AI Trajectory

null

{
  "EnableConfigs": [
    "MPTCP"
  ],
  "FocusSymbols": [
    "mptcp_token_join_cookie_init_state",
    "mptcp_subflow_init_cookie_req"
  ],
  "KMSANReasoning": "The patch adds an assignment to `subflow_req-\u003elocal_id` in `mptcp_token_join_cookie_init_state()`. `subflow_req` is a `struct mptcp_subflow_request_sock`, which is allocated via `reqsk_alloc()`. The `reqsk_alloc()` function allocates memory from a slab cache without the `__GFP_ZERO` flag, meaning the memory is uninitialized.\n\nWhile `subflow_init_req()` initializes several fields of the request socket, it does not initialize `local_id`. During a SYN cookie MP_JOIN, `mptcp_token_join_cookie_init_state()` is called to reconstruct the request socket state from the cookie. Before this patch, it failed to restore `local_id`, leaving `subflow_req-\u003elocal_id` uninitialized.\n\nThis uninitialized 1-byte value is later copied to the subflow context (`new_ctx-\u003elocal_id`) in `subflow_ulp_clone()`. From there, the uninitialized kernel heap memory can be leaked to userspace via Netlink (e.g., `MPTCP_SUBFLOW_ATTR_ID_LOC` in `subflow_get_info()`) or sent over the network in MPTCP TCP options.\n\nStandard KASAN does not detect reads of uninitialized memory; it only detects out-of-bounds accesses and use-after-free bugs. KMSAN is specifically designed to detect uninitialized memory uses and info-leaks. Therefore, a dedicated KMSAN fuzzing session is required to catch this and similar bugs.",
  "NeedsKMSAN": true,
  "Reasoning": "The patch fixes missing initialization of `subflow_req-\u003elocal_id` in `mptcp_token_join_cookie_init_state` which is called during MPTCP syncookie processing. This is a functional change in the core MPTCP logic that is reachable and should be fuzzed.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit a80a630c666666b8d4cce7e791d4e8023ab25fcd\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Sat Aug 15 12:30:29 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/net/mptcp/syncookies.c b/net/mptcp/syncookies.c\nindex 7f22526346a7e..b5cac57011221 100644\n--- a/net/mptcp/syncookies.c\n+++ b/net/mptcp/syncookies.c\n@@ -118,6 +118,7 @@ bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subfl\n \tsubflow_req-\u003elocal_nonce = e-\u003elocal_nonce;\n \tsubflow_req-\u003ebackup = e-\u003ebackup;\n \tsubflow_req-\u003eremote_id = e-\u003ejoin_id;\n+\tsubflow_req-\u003elocal_id = e-\u003elocal_id;\n \tsubflow_req-\u003etoken = e-\u003etoken;\n \tsubflow_req-\u003emsk = msk;\n \tspin_unlock_bh(\u0026join_entry_locks[i]);\n"
}

best-expensive

null

{
  "EnableConfigs": [
    "MPTCP"
  ],
  "FocusSymbols": [
    "mptcp_token_join_cookie_init_state",
    "mptcp_subflow_init_cookie_req"
  ],
  "Reasoning": "The patch fixes missing initialization of `subflow_req-\u003elocal_id` in `mptcp_token_join_cookie_init_state` which is called during MPTCP syncookie processing. This is a functional change in the core MPTCP logic that is reachable and should be fuzzed.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
  even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).
- Code in vendor-specific PCIe switch, SmartNIC, or GPU drivers (e.g., mlxsw, pds_core, qed,
  ionic, amdgpu) that require physical PCIe hardware cards not emulated in standard QEMU.
- Driver .remove, .shutdown, or pci_unregister_driver teardown callbacks (e.g., igb_remove)
  that are executed only during PCI hot-unplug or sysfs driver unbind operations.

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
   Prefer non-static, non-inlined API entrypoint functions over internal static helper functions
   (which are inlined by the compiler and do not have distinct symbol addresses).
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Also check "depends on" lines in Kconfig to include any non-standard parent subsystem configs
   needed for Kbuild to compile the code statically into vmlinux. List them in the EnableConfigs
   output array, and DO NOT add a '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.

For your convenience, here is the diff of the changes:
commit a80a630c666666b8d4cce7e791d4e8023ab25fcd
Author: syz-cluster <triage@syzkaller.com>
Date:   Sat Aug 15 12:30:29 2026 +0000

    syz-cluster: applied patch under review

diff --git a/net/mptcp/syncookies.c b/net/mptcp/syncookies.c
index 7f22526346a7e..b5cac57011221 100644
--- a/net/mptcp/syncookies.c
+++ b/net/mptcp/syncookies.c
@@ -118,6 +118,7 @@ bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subfl
 	subflow_req->local_nonce = e->local_nonce;
 	subflow_req->backup = e->backup;
 	subflow_req->remote_id = e->join_id;
+	subflow_req->local_id = e->local_id;
 	subflow_req->token = e->token;
 	subflow_req->msk = msk;
 	spin_unlock_bh(&join_entry_locks[i]);

gemini-3.1-pro-preview

null

null

							input: 2031
							output: 44
							thoughts: 89
						

Here's my summary, as though I'm thinking through this patch:

**Analyzing a Netfilter MPTCP Patch**

Okay, I'm looking at this patch for `net/mptcp/syncookies.c`. It's pretty straightforward – it seems to add `subflow_req->local_id = e->local_id;` within the `mptcp_token_join_cookie_init_state` function. My immediate thought is, "Okay, why are we doing this?". I need to understand the context. So, I need to really dig into `mptcp_token_join_cookie_init_state` itself. What’s the purpose of this function in the first place? And what is `subflow_req`? Is it an established data structure or an instance? And how does `e` relate to `local_id`? What kind of value are we dealing with? I'll probably need to understand the larger handshake process to which this cookie initialization is related to fully grasp the change. What part of the MPTCP handshake is being modified? Let's trace back where this `mptcp_token_join_cookie_init_state` is being called and see how `subflow_req` and `e` are used. This change likely has some impact on how we handle subflow join requests and their associated tokens, but I need to understand *exactly* what that impact is before I can assess the patch's merit. Is this a security fix, a performance optimization, or something else entirely? Time to dive into the code.

{
  "Expression": "mptcp_token_join_cookie_init_state",
  "PathPrefix": "net/mptcp/syncookies.c"
}

{
  "Output": "net/mptcp/syncookies.c=71=void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\n--\nnet/mptcp/syncookies.c-91- */\nnet/mptcp/syncookies.c:92:bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/syncookies.c-93-\t\t\t\t\tstruct sk_buff *skb)\n"
}

gemini-3.1-pro-preview

null

null

							input: 2656
							output: 38
							thoughts: 22
						

Here's a summary of my thought process, as if I were analyzing that function:

**Diving into `mptcp_token_join_cookie_init_state`**

Alright, let's get into the details of `mptcp_token_join_cookie_init_state`. My initial thought is to figure out precisely where this function sits within the larger MPTCP framework. What's its role, and what are its inputs and outputs? I'm already mentally running through the MPTCP connection establishment process. I'm guessing this function is involved in setting up or initializing some crucial state related to the join cookie and token mechanism. It's probably called during the handshake or when a new subflow is being established.

My immediate questions are:

*   What data structures is it modifying or populating? Are we talking about the MPTCP connection control block, the subflow's data, or some dedicated cookie-related structure?
*   What is the lifecycle of this state? Is it only initialized, or is it also updated or cleared later in the connection?
*   How does this initialization relate to the MPTCP's overall security and congestion control mechanisms?

I need to understand the function's internal logic. I'll need to examine the code to see if it's generating new cookies or tokens, or validating previously received ones. If I understand the underlying mechanics, it'll help me assess any potential vulnerabilities. I need to look for any potential areas for attacks.

{
  "File": "net/mptcp/syncookies.c",
  "FirstLine": 90,
  "LineCount": 40
}

{
  "Contents": "  90:\t * present in the cookie ACK mptcp option space will be checked later.\n  91:\t */\n  92:\tbool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\n  93:\t\t\t\t\t\tstruct sk_buff *skb)\n  94:\t{\n  95:\t\tstruct net *net = read_pnet(\u0026subflow_req-\u003esk.req.ireq_net);\n  96:\t\tu32 i = mptcp_join_entry_hash(skb, net);\n  97:\t\tstruct mptcp_sock *msk;\n  98:\t\tstruct join_entry *e;\n  99:\t\n 100:\t\te = \u0026join_entries[i];\n 101:\t\n 102:\t\tspin_lock_bh(\u0026join_entry_locks[i]);\n 103:\t\n 104:\t\tif (e-\u003evalid == 0) {\n 105:\t\t\tspin_unlock_bh(\u0026join_entry_locks[i]);\n 106:\t\t\treturn false;\n 107:\t\t}\n 108:\t\n 109:\t\te-\u003evalid = 0;\n 110:\t\n 111:\t\tmsk = mptcp_token_get_sock(net, e-\u003etoken);\n 112:\t\tif (!msk) {\n 113:\t\t\tspin_unlock_bh(\u0026join_entry_locks[i]);\n 114:\t\t\treturn false;\n 115:\t\t}\n 116:\t\n 117:\t\tsubflow_req-\u003eremote_nonce = e-\u003eremote_nonce;\n 118:\t\tsubflow_req-\u003elocal_nonce = e-\u003elocal_nonce;\n 119:\t\tsubflow_req-\u003ebackup = e-\u003ebackup;\n 120:\t\tsubflow_req-\u003eremote_id = e-\u003ejoin_id;\n 121:\t\tsubflow_req-\u003elocal_id = e-\u003elocal_id;\n 122:\t\tsubflow_req-\u003etoken = e-\u003etoken;\n 123:\t\tsubflow_req-\u003emsk = msk;\n 124:\t\tspin_unlock_bh(\u0026join_entry_locks[i]);\n 125:\t\treturn true;\n 126:\t}\n 127:\t\n 128:\tvoid __init mptcp_join_cookie_init(void)\n 129:\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 3662
							output: 32
							thoughts: 26
						

Okay, here's my summary, taking on the persona you requested:

**Assessing the MPTCP Syncookie Modification**

Alright, so this is about a functional change, a modification in how MPTCP syncookies work. My immediate reaction is, "Right, let's dive into the specifics." I need to see the configuration related to MPTCP. I need to understand exactly what parameters are being tweaked and how they're influencing the overall behavior. What are the potential performance implications? Any security ramifications? I'm going to have to check the config.

{
  "Expression": "config MPTCP",
  "PathPrefix": "net/mptcp/Kconfig"
}

{
  "Output": "net/mptcp/Kconfig-1-\nnet/mptcp/Kconfig:2:config MPTCP\nnet/mptcp/Kconfig-3-\tbool \"MPTCP: Multipath TCP\"\n--\nnet/mptcp/Kconfig=16=config INET_MPTCP_DIAG\n--\nnet/mptcp/Kconfig-19-\nnet/mptcp/Kconfig:20:config MPTCP_IPV6\nnet/mptcp/Kconfig-21-\tbool \"MPTCP: IPv6 support for Multipath TCP\"\n--\nnet/mptcp/Kconfig-24-\nnet/mptcp/Kconfig:25:config MPTCP_KUNIT_TEST\nnet/mptcp/Kconfig-26-\ttristate \"This builds the MPTCP KUnit tests\" if !KUNIT_ALL_TESTS\n"
}

gemini-3.1-pro-preview

null

null

							input: 4063
							output: 39
							thoughts: 43
						

Here's my summary, as though I'm thinking through this process:

**Diving into the MPTCP Token Handling**

Alright, the configuration in question is definitely `MPTCP`. Time to zero in on this `mptcp_token_join_cookie_init_state` function. My initial thought is to figure out its scope and dependencies. Let's see where it gets called from—what other parts of the MPTCP stack rely on its functionality? Understanding the call graph is always the first step for me to grasp its role within the larger picture. I need to trace its usage before I can understand its specific purpose and potential issues.

