AI Trajectory

null

{
  "EnableConfigs": null,
  "FocusSymbols": [
    "do_tcp_setsockopt",
    "tcp_retransmit_timer",
    "reqsk_timer_handler",
    "tcp_check_req"
  ],
  "KMSANReasoning": "The patch fixes an integer overflow and out-of-bounds shift in TCP timeout calculation (`req-\u003etimeout \u003c\u003c req-\u003enum_timeout`) by capping the maximum number of SYNACK retries to 127 and adding overflow checks in `tcp_reqsk_timeout_sk`. It does not introduce any new memory allocations, uninitialized variables, or data copied to userspace. Standard KASAN and UBSAN are sufficient to detect memory corruption or undefined behavior related to this code. KMSAN is not applicable.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch modifies TCP SYNACK retries limits and timeout calculation logic to prevent shift overflows and bounds `tcp_synack_retries` to 127. These changes affect core TCP connection establishment and retransmission logic. The modifications are reachable via TCP socket options and timer callbacks during connection handling.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 806434ca0328309a350aeafd7b616e304128681d\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Wed Aug 12 15:39:47 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst\nindex 208f46967ee59..fd5038b6cab9f 100644\n--- a/Documentation/networking/ip-sysctl.rst\n+++ b/Documentation/networking/ip-sysctl.rst\n@@ -954,7 +954,7 @@ tcp_stdurg - BOOLEAN\n \n tcp_synack_retries - INTEGER\n \tNumber of times SYNACKs for a passive TCP connection attempt will\n-\tbe retransmitted. Should not be higher than 255. Default value\n+\tbe retransmitted. Should not be higher than 127. Default value\n \tis 5, which corresponds to 31seconds till the last retransmission\n \twith the current initial RTO of 1second. With this the final timeout\n \tfor a passive TCP connection will happen after 63seconds.\ndiff --git a/include/net/tcp.h b/include/net/tcp.h\nindex 2c5b889530b55..8ab2fd368ed3b 100644\n--- a/include/net/tcp.h\n+++ b/include/net/tcp.h\n@@ -183,6 +183,8 @@ static_assert((1 \u003c\u003c ATO_BITS) \u003e TCP_DELACK_MAX);\n #define MAX_TCP_KEEPINTVL\t32767\n #define MAX_TCP_KEEPCNT\t\t127\n #define MAX_TCP_SYNCNT\t\t127\n+/* request_sock::num_timeout is a 7-bit field. */\n+#define MAX_TCP_SYNACK_RETRIES\t127\n \n /* Ensure that TCP PAWS checks are relaxed after ~2147 seconds\n  * to avoid overflows. This assumes a clock smaller than 1 Mhz.\n@@ -882,12 +884,22 @@ static inline u32 __tcp_set_rto(const struct tcp_sock *tp)\n \treturn usecs_to_jiffies((tp-\u003esrtt_us \u003e\u003e 3) + tp-\u003erttvar_us);\n }\n \n-static inline unsigned long tcp_reqsk_timeout(struct request_sock *req)\n+static inline unsigned long tcp_reqsk_timeout_sk(const struct sock *sk,\n+\t\t\t\t\t\t struct request_sock *req)\n {\n-\tu64 timeout = (u64)req-\u003etimeout \u003c\u003c req-\u003enum_timeout;\n+\tu32 rto_max = tcp_rto_max(sk);\n+\tu64 timeout = req-\u003etimeout;\n+\n+\tif (req-\u003enum_timeout \u003e= BITS_PER_TYPE(timeout) ||\n+\t    