AI Trajectory

null

{
  "EnableConfigs": [
    "UNIX",
    "AF_UNIX_OOB",
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "manage_oob",
    "unix_stream_read_skb",
    "unix_stream_read_generic"
  ],
  "KMSANReasoning": "The patch addresses socket queue length accounting and skb consumption handling in AF_UNIX stream sockets. Specifically:\n1. In `manage_oob()`, it corrects `u-\u003einq_len` accounting by decrementing it by 1 when unlinking an unread OOB skb.\n2. In `unix_stream_read_skb()`, it drops empty skbs (`!unix_skb_len(skb)`) and pulls already-consumed bytes via `pskb_pull()` before handing the skb to `recv_actor()`.\n\nNone of these changes allocate or read uninitialized memory, nor do they expose uninitialized kernel fields/padding to user space or conditional branching. All fields touched (`u-\u003einq_len`, `UNIXCB(skb).consumed`, skb pointers) are fully initialized socket and skb metadata. Any memory errors relating to skb lifecycle or bounds would be detected by KASAN or standard debuggers, not KMSAN. Therefore, a dedicated KMSAN fuzzing session is not warranted.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch modifies core networking code in net/unix/af_unix.c. Specifically, it corrects queue accounting (u-\u003einq_len) when dropping out-of-band skbs in manage_oob(), and alters skb handling in unix_stream_read_skb() by discarding empty skbs, orphaning SCMs, and pulling consumed bytes with pskb_pull(). These paths are reachable via standard UNIX domain sockets and BPF sockmap.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 81002efe86c7a9b86819e5f77caa0b15406c39b0\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Sat Sep 26 10:58:32 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/net/unix/af_unix.c b/net/unix/af_unix.c\nindex 42cffeafc8c14..a1c06b9995c7c 100644\n--- a/net/unix/af_unix.c\n+++ b/net/unix/af_unix.c\n@@ -2849,6 +2849,7 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\n \t\tWRITE_ONCE(u-\u003eoob_skb, NULL);\n \n \t\tif (!sock_flag(sk, SOCK_URGINLINE)) {\n+\t\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - 1);\n \t\t\t__skb_unlink(skb, \u0026sk-\u003esk_receive_queue);\n \t\t\tunread_skb = skb;\n \t\t\tskb = skb_peek(\u0026sk-\u003esk_receive_queue);\n@@ -2884,6 +2885,7 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n \t\treturn err;\n \n \tmutex_lock(\u0026u-\u003eiolock);\n+again:\n \tspin_lock(\u0026queue-\u003elock);\n \n \tskb = __skb_dequeue(queue);\n@@ -2893,6 +2895,13 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n \t\treturn -EAGAIN;\n \t}\n \n+\tif (!unix_skb_len(skb)) {\n+\t\tspin_unlock(\u0026queue-\u003elock);\n+\t\tunix_orphan_scm(sk, skb);\n+\t\tconsume_skb(skb);\n+\t\tgoto again;\n+\t}\n+\n \tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - unix_skb_len(skb));\n \n #if IS_ENABLED(CONFIG_AF_UNIX_OOB)\n@@ -2912,6 +2921,14 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n \n \tmutex_unlock(\u0026u-\u003eiolock);\n \n+\tif (UNIXCB(skb).consumed) {\n+\t\tif (!pskb_pull(skb, UNIXCB(skb).consumed)) {\n+\t\t\tkfree_skb(skb);\n+\t\t\treturn -ENOMEM;\n+\t\t}\n+\t\tUNIXCB(skb).consumed = 0;\n+\t}\n+\n \treturn recv_actor(sk, skb);\n }\n \n"
}

core

null

{
  "EnableConfigs": [
    "UNIX",
    "AF_UNIX_OOB",
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "manage_oob",
    "unix_stream_read_skb",
    "unix_stream_read_generic"
  ],
  "Reasoning": "The patch modifies core networking code in net/unix/af_unix.c. Specifically, it corrects queue accounting (u-\u003einq_len) when dropping out-of-band skbs in manage_oob(), and alters skb handling in unix_stream_read_skb() by discarding empty skbs, orphaning SCMs, and pulling consumed bytes with pskb_pull(). These paths are reachable via standard UNIX domain sockets and BPF sockmap.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer and security engineer.
Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on internal assumptions. You must actively use your code access
tools to inspect the actual source code, callers, and surrounding context.

================================================================================
1. CORE TRIAGE PHILOSOPHY
================================================================================
The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs,
and newly triggered assertions introduced by the patch series.

- REACHABILITY IS THE PRIMARY GATE:
  Fuzzing can only discover bugs in code that can actually execute in standard virtualized
  environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap).
  If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed,
  regardless of whether it adds assertions or complex logic.

- DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS:
  Patch authors routinely label changes as "cleanups", "refactorings", or state
  "No functional change intended". Do NOT take these claims at face value.
  Code refactorings that rearrange logic, introduce helper functions, or alter state management
  in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs.
  If reachable executable code is modified or refactored, it MUST be fuzzed.

- NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED:
  When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON*, VM_WARN_ON*,
  BUG_ON*, lockdep_assert*) in reachable code paths, it enforces new or stricter invariants.
  Even if the author believes the invariant always holds, fuzzing is essential to verify whether
  an unusual sequence of operations can violate it.

================================================================================
2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA)
================================================================================
Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories:

- Non-kernel and non-executable changes:
  * Modifications to Documentation/, comments, or spelling fixes.
  * User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/)
    that do not affect the compiled kernel image (vmlinux) or kernel modules.
  * Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints
    that do not alter control flow or data structures.
  * Build system or Kconfig changes that do not alter compiled C logic.
- Structurally unreachable hardware:
  * Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed,
    ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU.
- Unreachable execution paths:
  * Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during
    physical PCI hot-unplug or manual sysfs driver unbinding.
  * Code paths exclusive to architectures other than the target architecture.

================================================================================
3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA)
================================================================================
Return WorthFuzzing=true whenever the patch touches reachable executable code, including:
- Core Subsystems:
  * Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/),
    BPF, scheduler, core networking, VFS, or syscall handling.
- Refactorings and Code Cleanups:
  * Any restructuring of reachable data structures, helper abstractions, or algorithm flows.
- Runtime Assertions and Defensive Checks:
  * Any introduction or alteration of assertions (WARN_ON*, VM_WARN_ON*, BUG_ON*, etc.) in reachable paths.
- Reachable Drivers and Protocols:
  * Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.).

================================================================================
4. EXTRACTING FocusSymbols (PREVENTING DILUTION)
================================================================================
When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer:

- AVOID UBIQUITOUS LIFECYCLE HOT-PATHS:
  Do NOT list generic, ubiquitous functions called by almost every program in the corpus
  (including, but not limited to: general memory allocators and deallocators, page fault
  and trap handlers, or core synchronization primitives; this is not an exhaustive list).
  Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused",
  which severely dilutes fuzzing effort away from the actual changes.

- TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS:
  List functions that specifically implement the logic being added or altered, or direct API entrypoints
  for the subsystem feature under review.

- HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h):
  Compiler-inlined static functions (such as static inlines in mm/*.h or include/linux/*.h) lack
  distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters.
  If the changes are primarily in static inline helpers, identify non-static, feature-specific caller
  functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers).

================================================================================
5. IDENTIFYING EnableConfigs
================================================================================
Identify any specific CONFIG_ options required to properly compile and reach the modified code:
- Inspect Kconfig files and #ifdef guards; do not make assumptions.
- Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed.
- Strip any 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
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.

Target architecture: amd64

For your convenience, here is the diff of the changes:
commit 81002efe86c7a9b86819e5f77caa0b15406c39b0
Author: syz-cluster <triage@syzkaller.com>
Date:   Sat Sep 26 10:58:32 2026 +0000

    syz-cluster: applied patch under review

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 42cffeafc8c14..a1c06b9995c7c 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2849,6 +2849,7 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,
 		WRITE_ONCE(u->oob_skb, NULL);
 
 		if (!sock_flag(sk, SOCK_URGINLINE)) {
+			WRITE_ONCE(u->inq_len, u->inq_len - 1);
 			__skb_unlink(skb, &sk->sk_receive_queue);
 			unread_skb = skb;
 			skb = skb_peek(&sk->sk_receive_queue);
@@ -2884,6 +2885,7 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 		return err;
 
 	mutex_lock(&u->iolock);
+again:
 	spin_lock(&queue->lock);
 
 	skb = __skb_dequeue(queue);
@@ -2893,6 +2895,13 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 		return -EAGAIN;
 	}
 
+	if (!unix_skb_len(skb)) {
+		spin_unlock(&queue->lock);
+		unix_orphan_scm(sk, skb);
+		consume_skb(skb);
+		goto again;
+	}
+
 	WRITE_ONCE(u->inq_len, u->inq_len - unix_skb_len(skb));
 
 #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
@@ -2912,6 +2921,14 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 
 	mutex_unlock(&u->iolock);
 
+	if (UNIXCB(skb).consumed) {
+		if (!pskb_pull(skb, UNIXCB(skb).consumed)) {
+			kfree_skb(skb);
+			return -ENOMEM;
+		}
+		UNIXCB(skb).consumed = 0;
+	}
+
 	return recv_actor(sk, skb);
 }
 

gemini-3.8-flash

null

null

							input: 3339
							output: 38
							thoughts: 71
						

Here's my analysis of the situation:

**Diving into the `af_unix.c` Patch**

Okay, so the patch is touching `net/unix/af_unix.c`. That immediately tells me this is related to Unix domain sockets. Time to get down to specifics. My first step is to quickly analyze the diff itself, pinpointing the exact modifications and getting a handle on the surrounding context. Understanding the nature of the change is paramount.

Now, to truly grasp the implications, I need more detail. I'll need to scrutinize the code in `net/unix/af_unix.c` around lines 2840-2940. I will use a tool like `read-file` or `grepper` to read the sections of code, ensuring I understand the pre-patch state as well as the post-patch impact. I'll need to see precisely *what* is being changed and *why*. What are the potential consequences of this modification within the broader Unix domain socket framework? I'll be looking for any subtle nuances, potential edge cases, or optimizations. Let's get to work.

{
  "File": "net/unix/af_unix.c",
  "FirstLine": 2840,
  "LineCount": 95
}

{
  "Contents": "2840:\t\t\t\tgoto unlock;\n2841:\t\t}\n2842:\t\n2843:\t\tif (skb != u-\u003eoob_skb)\n2844:\t\t\tgoto unlock;\n2845:\t\n2846:\t\tif (copied) {\n2847:\t\t\tskb = NULL;\n2848:\t\t} else if (!(flags \u0026 MSG_PEEK)) {\n2849:\t\t\tWRITE_ONCE(u-\u003eoob_skb, NULL);\n2850:\t\n2851:\t\t\tif (!sock_flag(sk, SOCK_URGINLINE)) {\n2852:\t\t\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - 1);\n2853:\t\t\t\t__skb_unlink(skb, \u0026sk-\u003esk_receive_queue);\n2854:\t\t\t\tunread_skb = skb;\n2855:\t\t\t\tskb = skb_peek(\u0026sk-\u003esk_receive_queue);\n2856:\t\t\t\t*last = skb;\n2857:\t\t\t}\n2858:\t\t} else if (!sock_flag(sk, SOCK_URGINLINE)) {\n2859:\t\t\t*last = skb;\n2860:\t\t\tskb = skb_peek_next(skb, \u0026sk-\u003esk_receive_queue);\n2861:\t\t}\n2862:\t\n2863:\tunlock:\n2864:\t\tspin_unlock(\u0026sk-\u003esk_receive_queue.lock);\n2865:\t\n2866:\t\tconsume_skb(read_skb);\n2867:\t\tkfree_skb_reason(unread_skb, SKB_DROP_REASON_UNIX_SKIP_OOB);\n2868:\t\n2869:\t\treturn skb;\n2870:\t}\n2871:\t#endif\n2872:\t\n2873:\tstatic int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n2874:\t{\n2875:\t\tstruct sk_buff_head *queue = \u0026sk-\u003esk_receive_queue;\n2876:\t\tstruct unix_sock *u = unix_sk(sk);\n2877:\t\tstruct sk_buff *skb;\n2878:\t\tint err;\n2879:\t\n2880:\t\tif (unlikely(READ_ONCE(sk-\u003esk_state) != TCP_ESTABLISHED))\n2881:\t\t\treturn -ENOTCONN;\n2882:\t\n2883:\t\terr = sock_error(sk);\n2884:\t\tif (err)\n2885:\t\t\treturn err;\n2886:\t\n2887:\t\tmutex_lock(\u0026u-\u003eiolock);\n2888:\tagain:\n2889:\t\tspin_lock(\u0026queue-\u003elock);\n2890:\t\n2891:\t\tskb = __skb_dequeue(queue);\n2892:\t\tif (!skb) {\n2893:\t\t\tspin_unlock(\u0026queue-\u003elock);\n2894:\t\t\tmutex_unlock(\u0026u-\u003eiolock);\n2895:\t\t\treturn -EAGAIN;\n2896:\t\t}\n2897:\t\n2898:\t\tif (!unix_skb_len(skb)) {\n2899:\t\t\tspin_unlock(\u0026queue-\u003elock);\n2900:\t\t\tunix_orphan_scm(sk, skb);\n2901:\t\t\tconsume_skb(skb);\n2902:\t\t\tgoto again;\n2903:\t\t}\n2904:\t\n2905:\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - unix_skb_len(skb));\n2906:\t\n2907:\t#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\n2908:\t\tif (skb == u-\u003eoob_skb) {\n2909:\t\t\tWRITE_ONCE(u-\u003eoob_skb, NULL);\n2910:\t\t\tspin_unlock(\u0026queue-\u003elock);\n2911:\t\t\tmutex_unlock(\u0026u-\u003eiolock);\n2912:\t\n2913:\t\t\tkfree_skb_reason(skb, SKB_DROP_REASON_UNIX_SKIP_OOB);\n2914:\t\t\treturn -EAGAIN;\n2915:\t\t}\n2916:\t#endif\n2917:\t\n2918:\t\tspin_unlock(\u0026queue-\u003elock);\n2919:\t\n2920:\t\tunix_orphan_scm(sk, skb);\n2921:\t\n2922:\t\tmutex_unlock(\u0026u-\u003eiolock);\n2923:\t\n2924:\t\tif (UNIXCB(skb).consumed) {\n2925:\t\t\tif (!pskb_pull(skb, UNIXCB(skb).consumed)) {\n2926:\t\t\t\tkfree_skb(skb);\n2927:\t\t\t\treturn -ENOMEM;\n2928:\t\t\t}\n2929:\t\t\tUNIXCB(skb).consumed = 0;\n2930:\t\t}\n2931:\t\n2932:\t\treturn recv_actor(sk, skb);\n2933:\t}\n2934:\t\n"
}

gemini-3.8-flash

null

null

							input: 5063
							output: 22
							thoughts: 41
						

Okay, let's dive into this. Here's how I'd approach this task, as if these were my internal thoughts:

**Analyzing the `unix_stream_read_skb` Function Usage**

Alright, I need to understand the call graph and uses of the `unix_stream_read_skb` function within the kernel. My immediate thought is to trace the function's callers to get a clear picture of its integration and the points where data flows into it. Understanding its use will provide context for its function. To do this systematically, a good starting point is a simple, effective search.

My instinct is to leverage `grep` to quickly identify all instances where this function is called. This initial search will produce the immediate function calls and maybe the files that contain the call. From there, I can drill down further to analyze the surrounding code in each context. This should quickly highlight where the function is being used. I'll need to pay close attention to the arguments passed and the data structures involved, but this should be a fast and effective way to get my bearings and a high-level view of how `unix_stream_read_skb` fits into the overall scheme.

{
  "Expression": "unix_stream_read_skb"
}

{
  "Output": "net/unix/af_unix.c=867=static int unix_read_skb(struct sock *sk, skb_read_actor_t recv_actor);\nnet/unix/af_unix.c:868:static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor);\nnet/unix/af_unix.c-869-static int unix_dgram_connect(struct socket *, struct sockaddr_unsized *,\n--\nnet/unix/af_unix.c=976=static const struct proto_ops unix_stream_ops = {\n--\nnet/unix/af_unix.c-994-\t.recvmsg =\tunix_stream_recvmsg,\nnet/unix/af_unix.c:995:\t.read_skb =\tunix_stream_read_skb,\nnet/unix/af_unix.c-996-\t.mmap =\t\tsock_no_mmap,\n--\nnet/unix/af_unix.c=2815=static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\n--\nnet/unix/af_unix.c-2872-\nnet/unix/af_unix.c:2873:static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/unix/af_unix.c-2874-{\n"
}

gemini-3.8-flash

null

null

							input: 5747
							output: 26
							thoughts: 59
						

Here's my take on the thought process, as requested:

**Deconstructing the Unix Stream Socket Read Path**

Okay, so `unix_stream_read_skb`... right, that's the function that handles the Secure Kernel Buffer (`skb`) read operation for Unix stream sockets. Gotta keep that straight. But *when* exactly does this `read_skb` thing get triggered? That's the key question. I need to understand the call flow here.

Alright, time to crack open the code. I'll fire up `grep` and search the `net/` directory for either `.read_skb` (to catch direct field accesses) or just `read_skb` itself (to find any function calls or variable assignments related to that name, even if they're not directly associated with the structure itself). This should reveal the points in the networking stack where the `read_skb` operation is invoked. From there, I can trace back up the call stack to see what events, signals, or conditions lead to a Unix stream socket actually having its `.read_skb` function executed. This seems like a pretty standard debugging approach, and will almost certainly point to the entry point into this part of the kernel.

{
  "Expression": "read_skb",
  "PathPrefix": "net/"
}

{
  "Output": "net/core/skmsg.c=1234=static void sk_psock_verdict_data_ready(struct sock *sk)\n--\nnet/core/skmsg.c-1247-\trcu_read_unlock();\nnet/core/skmsg.c:1248:\tif (!ops || !ops-\u003eread_skb)\nnet/core/skmsg.c-1249-\t\treturn;\nnet/core/skmsg.c-1250-\nnet/core/skmsg.c:1251:\tcopied = ops-\u003eread_skb(sk, sk_psock_verdict_recv);\nnet/core/skmsg.c-1252-\tif (copied \u003e= 0) {\n--\nnet/ipv4/af_inet.c=1060=const struct proto_ops inet_stream_ops = {\n--\nnet/ipv4/af_inet.c-1084-\t.read_sock\t   = tcp_read_sock,\nnet/ipv4/af_inet.c:1085:\t.read_skb\t   = tcp_read_skb,\nnet/ipv4/af_inet.c-1086-\t.sendmsg_locked    = tcp_sendmsg_locked,\n--\nnet/ipv4/af_inet.c=1096=const struct proto_ops inet_dgram_ops = {\n--\nnet/ipv4/af_inet.c-1112-\t.sendmsg\t   = inet_sendmsg,\nnet/ipv4/af_inet.c:1113:\t.read_skb\t   = udp_read_skb,\nnet/ipv4/af_inet.c-1114-\t.recvmsg\t   = inet_recvmsg,\n--\nnet/ipv4/tcp.c=1748=int tcp_read_sock_noack(struct sock *sk, read_descriptor_t *desc,\n--\nnet/ipv4/tcp.c-1754-\nnet/ipv4/tcp.c:1755:int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/ipv4/tcp.c-1756-{\n--\nnet/ipv4/tcp_bpf.c=221=static int tcp_bpf_recvmsg_parser(struct sock *sk,\n--\nnet/ipv4/tcp_bpf.c-246-\t/* We may have received data on the sk_receive_queue pre-accept and\nnet/ipv4/tcp_bpf.c:247:\t * then we can not use read_skb in this context because we haven't\nnet/ipv4/tcp_bpf.c-248-\t * assigned a sk_socket yet so have no link to the ops. The work-around\nnet/ipv4/tcp_bpf.c-249-\t * is to check the sk_receive_queue and in these cases read skbs off\nnet/ipv4/tcp_bpf.c:250:\t * queue again. The read_skb hook is not running at this point because\nnet/ipv4/tcp_bpf.c:251:\t * of lock_sock so we avoid having multiple runners in read_skb.\nnet/ipv4/tcp_bpf.c-252-\t */\n--\nnet/ipv4/udp.c=2013=EXPORT_SYMBOL(__skb_recv_udp);\nnet/ipv4/udp.c-2014-\nnet/ipv4/udp.c:2015:int udp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/ipv4/udp.c-2016-{\n--\nnet/ipv6/af_inet6.c=660=const struct proto_ops inet6_stream_ops = {\n--\nnet/ipv6/af_inet6.c-685-\t.read_sock\t   = tcp_read_sock,\nnet/ipv6/af_inet6.c:686:\t.read_skb\t   = tcp_read_skb,\nnet/ipv6/af_inet6.c-687-\t.peek_len\t   = tcp_peek_len,\n--\nnet/ipv6/af_inet6.c=696=const struct proto_ops inet6_dgram_ops = {\n--\nnet/ipv6/af_inet6.c-713-\t.recvmsg\t   = inet6_recvmsg,\t\t/* retpoline's sake */\nnet/ipv6/af_inet6.c:714:\t.read_skb\t   = udp_read_skb,\nnet/ipv6/af_inet6.c-715-\t.mmap\t\t   = sock_no_mmap,\n--\nnet/sunrpc/xprtsock.c=1358=static void xs_destroy(struct rpc_xprt *xprt)\n--\nnet/sunrpc/xprtsock.c-1372-/**\nnet/sunrpc/xprtsock.c:1373: * xs_udp_data_read_skb - receive callback for UDP sockets\nnet/sunrpc/xprtsock.c-1374- * @xprt: transport\n--\nnet/sunrpc/xprtsock.c-1378- */\nnet/sunrpc/xprtsock.c:1379:static void xs_udp_data_read_skb(struct rpc_xprt *xprt,\nnet/sunrpc/xprtsock.c-1380-\t\tstruct sock *sk,\n--\nnet/sunrpc/xprtsock.c=1433=static void xs_udp_data_receive(struct sock_xprt *transport)\n--\nnet/sunrpc/xprtsock.c-1446-\t\t\tbreak;\nnet/sunrpc/xprtsock.c:1447:\t\txs_udp_data_read_skb(\u0026transport-\u003exprt, sk, skb);\nnet/sunrpc/xprtsock.c-1448-\t\tconsume_skb(skb);\n--\nnet/unix/af_unix.c=866=static int unix_dgram_recvmsg(struct socket *, struct msghdr *, size_t, int);\nnet/unix/af_unix.c:867:static int unix_read_skb(struct sock *sk, skb_read_actor_t recv_actor);\nnet/unix/af_unix.c:868:static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor);\nnet/unix/af_unix.c-869-static int unix_dgram_connect(struct socket *, struct sockaddr_unsized *,\n--\nnet/unix/af_unix.c=976=static const struct proto_ops unix_stream_ops = {\n--\nnet/unix/af_unix.c-994-\t.recvmsg =\tunix_stream_recvmsg,\nnet/unix/af_unix.c:995:\t.read_skb =\tunix_stream_read_skb,\nnet/unix/af_unix.c-996-\t.mmap =\t\tsock_no_mmap,\n--\nnet/unix/af_unix.c=1002=static const struct proto_ops unix_dgram_ops = {\n--\nnet/unix/af_unix.c-1019-\t.sendmsg =\tunix_dgram_sendmsg,\nnet/unix/af_unix.c:1020:\t.read_skb =\tunix_read_skb,\nnet/unix/af_unix.c-1021-\t.recvmsg =\tunix_dgram_recvmsg,\n--\nnet/unix/af_unix.c=2678=static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,\n--\nnet/unix/af_unix.c-2691-\nnet/unix/af_unix.c:2692:static int unix_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/unix/af_unix.c-2693-{\n--\nnet/unix/af_unix.c=2764=static int unix_stream_recv_urg(struct unix_stream_read_state *state)\nnet/unix/af_unix.c-2765-{\nnet/unix/af_unix.c:2766:\tstruct sk_buff *oob_skb, *read_skb = NULL;\nnet/unix/af_unix.c-2767-\tstruct socket *sock = state-\u003esocket;\n--\nnet/unix/af_unix.c-2790-\t\t    !unix_skb_len(oob_skb-\u003eprev)) {\nnet/unix/af_unix.c:2791:\t\t\tread_skb = oob_skb-\u003eprev;\nnet/unix/af_unix.c:2792:\t\t\t__skb_unlink(read_skb, \u0026sk-\u003esk_receive_queue);\nnet/unix/af_unix.c-2793-\t\t}\n--\nnet/unix/af_unix.c-2805-\nnet/unix/af_unix.c:2806:\tconsume_skb(read_skb);\nnet/unix/af_unix.c-2807-\n--\nnet/unix/af_unix.c=2815=static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\n--\nnet/unix/af_unix.c-2817-{\nnet/unix/af_unix.c:2818:\tstruct sk_buff *read_skb = NULL, *unread_skb = NULL;\nnet/unix/af_unix.c-2819-\tstruct unix_sock *u = unix_sk(sk);\n--\nnet/unix/af_unix.c-2832-\t\t} else {\nnet/unix/af_unix.c:2833:\t\t\tread_skb = skb;\nnet/unix/af_unix.c-2834-\t\t\tskb = skb_peek_next(skb, \u0026sk-\u003esk_receive_queue);\nnet/unix/af_unix.c:2835:\t\t\t__skb_unlink(read_skb, \u0026sk-\u003esk_receive_queue);\nnet/unix/af_unix.c-2836-\t\t\t*last = skb;\n--\nnet/unix/af_unix.c-2853-\t\t\t__skb_unlink(skb, \u0026sk-\u003esk_receive_queue);\nnet/unix/af_unix.c:2854:\t\t\tunread_skb = skb;\nnet/unix/af_unix.c-2855-\t\t\tskb = skb_peek(\u0026sk-\u003esk_receive_queue);\n--\nnet/unix/af_unix.c-2865-\nnet/unix/af_unix.c:2866:\tconsume_skb(read_skb);\nnet/unix/af_unix.c:2867:\tkfree_skb_reason(unread_skb, SKB_DROP_REASON_UNIX_SKIP_OOB);\nnet/unix/af_unix.c-2868-\n--\nnet/unix/af_unix.c-2872-\nnet/unix/af_unix.c:2873:static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/unix/af_unix.c-2874-{\n--\nnet/vmw_vsock/af_vsock.c=1302=static __poll_t vsock_poll(struct file *file, struct socket *sock,\n--\nnet/vmw_vsock/af_vsock.c-1418-\nnet/vmw_vsock/af_vsock.c:1419:static int vsock_read_skb(struct sock *sk, skb_read_actor_t read_actor)\nnet/vmw_vsock/af_vsock.c-1420-{\n--\nnet/vmw_vsock/af_vsock.c-1425-\nnet/vmw_vsock/af_vsock.c:1426:\treturn vsk-\u003etransport-\u003eread_skb(vsk, read_actor);\nnet/vmw_vsock/af_vsock.c-1427-}\n--\nnet/vmw_vsock/af_vsock.c=1653=static const struct proto_ops vsock_dgram_ops = {\n--\nnet/vmw_vsock/af_vsock.c-1668-\t.mmap = sock_no_mmap,\nnet/vmw_vsock/af_vsock.c:1669:\t.read_skb = vsock_read_skb,\nnet/vmw_vsock/af_vsock.c-1670-};\n--\nnet/vmw_vsock/af_vsock.c=2654=static const struct proto_ops vsock_stream_ops = {\n--\nnet/vmw_vsock/af_vsock.c-2672-\t.set_rcvlowat = vsock_set_rcvlowat,\nnet/vmw_vsock/af_vsock.c:2673:\t.read_skb = vsock_read_skb,\nnet/vmw_vsock/af_vsock.c-2674-};\n--\nnet/vmw_vsock/af_vsock.c=2676=static const struct proto_ops vsock_seqpacket_ops = {\n--\nnet/vmw_vsock/af_vsock.c-2693-\t.mmap = sock_no_mmap,\nnet/vmw_vsock/af_vsock.c:2694:\t.read_skb = vsock_read_skb,\nnet/vmw_vsock/af_vsock.c-2695-};\n--\nnet/vmw_vsock/virtio_transport.c=557=static struct virtio_transport virtio_transport = {\n--\nnet/vmw_vsock/virtio_transport.c-605-\nnet/vmw_vsock/virtio_transport.c:606:\t\t.read_skb = virtio_transport_read_skb,\nnet/vmw_vsock/virtio_transport.c-607-\t},\n--\nnet/vmw_vsock/virtio_transport_common.c=1922=EXPORT_SYMBOL_GPL(virtio_transport_purge_skbs);\nnet/vmw_vsock/virtio_transport_common.c-1923-\nnet/vmw_vsock/virtio_transport_common.c:1924:int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_actor)\nnet/vmw_vsock/virtio_transport_common.c-1925-{\n--\nnet/vmw_vsock/virtio_transport_common.c-1955-}\nnet/vmw_vsock/virtio_transport_common.c:1956:EXPORT_SYMBOL_GPL(virtio_transport_read_skb);\nnet/vmw_vsock/virtio_transport_common.c-1957-\n--\nnet/vmw_vsock/vsock_bpf.c=150=int vsock_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)\n--\nnet/vmw_vsock/vsock_bpf.c-163-\nnet/vmw_vsock/vsock_bpf.c:164:\tif (!vsk-\u003etransport-\u003eread_skb)\nnet/vmw_vsock/vsock_bpf.c-165-\t\treturn -EOPNOTSUPP;\n--\nnet/vmw_vsock/vsock_loopback.c=63=static struct virtio_transport loopback_transport = {\n--\nnet/vmw_vsock/vsock_loopback.c-110-\nnet/vmw_vsock/vsock_loopback.c:111:\t\t.read_skb = virtio_transport_read_skb,\nnet/vmw_vsock/vsock_loopback.c-112-\t},\n"
}

