoto tx_err;\n+\t}\n \n \tIPCB(skb)-\u003eflags = 0;\n \n@@ -980,8 +1030,10 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \n \t\ttun_info = skb_tunnel_info_txcheck(skb);\n \t\tif (IS_ERR(tun_info) \|\|\n-\t\t unlikely(ip_tunnel_info_af(tun_info) != AF_INET6))\n+\t\t unlikely(ip_tunnel_info_af(tun_info) != AF_INET6)) {\n+\t\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\t\tgoto tx_err;\n+\t\t}\n \n \t\tkey = \u0026tun_info-\u003ekey;\n \t\tmemset(\u0026fl6, 0, sizeof(fl6));\n@@ -993,10 +1045,14 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \n \t\tdsfield = key-\u003etos;\n \t\tif (!test_bit(IP_TUNNEL_ERSPAN_OPT_BIT,\n-\t\t\t tun_info-\u003ekey.tun_flags))\n+\t\t\t tun_info-\u003ekey.tun_flags)) {\n+\t\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\t\tgoto tx_err;\n-\t\tif (tun_info-\u003eoptions_len \u003c sizeof(md))\n+\t\t}\n+\t\tif (tun_info-\u003eoptions_len \u003c sizeof(md)) {\n+\t\t\treason = SKB_DROP_REASON_TUNNEL_TXINFO;\n \t\t\tgoto tx_err;\n+\t\t}\n \t\tmd = ip_tunnel_info_opts(tun_info);\n \n \t\ttun_id = tunnel_id_to_key32(key-\u003etun_id);\n@@ -1014,6 +1070,7 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \t\t\t\t\t truncate, false);\n \t\t\tproto = htons(ETH_P_ERSPAN2);\n \t\t} else {\n+\t\t\treason = SKB_DROP_REASON_UNHANDLED_PROTO;\n \t\t\tgoto tx_err;\n \t\t}\n \t} else {\n@@ -1024,11 +1081,16 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \t\t\t\t\t\t \u0026dsfield, \u0026encap_limit);\n \t\t\tbreak;\n \t\tcase htons(ETH_P_IPV6):\n-\t\t\tif (ipv6_addr_equal(\u0026t-\u003eparms.raddr, \u0026ipv6_hdr(skb)-\u003esaddr))\n+\t\t\tif (ipv6_addr_equal(\u0026t-\u003eparms.raddr,\n+\t\t\t\t\t \u0026ipv6_hdr(skb)-\u003esaddr)) {\n+\t\t\t\treason = SKB_DROP_REASON_RECURSION_LIMIT;\n \t\t\t\tgoto tx_err;\n+\t\t\t}\n \t\t\tif (prepare_ip6gre_xmit_ipv6(skb, dev, \u0026fl6,\n-\t\t\t\t\t\t \u0026dsfield, \u0026encap_limit))\n+\t\t\t\t\t\t \u0026dsfield, \u0026encap_limit)) {\n+\t\t\t\treason = SKB_DROP_REASON_IPV6_BAD_EXTHDR;\n \t\t\t\tgoto tx_err;\n+\t\t\t}\n \t\t\tbreak;\n \t\tdefault:\n \t\t\tmemcpy(\u0026fl6, \u0026t-\u003efl.u.ip6, sizeof(fl6));\n@@ -1047,6 +1109,7 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \t\t\t\t\t truncate, false);\n \t\t\tproto = htons(ETH_P_ERSPAN2);\n \t\t} else {\n+\t\t\treason = SKB_DROP_REASON_UNHANDLED_PROTO;\n \t\t\tgoto tx_err;\n \t\t}\n \n@@ -1065,7 +1128,7 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \t\t\tdst-\u003eops-\u003eupdate_pmtu(dst, NULL, skb, mtu, false);\n \t}\n \terr = ip6_tnl_xmit(skb, dev, dsfield, \u0026fl6, encap_limit, \u0026mtu,\n-\t\t\t NEXTHDR_GRE);\n+\t\t\t NEXTHDR_GRE, \u0026reason);\n \tif (err != 0) {\n \t\t/ XXX: send ICMP error even if DF is not set. /\n \t\tif (err == -EMSGSIZE) {\n@@ -1084,7 +1147,7 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff skb,\n \tif (!IS_ERR(tun_info))\n \t\tDEV_STATS_INC(dev, tx_errors);\n \tDEV_STATS_INC(dev, tx_dropped);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn NETDEV_TX_OK;\n }\n \n" }
17/2	2026/09/18 08:31	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 35049 output: 25 thoughts: 93 Thoughts: Examining the Drop Reason Implementation Okay, let's dive in. I need to verify what's happening with these changes. My first thought is to examine `include/net/dropreason-core.h`, `include/net/gre.h`, and `include/net/ip6_tunnel.h`. My initial impression is that this is simply the addition of drop reasons—replacing the basic `kfree_skb` calls with the more informative `kfree_skb_reason` calls—specifically within the context of GRE and IP tunnels. But, just to be sure, I need to confirm the change itself. Let me check `git-show include/net/dropreason-core.h` to see the exact modifications.
18/2	2026/09/18 08:31	tool	git-show	0m Args: { "File": "include/net/dropreason-core.h" } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h\nindex 12f9096515912..30378a0d22726 100644\n--- a/include/net/dropreason-core.h\n+++ b/include/net/dropreason-core.h\n@@ -129,6 +129,12 @@\n \tFN(PSP_INPUT)\t\t\t\\\n \tFN(PSP_OUTPUT)\t\t\t\\\n \tFN(RECURSION_LIMIT)\t\t\\\n+\tFN(TNL_OPT_MISMATCH)\t\t\\\n+\tFN(TNL_OLD_SEQ)\t\t\t\\\n+\tFN(GRE_INVALID_HDR)\t\t\\\n+\tFN(GRE_CSUM)\t\t\t\\\n+\tFN(GRE_TUNNEL_NOT_FOUND)\t\\\n+\tFN(TNL_ENCAP)\t\t\t\\\n \tFNe(MAX)\n \n /\n@@ -612,6 +618,38 @@ enum skb_drop_reason {\n \tSKB_DROP_REASON_PSP_OUTPUT,\n \t/ @SKB_DROP_REASON_RECURSION_LIMIT: Dead loop on virtual device. /\n \tSKB_DROP_REASON_RECURSION_LIMIT,\n+\t/\n+\t @SKB_DROP_REASON_TNL_OPT_MISMATCH: the tunnel options\n+\t * carried by the packet do not match the tunnel configuration, e.g.\n+\t * a GRE tunnel configured with 'icsum' or 'iseq' received a packet\n+\t * with no checksum or no sequence number.\n+\t /\n+\tSKB_DROP_REASON_TNL_OPT_MISMATCH,\n+\t/\n+\t @SKB_DROP_REASON_TNL_OLD_SEQ: the sequence number carried\n+\t * by the packet is older than the one expected by the tunnel, e.g.\n+\t * after the remote endpoint restarted and reset its sequence\n+\t * numbering.\n+\t /\n+\tSKB_DROP_REASON_TNL_OLD_SEQ,\n+\t/\n+\t @SKB_DROP_REASON_GRE_INVALID_HDR: the GRE header is invalid, e.g.\n+\t * an unsupported version or the routing bit is set.\n+\t /\n+\tSKB_DROP_REASON_GRE_INVALID_HDR,\n+\t/* @SKB_DROP_REASON_GRE_CSUM: GRE checksum error /\n+\tSKB_DROP_REASON_GRE_CSUM,\n+\t/\n+\t @SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND: no GRE tunnel found for the\n+\t * endpoints and the key the packet carries.\n+\t /\n+\tSKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND,\n+\t/\n+\t @SKB_DROP_REASON_TNL_ENCAP: failed to build the\n+\t * encapsulation header of a tunnel, e.g. an unknown or\n+\t * unregistered encapsulation type.\n+\t /\n+\tSKB_DROP_REASON_TNL_ENCAP,\n \t/\n \t @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which\n \t * shouldn't be used as a real 'reason' - only for tracing code gen\n" }
19/2	2026/09/18 08:31	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 36244 output: 22 thoughts: 27 Thoughts: Okay, here's the summary, rendered in the first person, assuming I'm an expert in the field: Diving into the Tunneling Headers Alright, time to dig in. To really understand how this tunneling implementation works, I need to get a clear picture of the relevant header files. Let's see... I should check `include/net/gre.h` and `include/net/ip6_tunnel.h`. Gotta refresh my memory of the GRE and IPv6 tunneling structures, data fields, and how the kernel handles the encapsulation and decapsulation process. This is where the core logic of these tunnels is defined. Time to look under the hood.
20/2	2026/09/18 08:31	tool	git-show	0m Args: { "File": "include/net/gre.h" } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/include/net/gre.h b/include/net/gre.h\nindex b55f67ecd2fc4..a63f26c3f78ed 100644\n--- a/include/net/gre.h\n+++ b/include/net/gre.h\n@@ -33,7 +33,7 @@ int gre_add_protocol(const struct gre_protocol proto, u8 version);\n int gre_del_protocol(const struct gre_protocol proto, u8 version);\n \n int gre_parse_header(struct sk_buff skb, struct tnl_ptk_info tpi,\n-\t\t bool csum_err, __be16 proto, int nhs);\n+\t\t enum skb_drop_reason reason, __be16 proto, int nhs);\n \n static inline bool netif_is_gretap(const struct net_device *dev)\n {\n" }
21/2	2026/09/18 08:31	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 36769 output: 25 thoughts: 16 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Diving into `ip6_tunnel.h` Alright, time to dig into the IPv6 tunnel header file, `include/net/ip6_tunnel.h`. I'm heading there specifically. I figure it's the right place to get a handle on the data structures and definitions related to IPv6 tunneling within the networking stack. I need to understand how these tunnels are configured, how packets are encapsulated and decapsulated, and what options are supported. I'm probably looking for structs like `ip6_tnl_parm` or similar if the implementation follows the expected pattern. I'll need to refresh my memory on any recent changes regarding addressing modes, MTU handling within the tunnels, and any particular complexities around flow labels if there's any IPv6 specific functionality. I'll also be focusing on the potential impact of IPv6 header extension handling with the tunneling logic. Got to be thorough and check all the defined macros and enum types.
22/2	2026/09/18 08:31	tool	git-show	0m Args: { "File": "include/net/ip6_tunnel.h" } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/include/net/ip6_tunnel.h b/include/net/ip6_tunnel.h\nindex b99805ee2fd14..95f6d12254df6 100644\n--- a/include/net/ip6_tunnel.h\n+++ b/include/net/ip6_tunnel.h\n@@ -143,7 +143,8 @@ int ip6_tnl_rcv(struct ip6_tnl tunnel, struct sk_buff skb,\n int ip6_tnl_xmit_ctl(struct ip6_tnl t, const struct in6_addr laddr,\n \t\t const struct in6_addr raddr);\n int ip6_tnl_xmit(struct sk_buff skb, struct net_device dev, __u8 dsfield,\n-\t\t struct flowi6 fl6, int encap_limit, __u32 pmtu, __u8 proto);\n+\t\t struct flowi6 fl6, int encap_limit, __u32 pmtu, __u8 proto,\n+\t\t enum skb_drop_reason reason);\n __u16 ip6_tnl_parse_tlv_enc_lim(struct sk_buff skb, __u8 raw);\n __u32 ip6_tnl_get_cap(struct ip6_tnl t, const struct in6_addr laddr,\n \t\t\t const struct in6_addr *raddr);\n" }
23/2	2026/09/18 08:31	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 37500 output: 29 thoughts: 219 Thoughts: Analyzing a Network Tunnel Crash Okay, so this patch series is focused solely on the "drop reasons" within tunnel code, specifically impacting `gre_demux.c`, `ip_gre.c`, `ip_tunnel.c`, `ip6_gre.c`, and `ip6_tunnel.c`. That's the scope. Now, let's dive into this crash report. The report flags a "task blocked for more than 143 seconds," which is a classic symptom. The blocked task is `syz.1.8682:26550`, and the call trace is key: `__schedule`, `schedule`, `__lock_sock`, `lock_sock_nested`, `sk_stream_wait_memory`, `tcp_sendmsg_locked`, `tcp_sendmsg`, `sock_sendmsg_nosec`, `__sys_sendto`, and finally, `__x64_sys_sendto`. This is a pretty standard trace; we're dealing with a send operation likely hitting a socket lock contention issue. My focus immediately goes to `sk_stream_wait_memory`. I know this is the function that the stack trace is stuck on. I'll need to check the code itself, which is in `net/core/stream.c`. Let's pull that up and see what's happening within `sk_stream_wait_memory` during the blocking period. Knowing the context will point me towards the root cause and which parts of the patch series could be implicated.