{
  "Expression": "mptcp_token_join_cookie_init_state",
  "PathPrefix": "net/mptcp/"
}

{
  "Output": "net/mptcp/protocol.h=1362=void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1363-\t\t\t\t       struct sk_buff *skb);\nnet/mptcp/protocol.h:1364:bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1365-\t\t\t\t\tstruct sk_buff *skb);\n--\nnet/mptcp/protocol.h=1371=static inline bool\nnet/mptcp/protocol.h:1372:mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1373-\t\t\t\t   struct sk_buff *skb)\n--\nnet/mptcp/subflow.c=263=int mptcp_subflow_init_cookie_req(struct request_sock *req,\n--\nnet/mptcp/subflow.c-289-\t} else if (opt_mp_join \u0026\u0026 listener-\u003erequest_mptcp) {\nnet/mptcp/subflow.c:290:\t\tif (!mptcp_token_join_cookie_init_state(subflow_req, skb))\nnet/mptcp/subflow.c-291-\t\t\treturn -EINVAL;\n--\nnet/mptcp/syncookies.c=71=void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\n--\nnet/mptcp/syncookies.c-91- */\nnet/mptcp/syncookies.c:92:bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/syncookies.c-93-\t\t\t\t\tstruct sk_buff *skb)\n"
}

gemini-3.1-pro-preview

null

null

							input: 4818
							output: 38
							thoughts: 37
						

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

**Analyzing the MPTCP Subflow Initialization**

Okay, so `mptcp_subflow_init_cookie_req` is the crucial function initiating the cookie request. I need to understand its behavior, as this is the starting point. Time to dive into the code for `mptcp_subflow_init_cookie_req` and see what it's doing. Let's see how it handles the initial handshake.

{
  "Expression": "mptcp_subflow_init_cookie_req",
  "PathPrefix": "net/mptcp/"
}

{
  "Output": "net/mptcp/subflow.c=147=static int subflow_check_req(struct request_sock *req,\n--\nnet/mptcp/subflow.c-262-\nnet/mptcp/subflow.c:263:int mptcp_subflow_init_cookie_req(struct request_sock *req,\nnet/mptcp/subflow.c-264-\t\t\t\t  const struct sock *sk_listener,\n--\nnet/mptcp/subflow.c-298-}\nnet/mptcp/subflow.c:299:EXPORT_SYMBOL_GPL(mptcp_subflow_init_cookie_req);\nnet/mptcp/subflow.c-300-\n"
}

gemini-3.1-pro-preview

null

null

							input: 5195
							output: 34
							thoughts: 27
						

Okay, here's my interpretation of those thoughts, framed as my own, given my expertise:

**Checking the Scope of `mptcp_subflow_init_cookie_req`**

Alright, let me think this through. The question is: is this `mptcp_subflow_init_cookie_req` function, the one dealing with initial cookie requests within MPTCP, called exclusively from other functions *within* the `net/mptcp/` directory, or does it have an external interface, i.e., is it invoked from outside that specific module? I'm trying to pinpoint its boundaries. This is important for understanding the function's dependencies, potential side effects, and how tightly coupled it is to the rest of the MPTCP implementation. Knowing if external code directly calls this could impact how I approach any modifications or debugging. I need to know the calling context. Let me trace the calls and do some cross-referencing.

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

{
  "Output": "net/ipv4/syncookies.c=263=static int cookie_tcp_reqsk_init(struct sock *sk, struct sk_buff *skb,\n--\nnet/ipv4/syncookies.c-294-\tif (treq-\u003eis_mptcp)\nnet/ipv4/syncookies.c:295:\t\treturn mptcp_subflow_init_cookie_req(req, sk, skb);\nnet/ipv4/syncookies.c-296-#endif\n--\nnet/mptcp/subflow.c=147=static int subflow_check_req(struct request_sock *req,\n--\nnet/mptcp/subflow.c-262-\nnet/mptcp/subflow.c:263:int mptcp_subflow_init_cookie_req(struct request_sock *req,\nnet/mptcp/subflow.c-264-\t\t\t\t  const struct sock *sk_listener,\n--\nnet/mptcp/subflow.c-298-}\nnet/mptcp/subflow.c:299:EXPORT_SYMBOL_GPL(mptcp_subflow_init_cookie_req);\nnet/mptcp/subflow.c-300-\n"
}

gemini-3.1-pro-preview

null

null

							input: 5781
							output: 130
							thoughts: 212
						

**Analyzing the MPTCP Token Join Cookie Initialization**

Okay, so I'm looking at `net/ipv4/syncookies.c`. I've honed in on `mptcp_subflow_init_cookie_req` and `mptcp_token_join_cookie_init_state` as the key functions to examine here. The relevant config is `MPTCP`, which I'll keep in mind.

First, I need to confirm something about `mptcp_token_join_cookie_init_state`. I need to check if it's static or global. Ah, it's not static; it's exported, so it's globally accessible. I'm looking at the function signature now: `bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req, struct sk_buff *skb)`.

Right, the core of this patch is addressing a missing initialization issue. It seems `subflow_req->local_id` wasn't being initialized in `mptcp_token_join_cookie_init_state`. This is a clear functional change, so I'll need to assess the implications of that.

Now, let's verify if any other configurations are needed. It seems `MPTCP` is the only relevant config.

Alright, I think I have a good grasp of the change. I'm ready to document my findings.

{
  "EnableConfigs": [
    "MPTCP"
  ],
  "FocusSymbols": [
    "mptcp_token_join_cookie_init_state",
    "mptcp_subflow_init_cookie_req"
  ],
  "Reasoning": "The patch fixes missing initialization of `subflow_req-\u003elocal_id` in `mptcp_token_join_cookie_init_state` which is called during MPTCP syncookie processing. This is a functional change in the core MPTCP logic that is reachable and should be fuzzed.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "MPTCP"
  ],
  "FocusSymbols": [
    "mptcp_token_join_cookie_init_state",
    "mptcp_subflow_init_cookie_req"
  ],
  "Reasoning": "The patch fixes missing initialization of `subflow_req-\u003elocal_id` in `mptcp_token_join_cookie_init_state` which is called during MPTCP syncookie processing. This is a functional change in the core MPTCP logic that is reachable and should be fuzzed.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

best-expensive

null

{
  "KMSANReasoning": "The patch adds an assignment to `subflow_req-\u003elocal_id` in `mptcp_token_join_cookie_init_state()`. `subflow_req` is a `struct mptcp_subflow_request_sock`, which is allocated via `reqsk_alloc()`. The `reqsk_alloc()` function allocates memory from a slab cache without the `__GFP_ZERO` flag, meaning the memory is uninitialized.\n\nWhile `subflow_init_req()` initializes several fields of the request socket, it does not initialize `local_id`. During a SYN cookie MP_JOIN, `mptcp_token_join_cookie_init_state()` is called to reconstruct the request socket state from the cookie. Before this patch, it failed to restore `local_id`, leaving `subflow_req-\u003elocal_id` uninitialized.\n\nThis uninitialized 1-byte value is later copied to the subflow context (`new_ctx-\u003elocal_id`) in `subflow_ulp_clone()`. From there, the uninitialized kernel heap memory can be leaked to userspace via Netlink (e.g., `MPTCP_SUBFLOW_ATTR_ID_LOC` in `subflow_get_info()`) or sent over the network in MPTCP TCP options.\n\nStandard KASAN does not detect reads of uninitialized memory; it only detects out-of-bounds accesses and use-after-free bugs. KMSAN is specifically designed to detect uninitialized memory uses and info-leaks. Therefore, a dedicated KMSAN fuzzing session is required to catch this and similar bugs.",
  "NeedsKMSAN": true
}

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.

For your convenience, here is the diff of the changes:
commit a80a630c666666b8d4cce7e791d4e8023ab25fcd
Author: syz-cluster <triage@syzkaller.com>
Date:   Sat Aug 15 12:30:29 2026 +0000

    syz-cluster: applied patch under review

diff --git a/net/mptcp/syncookies.c b/net/mptcp/syncookies.c
index 7f22526346a7e..b5cac57011221 100644
--- a/net/mptcp/syncookies.c
+++ b/net/mptcp/syncookies.c
@@ -118,6 +118,7 @@ bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subfl
 	subflow_req->local_nonce = e->local_nonce;
 	subflow_req->backup = e->backup;
 	subflow_req->remote_id = e->join_id;
+	subflow_req->local_id = e->local_id;
 	subflow_req->token = e->token;
 	subflow_req->msk = msk;
 	spin_unlock_bh(&join_entry_locks[i]);

gemini-3.1-pro-preview

null

null

							input: 2028
							output: 35
							thoughts: 218
						

**Analyzing the MPTCP Token Join Cookie Initialization Patch**

Okay, so I'm looking at this patch that adds `subflow_req->local_id = e->local_id;` to the `mptcp_token_join_cookie_init_state` function within `net/mptcp/syncookies.c`. My initial reaction is to immediately dive into the context to understand the implications. The patch itself is simple, just an assignment within the `mptcp_token_join_cookie_init_state` function, assigning a value from `e->local_id` to `subflow_req->local_id`.

My immediate concern, as always, is whether we're introducing a risk of uninitialized memory being copied around. I need to understand the source and destination of this assignment. I need to verify what `subflow_req` and `e` actually *are*. I know they're both likely structures, pointers in this context, so I need to check the definitions of `struct mptcp_subflow_request_sock` and `struct join_entry`.

Right, `subflow_req` is a pointer to `struct mptcp_subflow_request_sock`, and `e` is a pointer to `struct join_entry`. Now the crucial question is, is `e->local_id` guaranteed to be initialized before this assignment? If not, we could potentially be copying uninitialized data, which is a classic recipe for undefined behavior and potential security issues. Time to dig into the surrounding code in `net/mptcp/syncookies.c` to see how these structures are populated and where `e->local_id` gets its value. I need to trace back from this point to ensure that the variable is properly initialized.

{
  "Expression": "struct join_entry",
  "PathPrefix": "net/mptcp/syncookies.c"
}

{
  "Output": "net/mptcp/syncookies.c-22-\nnet/mptcp/syncookies.c:23:struct join_entry {\nnet/mptcp/syncookies.c-24-\tu32 token;\n--\nnet/mptcp/syncookies.c-34-\nnet/mptcp/syncookies.c:35:static struct join_entry join_entries[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;\nnet/mptcp/syncookies.c-36-static spinlock_t join_entry_locks[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;\n--\nnet/mptcp/syncookies.c=38=static u32 mptcp_join_entry_hash(struct sk_buff *skb, struct net *net)\n--\nnet/mptcp/syncookies.c-58-\nnet/mptcp/syncookies.c:59:static void mptcp_join_store_state(struct join_entry *entry,\nnet/mptcp/syncookies.c-60-\t\t\t\t   const struct mptcp_subflow_request_sock *subflow_req)\n--\nnet/mptcp/syncookies.c=92=bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\n--\nnet/mptcp/syncookies.c-97-\tstruct mptcp_sock *msk;\nnet/mptcp/syncookies.c:98:\tstruct join_entry *e;\nnet/mptcp/syncookies.c-99-\n"
}

gemini-3.1-pro-preview

null

null

							input: 3092
							output: 38
							thoughts: 12
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Diving into the `join_entry` Structure**

Okay, time to get my hands dirty. I'm going to start by taking a close look at the `struct join_entry` definition. It's the lynchpin for how joins are handled, so understanding its components is critical. I need to be sure I have a solid grasp of its fields and how they relate to the overall join operation. I'm thinking about memory layout, any potential alignment issues, and how the various fields contribute to efficient lookups and comparisons. This definition is going to dictate a lot about performance and scalability, so a deep understanding is essential before I move forward.