gemini-3.8-flash

null

null

							input: 10225
							output: 18
							thoughts: 149
						

**Investigating Socket Verdicts with Sk_PSock and Unix Sockets**

Okay, so I'm digging into how `sk_psock_verdict_data_ready` is interacting with sockmap and `sk_psock`. Right now, it looks like `ops->read_skb(sk, sk_psock_verdict_recv)` gets called when a sockmap or sk_psock is attached. Good start.

Now, I need to see how Unix sockets play into this. I should probably check `unix_bpf.c` or a similar file that might detail the interaction of Unix sockets with the sk_psock/BPF sockmap framework. That's probably the most direct approach.

Let's see, I can try searching for `CONFIG_AF_UNIX_OOB` since that might relate to the out-of-band features that could be relevant, or maybe `unix_stream_read_skb`. Or, a git commit log search could be the fastest way to get to the history.

Wait, I think the most efficient way to get a quick overview is to grep for `unix_stream_read_skb` within the git log if possible, or fall back to checking `unix_bpf.c`. That should give me a good handle on how the kernel handles data from Unix sockets within this context.

{
  "Expression": "unix_bpf"
}

{
  "Output": "MAINTAINERS=5016=F:\tnet/ipv4/udp_bpf.c\nMAINTAINERS:5017:F:\tnet/unix/unix_bpf.c\nMAINTAINERS-5018-\n--\nnet/unix/Makefile=9=unix-$(CONFIG_SYSCTL)\t+= sysctl_net_unix.o\nnet/unix/Makefile:10:unix-$(CONFIG_BPF_SYSCALL) += unix_bpf.o\nnet/unix/Makefile-11-\n--\nnet/unix/af_unix.c=1051=static void unix_close(struct sock *sk, long timeout)\n--\nnet/unix/af_unix.c-1057-\nnet/unix/af_unix.c:1058:static bool unix_bpf_bypass_getsockopt(int level, int optname)\nnet/unix/af_unix.c-1059-{\n--\nnet/unix/af_unix.c=1072=struct proto unix_dgram_proto = {\n--\nnet/unix/af_unix.c-1076-\t.close\t\t\t= unix_close,\nnet/unix/af_unix.c:1077:\t.bpf_bypass_getsockopt\t= unix_bpf_bypass_getsockopt,\nnet/unix/af_unix.c-1078-#ifdef CONFIG_BPF_SYSCALL\n--\nnet/unix/af_unix.c=1083=struct proto unix_stream_proto = {\n--\nnet/unix/af_unix.c-1087-\t.close\t\t\t= unix_close,\nnet/unix/af_unix.c:1088:\t.bpf_bypass_getsockopt\t= unix_bpf_bypass_getsockopt,\nnet/unix/af_unix.c-1089-#ifdef CONFIG_BPF_SYSCALL\n--\nnet/unix/af_unix.c=3962=static int __init af_unix_init(void)\n--\nnet/unix/af_unix.c-3987-\tregister_pernet_subsys(\u0026unix_net_ops);\nnet/unix/af_unix.c:3988:\tunix_bpf_build_proto();\nnet/unix/af_unix.c-3989-\n--\nnet/unix/af_unix.h=63=int unix_stream_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore);\nnet/unix/af_unix.h:64:void __init unix_bpf_build_proto(void);\nnet/unix/af_unix.h-65-#else\nnet/unix/af_unix.h:66:static inline void __init unix_bpf_build_proto(void)\nnet/unix/af_unix.h-67-{\n--\nnet/unix/unix_bpf.c=42=static int __unix_recvmsg(struct sock *sk, struct msghdr *msg,\n--\nnet/unix/unix_bpf.c-50-\nnet/unix/unix_bpf.c:51:static int unix_bpf_recvmsg(struct sock *sk, struct msghdr *msg,\nnet/unix/unix_bpf.c-52-\t\t\t    size_t len, int flags)\n--\nnet/unix/unix_bpf.c=106=static void unix_dgram_bpf_rebuild_protos(struct proto *prot, const struct proto *base)\n--\nnet/unix/unix_bpf.c-109-\tprot-\u003eclose  = sock_map_close;\nnet/unix/unix_bpf.c:110:\tprot-\u003erecvmsg = unix_bpf_recvmsg;\nnet/unix/unix_bpf.c-111-\tprot-\u003esock_is_readable = sk_msg_is_readable;\n--\nnet/unix/unix_bpf.c=114=static void unix_stream_bpf_rebuild_protos(struct proto *prot,\n--\nnet/unix/unix_bpf.c-118-\tprot-\u003eclose  = sock_map_close;\nnet/unix/unix_bpf.c:119:\tprot-\u003erecvmsg = unix_bpf_recvmsg;\nnet/unix/unix_bpf.c-120-\tprot-\u003esock_is_readable = sk_msg_is_readable;\n--\nnet/unix/unix_bpf.c=164=int unix_stream_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)\n--\nnet/unix/unix_bpf.c-199-\nnet/unix/unix_bpf.c:200:void __init unix_bpf_build_proto(void)\nnet/unix/unix_bpf.c-201-{\n--\nnet/vmw_vsock/vsock_bpf.c-3- *\nnet/vmw_vsock/vsock_bpf.c:4: * Based off of net/unix/unix_bpf.c\nnet/vmw_vsock/vsock_bpf.c-5- */\n"
}

gemini-3.8-flash

null

null

							input: 11969
							output: 21
							thoughts: 32
						

Okay, let's break this down.

**Investigating CONFIG_AF_UNIX_OOB**

Alright, I'm encountering `CONFIG_AF_UNIX_OOB`. I need to understand this. My immediate thought is to use a grep search. I want to see where this configuration option is defined, used, or referenced within the project. I need to understand its context. Where does this appear? What other configuration options relate to this? Let's use `grep` to quickly get an overview. This is the fastest way to get a quick overview of what is going on here.

{
  "Expression": "AF_UNIX_OOB"
}

{
  "Output": "include/net/af_unix.h=36=struct unix_sock {\n--\ninclude/net/af_unix.h-52-\tbool\t\t\tscm_rights_notrunc;\ninclude/net/af_unix.h:53:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\ninclude/net/af_unix.h-54-\tstruct sk_buff\t\t*oob_skb;\n--\nnet/unix/Kconfig=6=config UNIX\n--\nnet/unix/Kconfig-18-\nnet/unix/Kconfig:19:config\tAF_UNIX_OOB\nnet/unix/Kconfig-20-\tbool \"UNIX: out-of-bound messages\"\n--\nnet/unix/af_unix.c=665=static void unix_release_sock(struct sock *sk, int embrion)\n--\nnet/unix/af_unix.c-690-\nnet/unix/af_unix.c:691:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-692-\tu-\u003eoob_skb = NULL;\n--\nnet/unix/af_unix.c-700-\nnet/unix/af_unix.c:701:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-702-\t\t\tif (skb \u0026\u0026 !unix_skb_len(skb))\n--\nnet/unix/af_unix.c=2090=static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,\n--\nnet/unix/af_unix.c-2322-\nnet/unix/af_unix.c:2323:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-2324-static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,\n--\nnet/unix/af_unix.c=2384=static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,\n--\nnet/unix/af_unix.c-2400-\t\terr = -EOPNOTSUPP;\nnet/unix/af_unix.c:2401:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-2402-\t\tif (len)\n--\nnet/unix/af_unix.c-2502-\nnet/unix/af_unix.c:2503:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-2504-\tif (msg-\u003emsg_flags \u0026 MSG_OOB) {\n--\nnet/unix/af_unix.c=2752=struct unix_stream_read_state {\n--\nnet/unix/af_unix.c-2762-\nnet/unix/af_unix.c:2763:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-2764-static int unix_stream_recv_urg(struct unix_stream_read_state *state)\n--\nnet/unix/af_unix.c=2873=static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n--\nnet/unix/af_unix.c-2906-\nnet/unix/af_unix.c:2907:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-2908-\tif (skb == u-\u003eoob_skb) {\n--\nnet/unix/af_unix.c=2935=static int unix_stream_read_generic(struct unix_stream_read_state *state,\n--\nnet/unix/af_unix.c-2959-\t\terr = -EOPNOTSUPP;\nnet/unix/af_unix.c:2960:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-2961-\t\terr = unix_stream_recv_urg(state);\n--\nnet/unix/af_unix.c-2992-again:\nnet/unix/af_unix.c:2993:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-2994-\t\tif (skb) {\n--\nnet/unix/af_unix.c=3316=static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)\n--\nnet/unix/af_unix.c-3336-\t\tbreak;\nnet/unix/af_unix.c:3337:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-3338-\tcase SIOCATMARK:\n--\nnet/unix/af_unix.c=3382=static __poll_t unix_poll(struct file *file, struct socket *sock, poll_table *wait)\n--\nnet/unix/af_unix.c-3406-\t\tmask |= EPOLLIN | EPOLLRDNORM;\nnet/unix/af_unix.c:3407:#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c-3408-\tif (READ_ONCE(unix_sk(sk)-\u003eoob_skb))\n--\ntools/testing/selftests/landlock/config:1:CONFIG_AF_UNIX_OOB=y\ntools/testing/selftests/landlock/config-2-CONFIG_AUDIT=y\n--\ntools/testing/selftests/landlock/scoped_signal_test.c=395=static int setup_signal_handler(int signal)\n--\ntools/testing/selftests/landlock/scoped_signal_test.c-408-/*\ntools/testing/selftests/landlock/scoped_signal_test.c:409: * MSG_OOB might be disabled in the kernel via the CONFIG_AF_UNIX_OOB\ntools/testing/selftests/landlock/scoped_signal_test.c-410- * switch, so this function can be used for probing for its availability.\n--\ntools/testing/selftests/landlock/scoped_signal_test.c=479=TEST_F(fown, sigurg_socket)\n--\ntools/testing/selftests/landlock/scoped_signal_test.c-488-\tif (!has_af_unix_oob())\ntools/testing/selftests/landlock/scoped_signal_test.c:489:\t\tSKIP(return, \"CONFIG_AF_UNIX_OOB / MSG_OOB not available\");\ntools/testing/selftests/landlock/scoped_signal_test.c-490-\n--\ntools/testing/selftests/net/af_unix/config:1:CONFIG_AF_UNIX_OOB=y\ntools/testing/selftests/net/af_unix/config-2-CONFIG_BPF=y\n"
}

gemini-3.8-flash

null

null

							input: 13944
							output: 38
							thoughts: 758
						

**Analyzing the af_unix.c Patch**

Okay, let's break this down. First, I need to understand what this patch is doing in `net/unix/af_unix.c`. Specifically, I'm focusing on the changes around `manage_oob` and the `unix_stream_read_skb` function, as those seem to be the primary areas of modification.

Looking at `manage_oob`, the original code was handling Out-of-Band (OOB) data. It appears that it's clearing the `u->oob_skb`, and if the socket isn't in `SOCK_URGINLINE` mode, it's unlinking the `skb` and assigning it to `unread_skb`. A previous line in the same function does not look related to the change.

Now to the heart of the changes in `unix_stream_read_skb`. The key seems to be the addition of a few lines related to `inq_len`. I can see a decrement of `u->inq_len` if not `SOCK_URGINLINE` mode.

The added `again` label suggests a loop or retry mechanism. Inside the loop, it checks if `unix_skb_len(skb)` is zero. If so, it unlocks the queue, calls `unix_orphan_scm`, consumes and frees the skb, and jumps back to `again`, presumably to process the next skb in the queue. This is a crucial addition, effectively skipping empty skbs. This is important to ensure that we don't return zero length skbs for read.

Also, after the mutex unlock, there's a conditional check involving `UNIXCB(skb).consumed`. If `consumed` is set, the patch tries to `pskb_pull` the consumed bytes from the skb. If this fails, the patch frees the skb and returns -ENOMEM. It's likely that it's some kind of early consumption of bytes, and this is to ensure that consumed bytes are removed before passing it on to the read actor.

So, in essence, the patch seems to be addressing issues related to handling empty or partially consumed skbs within the UNIX domain socket stream read path. It makes sure that `inq_len` is handled correctly with these skbs, filters out zero-length `skb`s, and handles the situation where some bytes have already been consumed.

{
  "File": "net/unix/af_unix.c",
  "FirstLine": 2810,
  "LineCount": 50
}

{
  "Contents": "2810:\t\n2811:\t\tstate-\u003emsg-\u003emsg_flags |= MSG_OOB;\n2812:\t\treturn 1;\n2813:\t}\n2814:\t\n2815:\tstatic struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\n2816:\t\t\t\t\t  struct sock *sk, int flags, int copied)\n2817:\t{\n2818:\t\tstruct sk_buff *read_skb = NULL, *unread_skb = NULL;\n2819:\t\tstruct unix_sock *u = unix_sk(sk);\n2820:\t\n2821:\t\tif (likely(unix_skb_len(skb) \u0026\u0026 skb != READ_ONCE(u-\u003eoob_skb)))\n2822:\t\t\treturn skb;\n2823:\t\n2824:\t\tspin_lock(\u0026sk-\u003esk_receive_queue.lock);\n2825:\t\n2826:\t\tif (!unix_skb_len(skb)) {\n2827:\t\t\tif (copied \u0026\u0026 (!u-\u003eoob_skb || skb == u-\u003eoob_skb)) {\n2828:\t\t\t\tskb = NULL;\n2829:\t\t\t} else if (flags \u0026 MSG_PEEK) {\n2830:\t\t\t\t*last = skb;\n2831:\t\t\t\tskb = skb_peek_next(skb, \u0026sk-\u003esk_receive_queue);\n2832:\t\t\t} else {\n2833:\t\t\t\tread_skb = skb;\n2834:\t\t\t\tskb = skb_peek_next(skb, \u0026sk-\u003esk_receive_queue);\n2835:\t\t\t\t__skb_unlink(read_skb, \u0026sk-\u003esk_receive_queue);\n2836:\t\t\t\t*last = skb;\n2837:\t\t\t}\n2838:\t\n2839:\t\t\tif (!skb)\n2840:\t\t\t\tgoto unlock;\n2841:\t\t}\n2842:\t\n2843:\t\tif (skb != u-\u003eoob_skb)\n2844:\t\t\tgoto unlock;\n2845:\t\n2846:\t\tif (copied) {\n2847:\t\t\tskb = NULL;\n2848:\t\t} else if (!(flags \u0026 MSG_PEEK)) {\n2849:\t\t\tWRITE_ONCE(u-\u003eoob_skb, NULL);\n2850:\t\n2851:\t\t\tif (!sock_flag(sk, SOCK_URGINLINE)) {\n2852:\t\t\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - 1);\n2853:\t\t\t\t__skb_unlink(skb, \u0026sk-\u003esk_receive_queue);\n2854:\t\t\t\tunread_skb = skb;\n2855:\t\t\t\tskb = skb_peek(\u0026sk-\u003esk_receive_queue);\n2856:\t\t\t\t*last = skb;\n2857:\t\t\t}\n2858:\t\t} else if (!sock_flag(sk, SOCK_URGINLINE)) {\n2859:\t\t\t*last = skb;\n"
}

gemini-3.8-flash

null

null

							input: 16078
							output: 32
							thoughts: 534
						

**Analyzing Potential Impacts of Recent Code Changes**

Okay, here's what I'm seeing. I'm focusing on the interaction between out-of-band (OOB) data and UNIX domain sockets, particularly within the context of sockmap and verdict decisions. I notice a change within `manage_oob` where, when an OOB skb is dequeued or skipped (if `!sock_flag(sk, SOCK_URGINLINE)`), it now decrements `u->inq_len` using `WRITE_ONCE`. This seems straightforward, but I need to understand the full picture.

The crucial link is `unix_stream_read_skb`. This function is specifically invoked when a sockmap or verdict system is attached to a UNIX stream socket.  It loops, dequeuing skbs, handling empty skbs by orphaning them and consuming them, and then, if a skb has been partially consumed via `UNIXCB(skb).consumed`, it attempts to pull the remaining data. If the pull fails, memory is freed; otherwise, `recv_actor` is called on the remaining data. The crucial point here is that `UNIXCB(skb).consumed` is checked.

My initial question is how `UNIXCB(skb).consumed` gets set, especially with partially read or empty skbs in the queue. This is where I need to dig deeper into the control flow. The code is in `net/unix/af_unix.c`. That's a core network component; it's definitely a reachable code path.  Anyone can create an `AF_UNIX` socket (stream or datagram), send OOB data using `send(..., MSG_OOB)`, attach a BPF sockmap or `sk_psock`, and then call `read`/`recv`.  This is a widely used and common networking interface. The change to `manage_oob` could have a wide impact!

To fully understand this, I need to check the Kconfig entry for `AF_UNIX_OOB` in `net/unix/Kconfig`. I need to ensure that the feature is enabled to evaluate the potential impact.

In conclusion, this change looks interesting, but I need to correlate the changes in `manage_oob` with `unix_stream_read_skb` to fully evaluate potential race conditions or other issues, particularly if `UNIXCB(skb).consumed` becomes inconsistent with the queued data and `u->inq_len`. I must analyze all the dependent factors to be sure of the impact.

{
  "File": "net/unix/Kconfig",
  "FirstLine": 1,
  "LineCount": 40
}

{
  "Contents": "   1:\t# SPDX-License-Identifier: GPL-2.0-only\n   2:\t#\n   3:\t# Unix Domain Sockets\n   4:\t#\n   5:\t\n   6:\tconfig UNIX\n   7:\t\tbool \"Unix domain sockets\"\n   8:\t\thelp\n   9:\t\t  If you say Y here, you will include support for Unix domain sockets;\n  10:\t\t  sockets are the standard Unix mechanism for establishing and\n  11:\t\t  accessing network connections.  Many commonly used programs such as\n  12:\t\t  the X Window system and syslog use these sockets even if your\n  13:\t\t  machine is not connected to any network.  Unless you are working on\n  14:\t\t  an embedded system or something similar, you therefore definitely\n  15:\t\t  want to say Y here.\n  16:\t\n  17:\t\t  Say Y unless you know what you are doing.\n  18:\t\n  19:\tconfig\tAF_UNIX_OOB\n  20:\t\tbool \"UNIX: out-of-bound messages\"\n  21:\t\tdepends on UNIX\n  22:\t\tdefault y\n  23:\t\thelp\n  24:\t\t  Support for MSG_OOB in UNIX domain sockets. If unsure, say Y.\n  25:\t\n  26:\tconfig UNIX_DIAG\n  27:\t\ttristate \"UNIX: socket monitoring interface\"\n  28:\t\tdepends on UNIX\n  29:\t\tdefault n\n  30:\t\thelp\n  31:\t\t  Support for UNIX socket monitoring interface used by the ss tool.\n  32:\t\t  If unsure, say Y.\n"
}

gemini-3.8-flash

null

null

							input: 17600
							output: 24
							thoughts: 67
						

Okay, here's my assessment of the situation:

**BPF and Unix Sockmap Configuration - My Mental Checklist**

Alright, I need to verify something critical regarding the BPF configuration requirements for using unix sockmaps. Specifically, I'm concerned because `unix_stream_read_skb` is involved here, and that function gets called through the `sk_psock_verdict_data_ready` mechanism within a BPF sockmap. It's a critical point for performance and security, so I can't afford to overlook it.