24/2	2026/09/18 08:31	tool	grepper	0m Args: { "Expression": "sk_stream_wait_memory", "PathPrefix": "net/" } Results: { "Output": "net/core/stream.c=100=void sk_stream_wait_close(struct sock sk, long timeout)\n--\nnet/core/stream.c-116-/\nnet/core/stream.c:117: sk_stream_wait_memory - Wait for more memory for a socket\nnet/core/stream.c-118- * @sk: socket to wait for memory\n--\nnet/core/stream.c-120- /\nnet/core/stream.c:121:int sk_stream_wait_memory(struct sock sk, long timeo_p)\nnet/core/stream.c-122-{\n--\nnet/core/stream.c-186-}\nnet/core/stream.c:187:EXPORT_SYMBOL(sk_stream_wait_memory);\nnet/core/stream.c-188-\n--\nnet/ipv4/tcp.c=1119=int tcp_sendmsg_locked(struct sock sk, struct msghdr msg, size_t size)\n--\nnet/ipv4/tcp.c-1406-\nnet/ipv4/tcp.c:1407:\t\terr = sk_stream_wait_memory(sk, \u0026timeo);\nnet/ipv4/tcp.c-1408-\t\tif (err != 0)\n--\nnet/ipv4/tcp_bpf.c=534=static int tcp_bpf_sendmsg(struct sock sk, struct msghdr msg, size_t size)\n--\nnet/ipv4/tcp_bpf.c-606-wait_for_memory:\nnet/ipv4/tcp_bpf.c:607:\t\terr = sk_stream_wait_memory(sk, \u0026timeo);\nnet/ipv4/tcp_bpf.c-608-\t\tif (err) {\n--\nnet/ipv4/tcp_output.c=2972=static bool tcp_write_xmit(struct sock sk, unsigned int mss_now, int nonagle,\n--\nnet/ipv4/tcp_output.c-3062-\t\t/* Argh, we hit an empty skb(), presumably a thread\nnet/ipv4/tcp_output.c:3063:\t\t * is sleeping in sendmsg()/sk_stream_wait_memory().\nnet/ipv4/tcp_output.c-3064-\t\t * We do not want to send a pure-ack packet and have\n--\nnet/kcm/kcmsock.c=752=static int kcm_sendmsg(struct socket sock, struct msghdr msg, size_t len)\n--\nnet/kcm/kcmsock.c-782-\t\tset_bit(SOCK_NOSPACE, \u0026sk-\u003esk_socket-\u003eflags);\nnet/kcm/kcmsock.c:783:\t\terr = sk_stream_wait_memory(sk, \u0026timeo);\nnet/kcm/kcmsock.c-784-\t\tif (err)\n--\nnet/kcm/kcmsock.c-792-\t\t\tkcm_push(kcm);\nnet/kcm/kcmsock.c:793:\t\t\terr = sk_stream_wait_memory(sk, \u0026timeo);\nnet/kcm/kcmsock.c-794-\t\t\tif (err)\n--\nnet/kcm/kcmsock.c-893-\t\tkcm_push(kcm);\nnet/kcm/kcmsock.c:894:\t\terr = sk_stream_wait_memory(sk, \u0026timeo);\nnet/kcm/kcmsock.c-895-\t\tif (err)\n--\nnet/mptcp/protocol.c=1999=static int mptcp_sendmsg(struct sock sk, struct msghdr msg, size_t len)\n--\nnet/mptcp/protocol.c-2110-\t\t__mptcp_push_pending(sk, msg-\u003emsg_flags);\nnet/mptcp/protocol.c:2111:\t\tret = sk_stream_wait_memory(sk, \u0026timeo);\nnet/mptcp/protocol.c-2112-\t\tif (ret)\n--\nnet/sctp/socket.c=1560=static int sctp_error(struct sock sk, int flags, int err)\n--\nnet/sctp/socket.c-1589- /\nnet/sctp/socket.c:1590:/* BUG: We do not implement the equivalent of sk_stream_wait_memory(). /\nnet/sctp/socket.c-1591-\n--\nnet/smc/smc_tx.c=77=static int smc_tx_wait(struct smc_sock smc, int flags)\n--\nnet/smc/smc_tx.c-84-\nnet/smc/smc_tx.c:85:\t/* similar to sk_stream_wait_memory /\nnet/smc/smc_tx.c-86-\ttimeo = sock_sndtimeo(sk, flags \u0026 MSG_DONTWAIT);\n--\nnet/tls/tls_device.c=421=static int tls_push_data(struct sock sk,\n--\nnet/tls/tls_device.c-469-\t\tif (unlikely(rc)) {\nnet/tls/tls_device.c:470:\t\t\trc = sk_stream_wait_memory(sk, \u0026timeo);\nnet/tls/tls_device.c-471-\t\t\tif (!rc)\n--\nnet/tls/tls_sw.c=766=static int tls_sw_sendmsg_locked(struct sock sk, struct msghdr msg,\n--\nnet/tls/tls_sw.c-970-wait_for_memory:\nnet/tls/tls_sw.c:971:\t\tret = sk_stream_wait_memory(sk, \u0026timeo);\nnet/tls/tls_sw.c-972-\t\tif (ret) {\n--\nnet/xfrm/espintcp.c=311=static int espintcp_sendmsg(struct sock sk, struct msghdr msg, size_t size)\n--\nnet/xfrm/espintcp.c-350-\nnet/xfrm/espintcp.c:351:\t\terr = sk_stream_wait_memory(sk, \u0026timeo);\nnet/xfrm/espintcp.c-352-\t\tif (err)\n" }
25/2	2026/09/18 08:31	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 39689 output: 35 thoughts: 20 Thoughts: Here's a summary of my thought process, as requested: Diving into `net/core/stream.c` Alright, let's get down to brass tacks. I'm going to take a look at the `net/core/stream.c` file, specifically around line 121. I'm assuming there's something interesting or pertinent there, and I need to understand it in the context of whatever problem or investigation I'm currently focused on. Knowing the line number is crucial for my understanding. Maybe I saw a comment, a mention in some documentation, or maybe I encountered a strange behavior that suggests that particular section warrants my attention. I'm expecting to either refresh my memory of something I already know or learn something new, or confirm a suspicion. Let's see what's there.
26/2	2026/09/18 08:31	tool	read-file	0m Args: { "File": "net/core/stream.c", "FirstLine": 120, "LineCount": 70 } Results: { "Contents": " 120:\t /\n 121:\tint sk_stream_wait_memory(struct sock sk, long timeo_p)\n 122:\t{\n 123:\t\tint ret, err = 0;\n 124:\t\tlong vm_wait = 0;\n 125:\t\tlong current_timeo = timeo_p;\n 126:\t\tDEFINE_WAIT_FUNC(wait, woken_wake_function);\n 127:\t\n 128:\t\tif (sk_stream_memory_free(sk))\n 129:\t\t\tcurrent_timeo = vm_wait = get_random_u32_below(HZ / 5) + 2;\n 130:\t\n 131:\t\tadd_wait_queue(sk_sleep(sk), \u0026wait);\n 132:\t\n 133:\t\twhile (1) {\n 134:\t\t\tsk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);\n 135:\t\n 136:\t\t\tif (sk-\u003esk_err \|\| (sk-\u003esk_shutdown \u0026 SEND_SHUTDOWN))\n 137:\t\t\t\tgoto do_error;\n 138:\t\t\tif (!timeo_p)\n 139:\t\t\t\tgoto do_eagain;\n 140:\t\t\tif (signal_pending(current))\n 141:\t\t\t\tgoto do_interrupted;\n 142:\t\t\tsk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);\n 143:\t\t\tif (sk_stream_memory_free(sk) \u0026\u0026 !vm_wait)\n 144:\t\t\t\tbreak;\n 145:\t\n 146:\t\t\tset_bit(SOCK_NOSPACE, \u0026sk-\u003esk_socket-\u003eflags);\n 147:\t\t\tsk-\u003esk_write_pending++;\n 148:\t\t\tret = sk_wait_event(sk, \u0026current_timeo, READ_ONCE(sk-\u003esk_err) \|\|\n 149:\t\t\t\t\t (READ_ONCE(sk-\u003esk_shutdown) \u0026 SEND_SHUTDOWN) \|\|\n 150:\t\t\t\t\t (sk_stream_memory_free(sk) \u0026\u0026 !vm_wait),\n 151:\t\t\t\t\t \u0026wait);\n 152:\t\t\tsk-\u003esk_write_pending--;\n 153:\t\t\tif (ret \u003c 0)\n 154:\t\t\t\tgoto do_error;\n 155:\t\n 156:\t\t\tif (vm_wait) {\n 157:\t\t\t\tvm_wait -= current_timeo;\n 158:\t\t\t\tcurrent_timeo = timeo_p;\n 159:\t\t\t\tif (current_timeo != MAX_SCHEDULE_TIMEOUT \u0026\u0026\n 160:\t\t\t\t (current_timeo -= vm_wait) \u003c 0)\n 161:\t\t\t\t\tcurrent_timeo = 0;\n 162:\t\t\t\tvm_wait = 0;\n 163:\t\t\t}\n 164:\t\t\ttimeo_p = current_timeo;\n 165:\t\t}\n 166:\tout:\n 167:\t\tif (!sock_flag(sk, SOCK_DEAD))\n 168:\t\t\tremove_wait_queue(sk_sleep(sk), \u0026wait);\n 169:\t\treturn err;\n 170:\t\n 171:\tdo_error:\n 172:\t\terr = -EPIPE;\n 173:\t\tgoto out;\n 174:\tdo_eagain:\n 175:\t\t/ Make sure that whenever EAGAIN is returned, EPOLLOUT event can\n 176:\t\t * be generated later.\n 177:\t\t * When TCP receives ACK packets that make room, tcp_check_space()\n 178:\t\t * only calls tcp_new_space() if SOCK_NOSPACE is set.\n 179:\t\t /\n 180:\t\tset_bit(SOCK_NOSPACE, \u0026sk-\u003esk_socket-\u003eflags);\n 181:\t\terr = -EAGAIN;\n 182:\t\tgoto out;\n 183:\tdo_interrupted:\n 184:\t\terr = sock_intr_errno(timeo_p);\n 185:\t\tgoto out;\n 186:\t}\n 187:\tEXPORT_SYMBOL(sk_stream_wait_memory);\n 188:\t\n 189:\tint sk_stream_error(struct sock *sk, int flags, int err)\n" }
27/2	2026/09/18 08:31	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 41045 output: 27 thoughts: 1468 Thoughts: Analyzing a Potential Socket Lock Contention Issue Okay, so I'm looking at this `sk_wait_event` macro and how it functions. It's essentially releasing the socket lock (`release_sock(sk)`), scheduling, and then reacquiring it (`lock_sock(sk)`). That's standard practice, but now I see this stack trace showing a deadlock situation. Specifically, task 26550 is blocked within `__lock_sock` trying to get `sk_lock-AF_INET` on address `ffff88810f55b660`. The stack points to `sk_stream_wait_memory` calling `lock_sock_nested`, then `__lock_sock`, which is where it's stuck. So, who's holding that lock? Ah, task 26551 is also holding that same lock! It's at `sk_wait_data` with its lock, and the call chain shows it's also got a couple of `rcu_read_lock`'s active. Okay, interesting. Let's broaden the scope and look at other processes. I see a lot of threads holding the `rtnl_mutex`. That looks normal. I'm seeing a lot of these `rtnl_mutex` entries on various CPUs, indicating some network configuration activity. Not immediately worrying, but worth keeping an eye on for any interaction with the socket locking issue. Hang on... CPU 1 has an NMI backtrace from task syz.3.8783/26988. This is the one that's also in the `rtnl_mutex` and `tun_chr_close` function. Wait, it's at `zap_class`! That's odd. `zap_class` is a lockdep-related function. It's in `kernel/locking/lockdep.c`. I see a call trace that leads to `lockdep_unregister_key` and eventually, the task's dying. Let's drill down and see why this task is at `zap_class`. Let me look at the code for both `zap_class` and `lockdep_unregister_key`. I need to figure out the path that task 26988 took, and if it somehow relates to the socket lock contention I'm seeing in the other thread. This looks like a potentially tricky interaction between network device teardown and socket locking. It's possible that the device's cleanup routine, is somehow interfering with the socket locking, causing the deadlock.