{
  "File": "net/mptcp/syncookies.c",
  "FirstLine": 20,
  "LineCount": 20
}

{
  "Contents": "  20:\t * when the TCP ACK passed the cookie validation check.\n  21:\t */\n  22:\t\n  23:\tstruct join_entry {\n  24:\t\tu32 token;\n  25:\t\tu32 remote_nonce;\n  26:\t\tu32 local_nonce;\n  27:\t\tu8 join_id;\n  28:\t\tu8 local_id;\n  29:\t\tu8 backup;\n  30:\t\tu8 valid;\n  31:\t};\n  32:\t\n  33:\t#define COOKIE_JOIN_SLOTS\t1024\n  34:\t\n  35:\tstatic struct join_entry join_entries[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;\n  36:\tstatic spinlock_t join_entry_locks[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;\n  37:\t\n  38:\tstatic u32 mptcp_join_entry_hash(struct sk_buff *skb, struct net *net)\n  39:\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 3585
							output: 38
							thoughts: 33
						

Okay, here's my take on those thoughts, framed as my own:

**Initial Assessment of `join_entries` and Focus on `mptcp_join_store_state`**

Alright, so `join_entries` is a global array, meaning its contents are automatically zero-initialized at the start. That's good to know – prevents some unexpected values from popping up in the initial state, which is a common cause of hard-to-debug issues. Now, I should double-check the logic that manages it, but before I dig too deep, let's turn our attention to `mptcp_join_store_state` specifically. It's the core state management for the joining process, and I need to verify that it interacts with `join_entries` correctly. The initialization of the state looks important. Let's see what is involved.

{
  "File": "net/mptcp/syncookies.c",
  "FirstLine": 58,
  "LineCount": 30
}

{
  "Contents": "  58:\t\n  59:\tstatic void mptcp_join_store_state(struct join_entry *entry,\n  60:\t\t\t\t\t   const struct mptcp_subflow_request_sock *subflow_req)\n  61:\t{\n  62:\t\tentry-\u003etoken = subflow_req-\u003etoken;\n  63:\t\tentry-\u003eremote_nonce = subflow_req-\u003eremote_nonce;\n  64:\t\tentry-\u003elocal_nonce = subflow_req-\u003elocal_nonce;\n  65:\t\tentry-\u003ebackup = subflow_req-\u003ebackup;\n  66:\t\tentry-\u003ejoin_id = subflow_req-\u003eremote_id;\n  67:\t\tentry-\u003elocal_id = subflow_req-\u003elocal_id;\n  68:\t\tentry-\u003evalid = 1;\n  69:\t}\n  70:\t\n  71:\tvoid subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\n  72:\t\t\t\t\t       struct sk_buff *skb)\n  73:\t{\n  74:\t\tstruct net *net = read_pnet(\u0026subflow_req-\u003esk.req.ireq_net);\n  75:\t\tu32 i = mptcp_join_entry_hash(skb, net);\n  76:\t\n  77:\t\t/* No use in waiting if other cpu is already using this slot --\n  78:\t\t * would overwrite the data that got stored.\n  79:\t\t */\n  80:\t\tspin_lock_bh(\u0026join_entry_locks[i]);\n  81:\t\tmptcp_join_store_state(\u0026join_entries[i], subflow_req);\n  82:\t\tspin_unlock_bh(\u0026join_entry_locks[i]);\n  83:\t}\n  84:\t\n  85:\t/* Called for a cookie-ack with MP_JOIN option present.\n  86:\t * Look up the saved state based on skb hash \u0026 check token matches msk\n  87:\t * in same netns.\n"
}

gemini-3.1-pro-preview

null

null

							input: 4359
							output: 38
							thoughts: 56
						

Here's my take on those thoughts:

**Analyzing the MPTCP Token Join Cookie Initialization**

Okay, so this patch is introducing a change within `mptcp_token_join_cookie_init_state`. The key addition is `subflow_req->local_id = e->local_id;`. I need to understand the implications here. My initial thought is that we're essentially linking the `local_id` from some element `e` to the `subflow_req` structure during the token join cookie initialization. This suggests a direct mapping or association is being created. I have to look deeper into what `e` represents and what the `subflow_req` context is to determine the *why*. Is it setting up a per-subflow context, associating a local identifier with the state? Is there a subtle impact on concurrency or the way we're handling identifiers? Let me check how `mptcp_token_join_cookie_init_state` is actually used and what `e` and `subflow_req` are defined as to determine its impact.

{
  "File": "net/mptcp/syncookies.c",
  "FirstLine": 92,
  "LineCount": 40
}

{
  "Contents": "  92:\tbool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\n  93:\t\t\t\t\t\tstruct sk_buff *skb)\n  94:\t{\n  95:\t\tstruct net *net = read_pnet(\u0026subflow_req-\u003esk.req.ireq_net);\n  96:\t\tu32 i = mptcp_join_entry_hash(skb, net);\n  97:\t\tstruct mptcp_sock *msk;\n  98:\t\tstruct join_entry *e;\n  99:\t\n 100:\t\te = \u0026join_entries[i];\n 101:\t\n 102:\t\tspin_lock_bh(\u0026join_entry_locks[i]);\n 103:\t\n 104:\t\tif (e-\u003evalid == 0) {\n 105:\t\t\tspin_unlock_bh(\u0026join_entry_locks[i]);\n 106:\t\t\treturn false;\n 107:\t\t}\n 108:\t\n 109:\t\te-\u003evalid = 0;\n 110:\t\n 111:\t\tmsk = mptcp_token_get_sock(net, e-\u003etoken);\n 112:\t\tif (!msk) {\n 113:\t\t\tspin_unlock_bh(\u0026join_entry_locks[i]);\n 114:\t\t\treturn false;\n 115:\t\t}\n 116:\t\n 117:\t\tsubflow_req-\u003eremote_nonce = e-\u003eremote_nonce;\n 118:\t\tsubflow_req-\u003elocal_nonce = e-\u003elocal_nonce;\n 119:\t\tsubflow_req-\u003ebackup = e-\u003ebackup;\n 120:\t\tsubflow_req-\u003eremote_id = e-\u003ejoin_id;\n 121:\t\tsubflow_req-\u003elocal_id = e-\u003elocal_id;\n 122:\t\tsubflow_req-\u003etoken = e-\u003etoken;\n 123:\t\tsubflow_req-\u003emsk = msk;\n 124:\t\tspin_unlock_bh(\u0026join_entry_locks[i]);\n 125:\t\treturn true;\n 126:\t}\n 127:\t\n 128:\tvoid __init mptcp_join_cookie_init(void)\n 129:\t{\n 130:\t\tint i;\n 131:\t\n"
}

gemini-3.1-pro-preview

null

null

							input: 5298
							output: 33
							thoughts: 254
						

**Analyzing the Patch for Potential Memory Issues**

Okay, so this patch is straightforward enough. It seems like it's restoring `local_id` from the `join_entry` struct to `subflow_req->local_id`. The crucial part is that `e->local_id` was initially set using `subflow_req->local_id` via `mptcp_join_store_state`. My immediate thought is, "Is there a risk of using uninitialized memory here?" We're dealing with global array `join_entries`, which is zero-initialized, so that's not a concern. And `subflow_req`? It's part of a request socket, `struct mptcp_subflow_request_sock`. This patch is basically just copying a value that was previously assigned.

The potential issue I see is if `local_id` *wasn't* restored. What would it be? Zero? Uninitialized garbage? If we didn't restore it, whatever was in memory at the time `subflow_req` was allocated is what we'd be using later. That could be problematic. But wait, typically, request sockets are zeroed or initialized upon allocation. So it's probably *not* an issue.

To be absolutely sure, let's take a look at where `mptcp_token_join_cookie_init_state` is called and how the `subflow_req` is created. That should give me the final answer.

{
  "Expression": "mptcp_token_join_cookie_init_state",
  "PathPrefix": ""
}

{
  "Output": "net/mptcp/protocol.h=1362=void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1363-\t\t\t\t       struct sk_buff *skb);\nnet/mptcp/protocol.h:1364:bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1365-\t\t\t\t\tstruct sk_buff *skb);\n--\nnet/mptcp/protocol.h=1371=static inline bool\nnet/mptcp/protocol.h:1372:mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1373-\t\t\t\t   struct sk_buff *skb)\n--\nnet/mptcp/subflow.c=263=int mptcp_subflow_init_cookie_req(struct request_sock *req,\n--\nnet/mptcp/subflow.c-289-\t} else if (opt_mp_join \u0026\u0026 listener-\u003erequest_mptcp) {\nnet/mptcp/subflow.c:290:\t\tif (!mptcp_token_join_cookie_init_state(subflow_req, skb))\nnet/mptcp/subflow.c-291-\t\t\treturn -EINVAL;\n--\nnet/mptcp/syncookies.c=71=void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\n--\nnet/mptcp/syncookies.c-91- */\nnet/mptcp/syncookies.c:92:bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/syncookies.c-93-\t\t\t\t\tstruct sk_buff *skb)\n"
}

gemini-3.1-pro-preview

null

null

							input: 6441
							output: 38
							thoughts: 18
						

Okay, let's dive into this. Here's how I'd approach summarizing the "thoughts" as my own, given my expertise:

**Checking `mptcp_subflow_init_cookie_req`**

Right, so the system is telling me to check `mptcp_subflow_init_cookie_req`. That likely means there's something interesting happening related to the initialization of a Multipath TCP (MPTCP) subflow, specifically regarding the cookie request mechanism. Given the name, I'm immediately thinking about how the initiating endpoint of a subflow is handling the initial cookie exchange with the peer. We know the cookie is fundamental for MPTCP security and subflow identification, so problems there are going to quickly become catastrophic for MPTCP operation. I'll need to look at:

*   **The context**: Where is this function being called from? Is it during the initial connection setup, a re-establishment attempt, or something else entirely? The surrounding code will provide crucial clues.
*   **The input data**: What parameters are being passed to `mptcp_subflow_init_cookie_req`? That will tell me what the initiator is attempting to communicate to the other side, and what details are pertinent. I'm especially interested in the format and validity of the cookie data (if any).
*   **The function logic**: What steps does this function take? How does it generate/handle/validate the cookie request? Are there any obvious security vulnerabilities here (e.g., weak pseudo-random number generator, improper handling of buffer overflows, uninitialized variables)?
*   **The error handling**: What happens if the cookie request fails? Are there appropriate fallback mechanisms or error messages? Are potential errors being logged adequately for debugging? Is the function resilient to malicious attempts to corrupt the data?
*   **Performance aspects**: Is this a performance bottleneck? Are there opportunities for optimization? This is a core part of subflow initialization so slow initial setup could be detrimental to the performance of MPTCP.
*   **Security implications**: Are there any potential vulnerabilities, such as a malicious actor being able to manipulate the subflow cookie.