My first step is to dive right into the code. I'm going to carefully examine `net/unix/unix_bpf.c` because that's the likely location for the relevant BPF integration within the Unix domain socket code. I'll need to scrutinize the implementation for any potential caveats or limitations.

Furthermore, I have to cross-reference that code against the Kconfig configuration options. I'll need to ascertain which kernel features and modules need to be enabled at compile time to ensure that BPF sockmaps are properly functional with Unix domain sockets. I'll be looking for any dependencies, and I'll pay attention to whether there are specific configuration options that impact the behavior or security of this setup. It's a fundamental part of verifying this setup, and I can't leave any stone unturned.

{
  "Expression": "unix_stream_bpf_update_proto"
}

{
  "Output": "net/unix/af_unix.c=1083=struct proto unix_stream_proto = {\n--\nnet/unix/af_unix.c-1089-#ifdef CONFIG_BPF_SYSCALL\nnet/unix/af_unix.c:1090:\t.psock_update_sk_prot\t= unix_stream_bpf_update_proto,\nnet/unix/af_unix.c-1091-#endif\n--\nnet/unix/af_unix.h=62=int unix_dgram_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore);\nnet/unix/af_unix.h:63:int unix_stream_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore);\nnet/unix/af_unix.h-64-void __init unix_bpf_build_proto(void);\n--\nnet/unix/unix_bpf.c=148=int unix_dgram_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)\n--\nnet/unix/unix_bpf.c-163-\nnet/unix/unix_bpf.c:164:int unix_stream_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)\nnet/unix/unix_bpf.c-165-{\n"
}

gemini-3.8-flash

null

null

							input: 18344
							output: 25
							thoughts: 142
						

Okay, let's break this down.

**Investigating BPF Sockmap Configuration Dependencies**

Alright, first things first, I need to understand the configuration dependencies for BPF sockmaps. I'm going to start with the `net/unix/Makefile`.  I see a rule there: `unix-$(CONFIG_BPF_SYSCALL) += unix_bpf.o`. So BPF syscall support is directly implicated. Then, I need to consider `AF_UNIX_OOB`. Looks like that's a boolean, defaults to 'y' and depends on `UNIX`. So the relevant configuration options seem to be `UNIX`, `AF_UNIX_OOB`, and `BPF_SYSCALL`.

However, I'm not convinced that's the whole story. To be thorough, I'm going to look for *other* potential dependencies that are not immediately obvious. The goal is to determine all required configurations for enabling BPF sockmaps. I'll search for "sock_map" within `net/core/Makefile`, `kernel/bpf/Makefile`, and `net/Kconfig` to see if there are additional dependencies or other related configurations. This approach should provide a more complete picture of the build requirements.

{
  "Expression": "sock_map",
  "PathPrefix": "net/"
}

{
  "Output": "\nFull output is too long, showing 500 out of 715 lines.\nUse more precise expression if possible.\n\nnet/core/Makefile=44=obj-$(CONFIG_NET_SOCK_MSG) += skmsg.o\nnet/core/Makefile:45:obj-$(CONFIG_BPF_SYSCALL) += sock_map.o\nnet/core/Makefile-46-obj-$(CONFIG_BPF_SYSCALL) += bpf_sk_storage.o\n--\nnet/core/filter.c=8758=xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)\n--\nnet/core/filter.c-8828-\nnet/core/filter.c:8829:const struct bpf_func_proto bpf_sock_map_update_proto __weak;\nnet/core/filter.c-8830-const struct bpf_func_proto bpf_sock_hash_update_proto __weak;\n--\nnet/core/filter.c=8833=sock_ops_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)\n--\nnet/core/filter.c-8847-\t\treturn \u0026bpf_sock_ops_cb_flags_set_proto;\nnet/core/filter.c:8848:\tcase BPF_FUNC_sock_map_update:\nnet/core/filter.c:8849:\t\treturn \u0026bpf_sock_map_update_proto;\nnet/core/filter.c-8850-\tcase BPF_FUNC_sock_hash_update:\n--\nnet/core/filter.c=11724=BPF_CALL_4(sk_select_reuseport, struct sk_reuseport_kern *, reuse_kern,\n--\nnet/core/filter.c-11741-\t\t *\nnet/core/filter.c:11742:\t\t * Other maps (e.g. sock_map) do not provide this guarantee and\nnet/core/filter.c-11743-\t\t * the sk may never be in the reuseport group to begin with.\n--\nnet/core/filter.c-11766-error:\nnet/core/filter.c:11767:\t/* Lookup in sock_map can return TCP ESTABLISHED sockets. */\nnet/core/filter.c-11768-\tif (sk_is_refcounted(selected_sk))\n--\nnet/core/skmsg.c=671=static void sk_psock_backlog(struct work_struct *work)\n--\nnet/core/skmsg.c-688-\t/* Increment the psock refcnt to synchronize with close(fd) path in\nnet/core/skmsg.c:689:\t * sock_map_close(), ensuring we wait for backlog thread completion\nnet/core/skmsg.c-690-\t * before sk_socket freed. If refcnt increment fails, it indicates\nnet/core/skmsg.c:691:\t * sock_map_close() completed with sk_socket potentially already freed.\nnet/core/skmsg.c-692-\t */\n--\nnet/core/skmsg.c=905=EXPORT_SYMBOL_GPL(sk_psock_drop);\nnet/core/skmsg.c-906-\nnet/core/skmsg.c:907:static int sk_psock_map_verd(int verdict, bool redir)\nnet/core/skmsg.c-908-{\n--\nnet/core/skmsg.c=920=int sk_psock_msg_verdict(struct sock *sk, struct sk_psock *psock,\n--\nnet/core/skmsg.c-936-\tmsg-\u003esk = NULL;\nnet/core/skmsg.c:937:\tret = sk_psock_map_verd(ret, msg-\u003esk_redir);\nnet/core/skmsg.c-938-\tpsock-\u003eapply_bytes = msg-\u003eapply_bytes;\n--\nnet/core/skmsg.c=1079=static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb)\n--\nnet/core/skmsg.c-1099-\t\tskb_bpf_set_strparser(skb);\nnet/core/skmsg.c:1100:\t\tret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));\nnet/core/skmsg.c-1101-\t\tskb-\u003esk = NULL;\n--\nnet/core/skmsg.c=1202=static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)\n--\nnet/core/skmsg.c-1223-\t\tret = bpf_prog_run_pin_on_cpu(prog, skb);\nnet/core/skmsg.c:1224:\t\tret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));\nnet/core/skmsg.c-1225-\t}\n--\nnet/core/sock_map.c=32=static DEFINE_MUTEX(sockmap_mutex);\nnet/core/sock_map.c-33-\nnet/core/sock_map.c:34:static int sock_map_prog_update(struct bpf_map *map, struct bpf_prog *prog,\nnet/core/sock_map.c-35-\t\t\t\tstruct bpf_prog *old, struct bpf_link *link,\nnet/core/sock_map.c-36-\t\t\t\tu32 which);\nnet/core/sock_map.c:37:static struct sk_psock_progs *sock_map_progs(struct bpf_map *map);\nnet/core/sock_map.c-38-\nnet/core/sock_map.c:39:static struct bpf_map *sock_map_alloc(union bpf_attr *attr)\nnet/core/sock_map.c-40-{\n--\nnet/core/sock_map.c-68-\nnet/core/sock_map.c:69:int sock_map_get_from_fd(const union bpf_attr *attr, struct bpf_prog *prog)\nnet/core/sock_map.c-70-{\n--\nnet/core/sock_map.c-81-\tmutex_lock(\u0026sockmap_mutex);\nnet/core/sock_map.c:82:\tret = sock_map_prog_update(map, prog, NULL, NULL, attr-\u003eattach_type);\nnet/core/sock_map.c-83-\tmutex_unlock(\u0026sockmap_mutex);\n--\nnet/core/sock_map.c-86-\nnet/core/sock_map.c:87:int sock_map_prog_detach(const union bpf_attr *attr, enum bpf_prog_type ptype)\nnet/core/sock_map.c-88-{\n--\nnet/core/sock_map.c-110-\tmutex_lock(\u0026sockmap_mutex);\nnet/core/sock_map.c:111:\tret = sock_map_prog_update(map, NULL, prog, NULL, attr-\u003eattach_type);\nnet/core/sock_map.c-112-\tmutex_unlock(\u0026sockmap_mutex);\n--\nnet/core/sock_map.c-117-\nnet/core/sock_map.c:118:static void sock_map_sk_acquire(struct sock *sk)\nnet/core/sock_map.c-119-\t__acquires(\u0026sk-\u003esk_lock.slock)\n--\nnet/core/sock_map.c-124-\nnet/core/sock_map.c:125:static void sock_map_sk_release(struct sock *sk)\nnet/core/sock_map.c-126-\t__releases(\u0026sk-\u003esk_lock.slock)\n--\nnet/core/sock_map.c-131-\nnet/core/sock_map.c:132:static void sock_map_add_link(struct sk_psock *psock,\nnet/core/sock_map.c-133-\t\t\t      struct sk_psock_link *link,\n--\nnet/core/sock_map.c-142-\nnet/core/sock_map.c:143:static void sock_map_del_link(struct sock *sk,\nnet/core/sock_map.c-144-\t\t\t      struct sk_psock *psock, void *link_raw)\n--\nnet/core/sock_map.c-152-\t\t\tstruct bpf_map *map = link-\u003emap;\nnet/core/sock_map.c:153:\t\t\tstruct sk_psock_progs *progs = sock_map_progs(map);\nnet/core/sock_map.c-154-\n--\nnet/core/sock_map.c-179-\nnet/core/sock_map.c:180:static void sock_map_unref(struct sock *sk, void *link_raw)\nnet/core/sock_map.c-181-{\n--\nnet/core/sock_map.c-184-\tif (likely(psock)) {\nnet/core/sock_map.c:185:\t\tsock_map_del_link(sk, psock, link_raw);\nnet/core/sock_map.c-186-\t\tsk_psock_put(sk, psock);\n--\nnet/core/sock_map.c-189-\nnet/core/sock_map.c:190:static int sock_map_init_proto(struct sock *sk, struct sk_psock *psock)\nnet/core/sock_map.c-191-{\n--\nnet/core/sock_map.c-197-\nnet/core/sock_map.c:198:static struct sk_psock *sock_map_psock_get_checked(struct sock *sk)\nnet/core/sock_map.c-199-{\n--\nnet/core/sock_map.c-204-\tif (psock) {\nnet/core/sock_map.c:205:\t\tif (sk-\u003esk_prot-\u003eclose != sock_map_close) {\nnet/core/sock_map.c-206-\t\t\tpsock = ERR_PTR(-EBUSY);\n--\nnet/core/sock_map.c-217-\nnet/core/sock_map.c:218:static int sock_map_link(struct bpf_map *map, struct sock *sk)\nnet/core/sock_map.c-219-{\nnet/core/sock_map.c:220:\tstruct sk_psock_progs *progs = sock_map_progs(map);\nnet/core/sock_map.c-221-\tstruct bpf_prog *stream_verdict = NULL;\n--\nnet/core/sock_map.c-261-\nnet/core/sock_map.c:262:\tpsock = sock_map_psock_get_checked(sk);\nnet/core/sock_map.c-263-\tif (IS_ERR(psock)) {\n--\nnet/core/sock_map.c-298-\t */\nnet/core/sock_map.c:299:\tret = sock_map_init_proto(sk, psock);\nnet/core/sock_map.c-300-\tif (ret \u003c 0) {\n--\nnet/core/sock_map.c-339-\nnet/core/sock_map.c:340:static void sock_map_free(struct bpf_map *map)\nnet/core/sock_map.c-341-{\n--\nnet/core/sock_map.c-358-\t\t\trcu_read_lock();\nnet/core/sock_map.c:359:\t\t\tsock_map_unref(sk, psk);\nnet/core/sock_map.c-360-\t\t\trcu_read_unlock();\n--\nnet/core/sock_map.c-372-\nnet/core/sock_map.c:373:static void sock_map_release_progs(struct bpf_map *map)\nnet/core/sock_map.c-374-{\n--\nnet/core/sock_map.c-377-\nnet/core/sock_map.c:378:static struct sock *__sock_map_lookup_elem(struct bpf_map *map, u32 key)\nnet/core/sock_map.c-379-{\n--\nnet/core/sock_map.c-388-\nnet/core/sock_map.c:389:static void *sock_map_lookup(struct bpf_map *map, void *key)\nnet/core/sock_map.c-390-{\n--\nnet/core/sock_map.c-392-\nnet/core/sock_map.c:393:\tsk = __sock_map_lookup_elem(map, *(u32 *)key);\nnet/core/sock_map.c-394-\tif (!sk)\n--\nnet/core/sock_map.c-400-\nnet/core/sock_map.c:401:static void *sock_map_lookup_sys(struct bpf_map *map, void *key)\nnet/core/sock_map.c-402-{\n--\nnet/core/sock_map.c-407-\nnet/core/sock_map.c:408:\tsk = __sock_map_lookup_elem(map, *(u32 *)key);\nnet/core/sock_map.c-409-\tif (!sk)\n--\nnet/core/sock_map.c-415-\nnet/core/sock_map.c:416:static int __sock_map_delete(struct bpf_stab *stab, struct sock *sk_test,\nnet/core/sock_map.c-417-\t\t\t     struct sock **psk)\n--\nnet/core/sock_map.c-426-\tif (likely(sk))\nnet/core/sock_map.c:427:\t\tsock_map_unref(sk, psk);\nnet/core/sock_map.c-428-\telse\n--\nnet/core/sock_map.c-434-\nnet/core/sock_map.c:435:static void sock_map_delete_from_link(struct bpf_map *map, struct sock *sk,\nnet/core/sock_map.c-436-\t\t\t\t      void *link_raw)\n--\nnet/core/sock_map.c-439-\nnet/core/sock_map.c:440:\t__sock_map_delete(stab, sk, link_raw);\nnet/core/sock_map.c-441-}\nnet/core/sock_map.c-442-\nnet/core/sock_map.c:443:static long sock_map_delete_elem(struct bpf_map *map, void *key)\nnet/core/sock_map.c-444-{\n--\nnet/core/sock_map.c-452-\tpsk = \u0026stab-\u003esks[i];\nnet/core/sock_map.c:453:\treturn __sock_map_delete(stab, NULL, psk);\nnet/core/sock_map.c-454-}\nnet/core/sock_map.c-455-\nnet/core/sock_map.c:456:static int sock_map_get_next_key(struct bpf_map *map, void *key, void *next)\nnet/core/sock_map.c-457-{\n--\nnet/core/sock_map.c-470-\nnet/core/sock_map.c:471:static int sock_map_update_common(struct bpf_map *map, u32 idx,\nnet/core/sock_map.c-472-\t\t\t\t  struct sock *sk, u64 flags)\n--\nnet/core/sock_map.c-489-\nnet/core/sock_map.c:490:\tret = sock_map_link(map, sk);\nnet/core/sock_map.c-491-\tif (ret \u003c 0)\n--\nnet/core/sock_map.c-506-\nnet/core/sock_map.c:507:\tsock_map_add_link(psock, link, map, \u0026stab-\u003esks[idx]);\nnet/core/sock_map.c-508-\tstab-\u003esks[idx] = sk;\nnet/core/sock_map.c-509-\tif (osk)\nnet/core/sock_map.c:510:\t\tsock_map_unref(osk, \u0026stab-\u003esks[idx]);\nnet/core/sock_map.c-511-\tspin_unlock_bh(\u0026stab-\u003elock);\n--\nnet/core/sock_map.c-521-\nnet/core/sock_map.c:522:static bool sock_map_op_okay(const struct bpf_sock_ops_kern *ops)\nnet/core/sock_map.c-523-{\n--\nnet/core/sock_map.c-528-\nnet/core/sock_map.c:529:static bool sock_map_redirect_allowed(const struct sock *sk)\nnet/core/sock_map.c-530-{\n--\nnet/core/sock_map.c-536-\nnet/core/sock_map.c:537:static bool sock_map_sk_is_suitable(const struct sock *sk)\nnet/core/sock_map.c-538-{\n--\nnet/core/sock_map.c-541-\nnet/core/sock_map.c:542:static bool sock_map_sk_state_allowed(const struct sock *sk)\nnet/core/sock_map.c-543-{\n--\nnet/core/sock_map.c=556=static int sock_hash_update_common(struct bpf_map *map, void *key,\n--\nnet/core/sock_map.c-558-\nnet/core/sock_map.c:559:int sock_map_update_elem_sys(struct bpf_map *map, void *key, void *value,\nnet/core/sock_map.c-560-\t\t\t     u64 flags)\n--\nnet/core/sock_map.c-581-\t}\nnet/core/sock_map.c:582:\tif (!sock_map_sk_is_suitable(sk)) {\nnet/core/sock_map.c-583-\t\tret = -EOPNOTSUPP;\n--\nnet/core/sock_map.c-586-\nnet/core/sock_map.c:587:\tsock_map_sk_acquire(sk);\nnet/core/sock_map.c:588:\tif (!sock_map_sk_state_allowed(sk))\nnet/core/sock_map.c-589-\t\tret = -EOPNOTSUPP;\nnet/core/sock_map.c-590-\telse if (map-\u003emap_type == BPF_MAP_TYPE_SOCKMAP)\nnet/core/sock_map.c:591:\t\tret = sock_map_update_common(map, *(u32 *)key, sk, flags);\nnet/core/sock_map.c-592-\telse\nnet/core/sock_map.c-593-\t\tret = sock_hash_update_common(map, key, sk, flags);\nnet/core/sock_map.c:594:\tsock_map_sk_release(sk);\nnet/core/sock_map.c-595-out:\n--\nnet/core/sock_map.c-599-\nnet/core/sock_map.c:600:static long sock_map_update_elem(struct bpf_map *map, void *key,\nnet/core/sock_map.c-601-\t\t\t\t void *value, u64 flags)\n--\nnet/core/sock_map.c-608-\nnet/core/sock_map.c:609:\tif (!sock_map_sk_is_suitable(sk))\nnet/core/sock_map.c-610-\t\treturn -EOPNOTSUPP;\n--\nnet/core/sock_map.c-613-\tbh_lock_sock(sk);\nnet/core/sock_map.c:614:\tif (!sock_map_sk_state_allowed(sk))\nnet/core/sock_map.c-615-\t\tret = -EOPNOTSUPP;\nnet/core/sock_map.c-616-\telse if (map-\u003emap_type == BPF_MAP_TYPE_SOCKMAP)\nnet/core/sock_map.c:617:\t\tret = sock_map_update_common(map, *(u32 *)key, sk, flags);\nnet/core/sock_map.c-618-\telse\n--\nnet/core/sock_map.c-624-\nnet/core/sock_map.c:625:BPF_CALL_4(bpf_sock_map_update, struct bpf_sock_ops_kern *, sops,\nnet/core/sock_map.c-626-\t   struct bpf_map *, map, void *, key, u64, flags)\n--\nnet/core/sock_map.c-629-\nnet/core/sock_map.c:630:\tif (likely(sock_map_sk_is_suitable(sops-\u003esk) \u0026\u0026\nnet/core/sock_map.c:631:\t\t   sock_map_op_okay(sops)))\nnet/core/sock_map.c:632:\t\treturn sock_map_update_common(map, *(u32 *)key, sops-\u003esk,\nnet/core/sock_map.c-633-\t\t\t\t\t      flags);\n--\nnet/core/sock_map.c-636-\nnet/core/sock_map.c:637:const struct bpf_func_proto bpf_sock_map_update_proto = {\nnet/core/sock_map.c:638:\t.func\t\t= bpf_sock_map_update,\nnet/core/sock_map.c-639-\t.gpl_only\t= false,\n--\nnet/core/sock_map.c=648=BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,\n--\nnet/core/sock_map.c-655-\nnet/core/sock_map.c:656:\tsk = __sock_map_lookup_elem(map, key);\nnet/core/sock_map.c:657:\tif (unlikely(!sk || !sock_map_redirect_allowed(sk)))\nnet/core/sock_map.c-658-\t\treturn SK_DROP;\n--\nnet/core/sock_map.c=676=BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg,\n--\nnet/core/sock_map.c-683-\nnet/core/sock_map.c:684:\tsk = __sock_map_lookup_elem(map, key);\nnet/core/sock_map.c:685:\tif (unlikely(!sk || !sock_map_redirect_allowed(sk)))\nnet/core/sock_map.c-686-\t\treturn SK_DROP;\n--\nnet/core/sock_map.c=697=const struct bpf_func_proto bpf_msg_redirect_map_proto = {\n--\nnet/core/sock_map.c-706-\nnet/core/sock_map.c:707:struct sock_map_seq_info {\nnet/core/sock_map.c-708-\tstruct bpf_map *map;\n--\nnet/core/sock_map.c=720=DEFINE_BPF_ITER_FUNC(sockmap, struct bpf_iter_meta *meta,\n--\nnet/core/sock_map.c-723-\nnet/core/sock_map.c:724:static void *sock_map_seq_lookup_elem(struct sock_map_seq_info *info)\nnet/core/sock_map.c-725-{\n--\nnet/core/sock_map.c-728-\nnet/core/sock_map.c:729:\tinfo-\u003esk = __sock_map_lookup_elem(info-\u003emap, info-\u003eindex);\nnet/core/sock_map.c-730-\n--\nnet/core/sock_map.c-734-\nnet/core/sock_map.c:735:static void *sock_map_seq_start(struct seq_file *seq, loff_t *pos)\nnet/core/sock_map.c-736-\t__acquires(rcu)\nnet/core/sock_map.c-737-{\nnet/core/sock_map.c:738:\tstruct sock_map_seq_info *info = seq-\u003eprivate;\nnet/core/sock_map.c-739-\n--\nnet/core/sock_map.c-742-\nnet/core/sock_map.c:743:\t/* pairs with sock_map_seq_stop */\nnet/core/sock_map.c-744-\trcu_read_lock();\nnet/core/sock_map.c:745:\treturn sock_map_seq_lookup_elem(info);\nnet/core/sock_map.c-746-}\nnet/core/sock_map.c-747-\nnet/core/sock_map.c:748:static void *sock_map_seq_next(struct seq_file *seq, void *v, loff_t *pos)\nnet/core/sock_map.c-749-\t__must_hold(rcu)\nnet/core/sock_map.c-750-{\nnet/core/sock_map.c:751:\tstruct sock_map_seq_info *info = seq-\u003eprivate;\nnet/core/sock_map.c-752-\n--\nnet/core/sock_map.c-755-\nnet/core/sock_map.c:756:\treturn sock_map_seq_lookup_elem(info);\nnet/core/sock_map.c-757-}\nnet/core/sock_map.c-758-\nnet/core/sock_map.c:759:static int sock_map_seq_show(struct seq_file *seq, void *v)\nnet/core/sock_map.c-760-\t__must_hold(rcu)\nnet/core/sock_map.c-761-{\nnet/core/sock_map.c:762:\tstruct sock_map_seq_info *info = seq-\u003eprivate;\nnet/core/sock_map.c-763-\tstruct bpf_iter__sockmap ctx = {};\n--\nnet/core/sock_map.c-781-\nnet/core/sock_map.c:782:static void sock_map_seq_stop(struct seq_file *seq, void *v)\nnet/core/sock_map.c-783-\t__releases(rcu)\n--\nnet/core/sock_map.c-785-\tif (!v)\nnet/core/sock_map.c:786:\t\t(void)sock_map_seq_show(seq, NULL);\nnet/core/sock_map.c-787-\nnet/core/sock_map.c:788:\t/* pairs with sock_map_seq_start */\nnet/core/sock_map.c-789-\trcu_read_unlock();\n--\nnet/core/sock_map.c-791-\nnet/core/sock_map.c:792:static const struct seq_operations sock_map_seq_ops = {\nnet/core/sock_map.c:793:\t.start\t= sock_map_seq_start,\nnet/core/sock_map.c:794:\t.next\t= sock_map_seq_next,\nnet/core/sock_map.c:795:\t.stop\t= sock_map_seq_stop,\nnet/core/sock_map.c:796:\t.show\t= sock_map_seq_show,\nnet/core/sock_map.c-797-};\nnet/core/sock_map.c-798-\nnet/core/sock_map.c:799:static int sock_map_init_seq_private(void *priv_data,\nnet/core/sock_map.c-800-\t\t\t\t     struct bpf_iter_aux_info *aux)\nnet/core/sock_map.c-801-{\nnet/core/sock_map.c:802:\tstruct sock_map_seq_info *info = priv_data;\nnet/core/sock_map.c-803-\n--\nnet/core/sock_map.c-808-\nnet/core/sock_map.c:809:static void sock_map_fini_seq_private(void *priv_data)\nnet/core/sock_map.c-810-{\nnet/core/sock_map.c:811:\tstruct sock_map_seq_info *info = priv_data;\nnet/core/sock_map.c-812-\n--\nnet/core/sock_map.c-815-\nnet/core/sock_map.c:816:static u64 sock_map_mem_usage(const struct bpf_map *map)\nnet/core/sock_map.c-817-{\n--\nnet/core/sock_map.c-823-\nnet/core/sock_map.c:824:static const struct bpf_iter_seq_info sock_map_iter_seq_info = {\nnet/core/sock_map.c:825:\t.seq_ops\t\t= \u0026sock_map_seq_ops,\nnet/core/sock_map.c:826:\t.init_seq_private\t= sock_map_init_seq_private,\nnet/core/sock_map.c:827:\t.fini_seq_private\t= sock_map_fini_seq_private,\nnet/core/sock_map.c:828:\t.seq_priv_size\t\t= sizeof(struct sock_map_seq_info),\nnet/core/sock_map.c-829-};\nnet/core/sock_map.c-830-\nnet/core/sock_map.c:831:BTF_ID_LIST_SINGLE(sock_map_btf_ids, struct, bpf_stab)\nnet/core/sock_map.c:832:const struct bpf_map_ops sock_map_ops = {\nnet/core/sock_map.c-833-\t.map_meta_equal\t\t= bpf_map_meta_equal,\nnet/core/sock_map.c:834:\t.map_alloc\t\t= sock_map_alloc,\nnet/core/sock_map.c:835:\t.map_free\t\t= sock_map_free,\nnet/core/sock_map.c:836:\t.map_get_next_key\t= sock_map_get_next_key,\nnet/core/sock_map.c:837:\t.map_lookup_elem_sys_only = sock_map_lookup_sys,\nnet/core/sock_map.c:838:\t.map_update_elem\t= sock_map_update_elem,\nnet/core/sock_map.c:839:\t.map_delete_elem\t= sock_map_delete_elem,\nnet/core/sock_map.c:840:\t.map_lookup_elem\t= sock_map_lookup,\nnet/core/sock_map.c:841:\t.map_release_uref\t= sock_map_release_progs,\nnet/core/sock_map.c-842-\t.map_check_btf\t\t= map_check_no_btf,\nnet/core/sock_map.c:843:\t.map_mem_usage\t\t= sock_map_mem_usage,\nnet/core/sock_map.c:844:\t.map_btf_id\t\t= \u0026sock_map_btf_ids[0],\nnet/core/sock_map.c:845:\t.iter_seq_info\t\t= \u0026sock_map_iter_seq_info,\nnet/core/sock_map.c-846-};\n--\nnet/core/sock_map.c=919=static void sock_hash_delete_from_link(struct bpf_map *map, struct sock *sk,\n--\nnet/core/sock_map.c-937-\t\thlist_del_rcu(\u0026elem-\u003enode);\nnet/core/sock_map.c:938:\t\tsock_map_unref(elem-\u003esk, elem);\nnet/core/sock_map.c-939-\t\tsock_hash_free_elem(htab, elem);\n--\nnet/core/sock_map.c=944=static long sock_hash_delete_elem(struct bpf_map *map, void *key)\n--\nnet/core/sock_map.c-958-\t\thlist_del_rcu(\u0026elem-\u003enode);\nnet/core/sock_map.c:959:\t\tsock_map_unref(elem-\u003esk, elem);\nnet/core/sock_map.c-960-\t\tsock_hash_free_elem(htab, elem);\n--\nnet/core/sock_map.c=994=static int sock_hash_update_common(struct bpf_map *map, void *key,\n--\nnet/core/sock_map.c-1012-\nnet/core/sock_map.c:1013:\tret = sock_map_link(map, sk);\nnet/core/sock_map.c-1014-\tif (ret \u003c 0)\n--\nnet/core/sock_map.c-1038-\nnet/core/sock_map.c:1039:\tsock_map_add_link(psock, link, map, elem_new);\nnet/core/sock_map.c-1040-\t/* Add new element to the head of the list, so that\n--\nnet/core/sock_map.c-1045-\t\thlist_del_rcu(\u0026elem-\u003enode);\nnet/core/sock_map.c:1046:\t\tsock_map_unref(elem-\u003esk, elem);\nnet/core/sock_map.c-1047-\t\tsock_hash_free_elem(htab, elem);\n--\nnet/core/sock_map.c=1147=static void sock_hash_free(struct bpf_map *map)\n--\nnet/core/sock_map.c-1183-\t\t\trcu_read_lock();\nnet/core/sock_map.c:1184:\t\t\tsock_map_unref(elem-\u003esk, elem);\nnet/core/sock_map.c-1185-\t\t\trcu_read_unlock();\n--\nnet/core/sock_map.c=1232=BPF_CALL_4(bpf_sock_hash_update, struct bpf_sock_ops_kern *, sops,\n--\nnet/core/sock_map.c-1236-\nnet/core/sock_map.c:1237:\tif (likely(sock_map_sk_is_suitable(sops-\u003esk) \u0026\u0026\nnet/core/sock_map.c:1238:\t\t   sock_map_op_okay(sops)))\nnet/core/sock_map.c-1239-\t\treturn sock_hash_update_common(map, key, sops-\u003esk, flags);\n--\nnet/core/sock_map.c=1254=BPF_CALL_4(bpf_sk_redirect_hash, struct sk_buff *, skb,\n--\nnet/core/sock_map.c-1262-\tsk = __sock_hash_lookup_elem(map, key);\nnet/core/sock_map.c:1263:\tif (unlikely(!sk || !sock_map_redirect_allowed(sk)))\nnet/core/sock_map.c-1264-\t\treturn SK_DROP;\n--\nnet/core/sock_map.c=1282=BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg,\n--\nnet/core/sock_map.c-1290-\tsk = __sock_hash_lookup_elem(map, key);\nnet/core/sock_map.c:1291:\tif (unlikely(!sk || !sock_map_redirect_allowed(sk)))\nnet/core/sock_map.c-1292-\t\treturn SK_DROP;\n--\nnet/core/sock_map.c=1448=const struct bpf_map_ops sock_hash_ops = {\n--\nnet/core/sock_map.c-1452-\t.map_get_next_key\t= sock_hash_get_next_key,\nnet/core/sock_map.c:1453:\t.map_update_elem\t= sock_map_update_elem,\nnet/core/sock_map.c-1454-\t.map_delete_elem\t= sock_hash_delete_elem,\n--\nnet/core/sock_map.c-1463-\nnet/core/sock_map.c:1464:static struct sk_psock_progs *sock_map_progs(struct bpf_map *map)\nnet/core/sock_map.c-1465-{\n--\nnet/core/sock_map.c-1477-\nnet/core/sock_map.c:1478:static int sock_map_prog_link_lookup(struct bpf_map *map, struct bpf_prog ***pprog,\nnet/core/sock_map.c-1479-\t\t\t\t     struct bpf_link ***plink, u32 which)\nnet/core/sock_map.c-1480-{\nnet/core/sock_map.c:1481:\tstruct sk_psock_progs *progs = sock_map_progs(map);\nnet/core/sock_map.c-1482-\tstruct bpf_prog **cur_pprog;\n--\nnet/core/sock_map.c-1520-\nnet/core/sock_map.c:1521:static int sock_map_prog_attach_check(enum bpf_attach_type attach_type,\nnet/core/sock_map.c-1522-\t\t\t\t      struct bpf_prog *prog)\n--\nnet/core/sock_map.c-1537- */\nnet/core/sock_map.c:1538:static int sock_map_prog_update(struct bpf_map *map, struct bpf_prog *prog,\nnet/core/sock_map.c-1539-\t\t\t\tstruct bpf_prog *old, struct bpf_link *link,\n--\nnet/core/sock_map.c-1545-\nnet/core/sock_map.c:1546:\tret = sock_map_prog_link_lookup(map, \u0026pprog, \u0026plink, which);\nnet/core/sock_map.c-1547-\tif (ret)\n--\nnet/core/sock_map.c-1549-\nnet/core/sock_map.c:1550:\tret = sock_map_prog_attach_check(which, prog);\nnet/core/sock_map.c-1551-\tif (ret)\n--\nnet/core/sock_map.c-1572-\nnet/core/sock_map.c:1573:int sock_map_bpf_prog_query(const union bpf_attr *attr,\nnet/core/sock_map.c-1574-\t\t\t    union bpf_attr __user *uattr)\n--\nnet/core/sock_map.c-1593-\nnet/core/sock_map.c:1594:\tret = sock_map_prog_link_lookup(map, \u0026pprog, NULL, attr-\u003equery.attach_type);\nnet/core/sock_map.c-1595-\tif (ret)\n--\nnet/core/sock_map.c-1621-\nnet/core/sock_map.c:1622:static void sock_map_unlink(struct sock *sk, struct sk_psock_link *link)\nnet/core/sock_map.c-1623-{\n--\nnet/core/sock_map.c-1625-\tcase BPF_MAP_TYPE_SOCKMAP:\nnet/core/sock_map.c:1626:\t\treturn sock_map_delete_from_link(link-\u003emap, sk,\nnet/core/sock_map.c-1627-\t\t\t\t\t\t link-\u003elink_raw);\n--\nnet/core/sock_map.c-1635-\nnet/core/sock_map.c:1636:static void sock_map_remove_links(struct sock *sk, struct sk_psock *psock)\nnet/core/sock_map.c-1637-{\n--\n\n"
}