28/2	2026/09/18 08:32	tool	grepper	0m Args: { "Expression": "zap_class", "PathPrefix": "kernel/locking/" } Results: { "Output": "kernel/locking/lockdep.c=6322=static void remove_class_from_lock_chains(struct pending_free pf,\n--\nkernel/locking/lockdep.c-6339- /\nkernel/locking/lockdep.c:6340:static void zap_class(struct pending_free pf, struct lock_class class)\nkernel/locking/lockdep.c-6341-{\n--\nkernel/locking/lockdep.c=6489=static void __lockdep_free_key_range(struct pending_free pf, void start,\n--\nkernel/locking/lockdep.c-6502-\t\t\t\tcontinue;\nkernel/locking/lockdep.c:6503:\t\t\tzap_class(pf, class);\nkernel/locking/lockdep.c-6504-\t\t}\n--\nkernel/locking/lockdep.c=6592=static void __lockdep_reset_lock(struct pending_free *pf,\n--\nkernel/locking/lockdep.c-6606-\t\tif (class)\nkernel/locking/lockdep.c:6607:\t\t\tzap_class(pf, class);\nkernel/locking/lockdep.c-6608-\t}\n" }
29/2	2026/09/18 08:32	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 43412 output: 15 thoughts: 40 Thoughts: Okay, let's break this down. Investigating the `series-patches` Function Right, before I proceed any further, I need to make absolutely sure I understand the function `series-patches`, and how it interacts with patch numbers. My initial instinct is to iterate through it using `PatchNum = 1`, `PatchNum = 2`, and so on, but I can't do that until I have a solid understanding of how `series-patches` is designed to work. It's crucial I don't overlook any subtleties in its implementation. A review is required before I move forward, no assumptions can be made. Time for a code dive.
30/2	2026/09/18 08:32	tool	series-patches	0m Args: { "PatchNum": 1 } Results: { "Output": "Patch [1] [PATCH net-next v3 1/9] ip_tunnel: add drop reasons to the generic RX path:\n\nip_tunnel_rcv() collapses four distinct failures into a single plain\nkfree_skb(), so a packet dropped there simply vanishes:\n\n - the tunnel options carried by the packet do not match the tunnel\n configuration (checksum or sequence number),\n - the sequence number is older than the expected one,\n - the inner network header cannot be pulled,\n - the ECN decapsulation check fails (RFC 6040).\n\nOnly the device error counters (rx_crc_errors, rx_fifo_errors,\nrx_length_errors, rx_frame_errors) hint at the cause, and they are not\nreported to drop_monitor or to the skb:kfree_skb tracepoint.\n\nAdd two drop reasons for the tunnel specific cases and reuse the\nexisting ones for the rest:\n\n - SKB_DROP_REASON_TNL_OPT_MISMATCH is used when the packet\n does not carry the checksum or the sequence number option the tunnel\n is configured for. This is a configuration mismatch between the two\n endpoints rather than a corrupted checksum: the checksum itself is\n validated earlier, in gre_parse_header().\n\n - SKB_DROP_REASON_TNL_OLD_SEQ is used when the sequence number\n is older than the expected one. Unlike the previous one this is a\n property of the received traffic: a remote endpoint that restarts\n and resets its sequence numbering has all of its packets dropped\n until i_seqno catches up.\n\n - pskb_inet_may_pull_reason() already computes a drop reason,\n SKB_DROP_REASON_PKT_TOO_SMALL or SKB_DROP_REASON_NOMEM, which was\n discarded so far.\n\n - SKB_DROP_REASON_IP_TUNNEL_ECN already exists and documents exactly\n this check, but until now it was only used by vxlan.\n\nThe sequence number test is split in two so that the two cases can be\ntold apart. The error counters are left unchanged.\n\nip_tunnel_rcv() is the RX path of ip_gre, ipip and sit. The checksum\nand the sequence number options only exist for GRE, so the two new\nreasons are reachable through ip_gre alone, while the length and the\nECN ones apply to all three.\n\nAssisted-by: Claude-Code:claude-opus-5\nSigned-off-by: Anton Danilov \u003clittlesmilingcloud@gmail.com\u003e\n---\n include/net/dropreason-core.h \| 16 ++++++++++++++++\n net/ipv4/ip_tunnel.c \| 19 +++++++++++++++----\n 2 files changed, 31 insertions(+), 4 deletions(-)\n\ndiff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h\nindex 12f909651591..e1fdd11c939f 100644\n--- a/include/net/dropreason-core.h\n+++ b/include/net/dropreason-core.h\n@@ -129,6 +129,8 @@\n \tFN(PSP_INPUT)\t\t\t\\\n \tFN(PSP_OUTPUT)\t\t\t\\\n \tFN(RECURSION_LIMIT)\t\t\\\n+\tFN(TNL_OPT_MISMATCH)\t\t\\\n+\tFN(TNL_OLD_SEQ)\t\t\t\\\n \tFNe(MAX)\n \n /\n@@ -612,6 +614,20 @@ enum skb_drop_reason {\n \tSKB_DROP_REASON_PSP_OUTPUT,\n \t/ @SKB_DROP_REASON_RECURSION_LIMIT: Dead loop on virtual device. /\n \tSKB_DROP_REASON_RECURSION_LIMIT,\n+\t/\n+\t @SKB_DROP_REASON_TNL_OPT_MISMATCH: the tunnel options\n+\t * carried by the packet do not match the tunnel configuration, e.g.\n+\t * a GRE tunnel configured with 'icsum' or 'iseq' received a packet\n+\t * with no checksum or no sequence number.\n+\t /\n+\tSKB_DROP_REASON_TNL_OPT_MISMATCH,\n+\t/\n+\t @SKB_DROP_REASON_TNL_OLD_SEQ: the sequence number carried\n+\t * by the packet is older than the one expected by the tunnel, e.g.\n+\t * after the remote endpoint restarted and reset its sequence\n+\t * numbering.\n+\t /\n+\tSKB_DROP_REASON_TNL_OLD_SEQ,\n \t/\n \t @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which\n \t * shouldn't be used as a real 'reason' - only for tracing code gen\ndiff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c\nindex 13b5e35e8790..0260a97e990e 100644\n--- a/net/ipv4/ip_tunnel.c\n+++ b/net/ipv4/ip_tunnel.c\n@@ -378,6 +378,7 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n \t\t const struct tnl_ptk_info tpi, struct metadata_dst tun_dst,\n \t\t bool log_ecn_error)\n {\n+\tenum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;\n \tconst struct iphdr iph = ip_hdr(skb);\n \tint nh, err;\n \n@@ -392,14 +393,22 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n \t test_bit(IP_TUNNEL_CSUM_BIT, tpi-\u003eflags)) {\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_crc_errors);\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\treason = SKB_DROP_REASON_TNL_OPT_MISMATCH;\n \t\tgoto drop;\n \t}\n \n \tif (test_bit(IP_TUNNEL_SEQ_BIT, tunnel-\u003eparms.i_flags)) {\n-\t\tif (!test_bit(IP_TUNNEL_SEQ_BIT, tpi-\u003eflags) \|\|\n-\t\t (tunnel-\u003ei_seqno \u0026\u0026 (s32)(ntohl(tpi-\u003eseq) - tunnel-\u003ei_seqno) \u003c 0)) {\n+\t\tif (!test_bit(IP_TUNNEL_SEQ_BIT, tpi-\u003eflags)) {\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_fifo_errors);\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_TNL_OPT_MISMATCH;\n+\t\t\tgoto drop;\n+\t\t}\n+\t\tif (tunnel-\u003ei_seqno \u0026\u0026\n+\t\t (s32)(ntohl(tpi-\u003eseq) - tunnel-\u003ei_seqno) \u003c 0) {\n+\t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_fifo_errors);\n+\t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_TNL_OLD_SEQ;\n \t\t\tgoto drop;\n \t\t}\n \t\ttunnel-\u003ei_seqno = ntohl(tpi-\u003eseq) + 1;\n@@ -413,7 +422,8 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n \n \tskb_set_network_header(skb, (tunnel-\u003edev-\u003etype == ARPHRD_ETHER) ? ETH_HLEN : 0);\n \n-\tif (!pskb_inet_may_pull(skb)) {\n+\treason = pskb_inet_may_pull_reason(skb);\n+\tif (reason) {\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_length_errors);\n \t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n \t\tgoto drop;\n@@ -428,6 +438,7 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n \t\tif (err \u003e 1) {\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_frame_errors);\n \t\t\tDEV_STATS_INC(tunnel-\u003edev, rx_errors);\n+\t\t\treason = SKB_DROP_REASON_IP_TUNNEL_ECN;\n \t\t\tgoto drop;\n \t\t}\n \t}\n@@ -451,7 +462,7 @@ int ip_tunnel_rcv(struct ip_tunnel tunnel, struct sk_buff skb,\n drop:\n \tif (tun_dst)\n \t\tdst_release((struct dst_entry )tun_dst);\n-\tkfree_skb(skb);\n+\tkfree_skb_reason(skb, reason);\n \treturn 0;\n }\n EXPORT_SYMBOL_GPL(ip_tunnel_rcv);\n-- \n2.47.3" }
31/2	2026/09/18 08:32	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 45847 output: 32 thoughts: 672 Thoughts: Analyzing a Potentially Unrelated Kernel Crash Okay, let's break this down. First, I see a patch series related to adding drop reasons to various IP tunnel and GRE paths, both RX and TX. My initial thought is, "Could this be the culprit?" But let's hold off on that for a second. I need to understand this crash first. The crucial piece here is this: `INFO: task syz.1.8682:26550 blocked for more than 143 seconds`. That's a long time to be blocked. That is interesting, given how much these patches touch IP tunnels and GRE. Right, so task 26550, which is likely a syzkaller-generated test case, is blocked. The call trace says it's calling `sendto()` on a TCP socket. So, inside `tcp_sendmsg_locked`, the task ran out of send buffer memory. This led to a call to `sk_stream_wait_memory`, which then called `sk_wait_event`. This looks like the classic scenario where a socket needs to wait for more send buffer space to become available. Now, here's where it gets interesting and where my experience comes in. Inside `sk_wait_event`, the code releases the socket lock (`release_sock`), sleeps, and then attempts to reacquire the lock with `lock_sock`. It looks like it is going to `__lock_sock` to reacquire the lock. The lock is where the core issue might be, so now I need to dive into `__lock_sock` in the kernel source. The issue is likely a lock inversion or a deadlock condition. That will be the next place to investigate.
32/2	2026/09/18 08:32	tool	grepper	0m Args: { "Expression": "void __lock_sock", "PathPrefix": "net/core/sock.c" } Results: { "Output": "net/core/sock.c=3233=EXPORT_SYMBOL(sk_page_frag_refill);\nnet/core/sock.c-3234-\nnet/core/sock.c:3235:static void __lock_sock(struct sock *sk)\nnet/core/sock.c-3236-\t__releases(\u0026sk-\u003esk_lock.slock)\n" }
33/2	2026/09/18 08:32	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 47036 output: 36 thoughts: 20 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Diving into `__lock_sock` in `sock.c` Okay, so I'm looking at `__lock_sock` in `net/core/sock.c` again. I need to refresh my understanding of the intricacies of socket locking within the kernel. It's a critical area; a misstep here can lead to a world of pain – deadlocks, race conditions, and all sorts of fun. I want to pay particularly close attention to how it handles potential contention, especially given the various layers of locking that typically exist around socket operations. I'll need to remember the interactions with the `sk_lock`, `rcu`, and any relevant spinlocks. I know there are subtleties around nested locking and interrupt contexts. I'll be watching for any use of `try_` prefixes, and how the lock is actually acquired in relation to any associated wait queues. It's time to refresh and ensure that the basics are correct, so that it's easy to deal with any more complex issues that arise downstream. I'll be keeping an eye out for any edge cases, like how it deals with concurrent `send` and `recv` calls on the same socket from multiple threads. I'm going to pay close attention to the code paths that deal with socket state changes, and how those transitions are synchronized with the lock acquisition and release.