timeout \u003e U64_MAX \u003e\u003e req-\u003enum_timeout)\n+\t\treturn rto_max;\n+\n+\treturn (unsigned long)min_t(u64, timeout \u003c\u003c req-\u003enum_timeout, rto_max);\n+}\n \n-\treturn (unsigned long)min_t(u64, timeout,\n-\t\t\t\t    tcp_rto_max(req-\u003ersk_listener));\n+static inline unsigned long tcp_reqsk_timeout(struct request_sock *req)\n+{\n+\treturn tcp_reqsk_timeout_sk(req-\u003ersk_listener, req);\n }\n \n u32 tcp_delack_max(const struct sock *sk);\ndiff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c\nindex ca1180dba1dea..fc5152dfa3c86 100644\n--- a/net/ipv4/sysctl_net_ipv4.c\n+++ b/net/ipv4/sysctl_net_ipv4.c\n@@ -35,6 +35,7 @@ static int ip_ttl_min = 1;\n static int ip_ttl_max = 255;\n static int tcp_syn_retries_min = 1;\n static int tcp_syn_retries_max = MAX_TCP_SYNCNT;\n+static int tcp_synack_retries_max = MAX_TCP_SYNACK_RETRIES;\n static int tcp_syn_linear_timeouts_max = MAX_TCP_SYNCNT;\n static unsigned long ip_ping_group_range_min[] = { 0, 0 };\n static unsigned long ip_ping_group_range_max[] = { GID_T_MAX, GID_T_MAX };\n@@ -1034,6 +1035,7 @@ static struct ctl_table ipv4_net_table[] = {\n \t\t.maxlen\t\t= sizeof(u8),\n \t\t.mode\t\t= 0644,\n \t\t.proc_handler\t= proc_dou8vec_minmax,\n+\t\t.extra2\t\t= \u0026tcp_synack_retries_max,\n \t},\n #ifdef CONFIG_SYN_COOKIES\n \t{\ndiff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c\nindex 455441f1b6949..24896fa08a5d8 100644\n--- a/net/ipv4/tcp.c\n+++ b/net/ipv4/tcp.c\n@@ -357,7 +357,7 @@ static u8 secs_to_retrans(int seconds, int timeout, int rto_max)\n \t\tint period = timeout;\n \n \t\tres = 1;\n-\t\twhile (seconds \u003e period \u0026\u0026 res \u003c 255) {\n+\t\twhile (seconds \u003e period \u0026\u0026 res \u003c MAX_TCP_SYNACK_RETRIES) {\n \t\t\tres++;\n \t\t\ttimeout \u003c\u003c= 1;\n \t\t\tif (timeout \u003e rto_max)\ndiff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c\nindex bf171b5e1eb30..daa4eac072dd9 100644\n--- a/net/ipv4/tcp_timer.c\n+++ b/net/ipv4/tcp_timer.c\n@@ -462,11 +462,13 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)\n \n \ttcp_syn_ack_timeout(req);\n \n-\t/* Add one more retry for fastopen.\n+\t/* Add one more retry for fastopen when the timeout counter can\n+\t * represent it.\n \t * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()\n \t */\n \tmax_retries = READ_ONCE(icsk-\u003eicsk_syn_retries) ? :\n \t\tREAD_ONCE(sock_net(sk)-\u003eipv4.sysctl_tcp_synack_retries) + 1;\n+\tmax_retries = min_t(int, max_retries, MAX_TCP_SYNACK_RETRIES);\n \n \tif (req-\u003enum_timeout \u003e= max_retries) {\n \t\ttcp_write_err(sk);\n@@ -488,7 +490,7 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)\n \tif (!tp-\u003eretrans_stamp)\n \t\ttp-\u003eretrans_stamp = tcp_time_stamp_ts(tp);\n \ttcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,\n-\t\t\t  req-\u003etimeout \u003c\u003c req-\u003enum_timeout, false);\n+\t\t\t     tcp_reqsk_timeout_sk(sk, req), false);\n }\n \n static bool tcp_rtx_probe0_timed_out(const struct sock *sk,\n"
}