gemini-3.8-flash

null

null

							input: 29245
							output: 27
							thoughts: 45
						

Here's my thought process, as if I were considering this myself:

**Investigating Sock_Map Enablement**

Okay, so I'm trying to trace the dependencies for `sock_map`, and it looks like `CONFIG_NET_SOCK_MSG` and `CONFIG_BPF_SYSCALL` are the key enablers. That seems right, given my understanding of the architecture. Now, to be absolutely sure and to solidify the connection in my mind, I want to confirm where `NET_SOCK_MSG` is defined and how it relates to everything else. Time to dive into `net/Kconfig` and refresh my memory on the specific configuration options tied to `NET_SOCK_MSG`. This will confirm the bigger picture and highlight any other dependencies, implicit or explicit.

{
  "Expression": "NET_SOCK_MSG",
  "PathPrefix": "net/"
}

{
  "Output": "net/Kconfig=361=config BPF_STREAM_PARSER\n--\nnet/Kconfig-366-\tselect STREAM_PARSER\nnet/Kconfig:367:\tselect NET_SOCK_MSG\nnet/Kconfig-368-\thelp\n--\nnet/Kconfig=475=config NET_SELFTESTS\n--\nnet/Kconfig-478-\nnet/Kconfig:479:config NET_SOCK_MSG\nnet/Kconfig-480-\tbool\n--\nnet/Kconfig-482-\thelp\nnet/Kconfig:483:\t  The NET_SOCK_MSG provides a framework for plain sockets (e.g. TCP) or\nnet/Kconfig-484-\t  ULPs (upper layer modules, e.g. TLS) to process L7 application data\n--\nnet/core/Makefile=43=obj-$(CONFIG_FAILOVER) += failover.o\nnet/core/Makefile:44:obj-$(CONFIG_NET_SOCK_MSG) += skmsg.o\nnet/core/Makefile-45-obj-$(CONFIG_BPF_SYSCALL) += sock_map.o\n--\nnet/ipv4/Kconfig=382=config INET_ESPINTCP\n--\nnet/ipv4/Kconfig-385-\tselect STREAM_PARSER\nnet/ipv4/Kconfig:386:\tselect NET_SOCK_MSG\nnet/ipv4/Kconfig-387-\tselect XFRM_ESPINTCP\n--\nnet/ipv4/Makefile=62=obj-$(CONFIG_TCP_CONG_ILLINOIS) += tcp_illinois.o\nnet/ipv4/Makefile:63:obj-$(CONFIG_NET_SOCK_MSG) += tcp_bpf.o\nnet/ipv4/Makefile-64-obj-$(CONFIG_BPF_SYSCALL) += udp_bpf.o\n--\nnet/ipv6/Kconfig=90=config INET6_ESPINTCP\n--\nnet/ipv6/Kconfig-93-\tselect STREAM_PARSER\nnet/ipv6/Kconfig:94:\tselect NET_SOCK_MSG\nnet/ipv6/Kconfig-95-\tselect XFRM_ESPINTCP\n--\nnet/tls/Kconfig=5=config TLS\n--\nnet/tls/Kconfig-10-\tselect CRYPTO_GCM\nnet/tls/Kconfig:11:\tselect NET_SOCK_MSG\nnet/tls/Kconfig-12-\tdefault n\n"
}

gemini-3.8-flash

null

null

							input: 30100
							output: 32
							thoughts: 45
						

Okay, let's dive into this. Here's my thought process on the matter:

**Analyzing Network Packet Parsing Mechanisms**

Alright, I need to figure out the conditions that trigger the selection of either `NET_SOCK_MSG` or the enabling of `BPF_STREAM_PARSER`. My immediate instinct is to check the kernel configuration files. The goal is to understand the interplay between these two mechanisms, particularly what causes the system to choose one over the other, or if they're mutually exclusive or potentially work in conjunction.

So, I'll start by specifically investigating `BPF_STREAM_PARSER`. I'll immediately go check it's Kconfig definition in `net/Kconfig` to start, to see what options might affect it's activation. This should give me a good initial grounding on the topic.

{
  "File": "net/Kconfig",
  "FirstLine": 360,
  "LineCount": 20
}

{
  "Contents": " 360:\t\n 361:\tconfig BPF_STREAM_PARSER\n 362:\t\tbool \"enable BPF STREAM_PARSER\"\n 363:\t\tdepends on INET\n 364:\t\tdepends on BPF_SYSCALL\n 365:\t\tdepends on CGROUP_BPF\n 366:\t\tselect STREAM_PARSER\n 367:\t\tselect NET_SOCK_MSG\n 368:\t\thelp\n 369:\t\t  Enabling this allows a TCP stream parser to be used with\n 370:\t\t  BPF_MAP_TYPE_SOCKMAP.\n 371:\t\n 372:\tconfig NET_FLOW_LIMIT\n 373:\t\tbool \"Net flow limit\"\n 374:\t\tdepends on RPS\n 375:\t\tdefault y\n 376:\t\thelp\n 377:\t\t  The network stack has to drop packets when a receive processing CPU's\n 378:\t\t  backlog reaches netdev_max_backlog. If a few out of many active flows\n 379:\t\t  generate the vast majority of load, drop their traffic earlier to\n"
}

gemini-3.8-flash

null

null

							input: 30646
							output: 36
							thoughts: 174
						

**Investigating BPF Stream Parser and Unix Domain Sockets**

Okay, so I've noticed that `BPF_STREAM_PARSER` seems to be selecting `NET_SOCK_MSG`. That's interesting, let's dig a bit deeper. Time to check `net/unix/unix_bpf.c`. Ah, right, I see that `unix_stream_bpf_update_proto` is compiled only if `CONFIG_BPF_SYSCALL` is enabled.

Hang on a second, back to `net/unix/unix_bpf.c`. I need to be sure; does this code actually *use* `skmsg`? I don't want to make assumptions. Right, let's quickly check the `net/unix/Makefile`. Okay, here we go: `unix-$(CONFIG_BPF_SYSCALL) += unix_bpf.o`.

Wait, this is important; does `unix_bpf.c` itself actually *depend* on `NET_SOCK_MSG`? I need to verify that connection. Alright, let's go straight to the headers within `unix_bpf.c` and confirm that dependency.

{
  "File": "net/unix/unix_bpf.c",
  "FirstLine": 1,
  "LineCount": 40
}

{
  "Contents": "   1:\t// SPDX-License-Identifier: GPL-2.0\n   2:\t/* Copyright (c) 2021 Cong Wang \u003ccong.wang@bytedance.com\u003e */\n   3:\t\n   4:\t#include \u003clinux/bpf.h\u003e\n   5:\t#include \u003clinux/skmsg.h\u003e\n   6:\t#include \u003cnet/af_unix.h\u003e\n   7:\t\n   8:\t#include \"af_unix.h\"\n   9:\t\n  10:\t#define unix_sk_has_data(__sk, __psock)\t\t\t\t\t\\\n  11:\t\t\t({\t!skb_queue_empty(\u0026__sk-\u003esk_receive_queue) ||\t\\\n  12:\t\t\t\t!skb_queue_empty(\u0026__psock-\u003eingress_skb) ||\t\\\n  13:\t\t\t\t!list_empty(\u0026__psock-\u003eingress_msg);\t\t\\\n  14:\t\t\t})\n  15:\t\n  16:\tstatic int unix_msg_wait_data(struct sock *sk, struct sk_psock *psock,\n  17:\t\t\t\t      long timeo)\n  18:\t{\n  19:\t\tDEFINE_WAIT_FUNC(wait, woken_wake_function);\n  20:\t\tstruct unix_sock *u = unix_sk(sk);\n  21:\t\tint ret = 0;\n  22:\t\n  23:\t\tif (sk-\u003esk_shutdown \u0026 RCV_SHUTDOWN)\n  24:\t\t\treturn 1;\n  25:\t\n  26:\t\tif (!timeo)\n  27:\t\t\treturn ret;\n  28:\t\n  29:\t\tadd_wait_queue(sk_sleep(sk), \u0026wait);\n  30:\t\tsk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);\n  31:\t\tif (!unix_sk_has_data(sk, psock)) {\n  32:\t\t\tmutex_unlock(\u0026u-\u003eiolock);\n  33:\t\t\twait_woken(\u0026wait, TASK_INTERRUPTIBLE, timeo);\n  34:\t\t\tmutex_lock(\u0026u-\u003eiolock);\n  35:\t\t\tret = unix_sk_has_data(sk, psock);\n  36:\t\t}\n  37:\t\tsk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);\n  38:\t\tremove_wait_queue(sk_sleep(sk), \u0026wait);\n  39:\t\treturn ret;\n  40:\t}\n"
}

gemini-3.8-flash

null

null

							input: 31733
							output: 25
							thoughts: 347
						

**Analyzing the `unix_stream_read_skb` Function in the Linux Kernel**

Okay, let's break this down. My initial thought was to pinpoint where `unix_stream_read_skb` resides. It's in `net/unix/af_unix.c`. Now, the important question is: is it conditional? Specifically, is it compiled only when `CONFIG_BPF_SYSCALL` is defined?

A quick check of lines 2870-2940 in `af_unix.c` is in order. Line 2873, thankfully, confirms the function's declaration:
```c
static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
{
```
Excellent. And, further down, around line 995, I see how it's integrated:
```c
static const struct proto_ops unix_stream_ops = {
...
	.recvmsg =	unix_stream_recvmsg,
	.read_skb =	unix_stream_read_skb,
	.mmap =		sock_no_mmap,
```
Aha! No conditional compilation here. `unix_stream_read_skb` is always part of `unix_stream_ops` as `.read_skb`. This is good; one less thing to worry about.

Now, what *calls* `unix_stream_ops.read_skb`? We saw `sk_psock_verdict_data_ready`, which seems to be the crucial part:
```c
	copied = ops->read_skb(sk, sk_psock_verdict_recv);
```
So, where is `sk_psock_verdict_data_ready` actually being initialized? Time to grep for that symbol to trace its usage.

{
  "Expression": "sk_psock_verdict_data_ready"
}

{
  "Output": "net/core/skmsg.c=1202=static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)\n--\nnet/core/skmsg.c-1233-\nnet/core/skmsg.c:1234:static void sk_psock_verdict_data_ready(struct sock *sk)\nnet/core/skmsg.c-1235-{\n--\nnet/core/skmsg.c=1261=void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock)\n--\nnet/core/skmsg.c-1266-\tpsock-\u003esaved_data_ready = sk-\u003esk_data_ready;\nnet/core/skmsg.c:1267:\tWRITE_ONCE(sk-\u003esk_data_ready, sk_psock_verdict_data_ready);\nnet/core/skmsg.c-1268-\tWRITE_ONCE(sk-\u003esk_write_space, sk_psock_write_space);\n"
}

gemini-3.8-flash

null

null

							input: 32796
							output: 23
							thoughts: 79
						

Okay, here's my interpretation of this technical snippet, tailored for someone familiar with socket programming and the kernel:

**Understanding the `sk_psock_start_verdict` Function**

Right, so I see that `sk_psock_start_verdict` is the function that's setting `sk->sk_data_ready` to `sk_psock_verdict_data_ready`. That's the key. This is the mechanism for signaling that some data is ready, or that something specific needs to happen, on a socket (`sk`). And the *specific* event we're focusing on here is `sk_psock_verdict_data_ready`. From context, I'm inferring this has something to do with verdict programs, probably eBPF programs, and likely relates to socket maps. And the clue is that `sk_psock_start_verdict` is called when a verdict program is attached to a sockmap.

My next immediate step would be to dig deeper into the code to check exactly how these verdict programs are executed, when this event occurs, and the precise meaning of 'verdict'. Since I'm seeing this snippet, I'm thinking I'll need to do a full grepping for `sk_psock_start_verdict` to check where that function is actually getting invoked. I'll need to see the call paths to get a sense of the broader context. I expect this will reveal the interaction between the verdict program, the socket, and the sockmap. The goal here is to understand the control flow and data flow involved when this socket is used as part of a sockmap.

{
  "Expression": "sk_psock_start_verdict"
}

{
  "Output": "include/linux/skmsg.h=453=static inline void sk_psock_stop_strp(struct sock *sk, struct sk_psock *psock)\n--\ninclude/linux/skmsg.h-457-\ninclude/linux/skmsg.h:458:void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock);\ninclude/linux/skmsg.h-459-void sk_psock_stop_verdict(struct sock *sk, struct sk_psock *psock);\n--\nnet/core/skmsg.c=1234=static void sk_psock_verdict_data_ready(struct sock *sk)\n--\nnet/core/skmsg.c-1260-\nnet/core/skmsg.c:1261:void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock)\nnet/core/skmsg.c-1262-{\n--\nnet/core/sock_map.c=218=static int sock_map_link(struct bpf_map *map, struct sock *sk)\n--\nnet/core/sock_map.c-317-\t} else if (!stream_parser \u0026\u0026 stream_verdict \u0026\u0026 !psock-\u003esaved_data_ready) {\nnet/core/sock_map.c:318:\t\tsk_psock_start_verdict(sk,psock);\nnet/core/sock_map.c-319-\t} else if (!stream_verdict \u0026\u0026 skb_verdict \u0026\u0026 !psock-\u003esaved_data_ready) {\nnet/core/sock_map.c:320:\t\tsk_psock_start_verdict(sk, psock);\nnet/core/sock_map.c-321-\t}\n"
}

gemini-3.8-flash

null

null

							input: 33704
							output: 18
							thoughts: 150
						

Okay, let's see. My mind is jumping around a bit as I trace this.