34/2	2026/09/18 08:32	tool	read-file	0m Args: { "File": "net/core/sock.c", "FirstLine": 3235, "LineCount": 40 } Results: { "Contents": "3235:\tstatic void __lock_sock(struct sock sk)\n3236:\t\t__releases(\u0026sk-\u003esk_lock.slock)\n3237:\t\t__acquires(\u0026sk-\u003esk_lock.slock)\n3238:\t{\n3239:\t\tDEFINE_WAIT(wait);\n3240:\t\n3241:\t\tfor (;;) {\n3242:\t\t\tprepare_to_wait_exclusive(\u0026sk-\u003esk_lock.wq, \u0026wait,\n3243:\t\t\t\t\t\tTASK_UNINTERRUPTIBLE);\n3244:\t\t\tspin_unlock_bh(\u0026sk-\u003esk_lock.slock);\n3245:\t\t\tschedule();\n3246:\t\t\tspin_lock_bh(\u0026sk-\u003esk_lock.slock);\n3247:\t\t\tif (!sock_owned_by_user(sk))\n3248:\t\t\t\tbreak;\n3249:\t\t}\n3250:\t\tfinish_wait(\u0026sk-\u003esk_lock.wq, \u0026wait);\n3251:\t}\n3252:\t\n3253:\tvoid __release_sock(struct sock sk)\n3254:\t\t__releases(\u0026sk-\u003esk_lock.slock)\n3255:\t\t__acquires(\u0026sk-\u003esk_lock.slock)\n3256:\t{\n3257:\t\tstruct sk_buff skb, next;\n3258:\t\tint nb = 0;\n3259:\t\n3260:\t\twhile ((skb = sk-\u003esk_backlog.head) != NULL) {\n3261:\t\t\tsk-\u003esk_backlog.head = sk-\u003esk_backlog.tail = NULL;\n3262:\t\n3263:\t\t\tspin_unlock_bh(\u0026sk-\u003esk_lock.slock);\n3264:\t\n3265:\t\t\twhile (1) {\n3266:\t\t\t\tnext = skb-\u003enext;\n3267:\t\t\t\tprefetch(next);\n3268:\t\t\t\tDEBUG_NET_WARN_ON_ONCE(skb_dst_is_noref(skb));\n3269:\t\t\t\tskb_mark_not_on_list(skb);\n3270:\t\t\t\tsk_backlog_rcv(sk, skb);\n3271:\t\n3272:\t\t\t\tskb = next;\n3273:\t\t\t\tif (!skb)\n3274:\t\t\t\t\tbreak;\n" }
35/2	2026/09/18 08:32	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 48014 output: 27 thoughts: 609 Thoughts: Analyzing a Socket Lock Contention Okay, so I'm looking at a situation where `__lock_sock` is blocked, waiting for a socket not to be owned by a user, but it is owned. That's a red flag. Specifically, task 26550 is stuck. The key question is: who has this socket locked? Let's check the locks in the system. Bingo! Both task 26550 and task 26551 are holding a lock on the same socket, which is `ffff88810f55b660`. Clearly, that is the issue. Task 26550 has one lock: the socket lock, which is expected. But, why does task 26551 also have the socket lock? That's what I need to understand. Looking at 26551's lock situation, there it is: `sk_lock-AF_INET` on the same socket! It's also got a couple of `rcu_read_lock` locks, one in `__ip_queue_xmit` and one in `ip_output`. This is a classic concurrency problem. My next step is to examine what's going on in the `sk_wait_data` function, which is where 26551 is currently executing. I'll head over to `net/core/sock.c` (or wherever it's defined) to trace the execution path and figure out why that socket is being held by 26551 at the same time that 26550 needs to acquire it. This is likely a critical section issue or a race condition, and `sk_wait_data` should shed some light on the lock acquisition strategy.
36/2	2026/09/18 08:33	tool	grepper	0m Args: { "Expression": "sk_wait_data", "PathPrefix": "net/" } Results: { "Output": "net/core/sock.c=3301=EXPORT_SYMBOL_GPL(__sk_flush_backlog);\n--\nnet/core/sock.c-3303-/*\nnet/core/sock.c:3304: sk_wait_data - wait for data to arrive at sk_receive_queue\nnet/core/sock.c-3305- * @sk: sock to wait on\n--\nnet/core/sock.c-3313- /\nnet/core/sock.c:3314:int sk_wait_data(struct sock sk, long timeo, const struct sk_buff skb)\nnet/core/sock.c-3315-{\n--\nnet/core/sock.c-3325-}\nnet/core/sock.c:3326:EXPORT_SYMBOL(sk_wait_data);\nnet/core/sock.c-3327-\n--\nnet/ipv4/tcp.c=814=ssize_t tcp_splice_read(struct socket sock, loff_t ppos,\n--\nnet/ipv4/tcp.c-872-\t\t\t\tbreak;\nnet/ipv4/tcp.c:873:\t\t\tret = sk_wait_data(sk, \u0026timeo, NULL);\nnet/ipv4/tcp.c-874-\t\t\tif (ret \u003c 0)\n--\nnet/ipv4/tcp.c=2658=static int tcp_recvmsg_locked(struct sock sk, struct msghdr msg, size_t len,\n--\nnet/ipv4/tcp.c-2796-\t\t\ttcp_cleanup_rbuf(sk, copied);\nnet/ipv4/tcp.c:2797:\t\t\terr = sk_wait_data(sk, \u0026timeo, last);\nnet/ipv4/tcp.c-2798-\t\t\tif (err \u003c 0) {\n--\nnet/llc/af_llc.c=643=static int llc_wait_data(struct sock sk, long timeo)\n--\nnet/llc/af_llc.c-663-\t\trc = 0;\nnet/llc/af_llc.c:664:\t\tif (sk_wait_data(sk, \u0026timeo, NULL))\nnet/llc/af_llc.c-665-\t\t\tbreak;\n--\nnet/llc/af_llc.c=757=static int llc_ui_recvmsg(struct socket sock, struct msghdr msg, size_t len,\n--\nnet/llc/af_llc.c-853-\t\t} else\nnet/llc/af_llc.c:854:\t\t\tsk_wait_data(sk, \u0026timeo, NULL);\nnet/llc/af_llc.c-855-\n--\nnet/mptcp/protocol.c=2379=static int mptcp_recvmsg(struct sock sk, struct msghdr msg, size_t len,\n--\nnet/mptcp/protocol.c-2462-\t\tmptcp_cleanup_rbuf(msk, copied);\nnet/mptcp/protocol.c:2463:\t\terr = sk_wait_data(sk, \u0026timeo, last);\nnet/mptcp/protocol.c-2464-\t\tif (err \u003c 0) {\n--\nnet/mptcp/protocol.c=4640=static ssize_t mptcp_splice_read(struct socket sock, loff_t ppos,\n--\nnet/mptcp/protocol.c-4697-\t\t\t\tbreak;\nnet/mptcp/protocol.c:4698:\t\t\tret = sk_wait_data(sk, \u0026timeo, NULL);\nnet/mptcp/protocol.c-4699-\t\t\tif (ret \u003c 0)\n--\nnet/smc/af_smc.c=2714=int smc_accept(struct socket sock, struct socket *new_sock,\n--\nnet/smc/af_smc.c-2768-\t\t\tif (skb_queue_empty(\u0026clcsk-\u003esk_receive_queue))\nnet/smc/af_smc.c:2769:\t\t\t\tsk_wait_data(clcsk, \u0026timeo, NULL);\nnet/smc/af_smc.c-2770-\t\t\trelease_sock(clcsk);\n" }
37/2	2026/09/18 08:33	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 50143 output: 36 thoughts: 21 Thoughts: Here's a first-person summary, tailored for an expert audience, based on your instructions: Diving into `sk_wait_data` Okay, let's pull up the source code for `sk_wait_data` within `net/core/sock.c`. I need to refresh my understanding of how this function handles socket data availability signaling. I'm especially interested in the nuances of its interactions with wait queues, and the various conditions under which it might return prematurely or block. I want to look specifically at how it handles the interaction between `sk_receive_queue` and the wait queue. I know this is a critical section for performance so I'll be looking for any potential bottlenecks or race conditions. I need to refresh myself on how the `sk_data_ready` and `sk_error_report` flags are used and whether there are any subtle inefficiencies. My mind keeps returning to the ways that congestion, flow control, and interrupt handling will interact with these code paths. I want to look for potential optimizations here that will reduce the number of calls to the atomic functions. I'm ready to dig in and understand this function better.
38/2	2026/09/18 08:33	tool	read-file	0m Args: { "File": "net/core/sock.c", "FirstLine": 3305, "LineCount": 25 } Results: { "Contents": "3305:\t * @sk: sock to wait on\n3306:\t * @timeo: for how long\n3307:\t * @skb: last skb seen on sk_receive_queue\n3308:\t \n3309:\t Now socket state including sk-\u003esk_err is changed only under lock,\n3310:\t * hence we may omit checks after joining wait queue.\n3311:\t * We check receive queue before schedule() only as optimization;\n3312:\t * it is very likely that release_sock() added new data.\n3313:\t /\n3314:\tint sk_wait_data(struct sock sk, long timeo, const struct sk_buff skb)\n3315:\t{\n3316:\t\tDEFINE_WAIT_FUNC(wait, woken_wake_function);\n3317:\t\tint rc;\n3318:\t\n3319:\t\tadd_wait_queue(sk_sleep(sk), \u0026wait);\n3320:\t\tsk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);\n3321:\t\trc = sk_wait_event(sk, timeo, skb_peek_tail(\u0026sk-\u003esk_receive_queue) != skb, \u0026wait);\n3322:\t\tsk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);\n3323:\t\tremove_wait_queue(sk_sleep(sk), \u0026wait);\n3324:\t\treturn rc;\n3325:\t}\n3326:\tEXPORT_SYMBOL(sk_wait_data);\n3327:\t\n3328:\t/*\n3329:\t \t__sk_mem_raise_allocated - increase memory_allocated\n" }
39/2	2026/09/18 08:33	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 50893 output: 30 thoughts: 452 Thoughts: Decoding the Network Conundrum Okay, here's what's running through my head. I'm looking at the lock information for task 26551, and it's holding `sk_lock` and, crucially, two instances of `rcu_read_lock`. The fact that it's got `rcu_read_lock` acquired at `__ip_queue_xmit` and `ip_output` immediately raises a red flag. Why is a task holding a read lock in those parts of the network stack? I'm digging deeper into `sk_wait_data`, seeing if I can find a connection. I'm thinking, does `tcp_recvmsg_locked` have some interaction with `__ip_queue_xmit`? Okay, in `tcp_recvmsg_locked`, I see it calls `tcp_cleanup_rbuf` and then `sk_wait_data`. What's the deal with `tcp_cleanup_rbuf`? Oh, it looks like it's involved in sending ACKs and window updates! And that leads me to... yes! `tcp_send_ack(sk)` calls `__tcp_send_ack`, which calls `tcp_transmit_skb`, which does call `__ip_queue_xmit` which in turn calls `ip_output`! So, there it is – 26551 is holding the `rcu_read_lock` at `ip_output` because of an ACK or window update triggered by `tcp_cleanup_rbuf` within `tcp_recvmsg_locked`. This seems to be where `ip_output` goes in the process. Now I need to take a closer look at `ip_output`.
40/2	2026/09/18 08:34	tool	grepper	0m Args: { "Expression": "int ip_output\\(", "PathPrefix": "net/ipv4/" } Results: { "Output": "net/ipv4/ip_output.c=367=int ip_mc_output(struct net net, struct sock sk, struct sk_buff skb)\n--\nnet/ipv4/ip_output.c-426-\nnet/ipv4/ip_output.c:427:int ip_output(struct net net, struct sock sk, struct sk_buff skb)\nnet/ipv4/ip_output.c-428-{\n" }
41/2	2026/09/18 08:34	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 51878 output: 38 thoughts: 23 Thoughts: Here's a summary of my thought process, as requested: Diving into `ip_output.c` Alright, time to dig in. My mental radar is pinging a potential area of interest within the kernel's IPv4 output path. Based on my existing knowledge and the likely nature of the problem, I'm going to jump straight into `net/ipv4/ip_output.c`, specifically around line 427. This location often holds interesting code related to packet construction, fragmentation, or perhaps even queueing decisions. I expect to be focusing on the logic that is called when a packet leaves the IP layer. I'm hoping to understand a particular function and its interactions, and this area frequently provides the building blocks for those operations. I'm ready to parse the code and see what insights line 427, and its neighboring lines, have to offer.