best-expensive

null

{
  "EnableConfigs": null,
  "FocusSymbols": [
    "do_tcp_setsockopt",
    "tcp_retransmit_timer",
    "reqsk_timer_handler",
    "tcp_check_req"
  ],
  "Reasoning": "The patch modifies TCP SYNACK retries limits and timeout calculation logic to prevent shift overflows and bounds `tcp_synack_retries` to 127. These changes affect core TCP connection establishment and retransmission logic. The modifications are reachable via TCP socket options and timer callbacks during connection handling.",
  "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 806434ca0328309a350aeafd7b616e304128681d
Author: syz-cluster <triage@syzkaller.com>
Date:   Wed Aug 12 15:39:47 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 208f46967ee59..fd5038b6cab9f 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -954,7 +954,7 @@ tcp_stdurg - BOOLEAN
 
 tcp_synack_retries - INTEGER
 	Number of times SYNACKs for a passive TCP connection attempt will
-	be retransmitted. Should not be higher than 255. Default value
+	be retransmitted. Should not be higher than 127. Default value
 	is 5, which corresponds to 31seconds till the last retransmission
 	with the current initial RTO of 1second. With this the final timeout
 	for a passive TCP connection will happen after 63seconds.
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 2c5b889530b55..8ab2fd368ed3b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -183,6 +183,8 @@ static_assert((1 << ATO_BITS) > TCP_DELACK_MAX);
 #define MAX_TCP_KEEPINTVL	32767
 #define MAX_TCP_KEEPCNT		127
 #define MAX_TCP_SYNCNT		127
+/* request_sock::num_timeout is a 7-bit field. */
+#define MAX_TCP_SYNACK_RETRIES	127
 
 /* Ensure that TCP PAWS checks are relaxed after ~2147 seconds
  * to avoid overflows. This assumes a clock smaller than 1 Mhz.
@@ -882,12 +884,22 @@ static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
 	return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
 }
 
-static inline unsigned long tcp_reqsk_timeout(struct request_sock *req)
+static inline unsigned long tcp_reqsk_timeout_sk(const struct sock *sk,
+						 struct request_sock *req)
 {
-	u64 timeout = (u64)req->timeout << req->num_timeout;
+	u32 rto_max = tcp_rto_max(sk);
+	u64 timeout = req->timeout;
+
+	if (req->num_timeout >= BITS_PER_TYPE(timeout) ||
+	    timeout > U64_MAX >> req->num_timeout)
+		return rto_max;
+
+	return (unsigned long)min_t(u64, timeout << req->num_timeout, rto_max);
+}
 
-	return (unsigned long)min_t(u64, timeout,
-				    tcp_rto_max(req->rsk_listener));
+static inline unsigned long tcp_reqsk_timeout(struct request_sock *req)
+{
+	return tcp_reqsk_timeout_sk(req->rsk_listener, req);
 }
 
 u32 tcp_delack_max(const struct sock *sk);
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index ca1180dba1dea..fc5152dfa3c86 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -35,6 +35,7 @@ static int ip_ttl_min = 1;
 static int ip_ttl_max = 255;
 static int tcp_syn_retries_min = 1;
 static int tcp_syn_retries_max = MAX_TCP_SYNCNT;
+static int tcp_synack_retries_max = MAX_TCP_SYNACK_RETRIES;
 static int tcp_syn_linear_timeouts_max = MAX_TCP_SYNCNT;
 static unsigned long ip_ping_group_range_min[] = { 0, 0 };
 static unsigned long ip_ping_group_range_max[] = { GID_T_MAX, GID_T_MAX };
@@ -1034,6 +1035,7 @@ static struct ctl_table ipv4_net_table[] = {
 		.maxlen		= sizeof(u8),
 		.mode		= 0644,
 		.proc_handler	= proc_dou8vec_minmax,
+		.extra2		= &tcp_synack_retries_max,
 	},
 #ifdef CONFIG_SYN_COOKIES
 	{
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 455441f1b6949..24896fa08a5d8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -357,7 +357,7 @@ static u8 secs_to_retrans(int seconds, int timeout, int rto_max)
 		int period = timeout;
 
 		res = 1;
-		while (seconds > period && res < 255) {
+		while (seconds > period && res < MAX_TCP_SYNACK_RETRIES) {
 			res++;
 			timeout <<= 1;
 			if (timeout > rto_max)
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index bf171b5e1eb30..daa4eac072dd9 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -462,11 +462,13 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 
 	tcp_syn_ack_timeout(req);
 