In summary, I expect this `mptcp_subflow_init_cookie_req` is a vital piece of the MPTCP puzzle, so I'll need to understand it thoroughly, in all of its aspects, to identify any potential bugs, vulnerabilities, or areas for improvement.

{
  "File": "net/mptcp/subflow.c",
  "FirstLine": 263,
  "LineCount": 40
}

{
  "Contents": " 263:\tint mptcp_subflow_init_cookie_req(struct request_sock *req,\n 264:\t\t\t\t\t  const struct sock *sk_listener,\n 265:\t\t\t\t\t  struct sk_buff *skb)\n 266:\t{\n 267:\t\tstruct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);\n 268:\t\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\n 269:\t\tstruct mptcp_options_received mp_opt;\n 270:\t\tbool opt_mp_capable, opt_mp_join;\n 271:\t\tint err;\n 272:\t\n 273:\t\tsubflow_init_req(req, sk_listener);\n 274:\t\tmptcp_get_options(skb, \u0026mp_opt);\n 275:\t\n 276:\t\topt_mp_capable = !!(mp_opt.suboptions \u0026 OPTION_MPTCP_MPC_ACK);\n 277:\t\topt_mp_join = !!(mp_opt.suboptions \u0026 OPTION_MPTCP_MPJ_ACK);\n 278:\t\tif (opt_mp_capable \u0026\u0026 listener-\u003erequest_mptcp) {\n 279:\t\t\tif (mp_opt.sndr_key == 0)\n 280:\t\t\t\treturn -EINVAL;\n 281:\t\n 282:\t\t\tsubflow_req-\u003elocal_key = mp_opt.rcvr_key;\n 283:\t\t\terr = mptcp_token_new_request(req);\n 284:\t\t\tif (err)\n 285:\t\t\t\treturn err;\n 286:\t\n 287:\t\t\tsubflow_req-\u003emp_capable = 1;\n 288:\t\t\tsubflow_req-\u003essn_offset = TCP_SKB_CB(skb)-\u003eseq - 1;\n 289:\t\t} else if (opt_mp_join \u0026\u0026 listener-\u003erequest_mptcp) {\n 290:\t\t\tif (!mptcp_token_join_cookie_init_state(subflow_req, skb))\n 291:\t\t\t\treturn -EINVAL;\n 292:\t\n 293:\t\t\tsubflow_req-\u003emp_join = 1;\n 294:\t\t\tsubflow_req-\u003essn_offset = TCP_SKB_CB(skb)-\u003eseq - 1;\n 295:\t\t}\n 296:\t\n 297:\t\treturn 0;\n 298:\t}\n 299:\tEXPORT_SYMBOL_GPL(mptcp_subflow_init_cookie_req);\n 300:\t\n 301:\tstatic enum sk_rst_reason mptcp_get_rst_reason(const struct sk_buff *skb)\n 302:\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 7759
							output: 36
							thoughts: 21
						

Here's my summary, as though I'm thinking through this process:

**Diving into Subflow Initialization**

Okay, so we're starting this subflow. The first thing I need to confirm is how the `subflow_init_req` interacts with and initializes the core `subflow_req`. Let's dig in and make sure that setup is clean and efficient. I need to understand how the foundational request is being formed.

{
  "Expression": "subflow_init_req",
  "PathPrefix": "net/mptcp/subflow.c"
}

{
  "Output": "net/mptcp/subflow.c=85=static struct mptcp_sock *subflow_token_join_request(struct request_sock *req)\n--\nnet/mptcp/subflow.c-107-\nnet/mptcp/subflow.c:108:static void subflow_init_req(struct request_sock *req, const struct sock *sk_listener)\nnet/mptcp/subflow.c-109-{\n--\nnet/mptcp/subflow.c=147=static int subflow_check_req(struct request_sock *req,\n--\nnet/mptcp/subflow.c-252-\nnet/mptcp/subflow.c:253:\t\t\tsubflow_init_req_cookie_join_save(subflow_req, skb);\nnet/mptcp/subflow.c-254-\t\t}\n--\nnet/mptcp/subflow.c=263=int mptcp_subflow_init_cookie_req(struct request_sock *req,\n--\nnet/mptcp/subflow.c-272-\nnet/mptcp/subflow.c:273:\tsubflow_init_req(req, sk_listener);\nnet/mptcp/subflow.c-274-\tmptcp_get_options(skb, \u0026mp_opt);\n--\nnet/mptcp/subflow.c=311=static struct dst_entry *subflow_v4_route_req(const struct sock *sk,\n--\nnet/mptcp/subflow.c-320-\ttcp_rsk(req)-\u003eis_mptcp = 1;\nnet/mptcp/subflow.c:321:\tsubflow_init_req(req, sk);\nnet/mptcp/subflow.c-322-\n--\nnet/mptcp/subflow.c=380=static struct dst_entry *subflow_v6_route_req(const struct sock *sk,\n--\nnet/mptcp/subflow.c-389-\ttcp_rsk(req)-\u003eis_mptcp = 1;\nnet/mptcp/subflow.c:390:\tsubflow_init_req(req, sk);\nnet/mptcp/subflow.c-391-\n"
}

gemini-3.1-pro-preview

null

null

							input: 8502
							output: 38
							thoughts: 12
						

Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:

**Analyzing the Initialization Request**

Alright, time to get down to brass tacks. My initial thought process is always methodical, and right now, I'm zeroing in on `subflow_init_req`. That specific request structure is the cornerstone of how our subflows are launched, and understanding its contents is crucial. What are the key parameters being passed? Are there any potential vulnerabilities I should be aware of, perhaps related to data sanitization or access control? Is the request fully compliant with the protocol we've defined? The devil, as they say, is in the details. I need to quickly ascertain the intended usage to ensure its operation aligns with the broader architecture, without exposing any weaknesses. This is where I start. Let's see what we've got.

{
  "File": "net/mptcp/subflow.c",
  "FirstLine": 108,
  "LineCount": 20
}

{
  "Contents": " 108:\tstatic void subflow_init_req(struct request_sock *req, const struct sock *sk_listener)\n 109:\t{\n 110:\t\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\n 111:\t\n 112:\t\tsubflow_req-\u003emp_capable = 0;\n 113:\t\tsubflow_req-\u003emp_join = 0;\n 114:\t\tsubflow_req-\u003ecsum_reqd = mptcp_is_checksum_enabled(sock_net(sk_listener));\n 115:\t\tsubflow_req-\u003eallow_join_id0 = mptcp_allow_join_id0(sock_net(sk_listener));\n 116:\t\tsubflow_req-\u003emsk = NULL;\n 117:\t\tmptcp_token_init_request(req);\n 118:\t}\n 119:\t\n 120:\tstatic bool subflow_use_different_sport(struct mptcp_sock *msk, const struct sock *sk)\n 121:\t{\n 122:\t\treturn inet_sk(sk)-\u003einet_sport != inet_sk((struct sock *)msk)-\u003einet_sport;\n 123:\t}\n 124:\t\n 125:\tstatic void subflow_add_reset_reason(struct sk_buff *skb, u8 reason)\n 126:\t{\n 127:\t\tstruct mptcp_ext *mpext = skb_ext_add(skb, SKB_EXT_MPTCP);\n"
}

gemini-3.1-pro-preview

null

null

							input: 9155
							output: 33
							thoughts: 63
						

**Initial Thoughts on Subflow Initialization**

Okay, so `subflow_init_req` is the starting point here. I see it's explicitly clearing the fields like `mp_capable`, `mp_join`, and `msk`. That makes sense; it's a clean slate for the subflow. But hold on... it *doesn't* zero `local_id`. That's a point of potential confusion. We need to be aware of how that's handled later on. It could be important. And, if I remember correctly, the `struct request_sock` isn't just hanging out; it's being allocated through `reqsk_alloc`. Right. Let's make sure that allocation and initialization are happening as we expect. Time to dive into `reqsk_alloc` and see how it's setting things up. This is a critical point for understanding the subflow's lifecycle.

no matches

{
  "Expression": "reqsk_alloc",
  "PathPrefix": "net/core/request_sock.c"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 9459
							output: 26
							thoughts: 15
						

Here's my summary, as though I'm thinking through this process:

**Diving into the `net/` directory, specifically `reqsk_alloc`**

Okay, I need to get a handle on what's going on with this request socket allocation. Since I'm knee-deep in networking, it's pretty clear where I should start - the `net/` directory is where the core network stack resides. Now, let's zero in on `reqsk_alloc`. This function's name alone hints it is responsible for allocating resources for request sockets – that is, for the initial handshake of a connection. I'll need to remember this because, likely, this function is critical for all incoming connection requests. I'll be looking to understand the mechanics of resource allocation, any initialization happening, how it interacts with other networking structures, and, critically, potential areas for optimization or security vulnerabilities. It's time to dive into the code.

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

{
  "Output": "net/core/filter.c=12346=__bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __sk_buff *s, struct sock *sk,\n--\nnet/core/filter.c-12410-\nnet/core/filter.c:12411:\treq = inet_reqsk_alloc(ops, sk, false);\nnet/core/filter.c-12412-\tif (!req)\n--\nnet/ipv4/inet_connection_sock.c=849=static struct request_sock *\nnet/ipv4/inet_connection_sock.c:850:reqsk_alloc_noprof(const struct request_sock_ops *ops, struct sock *sk_listener,\nnet/ipv4/inet_connection_sock.c-851-\t\t   bool attach_listener)\n--\nnet/ipv4/inet_connection_sock.c-878-}\nnet/ipv4/inet_connection_sock.c:879:#define reqsk_alloc(...)\talloc_hooks(reqsk_alloc_noprof(__VA_ARGS__))\nnet/ipv4/inet_connection_sock.c-880-\nnet/ipv4/inet_connection_sock.c:881:struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,\nnet/ipv4/inet_connection_sock.c-882-\t\t\t\t      struct sock *sk_listener,\n--\nnet/ipv4/inet_connection_sock.c-884-{\nnet/ipv4/inet_connection_sock.c:885:\tstruct request_sock *req = reqsk_alloc(ops, sk_listener,\nnet/ipv4/inet_connection_sock.c-886-\t\t\t\t\t       attach_listener);\n--\nnet/ipv4/syncookies.c=302=struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb)\n--\nnet/ipv4/syncookies.c-317-\nnet/ipv4/syncookies.c:318:struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,\nnet/ipv4/syncookies.c-319-\t\t\t\t\t    struct sock *sk, struct sk_buff *skb,\n--\nnet/ipv4/syncookies.c-327-\tif (sk_is_mptcp(sk))\nnet/ipv4/syncookies.c:328:\t\treq = mptcp_subflow_reqsk_alloc(ops, sk, false);\nnet/ipv4/syncookies.c-329-\telse\nnet/ipv4/syncookies.c:330:\t\treq = inet_reqsk_alloc(ops, sk, false);\nnet/ipv4/syncookies.c-331-\n--\nnet/ipv4/syncookies.c=358=static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk,\n--\nnet/ipv4/syncookies.c-394-\nnet/ipv4/syncookies.c:395:\treturn cookie_tcp_reqsk_alloc(\u0026tcp_request_sock_ops, sk, skb,\nnet/ipv4/syncookies.c-396-\t\t\t\t      \u0026tcp_opt, mss, tsoff);\n--\nnet/ipv4/tcp_input.c=7620=int tcp_conn_request(struct request_sock_ops *rsk_ops,\n--\nnet/ipv4/tcp_input.c-7660-\nnet/ipv4/tcp_input.c:7661:\treq = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);\nnet/ipv4/tcp_input.c-7662-\tif (!req)\n--\nnet/ipv6/syncookies.c=131=static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk,\n--\nnet/ipv6/syncookies.c-167-\nnet/ipv6/syncookies.c:168:\treturn cookie_tcp_reqsk_alloc(\u0026tcp6_request_sock_ops, sk, skb,\nnet/ipv6/syncookies.c-169-\t\t\t\t      \u0026tcp_opt, mss, tsoff);\n--\nnet/mptcp/subflow.c=725=static void subflow_v6_req_destructor(struct request_sock *req)\n--\nnet/mptcp/subflow.c-731-\nnet/mptcp/subflow.c:732:struct request_sock *mptcp_subflow_reqsk_alloc(const struct request_sock_ops *ops,\nnet/mptcp/subflow.c-733-\t\t\t\t\t       struct sock *sk_listener,\n--\nnet/mptcp/subflow.c-742-\nnet/mptcp/subflow.c:743:\treturn inet_reqsk_alloc(ops, sk_listener, attach_listener);\nnet/mptcp/subflow.c-744-}\nnet/mptcp/subflow.c:745:EXPORT_SYMBOL(mptcp_subflow_reqsk_alloc);\nnet/mptcp/subflow.c-746-\n"
}