**Unix Stream Socket Data Flow with Sockmap and Verdicts**

Alright, so I'm observing the process when a socket is added to a sockmap and then has either a `stream_verdict` or `skb_verdict` attached, the function `sk_psock_start_verdict` is initiated. I'm noting that the data then comes in on the Unix stream socket. This triggers `sk->sk_data_ready`, which subsequently calls `sk_psock_verdict_data_ready`. Following the chain, this then hits `ops->read_skb(sk, sk_psock_verdict_recv)`, which I recognize as `unix_stream_read_skb`. So, that's the standard read operation.

But something else is nagging at me… What about `manage_oob`? Where does that fit into this picture? I need to understand its role. I need to know where it's called. Time for a quick grep.

{
  "Expression": "manage_oob"
}

{
  "Output": "net/unix/af_unix.c=2764=static int unix_stream_recv_urg(struct unix_stream_read_state *state)\n--\nnet/unix/af_unix.c-2814-\nnet/unix/af_unix.c:2815:static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\nnet/unix/af_unix.c-2816-\t\t\t\t  struct sock *sk, int flags, int copied)\n--\nnet/unix/af_unix.c=2935=static int unix_stream_read_generic(struct unix_stream_read_state *state,\n--\nnet/unix/af_unix.c-2994-\t\tif (skb) {\nnet/unix/af_unix.c:2995:\t\t\tskb = manage_oob(skb, \u0026last, sk, flags, copied);\nnet/unix/af_unix.c-2996-\t\t\tif (!skb \u0026\u0026 (copied || !state-\u003esize)) {\n"
}

gemini-3.8-flash

null

null

							input: 34375
							output: 21
							thoughts: 1813
						

**Analysis of AF_UNIX Stream Socket Changes**

Okay, so I've been looking at these changes in `net/unix/af_unix.c`, specifically concerning stream sockets and out-of-band (OOB) data handling. First, I see that `manage_oob` is getting called within `unix_stream_read_generic`, which itself is called from `unix_stream_recvmsg`. The change in `manage_oob` is pretty straightforward: it's correcting an issue where `u->inq_len` wasn't being decremented when an OOB `skb` was dequeued but *not* inlined. An OOB skb has length 1. This means the `SIOCINQ` / `FIONREAD` value was getting out of sync. This is fixed by adding `WRITE_ONCE(u->inq_len, u->inq_len - 1);`.

Next, I examined the modifications to `unix_stream_read_skb`. A notable change here is the handling of empty `skb`'s. Previously, if an empty `skb` was dequeued (e.g., SCM rights-only or empty packet), it went through some processing. Now, the code explicitly checks for empty skbs (`!unix_skb_len(skb)`) and *drops* them by calling `unix_orphan_scm` and then `consume_skb` with a `goto again`. This avoids potential misbehavior or a loop when passing the empty skb down the stack. Also, if there's consumed data, `pskb_pull` is called to ensure that the data is pulled. If `pskb_pull` fails, it frees the `skb` and returns `-ENOMEM`, which should prevent further processing with a potentially corrupted `skb`. Also, it clears `UNIXCB(skb).consumed = 0`.

Now, is this worthy of fuzzing? Based on my understanding, AF_UNIX sockets are perfect candidates. They're fully virtualized, standard networking components running in a standard Linux kernel environment, and these changes touch core networking logic, specifically related to memory management, flow control, and syscall handling in `net/unix/af_unix.c`. There are no negative criteria that apply to these modifications. They are not non-kernel, structurally unreachable, or unreachable execution paths. Therefore, I believe this is definitely fuzzable.

Regarding FocusSymbols, `manage_oob` is a static function and is called in `unix_stream_read_generic`, which is also static. `unix_stream_read_skb` is another static function that was modified in the same change, and it is part of the socket operations (`unix_stream_ops.read_skb`). These are both viable FocusSymbols. `unix_stream_recvmsg` could also be considered since it's ultimately involved.

{
  "Expression": "unix_stream_read_generic"
}

{
  "Output": "net/unix/af_unix.c=2873=static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n--\nnet/unix/af_unix.c-2934-\nnet/unix/af_unix.c:2935:static int unix_stream_read_generic(struct unix_stream_read_state *state,\nnet/unix/af_unix.c-2936-\t\t\t\t    bool freezable)\n--\nnet/unix/af_unix.c=3155=int __unix_stream_recvmsg(struct sock *sk, struct msghdr *msg,\n--\nnet/unix/af_unix.c-3165-\nnet/unix/af_unix.c:3166:\treturn unix_stream_read_generic(\u0026state, true);\nnet/unix/af_unix.c-3167-}\n--\nnet/unix/af_unix.c=3169=static int unix_stream_recvmsg(struct socket *sock, struct msghdr *msg,\n--\nnet/unix/af_unix.c-3186-#endif\nnet/unix/af_unix.c:3187:\treturn unix_stream_read_generic(\u0026state, true);\nnet/unix/af_unix.c-3188-}\n--\nnet/unix/af_unix.c=3199=static ssize_t unix_stream_splice_read(struct socket *sock,  loff_t *ppos,\n--\nnet/unix/af_unix.c-3217-\nnet/unix/af_unix.c:3218:\treturn unix_stream_read_generic(\u0026state, false);\nnet/unix/af_unix.c-3219-}\n--\ntools/testing/selftests/net/af_unix/so_peek_off.c=130=TEST_F(so_peek_off, two_chunks_blocking)\n--\ntools/testing/selftests/net/af_unix/so_peek_off.c-144-\ntools/testing/selftests/net/af_unix/so_peek_off.c:145:\t/* goto again; -\u003e goto redo; in unix_stream_read_generic(). */\ntools/testing/selftests/net/af_unix/so_peek_off.c-146-\trecveq(self-\u003efd[1], \"bbbb\", 100, MSG_PEEK);\n"
}

gemini-3.8-flash

null

null

							input: 37456
							output: 38
							thoughts: 1125
						

**Focus Symbol Refinement for AF_UNIX Socket Fuzzing**

Okay, let's nail down these FocusSymbols for fuzzing.  I need to be precise, avoiding those ubiquitous functions that'll just dilute the effort.  The key is to target the *specific* changes.

First, I need to list the modified functions, which are `manage_oob` and `unix_stream_read_skb`. Let's check if they have symbols in vmlinux, since syzkaller uses CONFIG_KALLSYMS_ALL. Since it's safer to avoid inlining issues, let's include modified functions *and* their callers.  So, I should include `manage_oob`, `unix_stream_read_skb`, `unix_stream_read_generic` (caller of `manage_oob`), and `unix_stream_recvmsg` (the entrypoint).

But, wait a minute, `unix_stream_recvmsg` is *the* entrypoint for Unix stream socket receives.  That's a lot of programs, and might be too generic.  Okay, let's think about `manage_oob` and `unix_stream_read_skb`.  `manage_oob` specifically deals with OOB data for Unix sockets. `unix_stream_read_skb` is the `read_skb` callback for these sockets, especially those used with sockmap. So, those are specific.

Okay, is `unix_stream_read_generic` specific enough? It's the core receive loop for AF_UNIX stream sockets.  I should check if there are other OOB functions, like `unix_stream_recv_urg`.

Also, what actually *calls* `manage_oob`? It looks like it's only called in `unix_stream_read_generic`. And what does `manage_oob` *do*? Reading line 2815, it's managing out-of-band data.

Now, a crucial point: Is `manage_oob` inlined into `unix_stream_read_generic`? Since it is only called in `af_unix.c` on line 2995, GCC *could* inline it. Because it's a static function with a single callsite, it very likely could be inlined.  If it is inlined, `unix_stream_read_generic` becomes its effective caller.

How about `unix_stream_read_skb`?  Its address is stored in `unix_stream_ops.read_skb`. Since its address is taken, the compiler can't completely optimize it away.  So, `unix_stream_read_skb` *will* be a symbol. `unix_stream_read_skb` is called by `sk_psock_verdict_data_ready`.  So it is a distinct symbol.

So, I should include `manage_oob`, `unix_stream_read_skb`, and `unix_stream_read_generic` to be safe.  No need for `unix_orphan_scm`, that's just an internal helper.

Let's quickly check the required configs.  AF_UNIX sockets require `CONFIG_UNIX`.  Now, around `manage_oob`: `#if IS_ENABLED(CONFIG_AF_UNIX_OOB)` is around `manage_oob`. This starts before manage_oob.

{
  "File": "net/unix/af_unix.c",
  "FirstLine": 2760,
  "LineCount": 25
}

{
  "Contents": "2760:\t\tunsigned int splice_flags;\n2761:\t};\n2762:\t\n2763:\t#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\n2764:\tstatic int unix_stream_recv_urg(struct unix_stream_read_state *state)\n2765:\t{\n2766:\t\tstruct sk_buff *oob_skb, *read_skb = NULL;\n2767:\t\tstruct socket *sock = state-\u003esocket;\n2768:\t\tstruct sock *sk = sock-\u003esk;\n2769:\t\tstruct unix_sock *u = unix_sk(sk);\n2770:\t\tint chunk = 1;\n2771:\t\n2772:\t\tmutex_lock(\u0026u-\u003eiolock);\n2773:\t\tunix_state_lock(sk);\n2774:\t\tspin_lock(\u0026sk-\u003esk_receive_queue.lock);\n2775:\t\n2776:\t\tif (sock_flag(sk, SOCK_URGINLINE) || !u-\u003eoob_skb) {\n2777:\t\t\tspin_unlock(\u0026sk-\u003esk_receive_queue.lock);\n2778:\t\t\tunix_state_unlock(sk);\n2779:\t\t\tmutex_unlock(\u0026u-\u003eiolock);\n2780:\t\t\treturn -EINVAL;\n2781:\t\t}\n2782:\t\n2783:\t\toob_skb = u-\u003eoob_skb;\n2784:\t\n"
}

gemini-3.8-flash

null

null

							input: 39768
							output: 30
							thoughts: 368
						

**Analyzing the Configuration Dependencies for AF_UNIX_OOB and BPF Sockmap**

Okay, so here's what I'm thinking. The `#if IS_ENABLED(CONFIG_AF_UNIX_OOB)` guard around `unix_stream_recv_urg` and `manage_oob` is pretty straightforward – `manage_oob` is only included if `CONFIG_AF_UNIX_OOB` is enabled. No surprises there. But now I'm thinking about how `unix_stream_read_skb` fits into this picture. I know that if `CONFIG_AF_UNIX_OOB` is set, lines 2907-2916 use the code that uses the `oob_skb`.

Now, to get to `unix_stream_read_skb`, we need BPF sockmap, which means `CONFIG_BPF_SYSCALL` *should* be required, right? Let me verify that. I'm going to double-check that `CONFIG_BPF_SYSCALL` is indeed needed for `unix_stream_bpf_update_proto` and `sock_map`. I need to be sure. I'll go back to `net/unix/unix_bpf.c` because `unix_stream_bpf_update_proto` is in there and that source file gets compiled when `CONFIG_BPF_SYSCALL=y`. And from `net/core/Makefile` I can see that `sock_map.o` is only included when `CONFIG_BPF_SYSCALL` is set.

But wait, I need to make sure that `CONFIG_BPF_SYSCALL` doesn't implicitly select something like `NET_SOCK_MSG`. I'll have to check the `init/Kconfig` or `kernel/bpf/Kconfig` files. That's the next step to confirm this fully.

{
  "Expression": "NET_SOCK_MSG",
  "PathPrefix": "kernel/bpf/"
}

{
  "Output": "kernel/bpf/Kconfig=27=config BPF_SYSCALL\n--\nkernel/bpf/Kconfig-33-\tselect BINARY_PRINTF\nkernel/bpf/Kconfig:34:\tselect NET_SOCK_MSG if NET\nkernel/bpf/Kconfig-35-\tselect NET_XGRESS if NET\n"
}

gemini-3.8-flash

null

null

							input: 40679
							output: 181
							thoughts: 461
						

**Configuration and Symbol Verification for Fuzzing**

Okay, so the automatic dependency of `NET_SOCK_MSG` on `CONFIG_BPF_SYSCALL` is important, which I already knew. And of course, `CONFIG_UNIX` is the unix sockets config. From that, and the dependency of `CONFIG_AF_UNIX_OOB` on `CONFIG_UNIX`, it's clear the base configs required are `UNIX`, `AF_UNIX_OOB`, and `BPF_SYSCALL`. I should check that `net/unix/Kconfig` to be sure I'm not missing anything. Ah yes, `UNIX_DIAG` is in there too, but that's not relevant here. So, `UNIX`, `AF_UNIX_OOB`, and `BPF_SYSCALL`, that makes sense. `BPF_SYSCALL` is there so `unix_stream_read_skb` can be used by the sockmap verdict program.

Now, the important part. Let's make sure my `FocusSymbols` are solid. Let's review them again: `manage_oob`, `unix_stream_read_skb`, and `unix_stream_read_generic`. I should check if `sk_psock_verdict_data_ready` is also needed here? No, no, `unix_stream_read_skb` and `manage_oob` are the main functions modified in the code, and `unix_stream_read_generic` is the caller of `manage_oob` in `net/unix/af_unix.c`. These three are precise and directly target the changes, and avoid bringing in unnecessary symbols.

Okay, everything looks good. Let's review the required fields for the `set-results` invocation:
*   `EnableConfigs`: `["UNIX", "AF_UNIX_OOB", "BPF_SYSCALL"]` - Yep, that's right.
*   `FocusSymbols`: `["manage_oob", "unix_stream_read_skb", "unix_stream_read_generic"]` - Yep, that's what I came up with!
*   `Reasoning`: Will write a concise explanation.
*   `WorthFuzzing`: Definitely, it's worth it.

Everything is verified and ready. I'll invoke `set-results` now.

{
  "EnableConfigs": [
    "UNIX",
    "AF_UNIX_OOB",
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "manage_oob",
    "unix_stream_read_skb",
    "unix_stream_read_generic"
  ],
  "Reasoning": "The patch modifies core networking code in net/unix/af_unix.c. Specifically, it corrects queue accounting (u-\u003einq_len) when dropping out-of-band skbs in manage_oob(), and alters skb handling in unix_stream_read_skb() by discarding empty skbs, orphaning SCMs, and pulling consumed bytes with pskb_pull(). These paths are reachable via standard UNIX domain sockets and BPF sockmap.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "UNIX",
    "AF_UNIX_OOB",
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "manage_oob",
    "unix_stream_read_skb",
    "unix_stream_read_generic"
  ],
  "Reasoning": "The patch modifies core networking code in net/unix/af_unix.c. Specifically, it corrects queue accounting (u-\u003einq_len) when dropping out-of-band skbs in manage_oob(), and alters skb handling in unix_stream_read_skb() by discarding empty skbs, orphaning SCMs, and pulling consumed bytes with pskb_pull(). These paths are reachable via standard UNIX domain sockets and BPF sockmap.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

core

null

{
  "KMSANReasoning": "The patch addresses socket queue length accounting and skb consumption handling in AF_UNIX stream sockets. Specifically:\n1. In `manage_oob()`, it corrects `u-\u003einq_len` accounting by decrementing it by 1 when unlinking an unread OOB skb.\n2. In `unix_stream_read_skb()`, it drops empty skbs (`!unix_skb_len(skb)`) and pulls already-consumed bytes via `pskb_pull()` before handing the skb to `recv_actor()`.\n\nNone of these changes allocate or read uninitialized memory, nor do they expose uninitialized kernel fields/padding to user space or conditional branching. All fields touched (`u-\u003einq_len`, `UNIXCB(skb).consumed`, skb pointers) are fully initialized socket and skb metadata. Any memory errors relating to skb lifecycle or bounds would be detected by KASAN or standard debuggers, not KMSAN. Therefore, a dedicated KMSAN fuzzing session is not warranted.",
  "NeedsKMSAN": false
}

You are an expert Linux kernel security engineer specializing in kernel memory
error detectors (KASAN and KMSAN). Your job is to review the provided patch series and
determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer)
fuzzing session in addition to standard KASAN fuzzing.

CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN:
- Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable
  a comprehensive suite of debugging tools and sanitizers, including KASAN
  (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP
  (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks.
- KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap,
  or page allocations) and kernel-to-user memory info-leaks.

Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN,
LOCKDEP, OR OTHER STANDARD BUG DETECTORS.
A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY
set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks
that are detected ONLY by KMSAN.

Look holistically at the patch series and surrounding code. Even if no direct
uninitialized field accesses or new buffer allocations are added in the diff itself,
a patch may alter control flow, bounds checking, or data length calculations in ways
that change how the rest of the code operates on existing buffers (e.g. allowing
uninitialized stack/heap memory to be read, copied to user space, or used in control
flow). Do not hesitate to use your code access tools to inspect the surrounding code,
called functions, and callers.

Set NeedsKMSAN=true ONLY IF the patch introduces or modifies:
1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb
   attributes, ioctl output arguments, socket options, or BPF buffers) where fields
   or structure padding might not be fully initialized/zeroed.
2. Conditional logic or branching that depends on potentially uninitialized variables
   or struct fields.
3. Allocation or initialization of complex data structures where uninitialized fields
   could be read later in reachable code paths.
4. Bounds checks, lengths, or logic in a way that allows surrounding code to access
   uninitialized bytes of existing buffers.

Set NeedsKMSAN=false IF:
- The code changes primarily risk out-of-bounds access, array overflows, NULL pointer
  dereferences, locking deadlocks, or use-after-free bugs (these are already caught
  by KASAN, LOCKDEP, or standard bug detectors).
- All stack/heap structures touched or introduced by the patch are fully zeroed
  or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied.
- The patch does not introduce any risk of uninitialized memory usage or info-leaks.

Use your code access tools to inspect the surrounding code if necessary, then provide
detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch.
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.

Target architecture: amd64

For your convenience, here is the diff of the changes:
commit 81002efe86c7a9b86819e5f77caa0b15406c39b0
Author: syz-cluster <triage@syzkaller.com>
Date:   Sat Sep 26 10:58:32 2026 +0000

    syz-cluster: applied patch under review

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 42cffeafc8c14..a1c06b9995c7c 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2849,6 +2849,7 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,
 		WRITE_ONCE(u->oob_skb, NULL);
 
 		if (!sock_flag(sk, SOCK_URGINLINE)) {
+			WRITE_ONCE(u->inq_len, u->inq_len - 1);
 			__skb_unlink(skb, &sk->sk_receive_queue);
 			unread_skb = skb;
 			skb = skb_peek(&sk->sk_receive_queue);
@@ -2884,6 +2885,7 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 		return err;
 
 	mutex_lock(&u->iolock);
+again:
 	spin_lock(&queue->lock);
 
 	skb = __skb_dequeue(queue);
@@ -2893,6 +2895,13 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 		return -EAGAIN;
 	}
 
+	if (!unix_skb_len(skb)) {
+		spin_unlock(&queue->lock);
+		unix_orphan_scm(sk, skb);
+		consume_skb(skb);
+		goto again;
+	}
+
 	WRITE_ONCE(u->inq_len, u->inq_len - unix_skb_len(skb));
 
 #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
@@ -2912,6 +2921,14 @@ static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 
 	mutex_unlock(&u->iolock);
 
+	if (UNIXCB(skb).consumed) {
+		if (!pskb_pull(skb, UNIXCB(skb).consumed)) {
+			kfree_skb(skb);
+			return -ENOMEM;
+		}
+		UNIXCB(skb).consumed = 0;
+	}
+
 	return recv_actor(sk, skb);
 }
 

gemini-3.8-flash

null

null

							input: 2551
							output: 38
							thoughts: 71
						

Here's my analysis of the situation:

**Reviewing the `af_unix.c` Diff**

Alright, let's dive into this. My initial action is to dissect the diff in `net/unix/af_unix.c`. I need to understand the change that was made. Given the location, this is related to the Unix domain socket implementation within the kernel, and the line numbers given 2840-2930 suggest a reasonable sized chunk of code.

To get a quick grasp of the surrounding code and ensure I understand the context, I'll employ either `grepper` or `read-file` to zero in on lines 2840 through 2930 in `net/unix/af_unix.c`. This will give me the immediate neighborhood of the diff, and help me spot what functions are involved, and how the changes are interwoven with the existing code structure. Knowing the context will be crucial before I can form any real conclusions about the implications of the change. This is standard operating procedure - always understanding the surrounding code to determine intent and effect.

{
  "File": "net/unix/af_unix.c",
  "FirstLine": 2840,
  "LineCount": 95
}

{
  "Contents": "2840:\t\t\t\tgoto unlock;\n2841:\t\t}\n2842:\t\n2843:\t\tif (skb != u-\u003eoob_skb)\n2844:\t\t\tgoto unlock;\n2845:\t\n2846:\t\tif (copied) {\n2847:\t\t\tskb = NULL;\n2848:\t\t} else if (!(flags \u0026 MSG_PEEK)) {\n2849:\t\t\tWRITE_ONCE(u-\u003eoob_skb, NULL);\n2850:\t\n2851:\t\t\tif (!sock_flag(sk, SOCK_URGINLINE)) {\n2852:\t\t\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - 1);\n2853:\t\t\t\t__skb_unlink(skb, \u0026sk-\u003esk_receive_queue);\n2854:\t\t\t\tunread_skb = skb;\n2855:\t\t\t\tskb = skb_peek(\u0026sk-\u003esk_receive_queue);\n2856:\t\t\t\t*last = skb;\n2857:\t\t\t}\n2858:\t\t} else if (!sock_flag(sk, SOCK_URGINLINE)) {\n2859:\t\t\t*last = skb;\n2860:\t\t\tskb = skb_peek_next(skb, \u0026sk-\u003esk_receive_queue);\n2861:\t\t}\n2862:\t\n2863:\tunlock:\n2864:\t\tspin_unlock(\u0026sk-\u003esk_receive_queue.lock);\n2865:\t\n2866:\t\tconsume_skb(read_skb);\n2867:\t\tkfree_skb_reason(unread_skb, SKB_DROP_REASON_UNIX_SKIP_OOB);\n2868:\t\n2869:\t\treturn skb;\n2870:\t}\n2871:\t#endif\n2872:\t\n2873:\tstatic int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n2874:\t{\n2875:\t\tstruct sk_buff_head *queue = \u0026sk-\u003esk_receive_queue;\n2876:\t\tstruct unix_sock *u = unix_sk(sk);\n2877:\t\tstruct sk_buff *skb;\n2878:\t\tint err;\n2879:\t\n2880:\t\tif (unlikely(READ_ONCE(sk-\u003esk_state) != TCP_ESTABLISHED))\n2881:\t\t\treturn -ENOTCONN;\n2882:\t\n2883:\t\terr = sock_error(sk);\n2884:\t\tif (err)\n2885:\t\t\treturn err;\n2886:\t\n2887:\t\tmutex_lock(\u0026u-\u003eiolock);\n2888:\tagain:\n2889:\t\tspin_lock(\u0026queue-\u003elock);\n2890:\t\n2891:\t\tskb = __skb_dequeue(queue);\n2892:\t\tif (!skb) {\n2893:\t\t\tspin_unlock(\u0026queue-\u003elock);\n2894:\t\t\tmutex_unlock(\u0026u-\u003eiolock);\n2895:\t\t\treturn -EAGAIN;\n2896:\t\t}\n2897:\t\n2898:\t\tif (!unix_skb_len(skb)) {\n2899:\t\t\tspin_unlock(\u0026queue-\u003elock);\n2900:\t\t\tunix_orphan_scm(sk, skb);\n2901:\t\t\tconsume_skb(skb);\n2902:\t\t\tgoto again;\n2903:\t\t}\n2904:\t\n2905:\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - unix_skb_len(skb));\n2906:\t\n2907:\t#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\n2908:\t\tif (skb == u-\u003eoob_skb) {\n2909:\t\t\tWRITE_ONCE(u-\u003eoob_skb, NULL);\n2910:\t\t\tspin_unlock(\u0026queue-\u003elock);\n2911:\t\t\tmutex_unlock(\u0026u-\u003eiolock);\n2912:\t\n2913:\t\t\tkfree_skb_reason(skb, SKB_DROP_REASON_UNIX_SKIP_OOB);\n2914:\t\t\treturn -EAGAIN;\n2915:\t\t}\n2916:\t#endif\n2917:\t\n2918:\t\tspin_unlock(\u0026queue-\u003elock);\n2919:\t\n2920:\t\tunix_orphan_scm(sk, skb);\n2921:\t\n2922:\t\tmutex_unlock(\u0026u-\u003eiolock);\n2923:\t\n2924:\t\tif (UNIXCB(skb).consumed) {\n2925:\t\t\tif (!pskb_pull(skb, UNIXCB(skb).consumed)) {\n2926:\t\t\t\tkfree_skb(skb);\n2927:\t\t\t\treturn -ENOMEM;\n2928:\t\t\t}\n2929:\t\t\tUNIXCB(skb).consumed = 0;\n2930:\t\t}\n2931:\t\n2932:\t\treturn recv_actor(sk, skb);\n2933:\t}\n2934:\t\n"
}

gemini-3.8-flash

null

null

							input: 4266
							output: 32
							thoughts: 708
						

**Analyzing a UNIX Domain Socket Patch**

Okay, let's dive into this patch. First, I'm going to quickly parse the code changes. It looks like we're dealing with UNIX domain sockets, specifically focusing on the handling of out-of-band (OOB) data and read operations within the stream socket. I see `manage_oob` and `unix_stream_read_skb` being modified.