-	/* Add one more retry for fastopen.
+	/* Add one more retry for fastopen when the timeout counter can
+	 * represent it.
 	 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()
 	 */
 	max_retries = READ_ONCE(icsk->icsk_syn_retries) ? :
 		READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;
+	max_retries = min_t(int, max_retries, MAX_TCP_SYNACK_RETRIES);
 
 	if (req->num_timeout >= max_retries) {
 		tcp_write_err(sk);
@@ -488,7 +490,7 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 	if (!tp->retrans_stamp)
 		tp->retrans_stamp = tcp_time_stamp_ts(tp);
 	tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-			  req->timeout << req->num_timeout, false);
+			     tcp_reqsk_timeout_sk(sk, req), false);
 }
 
 static bool tcp_rtx_probe0_timed_out(const struct sock *sk,

gemini-3.1-pro-preview

null

null

							input: 3665
							output: 23
							thoughts: 274
						

**Analyzing the TCP SYNACK Retry Patch**

Okay, so I've got this patch here that's tweaking the TCP SYNACK retry behavior, specifically the timeout calculations and retry limits. It looks like it's designed to prevent shift overflows by modifying `tcp_reqsk_timeout`, and it's capping `tcp_synack_retries` at 127. Seems sensible, given the potential for vulnerabilities in those areas.

Given the core nature of these changes, affecting `include/net/tcp.h`, `net/ipv4/sysctl_net_ipv4.c`, `net/ipv4/tcp.c`, and `net/ipv4/tcp_timer.c`, this *definitely* warrants some serious fuzzing. Let's dig in and figure out where to focus our efforts.

First, I need to get a handle on the key functions involved. The core ones touched seem to be:
*   `tcp_reqsk_timeout_sk` (inline, in `include/net/tcp.h`)
*   `tcp_reqsk_timeout` (inline, in `include/net/tcp.h`)
*   `secs_to_retrans` in `net/ipv4/tcp.c`
*   `tcp_fastopen_synack_timer` in `net/ipv4/tcp_timer.c`

Since those first two are inline, and therefore probably less critical for targeted fuzzing, I should look more deeply into the other two. `tcp_fastopen_synack_timer` is static, which is interesting - that means it's likely to be called only from within the same file. I need to track down where `tcp_fastopen_synack_timer` is called. Same goes for `secs_to_retrans` also being static.

{
  "Expression": "tcp_fastopen_synack_timer"
}

{
  "Output": "net/ipv4/tcp_input.c=7103=static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)\n--\nnet/ipv4/tcp_input.c-7115-\tWRITE_ONCE(inet_csk(sk)-\u003eicsk_retransmits, 0);\nnet/ipv4/tcp_input.c:7116:\t/* In tcp_fastopen_synack_timer() on the first SYNACK RTO we set\nnet/ipv4/tcp_input.c-7117-\t * retrans_stamp but don't enter CA_Loss, so in case that happened we\n--\nnet/ipv4/tcp_timer.c=440=static void tcp_update_rto_stats(struct sock *sk)\n--\nnet/ipv4/tcp_timer.c-456- */\nnet/ipv4/tcp_timer.c:457:static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)\nnet/ipv4/tcp_timer.c-458-{\n--\nnet/ipv4/tcp_timer.c=537=void tcp_retransmit_timer(struct sock *sk)\n--\nnet/ipv4/tcp_timer.c-549-\t\t\t     sk-\u003esk_state != TCP_FIN_WAIT1);\nnet/ipv4/tcp_timer.c:550:\t\ttcp_fastopen_synack_timer(sk, req);\nnet/ipv4/tcp_timer.c-551-\t\t/* Before we receive ACK to our SYN-ACK don't retransmit\n"
}

gemini-3.1-pro-preview

null

null

							input: 4761
							output: 20
							thoughts: 48
						

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

**Analyzing the Retransmission Timing**

Right, let's zero in on this `tcp_retransmit_timer`. It's a key function, and the way it interacts with `tcp_fastopen_synack_timer` is something I should focus on. That suggests an important connection to TCP Fast Open, a performance optimization that needs careful management.

Now, let's dig into how the retransmission timing is determined. I need to understand what's influencing the actual retransmission time. So, the first thing I need to do is to check the `secs_to_retrans` variable. That will tell me everything I need to know about the current retransmission backoff, or when the next retransmission will be attempted. I have to see how it's calculated, and what factors are feeding into it.