gemini-3.1-pro-preview

null

null

							input: 11032
							output: 40
							thoughts: 29
						

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

**Diving into inet_connection_sock.c: A Deep Dive into Socket Allocation**

Okay, time to get down to brass tacks. I need to take a look at `reqsk_alloc_noprof` function. I know this function is in `net/ipv4/inet_connection_sock.c` and is instrumental in allocating request sockets, specifically those that aren't subject to the usual profiling overhead. Understanding its behavior is critical for performance analysis, especially in high-load scenarios where profiling can become a bottleneck. I want to see how it handles memory allocation, initialization, and any relevant flags or checks involved. This should provide insights into potential resource contention or optimization opportunities. Let's see what's actually going on under the hood.

{
  "File": "net/ipv4/inet_connection_sock.c",
  "FirstLine": 849,
  "LineCount": 30
}

{
  "Contents": " 849:\tstatic struct request_sock *\n 850:\treqsk_alloc_noprof(const struct request_sock_ops *ops, struct sock *sk_listener,\n 851:\t\t\t   bool attach_listener)\n 852:\t{\n 853:\t\tstruct request_sock *req;\n 854:\t\n 855:\t\treq = kmem_cache_alloc_noprof(ops-\u003eslab, GFP_ATOMIC | __GFP_NOWARN);\n 856:\t\tif (!req)\n 857:\t\t\treturn NULL;\n 858:\t\treq-\u003ersk_listener = NULL;\n 859:\t\tif (attach_listener) {\n 860:\t\t\tif (unlikely(!refcount_inc_not_zero(\u0026sk_listener-\u003esk_refcnt))) {\n 861:\t\t\t\tkmem_cache_free(ops-\u003eslab, req);\n 862:\t\t\t\treturn NULL;\n 863:\t\t\t}\n 864:\t\t\treq-\u003ersk_listener = sk_listener;\n 865:\t\t}\n 866:\t\treq-\u003ersk_ops = ops;\n 867:\t\treq_to_sk(req)-\u003esk_prot = sk_listener-\u003esk_prot;\n 868:\t\tsk_node_init(\u0026req_to_sk(req)-\u003esk_node);\n 869:\t\tsk_tx_queue_clear(req_to_sk(req));\n 870:\t\treq-\u003esaved_syn = NULL;\n 871:\t\treq-\u003esyncookie = 0;\n 872:\t\treq-\u003enum_timeout = 0;\n 873:\t\treq-\u003enum_retrans = 0;\n 874:\t\treq-\u003esk = NULL;\n 875:\t\trefcount_set(\u0026req-\u003ersk_refcnt, 0);\n 876:\t\n 877:\t\treturn req;\n 878:\t}\n"
}

gemini-3.1-pro-preview

null

null

							input: 11773
							output: 37
							thoughts: 93
						

Okay, here's my interpretation of this technical thought process, from an expert's perspective:

**Memory Allocation Concerns for MPTCP Subflow Request Sockets**

Alright, so I'm looking at how `reqsk_alloc_noprof` is handling memory allocation. The key here is that it's using `kmem_cache_alloc_noprof` from the slab allocator, specifically from `ops->slab`. The problem jumps out immediately: it's missing the `__GFP_ZERO` flag. That means the allocated memory *isn't* being zeroed out. This is a potential security vulnerability and can lead to unexpected behavior if uninitialized data is read.

Now, my focus shifts to the `mptcp_subflow_request_sock` structure. I know this is either embedded directly within, or allocated alongside, a `request_sock`. This is standard practice for association. I need to understand this structure to determine the impact of the potentially uninitialized memory. Let's dig into the definition of `struct mptcp_subflow_request_sock`...I want to understand what data it contains and how it's used. This could be critical.

{
  "Expression": "struct mptcp_subflow_request_sock",
  "PathPrefix": "net/mptcp/"
}

{
  "Output": "net/mptcp/options.c=946=bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,\n--\nnet/mptcp/options.c-948-{\nnet/mptcp/options.c:949:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/options.c-950-\n--\nnet/mptcp/protocol.c=3564=struct sock *mptcp_sk_clone_init(const struct sock *sk,\n--\nnet/mptcp/protocol.c-3568-{\nnet/mptcp/protocol.c:3569:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/protocol.c-3570-\tstruct sock *nsk = sk_clone_lock(sk, GFP_ATOMIC);\n--\nnet/mptcp/protocol.h=495=struct csum_pseudo_header {\n--\nnet/mptcp/protocol.h-501-\nnet/mptcp/protocol.h:502:struct mptcp_subflow_request_sock {\nnet/mptcp/protocol.h-503-\tstruct\ttcp_request_sock sk;\n--\nnet/mptcp/protocol.h-522-\nnet/mptcp/protocol.h:523:static inline struct mptcp_subflow_request_sock *\nnet/mptcp/protocol.h-524-mptcp_subflow_rsk(const struct request_sock *rsk)\nnet/mptcp/protocol.h-525-{\nnet/mptcp/protocol.h:526:\treturn (struct mptcp_subflow_request_sock *)rsk;\nnet/mptcp/protocol.h-527-}\n--\nnet/mptcp/protocol.h=1080=int mptcp_token_new_connect(struct sock *ssk);\nnet/mptcp/protocol.h:1081:void mptcp_token_accept(struct mptcp_subflow_request_sock *r,\nnet/mptcp/protocol.h-1082-\t\t\tstruct mptcp_sock *msk);\n--\nnet/mptcp/protocol.h=1353=static inline bool subflow_simultaneous_connect(struct sock *sk)\n--\nnet/mptcp/protocol.h-1361-#ifdef CONFIG_SYN_COOKIES\nnet/mptcp/protocol.h:1362:void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1363-\t\t\t\t       struct sk_buff *skb);\nnet/mptcp/protocol.h:1364:bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1365-\t\t\t\t\tstruct sk_buff *skb);\n--\nnet/mptcp/protocol.h=1368=static inline void\nnet/mptcp/protocol.h:1369:subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1370-\t\t\t\t  struct sk_buff *skb) {}\nnet/mptcp/protocol.h=1371=static inline bool\nnet/mptcp/protocol.h:1372:mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/protocol.h-1373-\t\t\t\t   struct sk_buff *skb)\n--\nnet/mptcp/subflow.c=38=static void subflow_req_destructor(struct request_sock *req)\nnet/mptcp/subflow.c-39-{\nnet/mptcp/subflow.c:40:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/subflow.c-41-\n--\nnet/mptcp/subflow.c=61=static bool mptcp_can_accept_new_subflow(const struct mptcp_sock *msk)\n--\nnet/mptcp/subflow.c-69-/* validate received token and create truncated hmac and nonce for SYN-ACK */\nnet/mptcp/subflow.c:70:static void subflow_req_create_thmac(struct mptcp_subflow_request_sock *subflow_req)\nnet/mptcp/subflow.c-71-{\n--\nnet/mptcp/subflow.c=85=static struct mptcp_sock *subflow_token_join_request(struct request_sock *req)\nnet/mptcp/subflow.c-86-{\nnet/mptcp/subflow.c:87:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/subflow.c-88-\tstruct mptcp_sock *msk;\n--\nnet/mptcp/subflow.c=108=static void subflow_init_req(struct request_sock *req, const struct sock *sk_listener)\nnet/mptcp/subflow.c-109-{\nnet/mptcp/subflow.c:110:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/subflow.c-111-\n--\nnet/mptcp/subflow.c=147=static int subflow_check_req(struct request_sock *req,\n--\nnet/mptcp/subflow.c-151-\tstruct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);\nnet/mptcp/subflow.c:152:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/subflow.c-153-\tstruct mptcp_options_received mp_opt;\n--\nnet/mptcp/subflow.c=263=int mptcp_subflow_init_cookie_req(struct request_sock *req,\n--\nnet/mptcp/subflow.c-267-\tstruct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);\nnet/mptcp/subflow.c:268:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/subflow.c-269-\tstruct mptcp_options_received mp_opt;\n--\nnet/mptcp/subflow.c=745=EXPORT_SYMBOL(mptcp_subflow_reqsk_alloc);\n--\nnet/mptcp/subflow.c-747-/* validate hmac received in third ACK */\nnet/mptcp/subflow.c:748:static bool subflow_hmac_valid(const struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/subflow.c-749-\t\t\t       const struct mptcp_options_received *mp_opt)\n--\nnet/mptcp/subflow.c=801=static struct sock *subflow_syn_recv_sock(const struct sock *sk,\n--\nnet/mptcp/subflow.c-810-\tstruct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk);\nnet/mptcp/subflow.c:811:\tstruct mptcp_subflow_request_sock *subflow_req;\nnet/mptcp/subflow.c-812-\tstruct mptcp_options_received mp_opt;\n--\nnet/mptcp/subflow.c=2030=static void subflow_ulp_clone(const struct request_sock *req,\n--\nnet/mptcp/subflow.c-2033-{\nnet/mptcp/subflow.c:2034:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/subflow.c-2035-\tstruct mptcp_subflow_context *old_ctx = mptcp_subflow_ctx(newsk);\n--\nnet/mptcp/subflow.c=2121=static int subflow_ops_init(struct request_sock_ops *subflow_ops)\nnet/mptcp/subflow.c-2122-{\nnet/mptcp/subflow.c:2123:\tsubflow_ops-\u003eobj_size = sizeof(struct mptcp_subflow_request_sock);\nnet/mptcp/subflow.c-2124-\n--\nnet/mptcp/subflow.c=2170=void __init mptcp_subflow_v6_init(void)\nnet/mptcp/subflow.c-2171-{\nnet/mptcp/subflow.c:2172:\t/* In struct mptcp_subflow_request_sock, we assume the TCP request sock\nnet/mptcp/subflow.c-2173-\t * structures for v4 and v6 have the same size. It should not changed in\n--\nnet/mptcp/syncookies.c=59=static void mptcp_join_store_state(struct join_entry *entry,\nnet/mptcp/syncookies.c:60:\t\t\t\t   const struct mptcp_subflow_request_sock *subflow_req)\nnet/mptcp/syncookies.c-61-{\n--\nnet/mptcp/syncookies.c-70-\nnet/mptcp/syncookies.c:71:void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/syncookies.c-72-\t\t\t\t       struct sk_buff *skb)\n--\nnet/mptcp/syncookies.c-91- */\nnet/mptcp/syncookies.c:92:bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\nnet/mptcp/syncookies.c-93-\t\t\t\t\tstruct sk_buff *skb)\n--\nnet/mptcp/token.c=48=static struct token_bucket *token_bucket(u32 token)\n--\nnet/mptcp/token.c-53-/* called with bucket lock held */\nnet/mptcp/token.c:54:static struct mptcp_subflow_request_sock *\nnet/mptcp/token.c-55-__token_lookup_req(struct token_bucket *t, u32 token)\nnet/mptcp/token.c-56-{\nnet/mptcp/token.c:57:\tstruct mptcp_subflow_request_sock *req;\nnet/mptcp/token.c-58-\tstruct hlist_nulls_node *pos;\n--\nnet/mptcp/token.c=108=int mptcp_token_new_request(struct request_sock *req)\nnet/mptcp/token.c-109-{\nnet/mptcp/token.c:110:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/token.c-111-\tstruct token_bucket *bucket;\n--\nnet/mptcp/token.c=151=int mptcp_token_new_connect(struct sock *ssk)\n--\nnet/mptcp/token.c-190- */\nnet/mptcp/token.c:191:void mptcp_token_accept(struct mptcp_subflow_request_sock *req,\nnet/mptcp/token.c-192-\t\t\tstruct mptcp_sock *msk)\nnet/mptcp/token.c-193-{\nnet/mptcp/token.c:194:\tstruct mptcp_subflow_request_sock *pos;\nnet/mptcp/token.c-195-\tstruct sock *sk = (struct sock *)msk;\n--\nnet/mptcp/token.c=352=void mptcp_token_destroy_request(struct request_sock *req)\nnet/mptcp/token.c-353-{\nnet/mptcp/token.c:354:\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\nnet/mptcp/token.c:355:\tstruct mptcp_subflow_request_sock *pos;\nnet/mptcp/token.c-356-\tstruct token_bucket *bucket;\n--\nnet/mptcp/token_test.c-5-\nnet/mptcp/token_test.c:6:static struct mptcp_subflow_request_sock *build_req_sock(struct kunit *test)\nnet/mptcp/token_test.c-7-{\nnet/mptcp/token_test.c:8:\tstruct mptcp_subflow_request_sock *req;\nnet/mptcp/token_test.c-9-\nnet/mptcp/token_test.c:10:\treq = kunit_kzalloc(test, sizeof(struct mptcp_subflow_request_sock),\nnet/mptcp/token_test.c-11-\t\t\t    GFP_USER);\n--\nnet/mptcp/token_test.c=18=static void mptcp_token_test_req_basic(struct kunit *test)\nnet/mptcp/token_test.c-19-{\nnet/mptcp/token_test.c:20:\tstruct mptcp_subflow_request_sock *req = build_req_sock(test);\nnet/mptcp/token_test.c-21-\tstruct mptcp_sock *null_msk = NULL;\n--\nnet/mptcp/token_test.c=94=static void mptcp_token_test_accept(struct kunit *test)\nnet/mptcp/token_test.c-95-{\nnet/mptcp/token_test.c:96:\tstruct mptcp_subflow_request_sock *req = build_req_sock(test);\nnet/mptcp/token_test.c-97-\tstruct mptcp_sock *msk = build_msk(test);\n--\nnet/mptcp/token_test.c=113=static void mptcp_token_test_destroyed(struct kunit *test)\nnet/mptcp/token_test.c-114-{\nnet/mptcp/token_test.c:115:\tstruct mptcp_subflow_request_sock *req = build_req_sock(test);\nnet/mptcp/token_test.c-116-\tstruct mptcp_sock *msk = build_msk(test);\n"
}