42/2	2026/09/18 08:34	tool	read-file	0m Args: { "File": "net/ipv4/ip_output.c", "FirstLine": 420, "LineCount": 40 } Results: { "Contents": " 420:\t\n 421:\t\treturn NF_HOOK_COND(NFPROTO_IPV4, NF_INET_POST_ROUTING,\n 422:\t\t\t\t net, sk, skb, NULL, skb-\u003edev,\n 423:\t\t\t\t ip_finish_output,\n 424:\t\t\t\t !(IPCB(skb)-\u003eflags \u0026 IPSKB_REROUTED));\n 425:\t}\n 426:\t\n 427:\tint ip_output(struct net net, struct sock sk, struct sk_buff skb)\n 428:\t{\n 429:\t\tstruct net_device dev, indev = skb-\u003edev;\n 430:\t\tint ret_val;\n 431:\t\n 432:\t\trcu_read_lock();\n 433:\t\tdev = skb_dst_dev_rcu(skb);\n 434:\t\tskb-\u003edev = dev;\n 435:\t\tskb-\u003eprotocol = htons(ETH_P_IP);\n 436:\t\n 437:\t\tret_val = NF_HOOK_COND(NFPROTO_IPV4, NF_INET_POST_ROUTING,\n 438:\t\t\t\t\tnet, sk, skb, indev, dev,\n 439:\t\t\t\t\tip_finish_output,\n 440:\t\t\t\t\t!(IPCB(skb)-\u003eflags \u0026 IPSKB_REROUTED));\n 441:\t\trcu_read_unlock();\n 442:\t\treturn ret_val;\n 443:\t}\n 444:\tEXPORT_SYMBOL(ip_output);\n 445:\t\n 446:\t/\n 447:\t * copy saddr and daddr, possibly using 64bit load/stores\n 448:\t * Equivalent to :\n 449:\t * iph-\u003esaddr = fl4-\u003esaddr;\n 450:\t * iph-\u003edaddr = fl4-\u003edaddr;\n 451:\t /\n 452:\tstatic void ip_copy_addrs(struct iphdr iph, const struct flowi4 fl4)\n 453:\t{\n 454:\t\tBUILD_BUG_ON(offsetof(typeof(fl4), daddr) !=\n 455:\t\t\t offsetof(typeof(*fl4), saddr) + sizeof(fl4-\u003esaddr));\n 456:\t\n 457:\t\tiph-\u003esaddr = fl4-\u003esaddr;\n 458:\t\tiph-\u003edaddr = fl4-\u003edaddr;\n 459:\t}\n" }
43/2	2026/09/18 08:34	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 52786 output: 37 thoughts: 846 Thoughts: Analyzing a Potential RCU Read-Side Critical Section Issue Okay, let's break this down. I'm looking at the `ip_output` function, specifically the RCU read-side critical section defined by `rcu_read_lock()` and `rcu_read_unlock()`. Inside that section, the packet is ultimately transmitted, likely through `dev_queue_xmit` within `ip_finish_output`. Now, the concerning part. Task 26551 is apparently holding both `sk_lock-AF_INET` at `sk_wait_data` AND `rcu_read_lock` at `__ip_queue_xmit` and `ip_output` simultaneously. The lockdep trace clearly shows this: `sk_lock-AF_INET` at `sk_wait_data`, followed by two instances of `rcu_read_lock`, one at `__ip_queue_xmit` and the other at `ip_output`. The immediate red flag is whether 26551 is sleeping while holding `rcu_read_lock`. That's a definite no-no, right? But the trace doesn't suggest that 26551 is actually sleeping, and I see from the PREEMPT flag that we are dealing with a PREEMPT kernel. The fact that the task didn't get an NMI backtrace initially threw me. But then I remembered, we have a multi-CPU machine, with CPU 0 running `khungtaskd` and CPU 1 running `syz.3.8783`. Task 26551 wasn't running on the CPU that was being checked. So, 26551 wasn't necessarily sleeping but potentially preempted and scheduled out. That's a crucial distinction. In a PREEMPT kernel with `PREEMPT_RCU`, a task can be preempted inside an RCU read-side critical section. The system would manage this by placing the task in `rcu_node->blkd_tasks`. But then, why did 26551 stop where it did? The lockdep trace is key. It shows 26551 at `sk_wait_data` and inside `ip_output`. This is really odd. Is `sk_wait_data` calling something that calls `__ip_queue_xmit`? No, it doesn't appear so directly. However, it seems likely that this is from `tcp_recvmsg_locked`. I'm going to look in `net/ipv4/tcp.c` around line 2790 for a more complete picture. I need to understand how the control flow can go from `sk_wait_data` to `ip_output`, holding these seemingly conflicting locks.
44/2	2026/09/18 08:34	tool	read-file	0m Args: { "File": "net/ipv4/tcp.c", "FirstLine": 2785, "LineCount": 35 } Results: { "Contents": "2785:\t\n2786:\t\t\t\tif (signal_pending(current)) {\n2787:\t\t\t\t\tcopied = sock_intr_errno(timeo);\n2788:\t\t\t\t\tbreak;\n2789:\t\t\t\t}\n2790:\t\t\t}\n2791:\t\n2792:\t\t\tif (copied \u003e= target) {\n2793:\t\t\t\t/* Do not sleep, just process backlog. /\n2794:\t\t\t\t__sk_flush_backlog(sk);\n2795:\t\t\t} else {\n2796:\t\t\t\ttcp_cleanup_rbuf(sk, copied);\n2797:\t\t\t\terr = sk_wait_data(sk, \u0026timeo, last);\n2798:\t\t\t\tif (err \u003c 0) {\n2799:\t\t\t\t\terr = copied ? : err;\n2800:\t\t\t\t\tgoto out;\n2801:\t\t\t\t}\n2802:\t\t\t}\n2803:\t\n2804:\t\t\tif ((flags \u0026 MSG_PEEK) \u0026\u0026\n2805:\t\t\t (peek_seq - peek_offset - copied - urg_hole != tp-\u003ecopied_seq)) {\n2806:\t\t\t\tnet_dbg_ratelimited(\"TCP(%s:%d): Application bug, race in MSG_PEEK\\n\",\n2807:\t\t\t\t\t\t current-\u003ecomm,\n2808:\t\t\t\t\t\t task_pid_nr(current));\n2809:\t\t\t\tpeek_seq = tp-\u003ecopied_seq + peek_offset;\n2810:\t\t\t}\n2811:\t\t\tcontinue;\n2812:\t\n2813:\tfound_ok_skb:\n2814:\t\t\t/ Ok so how much can we use? /\n2815:\t\t\tused = skb-\u003elen - offset;\n2816:\t\t\tif (len \u003c used)\n2817:\t\t\t\tused = len;\n2818:\t\n2819:\t\t\t/ Do we have urgent data here? */\n" }
45/2	2026/09/18 08:34	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 54776 output: 34 thoughts: 188 Thoughts: Decoding a Lockdep Report Okay, here we go again. Lockdep's telling me: "locks held by syz.1.8682/26551: 3, last CPU#1:" and then it points out something at `sk_wait_data+0x301`. Hmm, let's see, what's at `sk_wait_data+0x301`? Oh, hold on! That `sk_wait_data` reference is making me think... I seem to recall that we're dealing with `sk_wait_event(sk, timeo, skb_peek_tail(&sk->sk_receive_queue) != skb, &wait);` in there somewhere. Right, `sk_wait_event`. Time to go back and check the exact definition of that function to see what's happening. I need to refresh my memory and pinpoint what this lock contention is really about.
46/2	2026/09/18 08:34	tool	grepper	0m Args: { "Expression": "#define sk_wait_event", "PathPrefix": "include/net/sock.h" } Results: { "Output": "include/net/sock.h=1217=static inline void sock_rps_reset_rxhash(struct sock *sk)\n--\ninclude/net/sock.h-1224-\ninclude/net/sock.h:1225:#define sk_wait_event(__sk, __timeo, __condition, __wait)\t\t\\\ninclude/net/sock.h-1226-\t({\tint __rc, __dis = __sk-\u003esk_disconnects;\t\t\t\\\n" }
47/2	2026/09/18 08:34	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 55338 output: 36 thoughts: 21 Thoughts: Here's my summary, as if I were thinking these thoughts: Diving into the Kernel's Socket Implementation Okay, time to get my hands dirty. I need to understand how this particular aspect of the networking stack functions. The best place to start, as usual, is the core definitions. Let's head over to `include/net/sock.h`. I recall there are some important structures and macros defined within that file which will give me the building blocks I need. Specifically, I'm thinking somewhere around line 1225 should contain some crucial details. Let's jump there and see what we can unearth. Hopefully, that location holds the key to the specific part of the networking behavior I'm investigating. This should be a good starting point to deconstruct the behavior.
48/2	2026/09/18 08:34	tool	read-file	0m Args: { "File": "include/net/sock.h", "FirstLine": 1224, "LineCount": 35 } Results: { "Contents": "1224:\t\n1225:\t#define sk_wait_event(__sk, __timeo, __condition, __wait)\t\t\\\n1226:\t\t({\tint __rc, __dis = __sk-\u003esk_disconnects;\t\t\t\\\n1227:\t\t\trelease_sock(__sk);\t\t\t\t\t\\\n1228:\t\t\t__rc = __condition;\t\t\t\t\t\\\n1229:\t\t\tif (!__rc) {\t\t\t\t\t\t\\\n1230:\t\t\t\t(__timeo) = wait_woken(__wait,\t\t\t\\\n1231:\t\t\t\t\t\t\tTASK_INTERRUPTIBLE,\t\\\n1232:\t\t\t\t\t\t\t(__timeo));\t\t\\\n1233:\t\t\t}\t\t\t\t\t\t\t\\\n1234:\t\t\tsched_annotate_sleep();\t\t\t\t\t\\\n1235:\t\t\tlock_sock(__sk);\t\t\t\t\t\\\n1236:\t\t\t__rc = __dis == __sk-\u003esk_disconnects ? __condition : -EPIPE; \\\n1237:\t\t\t__rc;\t\t\t\t\t\t\t\\\n1238:\t\t})\n1239:\t\n1240:\tint sk_stream_wait_connect(struct sock sk, long timeo_p);\n1241:\tint sk_stream_wait_memory(struct sock sk, long timeo_p);\n1242:\tvoid sk_stream_wait_close(struct sock sk, long timeo_p);\n1243:\tint sk_stream_error(struct sock sk, int flags, int err);\n1244:\tvoid sk_stream_kill_queues(struct sock sk);\n1245:\tvoid sk_set_memalloc(struct sock sk);\n1246:\tvoid sk_clear_memalloc(struct sock sk);\n1247:\t\n1248:\tvoid __sk_flush_backlog(struct sock sk);\n1249:\t\n1250:\tstatic inline bool sk_flush_backlog(struct sock *sk)\n1251:\t{\n1252:\t\tif (unlikely(READ_ONCE(sk-\u003esk_backlog.tail))) {\n1253:\t\t\t__sk_flush_backlog(sk);\n1254:\t\t\treturn true;\n1255:\t\t}\n1256:\t\treturn false;\n1257:\t}\n1258:\t\n" }
49/2	2026/09/18 08:34	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 56154 output: 28 thoughts: 2933 Thoughts: Deep Dive into Network Lock Contention Okay, here's what I'm seeing. I'm starting from `sk_wait_event`, and my mind jumps to the interaction with `sk_lock-AF_INET` within the network stack. I know `sk_lock` is acquired in `sk_wait_data`, which seems relevant, and I'm tracing the execution path. After the initial lock is acquired in `sk_wait_data`, the code calls `ip_output` which means it calls `rcu_read_lock()` and also calls `NF_HOOK_COND`. `ip_finish_output` is where things are getting interesting. My intuition suggests potential contention points down the line, specifically in calls to `neigh_output` or `dev_queue_xmit`, because this could be a point of sleeping. I'm trying to rule out various scenarios, like spinlocks under `rcu_read_lock`. That's not possible; lockdep would scream about scheduling while atomic. But now, I'm checking which locks are actually held. I've got this long list. And then it hits me: the kernel is showing a bunch of tasks each holding `rtnl_mutex`. AHA! The problem is `rtnl_mutex`. I'm going through the list and I'm seeing `rtnl_mutex` being "held" by various processes. I'm checking `dhcpcd`, a few `kworker` threads, and some `syz` processes. That's a classic red flag. Something isn't right. I'm expecting this to be a mutex, so only one task can hold it at a time. It's a mutex! But why would lockdep show multiple tasks holding it? I need to analyze the `lockdep` output carefully. Wait, this lockdep output seems to indicate the lock is being acquired by multiple tasks. I look at the code. `rtnl_mutex` is acquired using `rtnl_lock()`. I know `rtnl_lock` calls `mutex_lock` which means that the lockdep lock is acquired after the mutex is acquired. I'm trying to puzzle this out. Wait, why would multiple tasks be in the list, if they are calling `rtnl_lock()` in sequence? The answer has to be related to the `mutex_lock()` and its interaction with `lockdep`. I'm starting to suspect something about the timing or, perhaps, how lockdep tracks mutex acquisitions. I have to check the definition of `rtnl_lock` to understand this. It has to be that, when each task calls `rtnl_lock()`, that lockdep is accounting for it, even if there's a queue. I can see the code and the context in which it's being used. It's all starting to click now.