The first change seems to address something around `SOCK_URGINLINE`. We're decrementing `u->inq_len` if the socket isn't using urgent data inline. This likely has to do with correctly tracking the amount of data in the receive queue. I'll need to figure out what `u->inq_len` represents to fully understand that part. Is it the total number of bytes, or some other metric?

The more interesting part is in `unix_stream_read_skb`. A loop with a `goto` label `again` is introduced, and we have a condition checking `!unix_skb_len(skb)`. If the SKB is empty, it's orphaned, consumed, and the process goes back to the beginning of the `unix_stream_read_skb` function by the `goto again`. That indicates that the bug is likely related to handling zero-length SKBs. They were getting processed incorrectly. The logic might not have accounted for empty SKBs, potentially leading to inconsistencies in data tracking or unexpected behavior during reads. This change corrects the issue.

Also, after the read, there's a check for `UNIXCB(skb).consumed`, which is related to something being pulled from the `skb`. The `pskb_pull` is called. This part seems to be handling the consumption of data from the SKB. This is also likely related to handling OOB data.

To get the full picture, I'd need to understand the context of this patch. I'd definitely be checking the commit message and any associated bug reports or mailing list discussions. Understanding the specific scenario that triggered this patch would be invaluable. And, of course, I'd trace the execution flow with different data types to verify the fix.

{
  "Expression": "unix_stream_read_skb",
  "PathPrefix": "net/unix/"
}

{
  "Output": "net/unix/af_unix.c=867=static int unix_read_skb(struct sock *sk, skb_read_actor_t recv_actor);\nnet/unix/af_unix.c:868:static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor);\nnet/unix/af_unix.c-869-static int unix_dgram_connect(struct socket *, struct sockaddr_unsized *,\n--\nnet/unix/af_unix.c=976=static const struct proto_ops unix_stream_ops = {\n--\nnet/unix/af_unix.c-994-\t.recvmsg =\tunix_stream_recvmsg,\nnet/unix/af_unix.c:995:\t.read_skb =\tunix_stream_read_skb,\nnet/unix/af_unix.c-996-\t.mmap =\t\tsock_no_mmap,\n--\nnet/unix/af_unix.c=2815=static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\n--\nnet/unix/af_unix.c-2872-\nnet/unix/af_unix.c:2873:static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/unix/af_unix.c-2874-{\n"
}

gemini-3.8-flash

null

null

							input: 5847
							output: 30
							thoughts: 136
						

Okay, let's break this down.

**Understanding This Commit's Impact**

Right, so I need to piece together the implications of this commit. First, I'm zeroing in on this line: `WRITE_ONCE(u->inq_len, u->inq_len - 1);` within `manage_oob`. Okay, that's decreasing the `inq_len` for a UNIX socket. But why? The clue likely lies in how this interacts with the read path, specifically `unix_stream_read_skb`.

Now, looking at `unix_stream_read_skb`, the interesting bit is the handling of the Socket Buffer (SKB): We have `!unix_skb_len(skb)`, meaning empty SKBs are discarded, and then we have the same update to `u->inq_len`. I'm starting to see a pattern. And then there's the nuance of partially consumed SKBs:  `UNIXCB(skb).consumed` bytes get pulled *before* the call to `recv_actor`. So, we decrement the `inq_len` regardless if we handle an empty skb, or a skb with data, before passing the data to the user.

Now, that brings me back to `unix_skb_len`. This function is critical for understanding what actually constitutes a "valid" SKB length in this context. I'll need to know what that function is doing. That's the key to understanding the full picture here. I can get a better grip on the implications of this change by tracing what happens based on the length of an incoming SKB.

{
  "Expression": "unix_skb_len",
  "PathPrefix": "net/unix/"
}

{
  "Output": "net/unix/af_unix.c=635=static void unix_sock_destructor(struct sock *sk)\n--\nnet/unix/af_unix.c-659-\nnet/unix/af_unix.c:660:static unsigned int unix_skb_len(const struct sk_buff *skb)\nnet/unix/af_unix.c-661-{\n--\nnet/unix/af_unix.c=665=static void unix_release_sock(struct sock *sk, int embrion)\n--\nnet/unix/af_unix.c-701-#if IS_ENABLED(CONFIG_AF_UNIX_OOB)\nnet/unix/af_unix.c:702:\t\t\tif (skb \u0026\u0026 !unix_skb_len(skb))\nnet/unix/af_unix.c-703-\t\t\t\tskb = skb_peek_next(skb, \u0026sk-\u003esk_receive_queue);\n--\nnet/unix/af_unix.c=2764=static int unix_stream_recv_urg(struct unix_stream_read_state *state)\n--\nnet/unix/af_unix.c-2789-\t\tif (oob_skb-\u003eprev != (struct sk_buff *)\u0026sk-\u003esk_receive_queue \u0026\u0026\nnet/unix/af_unix.c:2790:\t\t    !unix_skb_len(oob_skb-\u003eprev)) {\nnet/unix/af_unix.c-2791-\t\t\tread_skb = oob_skb-\u003eprev;\n--\nnet/unix/af_unix.c=2815=static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\n--\nnet/unix/af_unix.c-2820-\nnet/unix/af_unix.c:2821:\tif (likely(unix_skb_len(skb) \u0026\u0026 skb != READ_ONCE(u-\u003eoob_skb)))\nnet/unix/af_unix.c-2822-\t\treturn skb;\n--\nnet/unix/af_unix.c-2825-\nnet/unix/af_unix.c:2826:\tif (!unix_skb_len(skb)) {\nnet/unix/af_unix.c-2827-\t\tif (copied \u0026\u0026 (!u-\u003eoob_skb || skb == u-\u003eoob_skb)) {\n--\nnet/unix/af_unix.c=2873=static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n--\nnet/unix/af_unix.c-2897-\nnet/unix/af_unix.c:2898:\tif (!unix_skb_len(skb)) {\nnet/unix/af_unix.c-2899-\t\tspin_unlock(\u0026queue-\u003elock);\n--\nnet/unix/af_unix.c-2904-\nnet/unix/af_unix.c:2905:\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - unix_skb_len(skb));\nnet/unix/af_unix.c-2906-\n--\nnet/unix/af_unix.c=2935=static int unix_stream_read_generic(struct unix_stream_read_state *state,\n--\nnet/unix/af_unix.c-3037-\nnet/unix/af_unix.c:3038:\t\twhile (skip \u003e= unix_skb_len(skb)) {\nnet/unix/af_unix.c:3039:\t\t\tskip -= unix_skb_len(skb);\nnet/unix/af_unix.c-3040-\t\t\tlast = skb;\n--\nnet/unix/af_unix.c-3068-\nnet/unix/af_unix.c:3069:\t\tchunk = min_t(unsigned int, unix_skb_len(skb) - skip, size);\nnet/unix/af_unix.c-3070-\t\tchunk = state-\u003erecv_actor(skb, skip, chunk, state);\n--\nnet/unix/af_unix.c-3091-\t\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - chunk);\nnet/unix/af_unix.c:3092:\t\t\tif (unix_skb_len(skb)) {\nnet/unix/af_unix.c-3093-\t\t\t\tspin_unlock(\u0026sk-\u003esk_receive_queue.lock);\n--\nnet/unix/af_unix.c=3270=long unix_inq_len(struct sock *sk)\n--\nnet/unix/af_unix.c-3283-\t\tskb_queue_walk(\u0026sk-\u003esk_receive_queue, skb)\nnet/unix/af_unix.c:3284:\t\t\tamount += unix_skb_len(skb);\nnet/unix/af_unix.c-3285-\t} else {\n--\nnet/unix/af_unix.c=3316=static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)\n--\nnet/unix/af_unix.c-3356-\t\t\t\tif (skb == oob_skb ||\nnet/unix/af_unix.c:3357:\t\t\t\t    (!unix_skb_len(skb) \u0026\u0026\nnet/unix/af_unix.c-3358-\t\t\t\t     (!oob_skb || next_skb == oob_skb)))\n"
}

gemini-3.8-flash

null

null

							input: 7763
							output: 37
							thoughts: 37
						

Here's my analysis of the provided snippet, framed as my own thought process:

**Diving into af_unix.c: Skb Length Calculation**

Alright, let's zoom in on `net/unix/af_unix.c`. Specifically, I want to take a close look at how the socket buffer length is calculated for Unix domain sockets. The function `unix_skb_len(skb)` is what I'm interested in, and the code I need to scrutinize is located between lines 660 and 664. I'll need to see how the kernel determines the size of the data in the socket buffer. Given my experience, I'm expecting this to be fairly straightforward - it likely involves checking the packet's metadata and probably the data size itself. The implementation should be crucial in preventing memory overruns and managing network traffic in general. I’m thinking the key will be understanding if this calculation accounts for control data, ancillary data, or just the pure payload. I’ll need to make sure to account for those possibilities as I review the code.

{
  "File": "net/unix/af_unix.c",
  "FirstLine": 658,
  "LineCount": 10
}

{
  "Contents": " 658:\t}\n 659:\t\n 660:\tstatic unsigned int unix_skb_len(const struct sk_buff *skb)\n 661:\t{\n 662:\t\treturn skb-\u003elen - UNIXCB(skb).consumed;\n 663:\t}\n 664:\t\n 665:\tstatic void unix_release_sock(struct sock *sk, int embrion)\n 666:\t{\n 667:\t\tstruct unix_sock *u = unix_sk(sk);\n"
}

gemini-3.8-flash

null

null

							input: 8217
							output: 26
							thoughts: 77
						

Here's my summary, as I see it:

**Digging into the Linux Unix Domain Socket Receive Path**

Alright, let's break this down. First, I see `unix_skb_len(skb)` is defined as `skb->len - UNIXCB(skb).consumed`. Okay, that's the *actual* data length within the socket buffer, taking into account any consumed bytes. Good to remember. Now, I need to understand how this is used within the receive path. I'm going to focus on `recv_actor` and start by looking for `unix_stream_read_skb` within that function or anywhere it's called. This is likely where the actual data consumption happens. But that's not all. I also want to find where `proto_ops.read_skb` is being used. This should expose the core of the read operation within the protocol operations structure, which is critical to how the sockets actually interact with the kernel. I need to understand this to have a good handle on data handling.

{
  "Expression": "read_skb",
  "PathPrefix": "net/"
}

{
  "Output": "net/core/skmsg.c=1234=static void sk_psock_verdict_data_ready(struct sock *sk)\n--\nnet/core/skmsg.c-1247-\trcu_read_unlock();\nnet/core/skmsg.c:1248:\tif (!ops || !ops-\u003eread_skb)\nnet/core/skmsg.c-1249-\t\treturn;\nnet/core/skmsg.c-1250-\nnet/core/skmsg.c:1251:\tcopied = ops-\u003eread_skb(sk, sk_psock_verdict_recv);\nnet/core/skmsg.c-1252-\tif (copied \u003e= 0) {\n--\nnet/ipv4/af_inet.c=1060=const struct proto_ops inet_stream_ops = {\n--\nnet/ipv4/af_inet.c-1084-\t.read_sock\t   = tcp_read_sock,\nnet/ipv4/af_inet.c:1085:\t.read_skb\t   = tcp_read_skb,\nnet/ipv4/af_inet.c-1086-\t.sendmsg_locked    = tcp_sendmsg_locked,\n--\nnet/ipv4/af_inet.c=1096=const struct proto_ops inet_dgram_ops = {\n--\nnet/ipv4/af_inet.c-1112-\t.sendmsg\t   = inet_sendmsg,\nnet/ipv4/af_inet.c:1113:\t.read_skb\t   = udp_read_skb,\nnet/ipv4/af_inet.c-1114-\t.recvmsg\t   = inet_recvmsg,\n--\nnet/ipv4/tcp.c=1748=int tcp_read_sock_noack(struct sock *sk, read_descriptor_t *desc,\n--\nnet/ipv4/tcp.c-1754-\nnet/ipv4/tcp.c:1755:int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/ipv4/tcp.c-1756-{\n--\nnet/ipv4/tcp_bpf.c=221=static int tcp_bpf_recvmsg_parser(struct sock *sk,\n--\nnet/ipv4/tcp_bpf.c-246-\t/* We may have received data on the sk_receive_queue pre-accept and\nnet/ipv4/tcp_bpf.c:247:\t * then we can not use read_skb in this context because we haven't\nnet/ipv4/tcp_bpf.c-248-\t * assigned a sk_socket yet so have no link to the ops. The work-around\nnet/ipv4/tcp_bpf.c-249-\t * is to check the sk_receive_queue and in these cases read skbs off\nnet/ipv4/tcp_bpf.c:250:\t * queue again. The read_skb hook is not running at this point because\nnet/ipv4/tcp_bpf.c:251:\t * of lock_sock so we avoid having multiple runners in read_skb.\nnet/ipv4/tcp_bpf.c-252-\t */\n--\nnet/ipv4/udp.c=2013=EXPORT_SYMBOL(__skb_recv_udp);\nnet/ipv4/udp.c-2014-\nnet/ipv4/udp.c:2015:int udp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/ipv4/udp.c-2016-{\n--\nnet/ipv6/af_inet6.c=660=const struct proto_ops inet6_stream_ops = {\n--\nnet/ipv6/af_inet6.c-685-\t.read_sock\t   = tcp_read_sock,\nnet/ipv6/af_inet6.c:686:\t.read_skb\t   = tcp_read_skb,\nnet/ipv6/af_inet6.c-687-\t.peek_len\t   = tcp_peek_len,\n--\nnet/ipv6/af_inet6.c=696=const struct proto_ops inet6_dgram_ops = {\n--\nnet/ipv6/af_inet6.c-713-\t.recvmsg\t   = inet6_recvmsg,\t\t/* retpoline's sake */\nnet/ipv6/af_inet6.c:714:\t.read_skb\t   = udp_read_skb,\nnet/ipv6/af_inet6.c-715-\t.mmap\t\t   = sock_no_mmap,\n--\nnet/sunrpc/xprtsock.c=1358=static void xs_destroy(struct rpc_xprt *xprt)\n--\nnet/sunrpc/xprtsock.c-1372-/**\nnet/sunrpc/xprtsock.c:1373: * xs_udp_data_read_skb - receive callback for UDP sockets\nnet/sunrpc/xprtsock.c-1374- * @xprt: transport\n--\nnet/sunrpc/xprtsock.c-1378- */\nnet/sunrpc/xprtsock.c:1379:static void xs_udp_data_read_skb(struct rpc_xprt *xprt,\nnet/sunrpc/xprtsock.c-1380-\t\tstruct sock *sk,\n--\nnet/sunrpc/xprtsock.c=1433=static void xs_udp_data_receive(struct sock_xprt *transport)\n--\nnet/sunrpc/xprtsock.c-1446-\t\t\tbreak;\nnet/sunrpc/xprtsock.c:1447:\t\txs_udp_data_read_skb(\u0026transport-\u003exprt, sk, skb);\nnet/sunrpc/xprtsock.c-1448-\t\tconsume_skb(skb);\n--\nnet/unix/af_unix.c=866=static int unix_dgram_recvmsg(struct socket *, struct msghdr *, size_t, int);\nnet/unix/af_unix.c:867:static int unix_read_skb(struct sock *sk, skb_read_actor_t recv_actor);\nnet/unix/af_unix.c:868:static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor);\nnet/unix/af_unix.c-869-static int unix_dgram_connect(struct socket *, struct sockaddr_unsized *,\n--\nnet/unix/af_unix.c=976=static const struct proto_ops unix_stream_ops = {\n--\nnet/unix/af_unix.c-994-\t.recvmsg =\tunix_stream_recvmsg,\nnet/unix/af_unix.c:995:\t.read_skb =\tunix_stream_read_skb,\nnet/unix/af_unix.c-996-\t.mmap =\t\tsock_no_mmap,\n--\nnet/unix/af_unix.c=1002=static const struct proto_ops unix_dgram_ops = {\n--\nnet/unix/af_unix.c-1019-\t.sendmsg =\tunix_dgram_sendmsg,\nnet/unix/af_unix.c:1020:\t.read_skb =\tunix_read_skb,\nnet/unix/af_unix.c-1021-\t.recvmsg =\tunix_dgram_recvmsg,\n--\nnet/unix/af_unix.c=2678=static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,\n--\nnet/unix/af_unix.c-2691-\nnet/unix/af_unix.c:2692:static int unix_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/unix/af_unix.c-2693-{\n--\nnet/unix/af_unix.c=2764=static int unix_stream_recv_urg(struct unix_stream_read_state *state)\nnet/unix/af_unix.c-2765-{\nnet/unix/af_unix.c:2766:\tstruct sk_buff *oob_skb, *read_skb = NULL;\nnet/unix/af_unix.c-2767-\tstruct socket *sock = state-\u003esocket;\n--\nnet/unix/af_unix.c-2790-\t\t    !unix_skb_len(oob_skb-\u003eprev)) {\nnet/unix/af_unix.c:2791:\t\t\tread_skb = oob_skb-\u003eprev;\nnet/unix/af_unix.c:2792:\t\t\t__skb_unlink(read_skb, \u0026sk-\u003esk_receive_queue);\nnet/unix/af_unix.c-2793-\t\t}\n--\nnet/unix/af_unix.c-2805-\nnet/unix/af_unix.c:2806:\tconsume_skb(read_skb);\nnet/unix/af_unix.c-2807-\n--\nnet/unix/af_unix.c=2815=static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\n--\nnet/unix/af_unix.c-2817-{\nnet/unix/af_unix.c:2818:\tstruct sk_buff *read_skb = NULL, *unread_skb = NULL;\nnet/unix/af_unix.c-2819-\tstruct unix_sock *u = unix_sk(sk);\n--\nnet/unix/af_unix.c-2832-\t\t} else {\nnet/unix/af_unix.c:2833:\t\t\tread_skb = skb;\nnet/unix/af_unix.c-2834-\t\t\tskb = skb_peek_next(skb, \u0026sk-\u003esk_receive_queue);\nnet/unix/af_unix.c:2835:\t\t\t__skb_unlink(read_skb, \u0026sk-\u003esk_receive_queue);\nnet/unix/af_unix.c-2836-\t\t\t*last = skb;\n--\nnet/unix/af_unix.c-2853-\t\t\t__skb_unlink(skb, \u0026sk-\u003esk_receive_queue);\nnet/unix/af_unix.c:2854:\t\t\tunread_skb = skb;\nnet/unix/af_unix.c-2855-\t\t\tskb = skb_peek(\u0026sk-\u003esk_receive_queue);\n--\nnet/unix/af_unix.c-2865-\nnet/unix/af_unix.c:2866:\tconsume_skb(read_skb);\nnet/unix/af_unix.c:2867:\tkfree_skb_reason(unread_skb, SKB_DROP_REASON_UNIX_SKIP_OOB);\nnet/unix/af_unix.c-2868-\n--\nnet/unix/af_unix.c-2872-\nnet/unix/af_unix.c:2873:static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\nnet/unix/af_unix.c-2874-{\n--\nnet/vmw_vsock/af_vsock.c=1302=static __poll_t vsock_poll(struct file *file, struct socket *sock,\n--\nnet/vmw_vsock/af_vsock.c-1418-\nnet/vmw_vsock/af_vsock.c:1419:static int vsock_read_skb(struct sock *sk, skb_read_actor_t read_actor)\nnet/vmw_vsock/af_vsock.c-1420-{\n--\nnet/vmw_vsock/af_vsock.c-1425-\nnet/vmw_vsock/af_vsock.c:1426:\treturn vsk-\u003etransport-\u003eread_skb(vsk, read_actor);\nnet/vmw_vsock/af_vsock.c-1427-}\n--\nnet/vmw_vsock/af_vsock.c=1653=static const struct proto_ops vsock_dgram_ops = {\n--\nnet/vmw_vsock/af_vsock.c-1668-\t.mmap = sock_no_mmap,\nnet/vmw_vsock/af_vsock.c:1669:\t.read_skb = vsock_read_skb,\nnet/vmw_vsock/af_vsock.c-1670-};\n--\nnet/vmw_vsock/af_vsock.c=2654=static const struct proto_ops vsock_stream_ops = {\n--\nnet/vmw_vsock/af_vsock.c-2672-\t.set_rcvlowat = vsock_set_rcvlowat,\nnet/vmw_vsock/af_vsock.c:2673:\t.read_skb = vsock_read_skb,\nnet/vmw_vsock/af_vsock.c-2674-};\n--\nnet/vmw_vsock/af_vsock.c=2676=static const struct proto_ops vsock_seqpacket_ops = {\n--\nnet/vmw_vsock/af_vsock.c-2693-\t.mmap = sock_no_mmap,\nnet/vmw_vsock/af_vsock.c:2694:\t.read_skb = vsock_read_skb,\nnet/vmw_vsock/af_vsock.c-2695-};\n--\nnet/vmw_vsock/virtio_transport.c=557=static struct virtio_transport virtio_transport = {\n--\nnet/vmw_vsock/virtio_transport.c-605-\nnet/vmw_vsock/virtio_transport.c:606:\t\t.read_skb = virtio_transport_read_skb,\nnet/vmw_vsock/virtio_transport.c-607-\t},\n--\nnet/vmw_vsock/virtio_transport_common.c=1922=EXPORT_SYMBOL_GPL(virtio_transport_purge_skbs);\nnet/vmw_vsock/virtio_transport_common.c-1923-\nnet/vmw_vsock/virtio_transport_common.c:1924:int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_actor)\nnet/vmw_vsock/virtio_transport_common.c-1925-{\n--\nnet/vmw_vsock/virtio_transport_common.c-1955-}\nnet/vmw_vsock/virtio_transport_common.c:1956:EXPORT_SYMBOL_GPL(virtio_transport_read_skb);\nnet/vmw_vsock/virtio_transport_common.c-1957-\n--\nnet/vmw_vsock/vsock_bpf.c=150=int vsock_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)\n--\nnet/vmw_vsock/vsock_bpf.c-163-\nnet/vmw_vsock/vsock_bpf.c:164:\tif (!vsk-\u003etransport-\u003eread_skb)\nnet/vmw_vsock/vsock_bpf.c-165-\t\treturn -EOPNOTSUPP;\n--\nnet/vmw_vsock/vsock_loopback.c=63=static struct virtio_transport loopback_transport = {\n--\nnet/vmw_vsock/vsock_loopback.c-110-\nnet/vmw_vsock/vsock_loopback.c:111:\t\t.read_skb = virtio_transport_read_skb,\nnet/vmw_vsock/vsock_loopback.c-112-\t},\n"
}

gemini-3.8-flash

null

null

							input: 12675
							output: 28
							thoughts: 1192
						

**Analyzing the AF_UNIX Stream Read Path**

Okay, let's break this down. My initial thought process starts with the known connection between `read_skb` in Unix sockets and `sockmap`/`sk_psock` via `sk_psock_verdict_data_ready`. I need to figure out how data actually gets *read* from a Unix socket, and the path to do so. So, the key function to examine is `unix_stream_read_skb`, and how it interacts with the `recv_actor`.

