AI Trajectory

null

{
  "EnableConfigs": [
    "MPTCP"
  ],
  "FocusSymbols": [
    "mptcp_subflow_reqsk_clone"
  ],
  "Reasoning": "The patch adds a new function `mptcp_subflow_reqsk_clone` to handle cloning of MPTCP subflow request sockets, fixing a reference counting issue. This is reachable core network logic and should be fuzzed.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 5b5d30e56d61d5a74d874597e03caa4a068e0840\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Tue Aug 4 11:20:18 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/include/net/mptcp.h b/include/net/mptcp.h\nindex 71b9fc5a57963..51d4b02f5afb2 100644\n--- a/include/net/mptcp.h\n+++ b/include/net/mptcp.h\n@@ -223,6 +223,7 @@ int mptcp_subflow_init_cookie_req(struct request_sock *req,\n struct request_sock *mptcp_subflow_reqsk_alloc(const struct request_sock_ops *ops,\n \t\t\t\t\t       struct sock *sk_listener,\n \t\t\t\t\t       bool attach_listener);\n+void mptcp_subflow_reqsk_clone(struct request_sock *req);\n \n __be32 mptcp_get_reset_option(const struct sk_buff *skb);\n \n@@ -309,6 +310,10 @@ static inline struct request_sock *mptcp_subflow_reqsk_alloc(const struct reques\n \treturn NULL;\n }\n \n+static inline void mptcp_subflow_reqsk_clone(struct request_sock *req)\n+{\n+}\n+\n static inline __be32 mptcp_reset_option(const struct sk_buff *skb)  { return htonl(0u); }\n \n static inline void mptcp_active_detect_blackhole(struct sock *sk, bool expired) { }\ndiff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c\nindex 56902bba54838..f3ef9c15ac359 100644\n--- a/net/ipv4/inet_connection_sock.c\n+++ b/net/ipv4/inet_connection_sock.c\n@@ -17,6 +17,7 @@\n #include \u003cnet/inet_timewait_sock.h\u003e\n #include \u003cnet/ip.h\u003e\n #include \u003cnet/route.h\u003e\n+#include \u003cnet/mptcp.h\u003e\n #include \u003cnet/tcp_states.h\u003e\n #include \u003cnet/xfrm.h\u003e\n #include \u003cnet/tcp.h\u003e\n@@ -946,8 +947,13 @@ static struct request_sock *inet_reqsk_clone(struct request_sock *req,\n \t/* We need not acquire fastopenq-\u003elock\n \t * because the child socket is locked in inet_csk_listen_stop().\n \t */\n-\tif (sk-\u003esk_protocol == IPPROTO_TCP \u0026\u0026 tcp_rsk(nreq)-\u003etfo_listener)\n-\t\trcu_assign_pointer(tcp_sk(nreq-\u003esk)-\u003efastopen_rsk, nreq);\n+\tif (sk-\u003esk_protocol == IPPROTO_TCP) {\n+\t\tif (tcp_rsk(nreq)-\u003etfo_listener)\n+\t\t\trcu_assign_pointer(tcp_sk(nreq-\u003esk)-\u003efastopen_rsk, nreq);\n+\n+\t\tif (rsk_is_mptcp(req))\n+\t\t\tmptcp_subflow_reqsk_clone(nreq);\n+\t}\n \n \treturn nreq;\n }\ndiff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c\nindex 8e386899ceb98..1b6aa5e8cfd73 100644\n--- a/net/mptcp/subflow.c\n+++ b/net/mptcp/subflow.c\n@@ -47,6 +47,14 @@ static void subflow_req_destructor(struct request_sock *req)\n \tmptcp_token_destroy_request(req);\n }\n \n+void mptcp_subflow_reqsk_clone(struct request_sock *req)\n+{\n+\tstruct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);\n+\n+\tif (subflow_req-\u003emsk)\n+\t\tsock_hold((struct sock *)subflow_req-\u003emsk);\n+}\n+\n static void subflow_generate_hmac(u64 key1, u64 key2, u32 nonce1, u32 nonce2,\n \t\t\t\t  void *hmac)\n {\n"
}

best-expensive

null

{
  "EnableConfigs": [
    "MPTCP"
  ],
  "FocusSymbols": [
    "mptcp_subflow_reqsk_clone"
  ],
  "Reasoning": "The patch adds a new function `mptcp_subflow_reqsk_clone` to handle cloning of MPTCP subflow request sockets, fixing a reference counting issue. This is reachable core network logic 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 5b5d30e56d61d5a74d874597e03caa4a068e0840
Author: syz-cluster <triage@syzkaller.com>
Date:   Tue Aug 4 11:20:18 2026 +0000

    syz-cluster: applied patch under review

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 71b9fc5a57963..51d4b02f5afb2 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -223,6 +223,7 @@ int mptcp_subflow_init_cookie_req(struct request_sock *req,
 struct request_sock *mptcp_subflow_reqsk_alloc(const struct request_sock_ops *ops,
 					       struct sock *sk_listener,
 					       bool attach_listener);
+void mptcp_subflow_reqsk_clone(struct request_sock *req);
 