50/2	2026/09/18 08:35	tool	grepper	0m Args: { "Expression": "void rtnl_lock\\(", "PathPrefix": "net/" } Results: { "Output": "net/core/rtnetlink.c=76=static DEFINE_MUTEX(rtnl_mutex);\nnet/core/rtnetlink.c-77-\nnet/core/rtnetlink.c:78:void rtnl_lock(void)\nnet/core/rtnetlink.c-79-{\n" }
51/2	2026/09/18 08:35	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 59816 output: 36 thoughts: 23 Thoughts: Here's a summary of my thought process, as if I were analyzing that code: Diving into the Heart of RTNL - A Closer Look at Initialization Okay, time to dig into `net/core/rtnetlink.c`, specifically lines 75-95. I need to refresh my understanding of the RTNL's core initialization. This section likely handles the registration of RTNL handlers or perhaps the initialization of some crucial data structures related to routing sockets. Given the position, I'm expecting to see something that sets the stage for how RTNL receives and dispatches messages. I'm hoping to confirm how the underlying netlink socket gets configured, how the associated message handlers are set up, and to get an idea of where the crucial callbacks will be set. Perhaps it's dealing with the allocation and initialization of `struct netlink_kernel_cfg` or similar structures. I'll be looking closely for any function calls that involve `netlink_kernel_create`, `rtnl_register`, or `netlink_add_handlers`. Ultimately, this is the foundational setup for the kernel's interaction with user-space regarding routing information, so I need to understand it thoroughly. This section is where the magic starts.
52/2	2026/09/18 08:35	tool	read-file	0m Args: { "File": "net/core/rtnetlink.c", "FirstLine": 75, "LineCount": 30 } Results: { "Contents": " 75:\t\n 76:\tstatic DEFINE_MUTEX(rtnl_mutex);\n 77:\t\n 78:\tvoid rtnl_lock(void)\n 79:\t{\n 80:\t\tmutex_lock(\u0026rtnl_mutex);\n 81:\t}\n 82:\tEXPORT_SYMBOL(rtnl_lock);\n 83:\t\n 84:\tint rtnl_lock_interruptible(void)\n 85:\t{\n 86:\t\treturn mutex_lock_interruptible(\u0026rtnl_mutex);\n 87:\t}\n 88:\t\n 89:\tint rtnl_lock_killable(void)\n 90:\t{\n 91:\t\treturn mutex_lock_killable(\u0026rtnl_mutex);\n 92:\t}\n 93:\t\n 94:\tstatic struct sk_buff defer_kfree_skb_list;\n 95:\tvoid rtnl_kfree_skbs(struct sk_buff head, struct sk_buff *tail)\n 96:\t{\n 97:\t\tif (head \u0026\u0026 tail) {\n 98:\t\t\ttail-\u003enext = defer_kfree_skb_list;\n 99:\t\t\tdefer_kfree_skb_list = head;\n 100:\t\t}\n 101:\t}\n 102:\tEXPORT_SYMBOL(rtnl_kfree_skbs);\n 103:\t\n 104:\tvoid __rtnl_unlock(void)\n" }
53/2	2026/09/18 08:35	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 60524 output: 30 thoughts: 39 Thoughts: Here's my summary, as if I were thinking these things: Digging into Mutex Locking Okay, hold on a second. I need to understand this locking behavior better. The code's using `mutex_lock_nested`... right, let me get a clear picture of what that's doing. But before I dive into nested locks specifically, I really need to understand the base `mutex_lock` function in the context of lockdep. Right, let's head over to `kernel/locking/mutex.c`. That's where I need to start. From there, I can figure out the fundamentals and then the nested stuff will hopefully be clearer.
54/2	2026/09/18 08:35	tool	grepper	0m Args: { "Expression": "mutex_acquire", "PathPrefix": "kernel/locking/mutex.c" } Results: { "Output": "kernel/locking/mutex.c=609=__mutex_lock_common(struct mutex lock, unsigned int state, unsigned int subclass,\n--\nkernel/locking/mutex.c-645-\tpreempt_disable();\nkernel/locking/mutex.c:646:\tmutex_acquire_nest(\u0026lock-\u003edep_map, subclass, 0, nest_lock, ip);\nkernel/locking/mutex.c-647-\n--\nkernel/locking/mutex.c=845=int ww_mutex_trylock(struct ww_mutex ww, struct ww_acquire_ctx ww_ctx)\n--\nkernel/locking/mutex.c-861-\t\tww_mutex_set_context_fastpath(ww, ww_ctx);\nkernel/locking/mutex.c:862:\t\tmutex_acquire_nest(\u0026ww-\u003ebase.dep_map, 0, 1, \u0026ww_ctx-\u003edep_map, _RET_IP_);\nkernel/locking/mutex.c-863-\t\treturn 1;\n--\nkernel/locking/mutex.c=1223=int __sched _mutex_trylock_nest_lock(struct mutex lock, struct lockdep_map *nest_lock)\n--\nkernel/locking/mutex.c-1229-\tif (locked)\nkernel/locking/mutex.c:1230:\t\tmutex_acquire_nest(\u0026lock-\u003edep_map, 0, 1, nest_lock, _RET_IP_);\nkernel/locking/mutex.c-1231-\n" }
55/2	2026/09/18 08:35	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 61113 output: 35 thoughts: 23 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience and written in the first person: Mutex Contention Analysis - A Deep Dive into kernel/locking/mutex.c Alright, let's dive right in. The problem's likely manifesting around the core mutex acquisition logic. My gut's telling me to examine the heart of the matter, so let's check out `kernel/locking/mutex.c` specifically, line 645. I want to zero in on how mutex contention is handled at that specific point. I'm expecting to see the critical section where a thread might be put to sleep, where the waiter queue is manipulated, or maybe where a backoff strategy is being invoked. It's the lynchpin for understanding any performance issues related to mutex contention and how the kernel handles those crucial lock/unlock transitions. I'm going to look for any potential bottlenecks, like excessive spinlocking or inefficient wake-up mechanisms that could indicate the cause. I'm hoping to identify the exact spot where a thread transitions between an active and a waiting state.
56/2	2026/09/18 08:35	tool	read-file	0m Args: { "File": "kernel/locking/mutex.c", "FirstLine": 640, "LineCount": 40 } Results: { "Contents": " 640:\t#ifdef CONFIG_DEBUG_LOCK_ALLOC\n 641:\t\t\tnest_lock = \u0026ww_ctx-\u003edep_map;\n 642:\t#endif\n 643:\t\t}\n 644:\t\n 645:\t\tpreempt_disable();\n 646:\t\tmutex_acquire_nest(\u0026lock-\u003edep_map, subclass, 0, nest_lock, ip);\n 647:\t\n 648:\t\ttrace_contention_begin(lock, LCB_F_MUTEX \| LCB_F_SPIN);\n 649:\t\tif (__mutex_trylock(lock) \|\|\n 650:\t\t mutex_optimistic_spin(lock, ww_ctx, NULL)) {\n 651:\t\t\t/* got the lock, yay! /\n 652:\t\t\tlock_acquired(\u0026lock-\u003edep_map, ip);\n 653:\t\t\tif (ww_ctx)\n 654:\t\t\t\tww_mutex_set_context_fastpath(ww, ww_ctx);\n 655:\t\t\ttrace_contention_end(lock, 0);\n 656:\t\t\tpreempt_enable();\n 657:\t\t\treturn 0;\n 658:\t\t}\n 659:\t\n 660:\t\traw_spin_lock_irqsave(\u0026lock-\u003ewait_lock, flags);\n 661:\t\t/\n 662:\t\t * After waiting to acquire the wait_lock, try again.\n 663:\t\t /\n 664:\t\tif (__mutex_trylock(lock)) {\n 665:\t\t\tif (ww_ctx)\n 666:\t\t\t\t__ww_mutex_check_waiters(lock, ww_ctx, \u0026wake_q);\n 667:\t\n 668:\t\t\tgoto skip_wait;\n 669:\t\t}\n 670:\t\n 671:\t\tdebug_mutex_lock_common(lock, \u0026waiter);\n 672:\t\twaiter.task = current;\n 673:\t\tif (use_ww_ctx)\n 674:\t\t\twaiter.ww_ctx = ww_ctx;\n 675:\t\n 676:\t\tlock_contended(\u0026lock-\u003edep_map, ip);\n 677:\t\n 678:\t\tif (!use_ww_ctx) {\n 679:\t\t\t/ add waiting tasks to the end of the waitqueue (FIFO): */\n" }
57/2	2026/09/18 08:35	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 62018 output: 37 thoughts: 2141 Thoughts: Analyzing a Concurrency Stall in the Kernel Okay, so here's what I'm seeing. `mutex_acquire_nest` is getting called before the mutex is actually acquired, which is fine, but it clues me into the lockdep information. It's adding the lock to `current->held_locks`, and this is key because it shows all tasks that are trying to acquire a lock, even if they're waiting. The system dump shows multiple tasks attempting to acquire `rtnl_mutex`. The critical question is, who is holding `rtnl_mutex`? My analysis points to task `syz.3.8783/26988`. The backtrace shows this task is in `tun_chr_close`, specifically at the line where `rtnl_lock()` is called. It successfully acquired the mutex. Then it proceeds through a series of calls: `__tun_detach`, `unregister_netdevice_queue`, `unregister_netdevice_many_notify`, `dev_shutdown`, `__qdisc_destroy`, and then into `lockdep_unregister_key` and finally `zap_class`. But, wait a minute, task 26988 is now running in `zap_class`. So, is that the problem? No! My primary concern shifts to a potentially hung task, `syz.1.8682/26550`, which has been blocked for over 143 seconds. The stack trace indicates it's waiting in `__lock_sock`, specifically on `sk_lock-AF_INET`. It's blocked in `tcp_sendmsg_locked`. This strongly suggests contention for a socket lock. Now, who's holding the sock lock? Task `syz.1.8682/26551`. It's holding `sk_lock-AF_INET`. That's the culprit! It's also holding `rcu_read_lock`. However, that's not possible! A task cannot sleep in uninterruptible state (D) while holding `rcu_read_lock`. The kernel's `might_sleep()` check would have triggered a "BUG: scheduling while atomic" if `schedule()` or uninterruptible sleep were called. So, this either means 26551 was preempted, or… …could it be an infinite loop? If 26551 were spinning within an RCU read lock, there should be an RCU stall or a watchdog bite. But if 26551 is running on CPU 1, that could explain why. Okay, let's examine the CPU context. The system only has two CPUs, CPU 0 and CPU 1. The `last CPU#1` designation for 26551 means the last CPU it ran on was CPU 1. Now, `khungtaskd` is running on CPU 0. Crucially, task 26988 is currently running on CPU 1 in `zap_class`. Is `zap_class` taking a long time? Could it be stuck in a loop and, in that case, monopolizing CPU 1? That looks very likely. I have to look at `zap_class` more closely.