gemini-3.1-pro-preview

null

null

							input: 16076
							output: 37
							thoughts: 30
						

Okay, here's my take on those thoughts, framed as an expert's internal monologue:

**Diving into the mptcp_subflow_request_sock Structure**

Right, let's get down to brass tacks. I need to refresh my memory on the specifics of how MPTCP handles subflow requests. The `struct mptcp_subflow_request_sock` is where I should begin. I'll open up `net/mptcp/protocol.h`, it's the usual place for core MPTCP data structures, and it should contain the complete definition. I'm especially interested in remembering the fields, their purpose, and how they relate to the overall subflow establishment process. Understanding this structure is fundamental to troubleshooting and debugging subflow-related issues or optimizing the handshake in the MPTCP stack. Time to refresh my knowledge.

{
  "File": "net/mptcp/protocol.h",
  "FirstLine": 502,
  "LineCount": 20
}

{
  "Contents": " 502:\tstruct mptcp_subflow_request_sock {\n 503:\t\tstruct\ttcp_request_sock sk;\n 504:\t\tu16\tmp_capable : 1,\n 505:\t\t\tmp_join : 1,\n 506:\t\t\tbackup : 1,\n 507:\t\t\trequest_bkup : 1,\n 508:\t\t\tcsum_reqd : 1,\n 509:\t\t\tallow_join_id0 : 1;\n 510:\t\tu8\tlocal_id;\n 511:\t\tu8\tremote_id;\n 512:\t\tu64\tlocal_key;\n 513:\t\tu64\tidsn;\n 514:\t\tu32\ttoken;\n 515:\t\tu32\tssn_offset;\n 516:\t\tu64\tthmac;\n 517:\t\tu32\tlocal_nonce;\n 518:\t\tu32\tremote_nonce;\n 519:\t\tstruct mptcp_sock\t*msk;\n 520:\t\tstruct hlist_nulls_node token_node;\n 521:\t};\n"
}

gemini-3.1-pro-preview

null

null

							input: 16642
							output: 29
							thoughts: 338
						

**My Analysis of MPTCP Subflow Request Socket Initialization**

Okay, so I'm looking at how this `local_id` field within the `mptcp_subflow_request_sock` struct is initialized, and I'm seeing a potential issue. It's a `u8`, so a single byte, but its initialization is a bit scattered.

Initially, `reqsk_alloc` allocates the request socket, and crucially, it *doesn't* zero the memory. That means whatever garbage happened to be there before remains. Then `subflow_init_req` gets called, and it sets a few flags and some other fields like `mp_capable`, `mp_join`, and so on. But it *doesn't* touch `local_id`, nor `remote_id`, or `local_key`, and the rest. My Spidey senses are tingling.

Ah, but wait... there's `mptcp_subflow_init_cookie_req`. That's where SYN cookies get handled. If an `opt_mp_join` option is present, we call `mptcp_token_join_cookie_init_state`, and *that's* where we're supposed to initialize `local_id` along with things like `remote_nonce`, `local_nonce`, etc.

The critical thing, before the patch I'm examining, is that `local_id` *wasn't* being initialized inside `mptcp_token_join_cookie_init_state`. That means `subflow_req->local_id` would be uninitialized memory, right after the call to `reqsk_alloc_noprof` and this creates a security vulnerability. Now I need to see exactly where `local_id` is used, to understand what the implications are of this uninitialized memory. Where does this byte get accessed, and how? This patch better fix it!