Looking at the original code, I can see how it dequeues an `skb` from the receive queue. I'm focusing on the modifications, so I see it checks the socket state, handles errors, locks the necessary mutexes and spinlocks, dequeues an `skb`, and decrements `u->inq_len`. There's also some OOB handling. Now, that is the *original* flow. I need to understand what changed.

The first clue comes from `manage_oob`. Here, if the socket doesn't use urgent data in-line (the `SOCK_URGINLINE` flag), and the OOB message (I assume it's one byte given that it decrements by 1) is dequeued, `u->inq_len` is decremented. This is interesting: there's an `inq_len` counter that's getting adjusted when an OOB message, of exactly one byte, gets processed. If that's the only place, it implies there's a bookkeeping issue around OOB data or a subtle accounting error.

Now, let's go back and examine the changes in `unix_stream_read_skb`. Okay, I see a few key additions. First, there's a new check after dequeuing the `skb`: `if (!unix_skb_len(skb))`. If the length is zero, the `skb` is orphaned and consumed and the process repeats. This is interesting. Why is the code checking for zero-length skbs *after* the dequeue? Was this something that needed to be specifically accounted for?

Next, if the `skb` is *not* zero-length, the code *still* decrements `u->inq_len` by the skb length. Then, after calling `recv_actor`, there's another check for `UNIXCB(skb).consumed`. If this flag is set, the code attempts to pull the specified number of bytes from the `skb` using `pskb_pull`. So the original assumption of subtracting only when an OOB is encountered doesn't hold. This also makes me question the usage of `consume_skb` here - what happens in the case of a zero length `skb`?

So, there has to be a reason why these checks and modifications were introduced. I need to investigate the git log for recent changes around `af_unix.c` to understand the *why*. Was there a race condition? A memory issue? Or, more likely, an accounting error with `u->inq_len` for zero length skbs and OOB data. Given the "consumed" field, it seems there's some sort of data consumption/offset problem, and that it's related to the skb *length* and not simply the OOB messages. I need to dig deeper into the history around `unix_stream_read_skb` and `u->inq_len` to fully understand.

{
  "Expression": "inq_len",
  "PathPrefix": "net/unix/"
}

{
  "Output": "net/unix/af_unix.c=2324=static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,\n--\nnet/unix/af_unix.c-2366-\tWRITE_ONCE(ousk-\u003eoob_skb, skb);\nnet/unix/af_unix.c:2367:\tWRITE_ONCE(ousk-\u003einq_len, ousk-\u003einq_len + 1);\nnet/unix/af_unix.c-2368-\t__skb_queue_tail(\u0026other-\u003esk_receive_queue, skb);\n--\nnet/unix/af_unix.c=2384=static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,\n--\nnet/unix/af_unix.c-2493-\t\tspin_lock(\u0026other-\u003esk_receive_queue.lock);\nnet/unix/af_unix.c:2494:\t\tWRITE_ONCE(otheru-\u003einq_len, otheru-\u003einq_len + skb-\u003elen);\nnet/unix/af_unix.c-2495-\t\t__skb_queue_tail(\u0026other-\u003esk_receive_queue, skb);\n--\nnet/unix/af_unix.c=2764=static int unix_stream_recv_urg(struct unix_stream_read_state *state)\n--\nnet/unix/af_unix.c-2786-\t\tWRITE_ONCE(u-\u003eoob_skb, NULL);\nnet/unix/af_unix.c:2787:\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - 1);\nnet/unix/af_unix.c-2788-\n--\nnet/unix/af_unix.c=2815=static struct sk_buff *manage_oob(struct sk_buff *skb, struct sk_buff **last,\n--\nnet/unix/af_unix.c-2851-\t\tif (!sock_flag(sk, SOCK_URGINLINE)) {\nnet/unix/af_unix.c:2852:\t\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - 1);\nnet/unix/af_unix.c-2853-\t\t\t__skb_unlink(skb, \u0026sk-\u003esk_receive_queue);\n--\nnet/unix/af_unix.c=2873=static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n--\nnet/unix/af_unix.c-2904-\nnet/unix/af_unix.c:2905:\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - unix_skb_len(skb));\nnet/unix/af_unix.c-2906-\n--\nnet/unix/af_unix.c=2935=static int unix_stream_read_generic(struct unix_stream_read_state *state,\n--\nnet/unix/af_unix.c-3090-\t\t\tspin_lock(\u0026sk-\u003esk_receive_queue.lock);\nnet/unix/af_unix.c:3091:\t\t\tWRITE_ONCE(u-\u003einq_len, u-\u003einq_len - chunk);\nnet/unix/af_unix.c-3092-\t\t\tif (unix_skb_len(skb)) {\n--\nnet/unix/af_unix.c-3131-\t\tif ((do_cmsg | msg-\u003emsg_get_inq) \u0026\u0026 (copied ?: err) \u003e= 0) {\nnet/unix/af_unix.c:3132:\t\t\tmsg-\u003emsg_inq = READ_ONCE(u-\u003einq_len);\nnet/unix/af_unix.c-3133-\t\t\tif (do_cmsg)\n--\nnet/unix/af_unix.c=3221=static int unix_shutdown(struct socket *sock, int mode)\n--\nnet/unix/af_unix.c-3269-\nnet/unix/af_unix.c:3270:long unix_inq_len(struct sock *sk)\nnet/unix/af_unix.c-3271-{\n--\nnet/unix/af_unix.c-3278-\tif (sk-\u003esk_type == SOCK_STREAM)\nnet/unix/af_unix.c:3279:\t\treturn READ_ONCE(unix_sk(sk)-\u003einq_len);\nnet/unix/af_unix.c-3280-\n--\nnet/unix/af_unix.c-3293-}\nnet/unix/af_unix.c:3294:EXPORT_SYMBOL_GPL(unix_inq_len);\nnet/unix/af_unix.c-3295-\n--\nnet/unix/af_unix.c=3316=static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)\n--\nnet/unix/af_unix.c-3327-\tcase SIOCINQ:\nnet/unix/af_unix.c:3328:\t\tamount = unix_inq_len(sk);\nnet/unix/af_unix.c-3329-\t\tif (amount \u003c 0)\n--\nnet/unix/af_unix.h=33=void unix_schedule_gc(struct user_struct *user);\n--\nnet/unix/af_unix.h-35-/* SOCK_DIAG */\nnet/unix/af_unix.h:36:long unix_inq_len(struct sock *sk);\nnet/unix/af_unix.h-37-long unix_outq_len(struct sock *sk);\n--\nnet/unix/diag.c=96=static int sk_diag_show_rqlen(struct sock *sk, struct sk_buff *nlskb)\n--\nnet/unix/diag.c-103-\t} else {\nnet/unix/diag.c:104:\t\trql.udiag_rqueue = (u32) unix_inq_len(sk);\nnet/unix/diag.c-105-\t\trql.udiag_wqueue = (u32) unix_outq_len(sk);\n"
}

gemini-3.8-flash

null

null

							input: 16212
							output: 26
							thoughts: 651
						

**Analysis of `u->inq_len` and Empty SKBs in Unix Stream Sockets**

Okay, here's what I've got so far. It looks like `u->inq_len` is used to track the "in queue" length for things like `SIOCINQ` ioctls and `SCM_INQ` control messages, essentially reflecting how much data is available to be read from the socket. I've spotted a crucial bug in `manage_oob`. When unlinking an unread out-of-band (OOB) `skb`, the code was *missing* a decrement of `u->inq_len`. This means the counter was getting out of sync with the actual data available on the socket, leading to potentially incorrect reporting of the socket's read buffer size. I can see that in `unix_stream_recv_urg` the decrement is present, so this is a clear oversight in `manage_oob`. That's a simple integer counter fix, thankfully.

Moving on, I'm now looking at `unix_stream_read_skb`. This function seems to be the one responsible for pulling `skb`s (socket buffers) off the socket's queue and passing them to `recv_actor`. A socket buffer, in the context of stream sockets, can sometimes be empty; it could contain just control messages (like SCMs) or have been completely consumed by a previous read.

Here's where it gets interesting. I see a check for empty `skb`s: `!unix_skb_len(skb)`. Previously, when an empty `skb` was dequeued, the code was still decrementing `u->inq_len` by zero ( `WRITE_ONCE(u->inq_len, u->inq_len - unix_skb_len(skb));`). This is unnecessary, but more importantly, the empty `skb` would have been passed to `recv_actor`. Now the fix is that, if `unix_skb_len(skb) == 0`, the empty `skb` is discarded and cleaned up via `unix_orphan_scm(sk, skb)` and `consume_skb(skb)`, then the code loops back to fetch the next `skb` from the queue. This is cleaner and more efficient.

Finally, I am seeing another check for `UNIXCB(skb).consumed`. I'll need to dig into what exactly that means, but it appears to be related to some sort of consumption or partially consumed state of the `skb`. I'll need to do some more code diving to understand the full implications of this. I will search the codebase for the definition of `UNIXCB(skb).consumed` to determine what it means and how it's used.

{
  "Expression": "\\.consumed",
  "PathPrefix": "net/unix/"
}

{
  "Output": "net/unix/af_unix.c=660=static unsigned int unix_skb_len(const struct sk_buff *skb)\nnet/unix/af_unix.c-661-{\nnet/unix/af_unix.c:662:\treturn skb-\u003elen - UNIXCB(skb).consumed;\nnet/unix/af_unix.c-663-}\n--\nnet/unix/af_unix.c=2764=static int unix_stream_recv_urg(struct unix_stream_read_state *state)\n--\nnet/unix/af_unix.c-2801-\tif (!(state-\u003eflags \u0026 MSG_PEEK))\nnet/unix/af_unix.c:2802:\t\tUNIXCB(oob_skb).consumed += 1;\nnet/unix/af_unix.c-2803-\n--\nnet/unix/af_unix.c=2873=static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n--\nnet/unix/af_unix.c-2923-\nnet/unix/af_unix.c:2924:\tif (UNIXCB(skb).consumed) {\nnet/unix/af_unix.c:2925:\t\tif (!pskb_pull(skb, UNIXCB(skb).consumed)) {\nnet/unix/af_unix.c-2926-\t\t\tkfree_skb(skb);\n--\nnet/unix/af_unix.c-2928-\t\t}\nnet/unix/af_unix.c:2929:\t\tUNIXCB(skb).consumed = 0;\nnet/unix/af_unix.c-2930-\t}\n--\nnet/unix/af_unix.c=2935=static int unix_stream_read_generic(struct unix_stream_read_state *state,\n--\nnet/unix/af_unix.c-3080-\t\tif (!(flags \u0026 MSG_PEEK)) {\nnet/unix/af_unix.c:3081:\t\t\tUNIXCB(skb).consumed += chunk;\nnet/unix/af_unix.c-3082-\n--\nnet/unix/af_unix.c=3144=static int unix_stream_read_actor(struct sk_buff *skb,\n--\nnet/unix/af_unix.c-3149-\nnet/unix/af_unix.c:3150:\tret = skb_copy_datagram_msg(skb, UNIXCB(skb).consumed + skip,\nnet/unix/af_unix.c-3151-\t\t\t\t    state-\u003emsg, chunk);\n--\nnet/unix/af_unix.c=3190=static int unix_stream_splice_actor(struct sk_buff *skb,\n--\nnet/unix/af_unix.c-3194-\treturn skb_splice_bits(skb, state-\u003esocket-\u003esk,\nnet/unix/af_unix.c:3195:\t\t\t       UNIXCB(skb).consumed + skip,\nnet/unix/af_unix.c-3196-\t\t\t       state-\u003epipe, chunk, state-\u003esplice_flags);\n"
}

gemini-3.8-flash

null

null

							input: 18308
							output: 31
							thoughts: 193
						

**Analyzing the Linux Socket Buffer (skb) Consumption Logic**

Okay, so I'm looking at this code and something's immediately jumping out at me. It seems when `unix_stream_read_generic` is reading data from an skb, or even just grabbing that one out-of-band byte with `unix_stream_recv_urg`, it increments `UNIXCB(skb).consumed`. Right, that makes sense – it's tracking what's been "consumed" from the socket buffer. But here's the kicker: the data isn't *actually* pulled from the skb at this point. No `pskb_pull` is happening. We're just incrementing this `consumed` counter within the control block (`cb`).

The problem surfaces later, because now `unix_stream_read_actor` comes into play. When it runs, it uses an offset that's based on `UNIXCB(skb).consumed + skip`. That seems normal so far.

But then I see something that makes me pause: `unix_stream_read_skb` *directly* passes the `skb` to `recv_actor(sk, skb)`. And this concerns me because the data hasn't actually been pulled. The question now becomes: What does `recv_actor` actually *expect*? I need to dig into `net/core/skmsg.c` to see how `sk_psock_verdict_recv` handles things. I need to understand if this direct passing of an un-pulled `skb` is a legitimate scenario, or if it represents some sort of potential issue or race condition in the buffer management. My expert eye is telling me to investigate this further.

{
  "Expression": "sk_psock_verdict_recv",
  "PathPrefix": "net/"
}

{
  "Output": "net/core/skmsg.c=1197=static void sk_psock_done_strp(struct sk_psock *psock)\n--\nnet/core/skmsg.c-1201-\nnet/core/skmsg.c:1202:static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)\nnet/core/skmsg.c-1203-{\n--\nnet/core/skmsg.c=1234=static void sk_psock_verdict_data_ready(struct sock *sk)\n--\nnet/core/skmsg.c-1250-\nnet/core/skmsg.c:1251:\tcopied = ops-\u003eread_skb(sk, sk_psock_verdict_recv);\nnet/core/skmsg.c-1252-\tif (copied \u003e= 0) {\n"
}

gemini-3.8-flash

null

null

							input: 19138
							output: 37
							thoughts: 26
						

Okay, here's my summary, presented as a stream of thought:

**Diving into `sk_psock_verdict_recv`**

Alright, time to dig into the guts of the `skmsg` subsystem. I want to see what's happening with `sk_psock_verdict_recv` in `net/core/skmsg.c`. This is where the verdict for packet socket filtering decisions is received, if I recall correctly. I'm especially interested in understanding the flow of data and control when a packet is being processed by a packet socket and how the kernel decides what to do with it – drop it, forward it, deliver it to userspace, etc. The name itself suggests a verdict, so that's a good starting point. I need to refresh my memory on the interactions of this function with the other skmsg functions and the packet socket infrastructure generally; it's easy to get lost in the complexity. Let's see what interesting tidbits await us in the code...

{
  "File": "net/core/skmsg.c",
  "FirstLine": 1200,
  "LineCount": 35
}

{
  "Contents": "1200:\t#endif /* CONFIG_BPF_STREAM_PARSER */\n1201:\t\n1202:\tstatic int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)\n1203:\t{\n1204:\t\tstruct sk_psock *psock;\n1205:\t\tstruct bpf_prog *prog;\n1206:\t\tint ret = __SK_DROP;\n1207:\t\tint len = skb-\u003elen;\n1208:\t\n1209:\t\trcu_read_lock();\n1210:\t\tpsock = sk_psock(sk);\n1211:\t\tif (unlikely(!psock)) {\n1212:\t\t\tlen = 0;\n1213:\t\t\ttcp_eat_skb(sk, skb);\n1214:\t\t\tsock_drop(sk, skb);\n1215:\t\t\tgoto out;\n1216:\t\t}\n1217:\t\tprog = READ_ONCE(psock-\u003eprogs.stream_verdict);\n1218:\t\tif (!prog)\n1219:\t\t\tprog = READ_ONCE(psock-\u003eprogs.skb_verdict);\n1220:\t\tif (likely(prog)) {\n1221:\t\t\tskb_dst_drop(skb);\n1222:\t\t\tskb_bpf_redirect_clear(skb);\n1223:\t\t\tret = bpf_prog_run_pin_on_cpu(prog, skb);\n1224:\t\t\tret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));\n1225:\t\t}\n1226:\t\tret = sk_psock_verdict_apply(psock, skb, ret);\n1227:\t\tif (ret \u003c 0)\n1228:\t\t\tlen = ret;\n1229:\tout:\n1230:\t\trcu_read_unlock();\n1231:\t\treturn len;\n1232:\t}\n1233:\t\n1234:\tstatic void sk_psock_verdict_data_ready(struct sock *sk)\n"
}

gemini-3.8-flash

null

null

							input: 19981
							output: 29
							thoughts: 1602
						

**Analyzing SKB Consumption and KMSAN Necessity**

Okay, so I've been carefully reviewing this code related to `sk_psock_verdict_recv` and how it handles Socket Buffer (SKB) data, particularly when dealing with partially consumed SKBs within the Unix domain socket context. The key concern, as I see it, is how the code interacts with the `UNIXCB(skb).consumed` field, which indicates how many bytes at the beginning of an SKB have already been read. The initial problem was the assumption of the SKB data starting at the beginning. If `UNIXCB(skb).consumed` was non-zero, the `skb` handed to `sk_psock_verdict_recv` would start from the middle of the buffer.

Now the code addresses this with the `pskb_pull` function, which seems to trim off the already consumed bytes to ensure only unread data is processed. Let me make sure that it does this correctly: the `pskb_pull` is called with the number of consumed bytes, and this value is deducted from the SKB's length, and the SKB data pointer is advanced accordingly. If there's no remaining data, it's freed and the process repeats.

My main focus is on whether these changes might introduce or expose risks of uninitialized memory usage, because that's what KMSAN is for. Based on the rules, if it's not a KMSAN issue, then it's a KASAN/LOCKDEP/etc issue and they already provide enough coverage. I have to see if this code touches any of the critical areas: structures sent to user space, logic relying on uninitialized variables, complex data structure initialization, or boundary checks that could leak uninitialized bytes.

Let's dissect the code changes. I see `manage_oob` updating the `u->inq_len` variable. This integer is initialized during socket creation, so it's not an issue. The loop with label `again:` seems safe: if an SKB is empty, it's orphaned, freed, and the code loops back to get the next SKB. Then, there's the `pskb_pull` call. This part *is* relevant. It's designed to remove consumed bytes. The crucial thing here is that `UNIXCB(skb).consumed` *must* be initialized. Let's verify that UNIXCB is initialized when the skb is allocated/queued (it seems it is, with `memset` calls, which makes it safe). Since it's only reducing the SKB length and advancing the data pointer, it won't cause uninitialized memory reads.

Based on this analysis, I'm confident that the code changes are safe from uninitialized memory reads or leaks. Therefore, I don't see any KMSAN-specific issues.

no matches

{
  "Expression": "memset\\(UNIXCB",
  "PathPrefix": "net/unix/"
}

{
  "error": "no matches"
}

gemini-3.8-flash

null

null

							input: 22232
							output: 27
							thoughts: 15
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Investigating the UNIXCB Flag**

Alright, let's get down to brass tacks. I need to understand the lifecycle of the `UNIXCB` variable. Where is this thing being initialized, set, cleared, or otherwise manipulated within this system? I need a clear map of its usage to fully grasp its impact. This means I'm going to have to dive into the codebase and trace its various states. I'm looking for the defining moments, the key sections of code that influence its value, and how those changes impact downstream functionality. This is the first step in debugging or understanding the rationale behind its implementation. I'll need to use my usual set of tools (grep, find, possibly a debugger) to track it down. Time to start digging.