58/2	2026/09/18 08:36	tool	read-file	0m Args: { "File": "kernel/locking/lockdep.c", "FirstLine": 6340, "LineCount": 80 } Results: { "Contents": "6340:\tstatic void zap_class(struct pending_free pf, struct lock_class class)\n6341:\t{\n6342:\t\tstruct lock_list entry;\n6343:\t\tint i;\n6344:\t\n6345:\t\tWARN_ON_ONCE(!class-\u003ekey);\n6346:\t\n6347:\t\t/\n6348:\t\t * Remove all dependencies this lock is\n6349:\t\t * involved in:\n6350:\t\t /\n6351:\t\tfor_each_set_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) {\n6352:\t\t\tentry = list_entries + i;\n6353:\t\t\tif (entry-\u003eclass != class \u0026\u0026 entry-\u003elinks_to != class)\n6354:\t\t\t\tcontinue;\n6355:\t\t\t__clear_bit(i, list_entries_in_use);\n6356:\t\t\tnr_list_entries--;\n6357:\t\t\tlist_del_rcu(\u0026entry-\u003eentry);\n6358:\t\t}\n6359:\t\tif (list_empty(\u0026class-\u003elocks_after) \u0026\u0026\n6360:\t\t list_empty(\u0026class-\u003elocks_before)) {\n6361:\t\t\tlist_move_tail(\u0026class-\u003elock_entry, \u0026pf-\u003ezapped);\n6362:\t\t\thlist_del_rcu(\u0026class-\u003ehash_entry);\n6363:\t\t\tWRITE_ONCE(class-\u003ekey, NULL);\n6364:\t\t\tWRITE_ONCE(class-\u003ename, NULL);\n6365:\t\t\t/ Class allocated but not used, -1 in nr_unused_locks /\n6366:\t\t\tif (class-\u003eusage_mask == 0)\n6367:\t\t\t\tdebug_atomic_dec(nr_unused_locks);\n6368:\t\t\tnr_lock_classes--;\n6369:\t\t\t__clear_bit(class - lock_classes, lock_classes_in_use);\n6370:\t\t\tif (class - lock_classes == max_lock_class_idx)\n6371:\t\t\t\tmax_lock_class_idx--;\n6372:\t\t} else {\n6373:\t\t\tWARN_ONCE(true, \"%s() failed for class %s\\n\", __func__,\n6374:\t\t\t\t class-\u003ename);\n6375:\t\t}\n6376:\t\n6377:\t\tremove_class_from_lock_chains(pf, class);\n6378:\t\tnr_zapped_classes++;\n6379:\t}\n6380:\t\n6381:\tstatic void reinit_class(struct lock_class class)\n6382:\t{\n6383:\t\tWARN_ON_ONCE(!class-\u003elock_entry.next);\n6384:\t\tWARN_ON_ONCE(!list_empty(\u0026class-\u003elocks_after));\n6385:\t\tWARN_ON_ONCE(!list_empty(\u0026class-\u003elocks_before));\n6386:\t\tmemset_startat(class, 0, key);\n6387:\t\tWARN_ON_ONCE(!class-\u003elock_entry.next);\n6388:\t\tWARN_ON_ONCE(!list_empty(\u0026class-\u003elocks_after));\n6389:\t\tWARN_ON_ONCE(!list_empty(\u0026class-\u003elocks_before));\n6390:\t}\n6391:\t\n6392:\tstatic inline int within(const void addr, void start, unsigned long size)\n6393:\t{\n6394:\t\treturn addr \u003e= start \u0026\u0026 addr \u003c start + size;\n6395:\t}\n6396:\t\n6397:\tstatic bool inside_selftest(void)\n6398:\t{\n6399:\t\treturn current == lockdep_selftest_task_struct;\n6400:\t}\n6401:\t\n6402:\t/* The caller must hold the graph lock. /\n6403:\tstatic struct pending_free get_pending_free(void)\n6404:\t{\n6405:\t\treturn delayed_free.pf + delayed_free.index;\n6406:\t}\n6407:\t\n6408:\tstatic void free_zapped_rcu(struct rcu_head cb);\n6409:\t\n6410:\t/\n6411:\t* See if we need to queue an RCU callback, must called with\n6412:\t* the lockdep lock held, returns false if either we don't have\n6413:\t* any pending free or the callback is already scheduled.\n6414:\t* Otherwise, a call_rcu() must follow this function call.\n6415:\t/\n6416:\tstatic bool prepare_call_rcu_zapped(struct pending_free pf)\n6417:\t{\n6418:\t\tWARN_ON_ONCE(inside_selftest());\n6419:\t\n" }
59/2	2026/09/18 08:36	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 66188 output: 37 thoughts: 71 Thoughts: Diving into `zap_class` Okay, so I'm digging into this `zap_class` function. My initial impression is that it seems to be iterating through some kind of list. Specifically, it's using `for_each_set_bit` on `list_entries_in_use`, which hints at a bitmask representation where each set bit signifies an entry in use. The second argument suggests this is using an array of some kind. The `ARRAY_SIZE` macro gives us the range we're working within. Seems fairly standard for a loop that works on sparse arrays. Now, the key function here is `remove_class_from_lock_chains(pf, class)`. This is where the real work happens. It's obviously designed to untangle a class from a series of lock chains. I need to understand this function in greater detail to grasp the full effect of `zap_class`. Let's see what's really happening inside `remove_class_from_lock_chains`.
60/2	2026/09/18 08:36	tool	read-file	0m Args: { "File": "kernel/locking/lockdep.c", "FirstLine": 6320, "LineCount": 25 } Results: { "Contents": "6320:\t\n6321:\t/* Must be called with the graph lock held. /\n6322:\tstatic void remove_class_from_lock_chains(struct pending_free pf,\n6323:\t\t\t\t\t\t struct lock_class class)\n6324:\t{\n6325:\t\tstruct lock_chain chain;\n6326:\t\tstruct hlist_head head;\n6327:\t\tint i;\n6328:\t\n6329:\t\tfor (i = 0; i \u003c ARRAY_SIZE(chainhash_table); i++) {\n6330:\t\t\thead = chainhash_table + i;\n6331:\t\t\thlist_for_each_entry_rcu(chain, head, entry) {\n6332:\t\t\t\tremove_class_from_lock_chain(pf, chain, class);\n6333:\t\t\t}\n6334:\t\t}\n6335:\t}\n6336:\t\n6337:\t/\n6338:\t * Remove all references to a lock class. The caller must hold the graph lock.\n6339:\t /\n6340:\tstatic void zap_class(struct pending_free pf, struct lock_class class)\n6341:\t{\n6342:\t\tstruct lock_list entry;\n6343:\t\tint i;\n6344:\t\n" }
61/2	2026/09/18 08:36	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 66876 output: 37 thoughts: 101 Thoughts: Analyzing the Lockdep Unregister Process Okay, let's break this down. I'm focusing on `zap_class` here. Immediately, I see it's dealing with a couple of potentially large data structures. It's iterating through `list_entries_in_use`, which, critically, can be as large as `MAX_LOCKDEP_ENTRIES`. That's the first potential performance bottleneck I need to keep in mind. Then, for each entry in `list_entries_in_use`, it dives into `chainhash_table`, iterating over its `CHAINHASH_SIZE` buckets. That's a nested loop, and nested loops are always suspect, especially with potentially large sizes involved. I need to understand the implications of `MAX_LOCKDEP_ENTRIES` and `CHAINHASH_SIZE` in context to gauge the severity of any performance issues. Now, I need to figure out how this `zap_class` function is being called, which will illuminate the context of its execution. The code mentions that `lockdep_unregister_key` calls this. That's a good starting point. I need to navigate to that function to understand the trigger point of this execution and its frequency, and I'll jump straight to around line 6500 to find it.
62/2	2026/09/18 08:36	tool	read-file	0m Args: { "File": "kernel/locking/lockdep.c", "FirstLine": 6480, "LineCount": 40 } Results: { "Contents": "6480:\t\n6481:\t}\n6482:\t\n6483:\t/\n6484:\t Remove all lock classes from the class hash table and from the\n6485:\t * all_lock_classes list whose key or name is in the address range [start,\n6486:\t * start + size). Move these lock classes to the zapped_classes list. Must\n6487:\t * be called with the graph lock held.\n6488:\t /\n6489:\tstatic void __lockdep_free_key_range(struct pending_free pf, void start,\n6490:\t\t\t\t\t unsigned long size)\n6491:\t{\n6492:\t\tstruct lock_class class;\n6493:\t\tstruct hlist_head head;\n6494:\t\tint i;\n6495:\t\n6496:\t\t/ Unhash all classes that were created by a module. /\n6497:\t\tfor (i = 0; i \u003c CLASSHASH_SIZE; i++) {\n6498:\t\t\thead = classhash_table + i;\n6499:\t\t\thlist_for_each_entry_rcu(class, head, hash_entry) {\n6500:\t\t\t\tif (!within(class-\u003ekey, start, size) \u0026\u0026\n6501:\t\t\t\t !within(class-\u003ename, start, size))\n6502:\t\t\t\t\tcontinue;\n6503:\t\t\t\tzap_class(pf, class);\n6504:\t\t\t}\n6505:\t\t}\n6506:\t}\n6507:\t\n6508:\t/\n6509:\t * Used in module.c to remove lock classes from memory that is going to be\n6510:\t * freed; and possibly re-used by other modules.\n6511:\t \n6512:\t We will have had one synchronize_rcu() before getting here, so we're\n6513:\t * guaranteed nobody will look up these exact classes -- they're properly dead\n6514:\t * but still allocated.\n6515:\t /\n6516:\tstatic void lockdep_free_key_range_reg(void start, unsigned long size)\n6517:\t{\n6518:\t\tstruct pending_free *pf;\n6519:\t\tunsigned long flags;\n" }
63/2	2026/09/18 08:36	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 67897 output: 37 thoughts: 29 Thoughts: Okay, let's dive into this. Investigating the `lockdep_unregister_key` Function Hmm, `lockdep_unregister_key`... what exactly is that function doing? I need to refresh my memory on the specifics, especially in this context. Alright, let's jump right to the code. Specifically, let's take a look at the section between lines 6530 and 6580. That should give me a good handle on its purpose and how it operates within the locking infrastructure. Time to get some clarity.