{
  "Expression": "local_id",
  "PathPrefix": "net/mptcp/"
}

{
  "Output": "net/mptcp/diag.c=15=static int subflow_get_info(struct sock *sk, struct sk_buff *skb, bool net_admin)\n--\nnet/mptcp/diag.c-60-\t    nla_put_u8(skb, MPTCP_SUBFLOW_ATTR_ID_REM, sf-\u003eremote_id) ||\nnet/mptcp/diag.c:61:\t    nla_put_u8(skb, MPTCP_SUBFLOW_ATTR_ID_LOC, subflow_get_local_id(sf))) {\nnet/mptcp/diag.c-62-\t\terr = -EMSGSIZE;\n--\nnet/mptcp/options.c=464=bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,\n--\nnet/mptcp/options.c-492-\t\topts-\u003esuboptions = OPTION_MPTCP_MPJ_SYN;\nnet/mptcp/options.c:493:\t\topts-\u003ejoin_id = subflow-\u003elocal_id;\nnet/mptcp/options.c-494-\t\topts-\u003etoken = subflow-\u003eremote_token;\n--\nnet/mptcp/options.c=946=bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,\n--\nnet/mptcp/options.c-962-\t\topts-\u003ebackup = subflow_req-\u003erequest_bkup;\nnet/mptcp/options.c:963:\t\topts-\u003ejoin_id = subflow_req-\u003elocal_id;\nnet/mptcp/options.c-964-\t\topts-\u003ethmac = subflow_req-\u003ethmac;\n--\nnet/mptcp/pm.c=250=static bool subflow_in_rm_list(const struct mptcp_subflow_context *subflow,\n--\nnet/mptcp/pm.c-252-{\nnet/mptcp/pm.c:253:\tu8 i, id = subflow_get_local_id(subflow);\nnet/mptcp/pm.c-254-\n--\nnet/mptcp/pm.c=498=int mptcp_pm_announce_addr(struct mptcp_sock *msk,\n--\nnet/mptcp/pm.c-503-\nnet/mptcp/pm.c:504:\tpr_debug(\"msk=%p, local_id=%d, echo=%d\\n\", msk, addr-\u003eid, echo);\nnet/mptcp/pm.c-505-\n--\nnet/mptcp/pm.c=764=static void mptcp_pm_rm_addr_or_subflow(struct mptcp_sock *msk,\n--\nnet/mptcp/pm.c-793-\t\t\tint how = RCV_SHUTDOWN | SEND_SHUTDOWN;\nnet/mptcp/pm.c:794:\t\t\tu8 id = subflow_get_local_id(subflow);\nnet/mptcp/pm.c-795-\n--\nnet/mptcp/pm.c-803-\nnet/mptcp/pm.c:804:\t\t\tpr_debug(\" -\u003e %s rm_list_ids[%d]=%u local_id=%u remote_id=%u mpc_id=%u\\n\",\nnet/mptcp/pm.c-805-\t\t\t\t rm_type == MPTCP_MIB_RMADDR ? \"address\" : \"subflow\",\n--\nnet/mptcp/pm.c=1001=bool mptcp_pm_rm_addr_signal(struct mptcp_sock *msk, unsigned int remaining,\n--\nnet/mptcp/pm.c-1031-\nnet/mptcp/pm.c:1032:int mptcp_pm_get_local_id(struct mptcp_sock *msk, struct sock_common *skc)\nnet/mptcp/pm.c-1033-{\n--\nnet/mptcp/pm.c-1051-\tif (mptcp_pm_is_userspace(msk))\nnet/mptcp/pm.c:1052:\t\treturn mptcp_userspace_pm_get_local_id(msk, \u0026skc_local);\nnet/mptcp/pm.c:1053:\treturn mptcp_pm_nl_get_local_id(msk, \u0026skc_local);\nnet/mptcp/pm.c-1054-}\n--\nnet/mptcp/pm_kernel.c=203=fill_remote_addresses_fullmesh(struct mptcp_sock *msk,\n--\nnet/mptcp/pm_kernel.c-219-\tmptcp_for_each_subflow(msk, subflow)\nnet/mptcp/pm_kernel.c:220:\t\tif (READ_ONCE(subflow-\u003elocal_id) == local-\u003eid)\nnet/mptcp/pm_kernel.c-221-\t\t\t__set_bit(subflow-\u003eremote_id, unavail_id);\n--\nnet/mptcp/pm_kernel.c=281=__lookup_addr(struct pm_nl_pernet *pernet, const struct mptcp_addr_info *info)\n--\nnet/mptcp/pm_kernel.c-292-\nnet/mptcp/pm_kernel.c:293:static u8 mptcp_endp_get_local_id(struct mptcp_sock *msk,\nnet/mptcp/pm_kernel.c-294-\t\t\t\t  const struct mptcp_addr_info *addr)\n--\nnet/mptcp/pm_kernel.c=507=fill_local_laminar_endp(struct mptcp_sock *msk, struct mptcp_addr_info *remote,\n--\nnet/mptcp/pm_kernel.c-529-\nnet/mptcp/pm_kernel.c:530:\t\t__set_bit(subflow_get_local_id(subflow), unavail_id);\nnet/mptcp/pm_kernel.c-531-\t}\n--\nnet/mptcp/pm_kernel.c-540-\nnet/mptcp/pm_kernel.c:541:\t\tif (test_bit(mptcp_endp_get_local_id(msk, \u0026entry-\u003eaddr),\nnet/mptcp/pm_kernel.c-542-\t\t\t     unavail_id))\n--\nnet/mptcp/pm_kernel.c=852=static int mptcp_pm_nl_create_listen_socket(struct sock *sk,\n--\nnet/mptcp/pm_kernel.c-917-\nnet/mptcp/pm_kernel.c:918:int mptcp_pm_nl_get_local_id(struct mptcp_sock *msk,\nnet/mptcp/pm_kernel.c-919-\t\t\t     struct mptcp_pm_addr_entry *skc)\n--\nnet/mptcp/pm_kernel.c=1056=static void mptcp_pm_remove_announced(struct mptcp_sock *msk,\n--\nnet/mptcp/pm_kernel.c-1062-\nnet/mptcp/pm_kernel.c:1063:\tlist.ids[list.nr++] = mptcp_endp_get_local_id(msk, addr);\nnet/mptcp/pm_kernel.c-1064-\n--\nnet/mptcp/pm_kernel.c=1083=static int mptcp_nl_remove_subflow_and_signal_addr(struct net *net,\n--\nnet/mptcp/pm_kernel.c-1104-\nnet/mptcp/pm_kernel.c:1105:\t\tlist.ids[0] = mptcp_endp_get_local_id(msk, addr);\nnet/mptcp/pm_kernel.c-1106-\n--\nnet/mptcp/pm_kernel.c=1225=static void mptcp_pm_flush_addrs_and_subflows(struct mptcp_sock *msk,\n--\nnet/mptcp/pm_kernel.c-1239-\t\tif (mptcp_pm_has_subflow_saddr(msk, \u0026entry-\u003eaddr))\nnet/mptcp/pm_kernel.c:1240:\t\t\tslist.ids[slist.nr++] = mptcp_endp_get_local_id(msk, \u0026entry-\u003eaddr);\nnet/mptcp/pm_kernel.c-1241-\nnet/mptcp/pm_kernel.c-1242-\t\tif (mptcp_pm_announced_remove(msk, \u0026entry-\u003eaddr))\nnet/mptcp/pm_kernel.c:1243:\t\t\talist.ids[alist.nr++] = mptcp_endp_get_local_id(msk, \u0026entry-\u003eaddr);\nnet/mptcp/pm_kernel.c-1244-\n--\nnet/mptcp/pm_kernel.c=1467=static void mptcp_pm_nl_fullmesh(struct mptcp_sock *msk,\n--\nnet/mptcp/pm_kernel.c-1471-\nnet/mptcp/pm_kernel.c:1472:\tlist.ids[list.nr++] = mptcp_endp_get_local_id(msk, addr);\nnet/mptcp/pm_kernel.c-1473-\n--\nnet/mptcp/pm_netlink.c=298=static int mptcp_event_add_subflow(struct sk_buff *skb, const struct sock *ssk)\n--\nnet/mptcp/pm_netlink.c-335-\nnet/mptcp/pm_netlink.c:336:\tif (nla_put_u8(skb, MPTCP_ATTR_LOC_ID, subflow_get_local_id(sf)))\nnet/mptcp/pm_netlink.c-337-\t\treturn -EMSGSIZE;\n--\nnet/mptcp/pm_userspace.c=122=mptcp_userspace_pm_lookup_addr_by_id(struct mptcp_sock *msk, unsigned int id)\n--\nnet/mptcp/pm_userspace.c-132-\nnet/mptcp/pm_userspace.c:133:int mptcp_userspace_pm_get_local_id(struct mptcp_sock *msk,\nnet/mptcp/pm_userspace.c-134-\t\t\t\t    struct mptcp_pm_addr_entry *skc)\n--\nnet/mptcp/pm_userspace.c=253=static int mptcp_userspace_pm_remove_id_zero_address(struct mptcp_sock *msk)\n--\nnet/mptcp/pm_userspace.c-262-\tmptcp_for_each_subflow(msk, subflow) {\nnet/mptcp/pm_userspace.c:263:\t\tif (READ_ONCE(subflow-\u003elocal_id) == 0) {\nnet/mptcp/pm_userspace.c-264-\t\t\thas_id_0 = true;\n--\nnet/mptcp/protocol.c=103=static int __mptcp_socket_create(struct mptcp_sock *msk)\n--\nnet/mptcp/protocol.c-122-\t/* This is the first subflow, always with id 0 */\nnet/mptcp/protocol.c:123:\tWRITE_ONCE(subflow-\u003elocal_id, 0);\nnet/mptcp/protocol.c-124-\tmptcp_sock_graft(msk-\u003efirst, sk-\u003esk_socket);\n--\nnet/mptcp/protocol.c=2684=void mptcp_close_ssk(struct sock *sk, struct sock *ssk,\n--\nnet/mptcp/protocol.c-2687-\t/* The first subflow can already be closed or disconnected */\nnet/mptcp/protocol.c:2688:\tif (subflow-\u003eclose_event_done || READ_ONCE(subflow-\u003elocal_id) \u003c 0)\nnet/mptcp/protocol.c-2689-\t\treturn;\n--\nnet/mptcp/protocol.c=3564=struct sock *mptcp_sk_clone_init(const struct sock *sk,\n--\nnet/mptcp/protocol.c-3627-\nnet/mptcp/protocol.c:3628:\t/* set msk addresses early to ensure mptcp_pm_get_local_id()\nnet/mptcp/protocol.c-3629-\t * uses the correct data\n--\nnet/mptcp/protocol.h=502=struct mptcp_subflow_request_sock {\n--\nnet/mptcp/protocol.h-509-\t\tallow_join_id0 : 1;\nnet/mptcp/protocol.h:510:\tu8\tlocal_id;\nnet/mptcp/protocol.h-511-\tu8\tremote_id;\n--\nnet/mptcp/protocol.h=544=struct mptcp_subflow_context {\n--\nnet/mptcp/protocol.h-601-\t};\nnet/mptcp/protocol.h:602:\ts16\tlocal_id;\t    /* if negative not initialized yet */\nnet/mptcp/protocol.h-603-\tu8\tremote_id;\n--\nnet/mptcp/protocol.h=649=mptcp_subflow_ctx_reset(struct mptcp_subflow_context *subflow)\n--\nnet/mptcp/protocol.h-652-\tsubflow-\u003erequest_mptcp = 1;\nnet/mptcp/protocol.h:653:\tWRITE_ONCE(subflow-\u003elocal_id, -1);\nnet/mptcp/protocol.h-654-}\n--\nnet/mptcp/protocol.h=1211=bool mptcp_pm_rm_addr_signal(struct mptcp_sock *msk, unsigned int remaining,\nnet/mptcp/protocol.h-1212-\t\t\t     struct mptcp_rm_list *rm_list, int *len);\nnet/mptcp/protocol.h:1213:int mptcp_pm_get_local_id(struct mptcp_sock *msk, struct sock_common *skc);\nnet/mptcp/protocol.h:1214:int mptcp_pm_nl_get_local_id(struct mptcp_sock *msk,\nnet/mptcp/protocol.h-1215-\t\t\t     struct mptcp_pm_addr_entry *skc);\nnet/mptcp/protocol.h:1216:int mptcp_userspace_pm_get_local_id(struct mptcp_sock *msk,\nnet/mptcp/protocol.h-1217-\t\t\t\t    struct mptcp_pm_addr_entry *skc);\n--\nnet/mptcp/protocol.h=1227=int mptcp_userspace_pm_get_addr(u8 id, struct mptcp_pm_addr_entry *addr,\n--\nnet/mptcp/protocol.h-1229-\nnet/mptcp/protocol.h:1230:static inline u8 subflow_get_local_id(const struct mptcp_subflow_context *subflow)\nnet/mptcp/protocol.h-1231-{\nnet/mptcp/protocol.h:1232:\tint local_id = READ_ONCE(subflow-\u003elocal_id);\nnet/mptcp/protocol.h-1233-\nnet/mptcp/protocol.h:1234:\tif (local_id \u003c 0)\nnet/mptcp/protocol.h-1235-\t\treturn 0;\nnet/mptcp/protocol.h:1236:\treturn local_id;\nnet/mptcp/protocol.h-1237-}\n--\nnet/mptcp/subflow.c=85=static struct mptcp_sock *subflow_token_join_request(struct request_sock *req)\n--\nnet/mptcp/subflow.c-88-\tstruct mptcp_sock *msk;\nnet/mptcp/subflow.c:89:\tint local_id;\nnet/mptcp/subflow.c-90-\n--\nnet/mptcp/subflow.c-96-\nnet/mptcp/subflow.c:97:\tlocal_id = mptcp_pm_get_local_id(msk, (struct sock_common *)req);\nnet/mptcp/subflow.c:98:\tif (local_id \u003c 0) {\nnet/mptcp/subflow.c-99-\t\tsock_put((struct sock *)msk);\n--\nnet/mptcp/subflow.c-101-\t}\nnet/mptcp/subflow.c:102:\tsubflow_req-\u003elocal_id = local_id;\nnet/mptcp/subflow.c-103-\tsubflow_req-\u003erequest_bkup = mptcp_pm_is_backup(msk, (struct sock_common *)req);\n--\nnet/mptcp/subflow.c=521=static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)\n--\nnet/mptcp/subflow.c-618-\nnet/mptcp/subflow.c:619:static void subflow_set_local_id(struct mptcp_subflow_context *subflow, int local_id)\nnet/mptcp/subflow.c-620-{\nnet/mptcp/subflow.c:621:\tWARN_ON_ONCE(local_id \u003c 0 || local_id \u003e 255);\nnet/mptcp/subflow.c:622:\tWRITE_ONCE(subflow-\u003elocal_id, local_id);\nnet/mptcp/subflow.c-623-}\nnet/mptcp/subflow.c-624-\nnet/mptcp/subflow.c:625:static int subflow_chk_local_id(struct sock *sk)\nnet/mptcp/subflow.c-626-{\n--\nnet/mptcp/subflow.c-630-\nnet/mptcp/subflow.c:631:\tif (likely(subflow-\u003elocal_id \u003e= 0))\nnet/mptcp/subflow.c-632-\t\treturn 0;\nnet/mptcp/subflow.c-633-\nnet/mptcp/subflow.c:634:\terr = mptcp_pm_get_local_id(msk, (struct sock_common *)sk);\nnet/mptcp/subflow.c-635-\tif (err \u003c 0)\n--\nnet/mptcp/subflow.c-637-\nnet/mptcp/subflow.c:638:\tsubflow_set_local_id(subflow, err);\nnet/mptcp/subflow.c-639-\tsubflow-\u003erequest_bkup = mptcp_pm_is_backup(msk, (struct sock_common *)sk);\n--\nnet/mptcp/subflow.c=644=static int subflow_rebuild_header(struct sock *sk)\nnet/mptcp/subflow.c-645-{\nnet/mptcp/subflow.c:646:\tint err = subflow_chk_local_id(sk);\nnet/mptcp/subflow.c-647-\n--\nnet/mptcp/subflow.c=655=static int subflow_v6_rebuild_header(struct sock *sk)\nnet/mptcp/subflow.c-656-{\nnet/mptcp/subflow.c:657:\tint err = subflow_chk_local_id(sk);\nnet/mptcp/subflow.c-658-\n--\nnet/mptcp/subflow.c=1608=int __mptcp_subflow_connect(struct sock *sk, const struct mptcp_pm_local *local,\n--\nnet/mptcp/subflow.c-1612-\tstruct mptcp_subflow_context *subflow;\nnet/mptcp/subflow.c:1613:\tint local_id = local-\u003eaddr.id;\nnet/mptcp/subflow.c-1614-\tstruct sockaddr_storage addr;\n--\nnet/mptcp/subflow.c-1629-\t\tpr_debug(\"msk=%p local=%d remote=%d create sock error: %d\\n\",\nnet/mptcp/subflow.c:1630:\t\t\t msk, local_id, remote_id, err);\nnet/mptcp/subflow.c-1631-\t\tgoto err_out;\n--\nnet/mptcp/subflow.c-1642-\t\tif (!local-\u003eaddr.addr.s_addr)\nnet/mptcp/subflow.c:1643:\t\t\tlocal_id = -1;\nnet/mptcp/subflow.c-1644-#if IS_ENABLED(CONFIG_MPTCP_IPV6)\n--\nnet/mptcp/subflow.c-1646-\t\tif (ipv6_addr_any(\u0026local-\u003eaddr.addr6))\nnet/mptcp/subflow.c:1647:\t\t\tlocal_id = -1;\nnet/mptcp/subflow.c-1648-#endif\n--\nnet/mptcp/subflow.c-1650-\nnet/mptcp/subflow.c:1651:\tif (local_id \u003e= 0)\nnet/mptcp/subflow.c:1652:\t\tsubflow_set_local_id(subflow, local_id);\nnet/mptcp/subflow.c-1653-\n--\nnet/mptcp/subflow.c-1669-\t\tpr_debug(\"msk=%p local=%d remote=%d bind error: %d\\n\",\nnet/mptcp/subflow.c:1670:\t\t\t msk, local_id, remote_id, err);\nnet/mptcp/subflow.c-1671-\t\tgoto failed;\n--\nnet/mptcp/subflow.c-1674-\tmptcp_crypto_key_sha(subflow-\u003eremote_key, \u0026remote_token, NULL);\nnet/mptcp/subflow.c:1675:\tpr_debug(\"msk=%p remote_token=%u local_id=%d remote_id=%d\\n\", msk,\nnet/mptcp/subflow.c:1676:\t\t remote_token, local_id, remote_id);\nnet/mptcp/subflow.c-1677-\tsubflow-\u003eremote_token = remote_token;\n--\nnet/mptcp/subflow.c-1689-\t\tpr_debug(\"msk=%p local=%d remote=%d connect error: %d\\n\",\nnet/mptcp/subflow.c:1690:\t\t\t msk, local_id, remote_id, err);\nnet/mptcp/subflow.c-1691-\t\tgoto failed_unlink;\n--\nnet/mptcp/subflow.c=1836=static struct mptcp_subflow_context *subflow_create_ctx(struct sock *sk,\n--\nnet/mptcp/subflow.c-1852-\tctx-\u003etcp_sock = sk;\nnet/mptcp/subflow.c:1853:\tWRITE_ONCE(ctx-\u003elocal_id, -1);\nnet/mptcp/subflow.c-1854-\n--\nnet/mptcp/subflow.c=2030=static void subflow_ulp_clone(const struct request_sock *req,\n--\nnet/mptcp/subflow.c-2066-\t\t/* this is the first subflow, id is always 0 */\nnet/mptcp/subflow.c:2067:\t\tsubflow_set_local_id(new_ctx, 0);\nnet/mptcp/subflow.c-2068-\t} else if (subflow_req-\u003emp_join) {\n--\nnet/mptcp/subflow.c-2081-\t\t */\nnet/mptcp/subflow.c:2082:\t\tsubflow_set_local_id(new_ctx, subflow_req-\u003elocal_id);\nnet/mptcp/subflow.c-2083-\t}\n--\nnet/mptcp/syncookies.c=23=struct join_entry {\n--\nnet/mptcp/syncookies.c-27-\tu8 join_id;\nnet/mptcp/syncookies.c:28:\tu8 local_id;\nnet/mptcp/syncookies.c-29-\tu8 backup;\n--\nnet/mptcp/syncookies.c=59=static void mptcp_join_store_state(struct join_entry *entry,\n--\nnet/mptcp/syncookies.c-66-\tentry-\u003ejoin_id = subflow_req-\u003eremote_id;\nnet/mptcp/syncookies.c:67:\tentry-\u003elocal_id = subflow_req-\u003elocal_id;\nnet/mptcp/syncookies.c-68-\tentry-\u003evalid = 1;\n--\nnet/mptcp/syncookies.c=92=bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,\n--\nnet/mptcp/syncookies.c-120-\tsubflow_req-\u003eremote_id = e-\u003ejoin_id;\nnet/mptcp/syncookies.c:121:\tsubflow_req-\u003elocal_id = e-\u003elocal_id;\nnet/mptcp/syncookies.c-122-\tsubflow_req-\u003etoken = e-\u003etoken;\n"
}