{
  "Expression": "UNIXCB",
  "PathPrefix": "net/unix/"
}

{
  "Output": "net/unix/af_unix.c=256=static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-257-{\nnet/unix/af_unix.c:258:\tUNIXCB(skb).secid = scm-\u003esecid;\nnet/unix/af_unix.c-259-}\n--\nnet/unix/af_unix.c=261=static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-262-{\nnet/unix/af_unix.c:263:\tscm-\u003esecid = UNIXCB(skb).secid;\nnet/unix/af_unix.c-264-}\n--\nnet/unix/af_unix.c=266=static inline bool unix_secdata_eq(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-267-{\nnet/unix/af_unix.c:268:\treturn (scm-\u003esecid == UNIXCB(skb).secid);\nnet/unix/af_unix.c-269-}\n--\nnet/unix/af_unix.c=660=static unsigned int unix_skb_len(const struct sk_buff *skb)\nnet/unix/af_unix.c-661-{\nnet/unix/af_unix.c:662:\treturn skb-\u003elen - UNIXCB(skb).consumed;\nnet/unix/af_unix.c-663-}\n--\nnet/unix/af_unix.c=1943=static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)\n--\nnet/unix/af_unix.c-1947-\nnet/unix/af_unix.c:1948:\tUNIXCB(skb).fp = scm-\u003efp;\nnet/unix/af_unix.c-1949-\tscm-\u003efp = NULL;\nnet/unix/af_unix.c-1950-\nnet/unix/af_unix.c:1951:\tif (unix_prepare_fpl(UNIXCB(skb).fp))\nnet/unix/af_unix.c-1952-\t\treturn -ENOMEM;\n--\nnet/unix/af_unix.c=1957=static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-1958-{\nnet/unix/af_unix.c:1959:\tscm-\u003efp = UNIXCB(skb).fp;\nnet/unix/af_unix.c:1960:\tUNIXCB(skb).fp = NULL;\nnet/unix/af_unix.c-1961-\n--\nnet/unix/af_unix.c=1965=static void unix_peek_fds(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-1966-{\nnet/unix/af_unix.c:1967:\tscm-\u003efp = scm_fp_dup(UNIXCB(skb).fp);\nnet/unix/af_unix.c-1968-\n--\nnet/unix/af_unix.c=1972=static void unix_destruct_scm(struct sk_buff *skb)\n--\nnet/unix/af_unix.c-1975-\nnet/unix/af_unix.c:1976:\tswap(scm.pid, UNIXCB(skb).pid);\nnet/unix/af_unix.c-1977-\nnet/unix/af_unix.c:1978:\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-1979-\t\tunix_detach_fds(\u0026scm, skb);\n--\nnet/unix/af_unix.c=1990=static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool send_fds)\n--\nnet/unix/af_unix.c-1993-\nnet/unix/af_unix.c:1994:\tUNIXCB(skb).pid = get_pid(scm-\u003epid);\nnet/unix/af_unix.c:1995:\tUNIXCB(skb).uid = scm-\u003ecreds.uid;\nnet/unix/af_unix.c:1996:\tUNIXCB(skb).gid = scm-\u003ecreds.gid;\nnet/unix/af_unix.c:1997:\tUNIXCB(skb).fp = NULL;\nnet/unix/af_unix.c-1998-\tunix_get_secdata(scm, skb);\n--\nnet/unix/af_unix.c=2006=static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)\nnet/unix/af_unix.c-2007-{\nnet/unix/af_unix.c:2008:\tscm_set_cred(scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);\nnet/unix/af_unix.c-2009-\tunix_set_secdata(scm, skb);\n--\nnet/unix/af_unix.c=2025=static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,\n--\nnet/unix/af_unix.c-2027-{\nnet/unix/af_unix.c:2028:\tif (UNIXCB(skb).pid)\nnet/unix/af_unix.c-2029-\t\treturn 0;\n--\nnet/unix/af_unix.c-2040-\nnet/unix/af_unix.c:2041:\t\tUNIXCB(skb).pid = get_pid(pid);\nnet/unix/af_unix.c:2042:\t\tcurrent_uid_gid(\u0026UNIXCB(skb).uid, \u0026UNIXCB(skb).gid);\nnet/unix/af_unix.c-2043-\t}\n--\nnet/unix/af_unix.c=2048=static bool unix_skb_scm_eq(struct sk_buff *skb,\n--\nnet/unix/af_unix.c-2050-{\nnet/unix/af_unix.c:2051:\treturn UNIXCB(skb).pid == scm-\u003epid \u0026\u0026\nnet/unix/af_unix.c:2052:\t       uid_eq(UNIXCB(skb).uid, scm-\u003ecreds.uid) \u0026\u0026\nnet/unix/af_unix.c:2053:\t       gid_eq(UNIXCB(skb).gid, scm-\u003ecreds.gid) \u0026\u0026\nnet/unix/af_unix.c-2054-\t       unix_secdata_eq(scm, skb);\n--\nnet/unix/af_unix.c=2057=static void scm_stat_add(struct sock *sk, struct sk_buff *skb)\nnet/unix/af_unix.c-2058-{\nnet/unix/af_unix.c:2059:\tstruct scm_fp_list *fp = UNIXCB(skb).fp;\nnet/unix/af_unix.c-2060-\tstruct unix_sock *u = unix_sk(sk);\n--\nnet/unix/af_unix.c=2068=static void scm_stat_del(struct sock *sk, struct sk_buff *skb)\nnet/unix/af_unix.c-2069-{\nnet/unix/af_unix.c:2070:\tstruct scm_fp_list *fp = UNIXCB(skb).fp;\nnet/unix/af_unix.c-2071-\tstruct unix_sock *u = unix_sk(sk);\n--\nnet/unix/af_unix.c=2090=static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,\n--\nnet/unix/af_unix.c-2244-\nnet/unix/af_unix.c:2245:\tif (UNIXCB(skb).fp \u0026\u0026 !other-\u003esk_scm_rights) {\nnet/unix/af_unix.c-2246-\t\terr = -EPERM;\n--\nnet/unix/af_unix.c=2324=static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,\n--\nnet/unix/af_unix.c-2357-\nnet/unix/af_unix.c:2358:\tif (UNIXCB(skb).fp \u0026\u0026 !other-\u003esk_scm_rights) {\nnet/unix/af_unix.c-2359-\t\terr = -EPERM;\n--\nnet/unix/af_unix.c=2384=static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,\n--\nnet/unix/af_unix.c-2484-\nnet/unix/af_unix.c:2485:\t\tif (UNIXCB(skb).fp \u0026\u0026 !other-\u003esk_scm_rights) {\nnet/unix/af_unix.c-2486-\t\t\tunix_state_unlock(other);\n--\nnet/unix/af_unix.c=2569=int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,\n--\nnet/unix/af_unix.c-2643-\tif (!(flags \u0026 MSG_PEEK)) {\nnet/unix/af_unix.c:2644:\t\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-2645-\t\t\tunix_detach_fds(\u0026scm, skb);\n--\nnet/unix/af_unix.c-2663-\nnet/unix/af_unix.c:2664:\t\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-2665-\t\t\tunix_peek_fds(\u0026scm, skb);\n--\nnet/unix/af_unix.c=2764=static int unix_stream_recv_urg(struct unix_stream_read_state *state)\n--\nnet/unix/af_unix.c-2801-\tif (!(state-\u003eflags \u0026 MSG_PEEK))\nnet/unix/af_unix.c:2802:\t\tUNIXCB(oob_skb).consumed += 1;\nnet/unix/af_unix.c-2803-\n--\nnet/unix/af_unix.c=2873=static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n--\nnet/unix/af_unix.c-2923-\nnet/unix/af_unix.c:2924:\tif (UNIXCB(skb).consumed) {\nnet/unix/af_unix.c:2925:\t\tif (!pskb_pull(skb, UNIXCB(skb).consumed)) {\nnet/unix/af_unix.c-2926-\t\t\tkfree_skb(skb);\n--\nnet/unix/af_unix.c-2928-\t\t}\nnet/unix/af_unix.c:2929:\t\tUNIXCB(skb).consumed = 0;\nnet/unix/af_unix.c-2930-\t}\n--\nnet/unix/af_unix.c=2935=static int unix_stream_read_generic(struct unix_stream_read_state *state,\n--\nnet/unix/af_unix.c-3080-\t\tif (!(flags \u0026 MSG_PEEK)) {\nnet/unix/af_unix.c:3081:\t\t\tUNIXCB(skb).consumed += chunk;\nnet/unix/af_unix.c-3082-\n--\nnet/unix/af_unix.c-3084-\nnet/unix/af_unix.c:3085:\t\t\tif (UNIXCB(skb).fp) {\nnet/unix/af_unix.c-3086-\t\t\t\tscm_stat_del(sk, skb);\n--\nnet/unix/af_unix.c-3105-\t\t\t */\nnet/unix/af_unix.c:3106:\t\t\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-3107-\t\t\t\tunix_peek_fds(\u0026scm, skb);\n--\nnet/unix/af_unix.c-3110-\nnet/unix/af_unix.c:3111:\t\t\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-3112-\t\t\t\tbreak;\n--\nnet/unix/af_unix.c=3144=static int unix_stream_read_actor(struct sk_buff *skb,\n--\nnet/unix/af_unix.c-3149-\nnet/unix/af_unix.c:3150:\tret = skb_copy_datagram_msg(skb, UNIXCB(skb).consumed + skip,\nnet/unix/af_unix.c-3151-\t\t\t\t    state-\u003emsg, chunk);\n--\nnet/unix/af_unix.c=3190=static int unix_stream_splice_actor(struct sk_buff *skb,\n--\nnet/unix/af_unix.c-3194-\treturn skb_splice_bits(skb, state-\u003esocket-\u003esk,\nnet/unix/af_unix.c:3195:\t\t\t       UNIXCB(skb).consumed + skip,\nnet/unix/af_unix.c-3196-\t\t\t       state-\u003epipe, chunk, state-\u003esplice_flags);\n--\nnet/unix/af_unix.h=13=struct unix_skb_parms {\n--\nnet/unix/af_unix.h-23-\nnet/unix/af_unix.h:24:#define UNIXCB(skb)\t(*(struct unix_skb_parms *)\u0026((skb)-\u003ecb))\nnet/unix/af_unix.h-25-\n--\nnet/unix/garbage.c=609=static void unix_gc(struct work_struct *work)\n--\nnet/unix/garbage.c-632-\tskb_queue_walk(\u0026hitlist, skb) {\nnet/unix/garbage.c:633:\t\tif (UNIXCB(skb).fp)\nnet/unix/garbage.c:634:\t\t\tUNIXCB(skb).fp-\u003edead = true;\nnet/unix/garbage.c-635-\t}\n"
}

gemini-3.8-flash

null

null

							input: 26182
							output: 38
							thoughts: 87
						

Here's my thought process, as it stands:

**Analyzing the `UNIXCB` Macro and Initialization in `unix_stream_sendmsg`**

Okay, so I'm looking at how the `UNIXCB` macro works within the context of Unix domain sockets. The text reminds me that `UNIXCB` is just a pointer-arithmetic trick; it's effectively a way to access the Unix-specific control block within the `skb->cb` field. Specifically, it's defined as casting `(skb)->cb` to a pointer to a `struct unix_skb_parms`. That makes sense; it's a common pattern in the kernel.

Now, a key point:  When an `skb` is allocated, like with `sock_alloc_send_pskb`, the `cb` field (which is where `UNIXCB` points to) is zeroed out.  That's important. It means any data I'm expecting to be in `UNIXCB` has to be *explicitly* initialized later.

Therefore, my immediate task is to track down where `UNIXCB(skb)` *gets* initialized, in the `unix_stream_sendmsg` function. I need to understand how the Unix-specific parameters are populated within that control block.  That's where the critical connection happens between the socket's data and the network stack's processing for Unix domain sockets. Understanding the initialization sequence is fundamental. This tells me about the integrity and dependencies of the Unix domain socket.

{
  "Expression": "UNIXCB\\(skb\\)\\.",
  "PathPrefix": "net/unix/af_unix.c"
}

{
  "Output": "net/unix/af_unix.c=256=static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-257-{\nnet/unix/af_unix.c:258:\tUNIXCB(skb).secid = scm-\u003esecid;\nnet/unix/af_unix.c-259-}\n--\nnet/unix/af_unix.c=261=static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-262-{\nnet/unix/af_unix.c:263:\tscm-\u003esecid = UNIXCB(skb).secid;\nnet/unix/af_unix.c-264-}\n--\nnet/unix/af_unix.c=266=static inline bool unix_secdata_eq(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-267-{\nnet/unix/af_unix.c:268:\treturn (scm-\u003esecid == UNIXCB(skb).secid);\nnet/unix/af_unix.c-269-}\n--\nnet/unix/af_unix.c=660=static unsigned int unix_skb_len(const struct sk_buff *skb)\nnet/unix/af_unix.c-661-{\nnet/unix/af_unix.c:662:\treturn skb-\u003elen - UNIXCB(skb).consumed;\nnet/unix/af_unix.c-663-}\n--\nnet/unix/af_unix.c=1943=static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)\n--\nnet/unix/af_unix.c-1947-\nnet/unix/af_unix.c:1948:\tUNIXCB(skb).fp = scm-\u003efp;\nnet/unix/af_unix.c-1949-\tscm-\u003efp = NULL;\nnet/unix/af_unix.c-1950-\nnet/unix/af_unix.c:1951:\tif (unix_prepare_fpl(UNIXCB(skb).fp))\nnet/unix/af_unix.c-1952-\t\treturn -ENOMEM;\n--\nnet/unix/af_unix.c=1957=static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-1958-{\nnet/unix/af_unix.c:1959:\tscm-\u003efp = UNIXCB(skb).fp;\nnet/unix/af_unix.c:1960:\tUNIXCB(skb).fp = NULL;\nnet/unix/af_unix.c-1961-\n--\nnet/unix/af_unix.c=1965=static void unix_peek_fds(struct scm_cookie *scm, struct sk_buff *skb)\nnet/unix/af_unix.c-1966-{\nnet/unix/af_unix.c:1967:\tscm-\u003efp = scm_fp_dup(UNIXCB(skb).fp);\nnet/unix/af_unix.c-1968-\n--\nnet/unix/af_unix.c=1972=static void unix_destruct_scm(struct sk_buff *skb)\n--\nnet/unix/af_unix.c-1975-\nnet/unix/af_unix.c:1976:\tswap(scm.pid, UNIXCB(skb).pid);\nnet/unix/af_unix.c-1977-\nnet/unix/af_unix.c:1978:\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-1979-\t\tunix_detach_fds(\u0026scm, skb);\n--\nnet/unix/af_unix.c=1990=static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool send_fds)\n--\nnet/unix/af_unix.c-1993-\nnet/unix/af_unix.c:1994:\tUNIXCB(skb).pid = get_pid(scm-\u003epid);\nnet/unix/af_unix.c:1995:\tUNIXCB(skb).uid = scm-\u003ecreds.uid;\nnet/unix/af_unix.c:1996:\tUNIXCB(skb).gid = scm-\u003ecreds.gid;\nnet/unix/af_unix.c:1997:\tUNIXCB(skb).fp = NULL;\nnet/unix/af_unix.c-1998-\tunix_get_secdata(scm, skb);\n--\nnet/unix/af_unix.c=2006=static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)\nnet/unix/af_unix.c-2007-{\nnet/unix/af_unix.c:2008:\tscm_set_cred(scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);\nnet/unix/af_unix.c-2009-\tunix_set_secdata(scm, skb);\n--\nnet/unix/af_unix.c=2025=static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,\n--\nnet/unix/af_unix.c-2027-{\nnet/unix/af_unix.c:2028:\tif (UNIXCB(skb).pid)\nnet/unix/af_unix.c-2029-\t\treturn 0;\n--\nnet/unix/af_unix.c-2040-\nnet/unix/af_unix.c:2041:\t\tUNIXCB(skb).pid = get_pid(pid);\nnet/unix/af_unix.c:2042:\t\tcurrent_uid_gid(\u0026UNIXCB(skb).uid, \u0026UNIXCB(skb).gid);\nnet/unix/af_unix.c-2043-\t}\n--\nnet/unix/af_unix.c=2048=static bool unix_skb_scm_eq(struct sk_buff *skb,\n--\nnet/unix/af_unix.c-2050-{\nnet/unix/af_unix.c:2051:\treturn UNIXCB(skb).pid == scm-\u003epid \u0026\u0026\nnet/unix/af_unix.c:2052:\t       uid_eq(UNIXCB(skb).uid, scm-\u003ecreds.uid) \u0026\u0026\nnet/unix/af_unix.c:2053:\t       gid_eq(UNIXCB(skb).gid, scm-\u003ecreds.gid) \u0026\u0026\nnet/unix/af_unix.c-2054-\t       unix_secdata_eq(scm, skb);\n--\nnet/unix/af_unix.c=2057=static void scm_stat_add(struct sock *sk, struct sk_buff *skb)\nnet/unix/af_unix.c-2058-{\nnet/unix/af_unix.c:2059:\tstruct scm_fp_list *fp = UNIXCB(skb).fp;\nnet/unix/af_unix.c-2060-\tstruct unix_sock *u = unix_sk(sk);\n--\nnet/unix/af_unix.c=2068=static void scm_stat_del(struct sock *sk, struct sk_buff *skb)\nnet/unix/af_unix.c-2069-{\nnet/unix/af_unix.c:2070:\tstruct scm_fp_list *fp = UNIXCB(skb).fp;\nnet/unix/af_unix.c-2071-\tstruct unix_sock *u = unix_sk(sk);\n--\nnet/unix/af_unix.c=2090=static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,\n--\nnet/unix/af_unix.c-2244-\nnet/unix/af_unix.c:2245:\tif (UNIXCB(skb).fp \u0026\u0026 !other-\u003esk_scm_rights) {\nnet/unix/af_unix.c-2246-\t\terr = -EPERM;\n--\nnet/unix/af_unix.c=2324=static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,\n--\nnet/unix/af_unix.c-2357-\nnet/unix/af_unix.c:2358:\tif (UNIXCB(skb).fp \u0026\u0026 !other-\u003esk_scm_rights) {\nnet/unix/af_unix.c-2359-\t\terr = -EPERM;\n--\nnet/unix/af_unix.c=2384=static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,\n--\nnet/unix/af_unix.c-2484-\nnet/unix/af_unix.c:2485:\t\tif (UNIXCB(skb).fp \u0026\u0026 !other-\u003esk_scm_rights) {\nnet/unix/af_unix.c-2486-\t\t\tunix_state_unlock(other);\n--\nnet/unix/af_unix.c=2569=int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,\n--\nnet/unix/af_unix.c-2643-\tif (!(flags \u0026 MSG_PEEK)) {\nnet/unix/af_unix.c:2644:\t\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-2645-\t\t\tunix_detach_fds(\u0026scm, skb);\n--\nnet/unix/af_unix.c-2663-\nnet/unix/af_unix.c:2664:\t\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-2665-\t\t\tunix_peek_fds(\u0026scm, skb);\n--\nnet/unix/af_unix.c=2873=static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)\n--\nnet/unix/af_unix.c-2923-\nnet/unix/af_unix.c:2924:\tif (UNIXCB(skb).consumed) {\nnet/unix/af_unix.c:2925:\t\tif (!pskb_pull(skb, UNIXCB(skb).consumed)) {\nnet/unix/af_unix.c-2926-\t\t\tkfree_skb(skb);\n--\nnet/unix/af_unix.c-2928-\t\t}\nnet/unix/af_unix.c:2929:\t\tUNIXCB(skb).consumed = 0;\nnet/unix/af_unix.c-2930-\t}\n--\nnet/unix/af_unix.c=2935=static int unix_stream_read_generic(struct unix_stream_read_state *state,\n--\nnet/unix/af_unix.c-3080-\t\tif (!(flags \u0026 MSG_PEEK)) {\nnet/unix/af_unix.c:3081:\t\t\tUNIXCB(skb).consumed += chunk;\nnet/unix/af_unix.c-3082-\n--\nnet/unix/af_unix.c-3084-\nnet/unix/af_unix.c:3085:\t\t\tif (UNIXCB(skb).fp) {\nnet/unix/af_unix.c-3086-\t\t\t\tscm_stat_del(sk, skb);\n--\nnet/unix/af_unix.c-3105-\t\t\t */\nnet/unix/af_unix.c:3106:\t\t\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-3107-\t\t\t\tunix_peek_fds(\u0026scm, skb);\n--\nnet/unix/af_unix.c-3110-\nnet/unix/af_unix.c:3111:\t\t\tif (UNIXCB(skb).fp)\nnet/unix/af_unix.c-3112-\t\t\t\tbreak;\n--\nnet/unix/af_unix.c=3144=static int unix_stream_read_actor(struct sk_buff *skb,\n--\nnet/unix/af_unix.c-3149-\nnet/unix/af_unix.c:3150:\tret = skb_copy_datagram_msg(skb, UNIXCB(skb).consumed + skip,\nnet/unix/af_unix.c-3151-\t\t\t\t    state-\u003emsg, chunk);\n--\nnet/unix/af_unix.c=3190=static int unix_stream_splice_actor(struct sk_buff *skb,\n--\nnet/unix/af_unix.c-3194-\treturn skb_splice_bits(skb, state-\u003esocket-\u003esk,\nnet/unix/af_unix.c:3195:\t\t\t       UNIXCB(skb).consumed + skip,\nnet/unix/af_unix.c-3196-\t\t\t       state-\u003epipe, chunk, state-\u003esplice_flags);\n"
}

gemini-3.8-flash

null

null

							input: 30033
							output: 35
							thoughts: 46
						

Here's my summary, as if I were thinking it:

**Diving into the UNIXCB Structure**

Alright, let's get down to brass tacks. I need to understand this `UNIXCB` structure. My instinct is always to go right to the source code, so I'm pulling up `net/unix/af_unix.h`. Let's just focus on the declaration for now, so I'll scan the first 30 lines. I figure that'll give me a solid foundation and I can always dive deeper as needed.

{
  "File": "net/unix/af_unix.h",
  "FirstLine": 1,
  "LineCount": 30
}

{
  "Contents": "   1:\t/* SPDX-License-Identifier: GPL-2.0 */\n   2:\t#ifndef __AF_UNIX_H\n   3:\t#define __AF_UNIX_H\n   4:\t\n   5:\t#include \u003clinux/uidgid.h\u003e\n   6:\t\n   7:\t#define UNIX_HASH_MOD\t(256 - 1)\n   8:\t#define UNIX_HASH_SIZE\t(256 * 2)\n   9:\t#define UNIX_HASH_BITS\t8\n  10:\t\n  11:\tstruct sock *unix_peer_get(struct sock *sk);\n  12:\t\n  13:\tstruct unix_skb_parms {\n  14:\t\tstruct pid\t\t*pid;\t\t/* skb credentials\t*/\n  15:\t\tkuid_t\t\t\tuid;\n  16:\t\tkgid_t\t\t\tgid;\n  17:\t\tstruct scm_fp_list\t*fp;\t\t/* Passed files\t\t*/\n  18:\t#ifdef CONFIG_SECURITY_NETWORK\n  19:\t\tu32\t\t\tsecid;\t\t/* Security ID\t\t*/\n  20:\t#endif\n  21:\t\tu32\t\t\tconsumed;\n  22:\t} __randomize_layout;\n  23:\t\n  24:\t#define UNIXCB(skb)\t(*(struct unix_skb_parms *)\u0026((skb)-\u003ecb))\n  25:\t\n  26:\t/* GC for SCM_RIGHTS */\n  27:\tvoid unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver);\n  28:\tvoid unix_del_edges(struct scm_fp_list *fpl);\n  29:\tvoid unix_update_edges(struct unix_sock *receiver);\n  30:\tint unix_prepare_fpl(struct scm_fp_list *fpl);\n"
}

gemini-3.8-flash

null

null

							input: 30712
							output: 248
							thoughts: 898
						

**KMSAN Assessment: No Risk of Uninitialized Memory**

Okay, let's break this down. My analysis indicates that KMSAN is *not* needed here. The core of this patch seems pretty straightforward, so I'm confident in that assessment.

First, I looked at how the patch interacts with memory initialization and potential information leaks. Standard SKB allocation in `alloc_skb_with_frags` and `__alloc_skb` involves `memset` of the control block (`skb->cb`), and the same is done during `sock_alloc_send_pskb`. This means `UNIXCB(skb).consumed` is reliably zeroed upon allocation.

The patch's changes themselves are focused on:

1.  **Correcting `u->inq_len`:** The `manage_oob` function is updated. It fixes an `inq_len` count issue when an unread OOB SKB is removed. This involves a simple integer update (`WRITE_ONCE`). This integer is exposed via `SIOCINQ` or `SCM_INQ`, but the patch just makes the calculation accurate; it's not a new or uninitialized value being exposed.
2.  **Handling Consumed Data in `unix_stream_read_skb`:** The patch introduces a few tweaks to `unix_stream_read_skb`. It now drops empty SKBs (`!unix_skb_len(skb)`) – these could be leftover after data is fully consumed, and the code jumps to process the next SKB. Crucially, if `UNIXCB(skb).consumed` is non-zero, it means that part of the SKB has already been read. The patch correctly uses `pskb_pull(skb, UNIXCB(skb).consumed)` to pull those already consumed bytes, resets the `consumed` counter to zero, and then passes the remaining (valid) data on to `recv_actor`.

Now, does any of this introduce uninitialized memory issues? Absolutely not.

*   **No Uninitialized Data Structures:** The patch doesn't introduce any new kernel structures passed to userspace where fields *might* be uninitialized. `u->inq_len` is an integer read by a helper and returned as an integer, and the fix only ensures the integer math is correct.
*   **No Conditional Logic on Uninitialized Values:** No conditional logic or branching relies on *uninitialized* variables. `unix_skb_len(skb)` and `UNIXCB(skb).consumed` are both reliably initialized integer fields.
*   **No New Allocations:** No new data structure allocations occur within the scope of the patch that might leave fields uninitialized.
*   **No Memory Corruption:** There is no risk of exposing uninitialized bytes through buffer manipulation. `pskb_pull` is designed to advance the buffer head, safely managing already-consumed bytes. `recv_actor` works on valid data. The new check discarding empty SKBs before `recv_actor` also contributes to safety.

Regarding memory safety in general (out-of-bounds, use-after-free, leaks), I don't see anything here. Those are KASAN / standard sanitizers domain anyway. These are the kinds of issues that KASAN and other standard debugging tools would catch – not KMSAN, which is more focused on the *leakage* of uninitialized values. Therefore, I believe `NeedsKMSAN` should be false.

{
  "KMSANReasoning": "The patch addresses socket queue length accounting and skb consumption handling in AF_UNIX stream sockets. Specifically:\n1. In `manage_oob()`, it corrects `u-\u003einq_len` accounting by decrementing it by 1 when unlinking an unread OOB skb.\n2. In `unix_stream_read_skb()`, it drops empty skbs (`!unix_skb_len(skb)`) and pulls already-consumed bytes via `pskb_pull()` before handing the skb to `recv_actor()`.\n\nNone of these changes allocate or read uninitialized memory, nor do they expose uninitialized kernel fields/padding to user space or conditional branching. All fields touched (`u-\u003einq_len`, `UNIXCB(skb).consumed`, skb pointers) are fully initialized socket and skb metadata. Any memory errors relating to skb lifecycle or bounds would be detected by KASAN or standard debuggers, not KMSAN. Therefore, a dedicated KMSAN fuzzing session is not warranted.",
  "NeedsKMSAN": false
}

{
  "KMSANReasoning": "The patch addresses socket queue length accounting and skb consumption handling in AF_UNIX stream sockets. Specifically:\n1. In `manage_oob()`, it corrects `u-\u003einq_len` accounting by decrementing it by 1 when unlinking an unread OOB skb.\n2. In `unix_stream_read_skb()`, it drops empty skbs (`!unix_skb_len(skb)`) and pulls already-consumed bytes via `pskb_pull()` before handing the skb to `recv_actor()`.\n\nNone of these changes allocate or read uninitialized memory, nor do they expose uninitialized kernel fields/padding to user space or conditional branching. All fields touched (`u-\u003einq_len`, `UNIXCB(skb).consumed`, skb pointers) are fully initialized socket and skb metadata. Any memory errors relating to skb lifecycle or bounds would be detected by KASAN or standard debuggers, not KMSAN. Therefore, a dedicated KMSAN fuzzing session is not warranted.",
  "NeedsKMSAN": false
}