64/2	2026/09/18 08:36	tool	read-file	0m Args: { "File": "kernel/locking/lockdep.c", "FirstLine": 6540, "LineCount": 40 } Results: { "Contents": "6540:\t/\n6541:\t Free all lockdep keys in the range [start, start+size). Does not sleep.\n6542:\t * Ignores debug_locks. Must only be used by the lockdep selftests.\n6543:\t /\n6544:\tstatic void lockdep_free_key_range_imm(void start, unsigned long size)\n6545:\t{\n6546:\t\tstruct pending_free pf = delayed_free.pf;\n6547:\t\tunsigned long flags;\n6548:\t\n6549:\t\tinit_data_structures_once();\n6550:\t\n6551:\t\traw_local_irq_save(flags);\n6552:\t\tlockdep_lock();\n6553:\t\t__lockdep_free_key_range(pf, start, size);\n6554:\t\t__free_zapped_classes(pf);\n6555:\t\tlockdep_unlock();\n6556:\t\traw_local_irq_restore(flags);\n6557:\t}\n6558:\t\n6559:\tvoid lockdep_free_key_range(void start, unsigned long size)\n6560:\t{\n6561:\t\tinit_data_structures_once();\n6562:\t\n6563:\t\tif (inside_selftest())\n6564:\t\t\tlockdep_free_key_range_imm(start, size);\n6565:\t\telse\n6566:\t\t\tlockdep_free_key_range_reg(start, size);\n6567:\t}\n6568:\t\n6569:\t/\n6570:\t Check whether any element of the @lock-\u003eclass_cache[] array refers to a\n6571:\t * registered lock class. The caller must hold either the graph lock or the\n6572:\t * RCU read lock.\n6573:\t /\n6574:\tstatic bool lock_class_cache_is_registered(struct lockdep_map lock)\n6575:\t{\n6576:\t\tstruct lock_class class;\n6577:\t\tstruct hlist_head head;\n6578:\t\tint i, j;\n6579:\t\n" }
65/2	2026/09/18 08:36	llm	finding-triage-evaluator-compressor	0m Model: gemini-3.8-flash Args: null Results: null Reply: ### State of Investigation and Workspace Summary #### 1. Approaches Tried and Results * Analysis of Crash Report: * Crash signature: `INFO: task syz.1.8682:26550 blocked for more than 143 seconds.` (Hung task / D-state lockup). * Task 26550 call trace: `__schedule` -> `schedule` -> `__lock_sock` -> `lock_sock_nested` -> `sk_stream_wait_memory` -> `tcp_sendmsg_locked` -> `tcp_sendmsg` -> `sock_sendmsg_nosec` -> `__sys_sendto` -> `__x64_sys_sendto`. * System lock analysis: * Task `syz.1.8682/26550` holds `sk_lock-AF_INET` (`ffff88810f55b660`) at `sk_stream_wait_memory+0x8d8/0xf80` and is blocked in `__lock_sock` trying to acquire the user socket lock. * Task `syz.1.8682/26551` holds the same `sk_lock-AF_INET` (`ffff88810f55b660`) at `sk_wait_data+0x301/0x4d0`, plus `rcu_read_lock` at `__ip_queue_xmit` and `ip_output`. * Numerous tasks and workers (`dhcpcd`, `kworker/u8:4`, `kworker/u9:8`, `syz-executor/26829`, `syz-executor/26963`, `syz.3.8783/26988`, `syz-executor/27000`, `syz-executor/27007`) are holding or contending on `rtnl_mutex` (`ffffffff902533a0`). * CPU 1 NMI backtrace: `syz.3.8783/26988` running `zap_class` inside `lockdep_unregister_key` -> `__qdisc_destroy` -> `dev_shutdown` -> `unregister_netdevice_many_notify` -> `unregister_netdevice_queue` -> `__tun_detach` -> `tun_chr_close` while exiting/closing a TUN fd. * Workspace Diff / Patch Series Inspection: * Inspected patch series commits and workspace changes across all 8 modified files: * `include/net/dropreason-core.h` * `include/net/gre.h` * `include/net/ip6_tunnel.h` * `net/ipv4/gre_demux.c` * `net/ipv4/ip_gre.c` * `net/ipv4/ip_tunnel.c` * `net/ipv6/ip6_gre.c` * `net/ipv6/ip6_tunnel.c` * Diffs show that the 9-patch series strictly adds SKB drop reasons (e.g., `SKB_DROP_REASON_TNL_OPT_MISMATCH`, `SKB_DROP_REASON_TNL_OLD_SEQ`, `SKB_DROP_REASON_GRE_INVALID_HDR`, `SKB_DROP_REASON_GRE_CSUM`, `SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND`, `SKB_DROP_REASON_TNL_ENCAP`) to the generic RX and TX paths of IP/IPv6 GRE and IP tunnels, replacing calls to `kfree_skb()` with `kfree_skb_reason(skb, reason)`. * Checked patch 1 (`PatchNum=1`) via `series-patches` confirming commit description and diff format. * Dead-ends: * Initial call to `series-patches` with `{}` failed because argument `PatchNum` is required by the tool. #### 2. Hypotheses and Theories * Hypothesis 1 (Unrelated pre-existing bug / lock contention): * The hung task occurs in core TCP socket code (`sk_stream_wait_memory` / `tcp_sendmsg_locked` waiting on `sock_owned_by_user(sk)` in `__lock_sock`). * The system is severely bogged down by lockdep overhead / key unregistration (`zap_class` called during `tun_chr_close` via `unregister_netdevice_queue` -> `dev_shutdown` -> `__qdisc_destroy` -> `lockdep_unregister_key`) and heavy `rtnl_mutex` contention across multiple tasks. * Task 26550 and task 26551 share the same socket `ffff88810f55b660`; 26550 is waiting in `__lock_sock` for 26551 to release socket ownership, while scheduling/execution is delayed across CPUs. * None of the code paths in the stack traces (`tcp_sendmsg`, `sk_stream_wait_memory`, `__lock_sock`, `tun_chr_close`, `lockdep_unregister_key`, `zap_class`) involve any of the tunnel or GRE code modified by the patch series (`net/ipv4/ip_tunnel.c`, `net/ipv4/ip_gre.c`, `net/ipv4/gre_demux.c`, `net/ipv6/ip6_tunnel.c`, `net/ipv6/ip6_gre.c`, `include/net/dropreason-core.h`). * Therefore, the bug was NOT introduced by the patch series (`Introduced=false`). #### 3. Key Files, Functions, and Code References * Faulting stack files: * `net/core/stream.c`: `sk_stream_wait_memory()` (lines 121–186) calls `sk_wait_event()` which releases and re-acquires socket lock using `release_sock(sk)` and `lock_sock(sk)` / `lock_sock_nested()`. * `net/core/sock.c`: `__lock_sock()` (lines 3235–3251): ```c static void __lock_sock(struct sock sk) { DEFINE_WAIT(wait); for (;;) { prepare_to_wait_exclusive(&sk->sk_lock.wq, &wait, TASK_UNINTERRUPTIBLE); spin_unlock_bh(&sk->sk_lock.slock); schedule(); spin_lock_bh(&sk->sk_lock.slock); if (!sock_owned_by_user(sk)) break; } finish_wait(&sk->sk_lock.wq, &wait); } ``` `net/ipv4/tcp.c`: `tcp_sendmsg_locked()` calls `sk_stream_wait_memory(sk, &timeo)`. * `kernel/locking/lockdep.c`: `zap_class()` / `lockdep_unregister_key()`. * `drivers/net/tun.c`: `tun_chr_close()`. * Files modified by patch series (none in call traces): * `include/net/dropreason-core.h` * `include/net/gre.h` * `include/net/ip6_tunnel.h` * `net/ipv4/gre_demux.c` * `net/ipv4/ip_gre.c` * `net/ipv4/ip_tunnel.c` * `net/ipv6/ip6_gre.c` * `net/ipv6/ip6_tunnel.c` #### 4. Observations & Next Steps * No reasoning loops encountered. * Investigation is conclusive: the hung task is in core TCP socket locking and device teardown / lockdep key unregistration, completely disjoint from the tunnel drop reason changes in the patch series. * Ready to set verdict via `set-results` (`Introduced=false`) and formulate the final triage explanation. Tokens: input: 48460 output: 1901 thoughts: 0
66/2	2026/09/18 08:37	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 22137 output: 37 thoughts: 0
67/2	2026/09/18 08:37	tool	read-file	0m Args: { "File": "kernel/locking/lockdep.c", "FirstLine": 6600, "LineCount": 40 } Results: { "Contents": "6600:\t\t /\n6601:\t\tfor (j = 0; j \u003c MAX_LOCKDEP_SUBCLASSES; j++) {\n6602:\t\t\t/\n6603:\t\t\t * If the class exists we look it up and zap it:\n6604:\t\t\t /\n6605:\t\t\tclass = look_up_lock_class(lock, j);\n6606:\t\t\tif (class)\n6607:\t\t\t\tzap_class(pf, class);\n6608:\t\t}\n6609:\t\t/\n6610:\t\t * Debug check: in the end all mapped classes should\n6611:\t\t * be gone.\n6612:\t\t /\n6613:\t\tif (WARN_ON_ONCE(lock_class_cache_is_registered(lock)))\n6614:\t\t\tdebug_locks_off();\n6615:\t}\n6616:\t\n6617:\t/\n6618:\t * Remove all information lockdep has about a lock if debug_locks == 1. Free\n6619:\t * released data structures from RCU context.\n6620:\t /\n6621:\tstatic void lockdep_reset_lock_reg(struct lockdep_map lock)\n6622:\t{\n6623:\t\tstruct pending_free *pf;\n6624:\t\tunsigned long flags;\n6625:\t\tint locked;\n6626:\t\tbool need_callback = false;\n6627:\t\n6628:\t\traw_local_irq_save(flags);\n6629:\t\tlocked = graph_lock();\n6630:\t\tif (!locked)\n6631:\t\t\tgoto out_irq;\n6632:\t\n6633:\t\tpf = get_pending_free();\n6634:\t\t__lockdep_reset_lock(pf, lock);\n6635:\t\tneed_callback = prepare_call_rcu_zapped(pf);\n6636:\t\n6637:\t\tgraph_unlock();\n6638:\tout_irq:\n6639:\t\traw_local_irq_restore(flags);\n" }
68/2	2026/09/18 08:37	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 22729 output: 20 thoughts: 0
69/2	2026/09/18 08:37	tool	git-show	0m Args: { "Commit": "HEAD", "Stat": true } Results: { "Output": "commit cf46b1cdceff8b56bf9238b428c6b84e96b7595a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 08:29:11 2026 +0000\n\n syz-cluster: applied patch under review\n\n include/net/dropreason-core.h \| 38 +++++++++\n include/net/gre.h \| 2 +-\n include/net/ip6_tunnel.h \| 3 +-\n net/ipv4/gre_demux.c \| 52 ++++++++++---\n net/ipv4/ip_gre.c \| 144 +++++++++++++++++++++++-----------\n net/ipv4/ip_tunnel.c \| 60 ++++++++++++---\n net/ipv6/ip6_gre.c \| 175 ++++++++++++++++++++++++++++--------------\n net/ipv6/ip6_tunnel.c \| 95 +++++++++++++++++------\n 8 files changed, 419 insertions(+), 150 deletions(-)\n" }
70/2	2026/09/18 08:37	llm	finding-triage-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 23025 output: 470 thoughts: 0
71/2	2026/09/18 08:37	tool	set-results	0m Args: { "Introduced": false, "Reasoning": "The crash report is a hung task timeout: `INFO: task syz.1.8682:26550 blocked for more than 143 seconds.`\nTask 26550 is blocked in `__lock_sock()` waiting to acquire user ownership of socket `ffff88810f55b660` while in `sk_stream_wait_memory()` called from `tcp_sendmsg_locked()`.\nMeanwhile, task 26551 holds the same socket lock at `sk_wait_data()` in `tcp_recvmsg_locked()`, and the system is under extreme contention on `rtnl_mutex` with lockdep overhead (specifically lock class unregistration in `zap_class()` / `lockdep_unregister_key()` during network device unregistration / tun detach).\n\nThe patch series under test consists of 9 commits (\"net-next: ip_tunnel/ip_gre/ip6_tunnel/ip6_gre drop reasons\") which solely add `SKB_DROP_REASON_` enum definitions and annotate packet drops in the RX and TX paths of GRE and IPv4/IPv6 tunnels (`include/net/dropreason-core.h`, `include/net/gre.h`, `include/net/ip6_tunnel.h`, `net/ipv4/gre_demux.c`, `net/ipv4/ip_gre.c`, `net/ipv4/ip_tunnel.c`, `net/ipv6/ip6_gre.c`, `net/ipv6/ip6_tunnel.c`).\n\nNone of the files, data structures, or functions involved in the blocked task or in any of the active threads shown in the report (`net/core/stream.c`, `net/core/sock.c`, `net/ipv4/tcp.c`, `kernel/locking/lockdep.c`, `drivers/net/tun.c`) were touched or influenced by the patch series. Therefore, this hung task is an unrelated pre-existing issue / scheduling stall under heavy lock contention." } Results:* { "Introduced": false, "Reasoning": "The crash report is a hung task timeout: `INFO: task syz.1.8682:26550 blocked for more than 143 seconds.`\nTask 26550 is blocked in `__lock_sock()` waiting to acquire user ownership of socket `ffff88810f55b660` while in `sk_stream_wait_memory()` called from `tcp_sendmsg_locked()`.\nMeanwhile, task 26551 holds the same socket lock at `sk_wait_data()` in `tcp_recvmsg_locked()`, and the system is under extreme contention on `rtnl_mutex` with lockdep overhead (specifically lock class unregistration in `zap_class()` / `lockdep_unregister_key()` during network device unregistration / tun detach).\n\nThe patch series under test consists of 9 commits (\"net-next: ip_tunnel/ip_gre/ip6_tunnel/ip6_gre drop reasons\") which solely add `SKB_DROP_REASON_*` enum definitions and annotate packet drops in the RX and TX paths of GRE and IPv4/IPv6 tunnels (`include/net/dropreason-core.h`, `include/net/gre.h`, `include/net/ip6_tunnel.h`, `net/ipv4/gre_demux.c`, `net/ipv4/ip_gre.c`, `net/ipv4/ip_tunnel.c`, `net/ipv6/ip6_gre.c`, `net/ipv6/ip6_tunnel.c`).\n\nNone of the files, data structures, or functions involved in the blocked task or in any of the active threads shown in the report (`net/core/stream.c`, `net/core/sock.c`, `net/ipv4/tcp.c`, `kernel/locking/lockdep.c`, `drivers/net/tun.c`) were touched or influenced by the patch series. Therefore, this hung task is an unrelated pre-existing issue / scheduling stall under heavy lock contention." }

LLM Calls Summary:
Total Calls	Total Tokens	Avg Tokens	Total Duration (Seconds)	Avg Duration (Seconds)

Tool Calls Summary:
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