gemini-3.1-pro-preview

null

null

							input: 24065
							output: 371
							thoughts: 1977
						

**Uninitialized Memory Info-Leak in MPTCP SYN Cookie Handling**

Okay, so here's what I've got. I'm looking at how MPTCP handles subflows, specifically when a SYN cookie is involved. The key function here is `mptcp_synack_options`, which deals with SYN-ACK packets, and `mptcp_token_join_cookie_init_state`, which is called when the server receives the ACK in a SYN cookie handshake. I can see the potential issue immediately.

When an ACK with a SYN cookie comes in, the server reconstructs the request socket. The function `mptcp_subflow_init_cookie_req` creates a new `request_sock`, and then calls `mptcp_token_join_cookie_init_state` to populate it using the cookie data. Then, this reconstructed request socket is used to create the actual subflow socket. This is handled by `subflow_ulp_clone`.

Now, if we dive into the code, especially `subflow_ulp_clone`, it copies data from the `subflow_req` structure into the new subflow context. I noticed that `subflow_req->local_id` is part of this copying. If this value is uninitialized, the code uses an uninitialized value, because it can be used for things like netlink messages or sent over the network in MPTCP packets.

Here's the problem: `subflow_req` comes from `reqsk_alloc`, and this function allocates memory from a slab cache. Importantly, this allocation does *not* zero the memory by default. This means that if something isn't explicitly initialized, it will hold whatever garbage value was previously in that memory location. So I start to think this `local_id` could be uninitialized.

Now, if `subflow_req->local_id` is uninitialized when `subflow_ulp_clone` is called and `local_id` is *not* specifically assigned elsewhere, then this uninitialized data gets copied into the new subflow context, then used in various places like netlink messages, the network, etc. I've found places where the `local_id` is sent to userspace via `nla_put_u8` which translates to a potential one-byte info-leak.

The critical bit is that this uninitialized memory is then sent out to userspace. I'm wondering if standard tools like KASAN would catch this, but no, KASAN doesn't detect reads of uninitialized memory. Only KMSAN does. This is a classic case where KMSAN really shines.

Let's double-check how memory is allocated for `request_sock`. I see that `kmem_cache_alloc_noprof` does *not* have `__GFP_ZERO` which confirms it doesn't zero the allocated memory. I verify that `subflow_init_req` doesn't set `local_id`. Therefore `local_id` is indeed uninitialized.

So, the patch here is crucial. The patch adds an assignment of `local_id` in `mptcp_token_join_cookie_init_state()`. So before the patch, `local_id` was uninitialized from the `reqsk_alloc()` allocation. This would be a perfect spot to test with KMSAN, given the vulnerability to uninitialized memory info-leaks.

I conclude that this patch effectively fixes an uninitialized memory issue that could leak sensitive information to userspace or the network, therefore a KMSAN fuzzing session is highly recommended.

{
  "KMSANReasoning": "The patch adds an assignment to `subflow_req-\u003elocal_id` in `mptcp_token_join_cookie_init_state()`. `subflow_req` is a `struct mptcp_subflow_request_sock`, which is allocated via `reqsk_alloc()`. The `reqsk_alloc()` function allocates memory from a slab cache without the `__GFP_ZERO` flag, meaning the memory is uninitialized.\n\nWhile `subflow_init_req()` initializes several fields of the request socket, it does not initialize `local_id`. During a SYN cookie MP_JOIN, `mptcp_token_join_cookie_init_state()` is called to reconstruct the request socket state from the cookie. Before this patch, it failed to restore `local_id`, leaving `subflow_req-\u003elocal_id` uninitialized.\n\nThis uninitialized 1-byte value is later copied to the subflow context (`new_ctx-\u003elocal_id`) in `subflow_ulp_clone()`. From there, the uninitialized kernel heap memory can be leaked to userspace via Netlink (e.g., `MPTCP_SUBFLOW_ATTR_ID_LOC` in `subflow_get_info()`) or sent over the network in MPTCP TCP options.\n\nStandard KASAN does not detect reads of uninitialized memory; it only detects out-of-bounds accesses and use-after-free bugs. KMSAN is specifically designed to detect uninitialized memory uses and info-leaks. Therefore, a dedicated KMSAN fuzzing session is required to catch this and similar bugs.",
  "NeedsKMSAN": true
}

{
  "KMSANReasoning": "The patch adds an assignment to `subflow_req-\u003elocal_id` in `mptcp_token_join_cookie_init_state()`. `subflow_req` is a `struct mptcp_subflow_request_sock`, which is allocated via `reqsk_alloc()`. The `reqsk_alloc()` function allocates memory from a slab cache without the `__GFP_ZERO` flag, meaning the memory is uninitialized.\n\nWhile `subflow_init_req()` initializes several fields of the request socket, it does not initialize `local_id`. During a SYN cookie MP_JOIN, `mptcp_token_join_cookie_init_state()` is called to reconstruct the request socket state from the cookie. Before this patch, it failed to restore `local_id`, leaving `subflow_req-\u003elocal_id` uninitialized.\n\nThis uninitialized 1-byte value is later copied to the subflow context (`new_ctx-\u003elocal_id`) in `subflow_ulp_clone()`. From there, the uninitialized kernel heap memory can be leaked to userspace via Netlink (e.g., `MPTCP_SUBFLOW_ATTR_ID_LOC` in `subflow_get_info()`) or sent over the network in MPTCP TCP options.\n\nStandard KASAN does not detect reads of uninitialized memory; it only detects out-of-bounds accesses and use-after-free bugs. KMSAN is specifically designed to detect uninitialized memory uses and info-leaks. Therefore, a dedicated KMSAN fuzzing session is required to catch this and similar bugs.",
  "NeedsKMSAN": true
}