 __be32 mptcp_get_reset_option(const struct sk_buff *skb);
 
@@ -309,6 +310,10 @@ static inline struct request_sock *mptcp_subflow_reqsk_alloc(const struct reques
 	return NULL;
 }
 
+static inline void mptcp_subflow_reqsk_clone(struct request_sock *req)
+{
+}
+
 static inline __be32 mptcp_reset_option(const struct sk_buff *skb)  { return htonl(0u); }
 
 static inline void mptcp_active_detect_blackhole(struct sock *sk, bool expired) { }
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 56902bba54838..f3ef9c15ac359 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -17,6 +17,7 @@
 #include <net/inet_timewait_sock.h>
 #include <net/ip.h>
 #include <net/route.h>
+#include <net/mptcp.h>
 #include <net/tcp_states.h>
 #include <net/xfrm.h>
 #include <net/tcp.h>
@@ -946,8 +947,13 @@ static struct request_sock *inet_reqsk_clone(struct request_sock *req,
 	/* We need not acquire fastopenq->lock
 	 * because the child socket is locked in inet_csk_listen_stop().
 	 */
-	if (sk->sk_protocol == IPPROTO_TCP && tcp_rsk(nreq)->tfo_listener)
-		rcu_assign_pointer(tcp_sk(nreq->sk)->fastopen_rsk, nreq);
+	if (sk->sk_protocol == IPPROTO_TCP) {
+		if (tcp_rsk(nreq)->tfo_listener)
+			rcu_assign_pointer(tcp_sk(nreq->sk)->fastopen_rsk, nreq);
+
+		if (rsk_is_mptcp(req))
+			mptcp_subflow_reqsk_clone(nreq);
+	}
 
 	return nreq;
 }
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 8e386899ceb98..1b6aa5e8cfd73 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -47,6 +47,14 @@ static void subflow_req_destructor(struct request_sock *req)
 	mptcp_token_destroy_request(req);
 }
 
+void mptcp_subflow_reqsk_clone(struct request_sock *req)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+
+	if (subflow_req->msk)
+		sock_hold((struct sock *)subflow_req->msk);
+}
+
 static void subflow_generate_hmac(u64 key1, u64 key2, u32 nonce1, u32 nonce2,
 				  void *hmac)
 {

gemini-3.1-pro-preview

null

null

							input: 2920
							output: 32
							thoughts: 127
						

Okay, here's my take on those thoughts, framed from my perspective as an expert in this area:

**Analyzing the MPTCP and IPv4 Connection Code Patch**

Alright, I'm looking at this patch and it's making some modifications to the MPTCP and IPv4 connection socket code, specifically focusing on the connection establishment process. I see they've added a new function, `mptcp_subflow_reqsk_clone`, which is being called from within `inet_reqsk_clone` in `net/ipv4/inet_connection_sock.c`. That's a key spot; `inet_reqsk_clone` is fundamental to creating new connection requests.

It looks like the `mptcp_subflow_reqsk_clone` function is handling the potential association of the MPTCP subflow's request socket (`subflow_req`) with its MultiPath TCP Key (`msk`).  The code explicitly holds a reference to `subflow_req->msk` if one exists. This is important: holding that reference is crucial to guarantee that the MPTCP key doesn't get cleaned up before it's needed during connection establishment. I have to think about the locking and reference counting in this area. It will be interesting to see how this function handles cloning and potential resource management in relation to IPv4 connection.

Now, I need to verify how MPTCP is configured in this setup. Let's see... I'll use `grepper` to quickly find the relevant MPTCP configuration options and make sure everything is consistent with my expectations. I need to understand what's enabled, disabled, and the default settings in order to fully assess the implications of this patch. The context of these configurations are important for understanding the implications of the change to the MPTCP code.

{
  "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: 3685
							output: 38
							thoughts: 117
						

**Analyzing the MPTCP Configuration Patch**

Okay, so the key configuration option here is `MPTCP`. The patch itself appears to focus on modifications within the networking stack, specifically `net/ipv4/inet_connection_sock.c` and `net/mptcp/subflow.c`. I need to understand how the changes impact the connection socket and subflow creation.

The core addition is likely the `mptcp_subflow_reqsk_clone` function. I recognize that the changes also touch `inet_reqsk_clone`, and the latter is where I want to start. It's a static function, which often means it's limited in scope and used internally within the same source file, which isn't always obvious without further digging. But, I think this function is also called by or related to `inet_csk_listen_stop` or a similar function, so I'll need to check the call graph to confirm its usage and its relationship to the new `mptcp_subflow_reqsk_clone`. It's essential to grasp how the `inet_reqsk_clone` function, the more established function, is leveraged or modified by this new MPTCP implementation. This information will be key to understanding the integration and functionality of the feature.

{
  "Expression": "inet_reqsk_clone",
  "PathPrefix": "net/ipv4/inet_connection_sock.c"
}

{
  "Output": "net/ipv4/inet_connection_sock.c=905=void __reqsk_free(struct request_sock *req)\n--\nnet/ipv4/inet_connection_sock.c-913-\nnet/ipv4/inet_connection_sock.c:914:static struct request_sock *inet_reqsk_clone(struct request_sock *req,\nnet/ipv4/inet_connection_sock.c-915-\t\t\t\t\t     struct sock *sk)\n--\nnet/ipv4/inet_connection_sock.c=1027=static void reqsk_timer_handler(struct timer_list *t)\n--\nnet/ipv4/inet_connection_sock.c-1043-\nnet/ipv4/inet_connection_sock.c:1044:\t\tnreq = inet_reqsk_clone(req, nsk);\nnet/ipv4/inet_connection_sock.c-1045-\t\tif (!nreq)\n--\nnet/ipv4/inet_connection_sock.c=1411=struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child,\n--\nnet/ipv4/inet_connection_sock.c-1424-\t\t\t/* hold a refcnt for the nreq-\u003ersk_listener\nnet/ipv4/inet_connection_sock.c:1425:\t\t\t * which is assigned in inet_reqsk_clone()\nnet/ipv4/inet_connection_sock.c-1426-\t\t\t */\nnet/ipv4/inet_connection_sock.c-1427-\t\t\tsock_hold(sk);\nnet/ipv4/inet_connection_sock.c:1428:\t\t\tnreq = inet_reqsk_clone(req, sk);\nnet/ipv4/inet_connection_sock.c-1429-\t\t\tif (!nreq) {\n--\nnet/ipv4/inet_connection_sock.c=1460=void inet_csk_listen_stop(struct sock *sk)\n--\nnet/ipv4/inet_connection_sock.c-1484-\t\tif (nsk) {\nnet/ipv4/inet_connection_sock.c:1485:\t\t\tnreq = inet_reqsk_clone(req, nsk);\nnet/ipv4/inet_connection_sock.c-1486-\t\t\tif (nreq) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 4702
							output: 30
							thoughts: 314
						

**Analyzing the Request Socket Cloning Patch**

Okay, so I'm looking at this patch and immediately, I see that `inet_reqsk_clone` is the central function being modified. It's called from a few different places: `reqsk_timer_handler`, `inet_csk_complete_hashdance`, and `inet_csk_listen_stop`. Hmm, all reachable. The issue the patch addresses is the missing reference count increment for `subflow_req->msk` when a request socket gets cloned. Got it.

Now, a new function, `mptcp_subflow_reqsk_clone`, has been added. That's the key here. It's not static, which means it's exported and can be called from outside its source file. Let me confirm that... Yup, defined in `net/mptcp/subflow.c` and declared in `include/net/mptcp.h`. Bingo. This `mptcp_subflow_reqsk_clone` function looks like my primary focus symbol. Let me double-check - `inet_reqsk_clone` is static, so it *shouldn't* be in my FocusSymbols. `inet_csk_listen_stop` is a general hot-path function, so likely common.

Alright, is `mptcp_subflow_reqsk_clone` the *only* significant change here? Yes, it is. It's the new functionality introduced by the patch.

Now, I'll quickly check the config options. This relies on `MPTCP` which depends on `INET`. Okay, I'll need to check the `net/mptcp/Kconfig` file.

{
  "Expression": "depends on",
  "PathPrefix": "net/mptcp/Kconfig"
}

{
  "Output": "net/mptcp/Kconfig=2=config MPTCP\nnet/mptcp/Kconfig-3-\tbool \"MPTCP: Multipath TCP\"\nnet/mptcp/Kconfig:4:\tdepends on INET\nnet/mptcp/Kconfig-5-\tselect SKB_EXTENSIONS\n--\nnet/mptcp/Kconfig=16=config INET_MPTCP_DIAG\nnet/mptcp/Kconfig:17:\tdepends on INET_DIAG\nnet/mptcp/Kconfig-18-\tdef_tristate INET_DIAG\n--\nnet/mptcp/Kconfig=20=config MPTCP_IPV6\nnet/mptcp/Kconfig-21-\tbool \"MPTCP: IPv6 support for Multipath TCP\"\nnet/mptcp/Kconfig:22:\tdepends on IPV6=y\nnet/mptcp/Kconfig-23-\tdefault y\n--\nnet/mptcp/Kconfig=25=config MPTCP_KUNIT_TEST\nnet/mptcp/Kconfig-26-\ttristate \"This builds the MPTCP KUnit tests\" if !KUNIT_ALL_TESTS\nnet/mptcp/Kconfig:27:\tdepends on KUNIT\nnet/mptcp/Kconfig-28-\tdefault KUNIT_ALL_TESTS\n"
}

gemini-3.1-pro-preview

null

null

							input: 5756
							output: 41
							thoughts: 408
						

**Fuzzing the MPTCP Subflow Request Socket Cloning**

Okay, so I'm looking at this MPTCP configuration, and this patch introduces some functional changes specifically related to MPTCP. The key function I want to focus on is this `mptcp_subflow_reqsk_clone` – it's the new addition and seems like a good target for fuzzing. `MPTCP` is enabled, and that's the starting point.

First, let's just confirm something. I need to quickly verify if `inet_reqsk_clone` is static. Yes, it is. That's good to know. Now, are there any other functions in this general area that might be relevant? Hmmm, `inet_csk_listen_stop` is a possibility; it's a bit generic but it's where the cloning action actually happens. But, no, I think `mptcp_subflow_reqsk_clone` is still the best focus, especially when I recall that `inet_reqsk_clone` gets called from `reqsk_timer_handler`, `inet_csk_complete_hashdance`, and `inet_csk_listen_stop`. All those functions are located in `net/ipv4/inet_connection_sock.c`. That solidifies the reasoning to focus on that cloning function!

Okay, is this `mptcp_subflow_reqsk_clone` function exported? It's not explicitly exported with `EXPORT_SYMBOL`, but it also isn't static, so it should have a distinct symbol address. It's called from `inet_reqsk_clone`, which resides in `net/ipv4/inet_connection_sock.c`. Since `net/ipv4/inet_connection_sock.c` is built-in and `net/mptcp/subflow.c` is also built-in if `MPTCP=y`, it should be linked. Finally, let me just confirm that `mptcp_subflow_reqsk_clone` is indeed located in `net/mptcp/subflow.c`.

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

{
  "Output": "net/mptcp/subflow.c=38=static void subflow_req_destructor(struct request_sock *req)\n--\nnet/mptcp/subflow.c-49-\nnet/mptcp/subflow.c:50:void mptcp_subflow_reqsk_clone(struct request_sock *req)\nnet/mptcp/subflow.c-51-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 6772
							output: 98
							thoughts: 82
						

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

**Analyzing the Configuration and Applying a Fix**

Yes, that confirms it. Now, I need to make sure we've exhausted any other related configurations. My initial assessment is correct; the `MPTCP` configuration is the relevant one here.

Here's why: the core of the problem lies in the patch's addition of the `mptcp_subflow_reqsk_clone` function. The key takeaway is that this addresses a reference counting issue within the process of cloning MPTCP subflow request sockets. We are firmly in the realm of critical, reachable core network logic.

Therefore, the next logical step is to call `set-results`.

{
  "EnableConfigs": [
    "MPTCP"
  ],
  "FocusSymbols": [
    "mptcp_subflow_reqsk_clone"
  ],
  "Reasoning": "The patch adds a new function `mptcp_subflow_reqsk_clone` to handle cloning of MPTCP subflow request sockets, fixing a reference counting issue. This is reachable core network logic and should be fuzzed.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "MPTCP"
  ],
  "FocusSymbols": [
    "mptcp_subflow_reqsk_clone"
  ],
  "Reasoning": "The patch adds a new function `mptcp_subflow_reqsk_clone` to handle cloning of MPTCP subflow request sockets, fixing a reference counting issue. This is reachable core network logic and should be fuzzed.",
  "WorthFuzzing": true
}