{
  "Expression": "secs_to_retrans"
}

{
  "Output": "net/ipv4/tcp.c=339=void tcp_leave_memory_pressure(struct sock *sk)\n--\nnet/ipv4/tcp.c-351-/* Convert seconds to retransmits based on initial and max timeout */\nnet/ipv4/tcp.c:352:static u8 secs_to_retrans(int seconds, int timeout, int rto_max)\nnet/ipv4/tcp.c-353-{\n--\nnet/ipv4/tcp.c=3837=int do_tcp_setsockopt(struct sock *sk, int level, int optname,\n--\nnet/ipv4/tcp.c-3935-\t\tWRITE_ONCE(icsk-\u003eicsk_accept_queue.rskq_defer_accept,\nnet/ipv4/tcp.c:3936:\t\t\t   secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,\nnet/ipv4/tcp.c-3937-\t\t\t\t\t   TCP_RTO_MAX / HZ));\n"
}

gemini-3.1-pro-preview

null

null

							input: 5281
							output: 20
							thoughts: 31
						

Okay, here's my take on those thoughts, framed as my own mental process, given my expertise:

**Checking Socket Options and Retransmission Timeouts**

Right, `do_tcp_setsockopt` – that's the function that handles socket option configurations at the TCP level. I need to keep in mind that this function is directly related to `secs_to_retrans`. So, I'm thinking, "Is there a direct link here?".

Okay, so I will now analyze the value returned by `secs_to_retrans`. This will help determine if there are issues. Now I should check `tcp_reqsk_timeout`. Is it in this same area? I should check it, because it is related to retransmission values. It might affect TCP requests and their timeouts, and that's something I need to keep in mind with regards to socket configuration. I want to make sure these values are consistent and correctly set to achieve optimal performance. I'm going to look into this now.

{
  "Expression": "tcp_reqsk_timeout"
}

{
  "Output": "include/net/tcp.h=882=static inline u32 __tcp_set_rto(const struct tcp_sock *tp)\n--\ninclude/net/tcp.h-886-\ninclude/net/tcp.h:887:static inline unsigned long tcp_reqsk_timeout_sk(const struct sock *sk,\ninclude/net/tcp.h-888-\t\t\t\t\t\t struct request_sock *req)\n--\ninclude/net/tcp.h-899-\ninclude/net/tcp.h:900:static inline unsigned long tcp_reqsk_timeout(struct request_sock *req)\ninclude/net/tcp.h-901-{\ninclude/net/tcp.h:902:\treturn tcp_reqsk_timeout_sk(req-\u003ersk_listener, req);\ninclude/net/tcp.h-903-}\n--\nnet/ipv4/inet_connection_sock.c=1033=static void reqsk_timer_handler(struct timer_list *t)\n--\nnet/ipv4/inet_connection_sock.c-1112-\t\t\tatomic_dec(\u0026queue-\u003eyoung);\nnet/ipv4/inet_connection_sock.c:1113:\t\tmod_timer(\u0026req-\u003ersk_timer, jiffies + tcp_reqsk_timeout(req));\nnet/ipv4/inet_connection_sock.c-1114-\n--\nnet/ipv4/tcp_minisocks.c=687=struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,\n--\nnet/ipv4/tcp_minisocks.c-718-\t\t\ttmp_opt.ts_recent_stamp = ktime_get_seconds() -\nnet/ipv4/tcp_minisocks.c:719:\t\t\t\ttcp_reqsk_timeout(req) / HZ;\nnet/ipv4/tcp_minisocks.c-720-\t\t\tpaws_reject = tcp_paws_reject(\u0026tmp_opt, th-\u003erst);\n--\nnet/ipv4/tcp_minisocks.c-767-\nnet/ipv4/tcp_minisocks.c:768:\t\t\t\texpires += tcp_reqsk_timeout(req);\nnet/ipv4/tcp_minisocks.c-769-\t\t\t\tif (!fastopen)\n--\nnet/ipv4/tcp_timer.c=457=static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)\n--\nnet/ipv4/tcp_timer.c-492-\ttcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,\nnet/ipv4/tcp_timer.c:493:\t\t\t     tcp_reqsk_timeout_sk(sk, req), false);\nnet/ipv4/tcp_timer.c-494-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 6250
							output: 20
							thoughts: 195
						

**Analyzing TCP Request Socket Timeouts**

Okay, so I'm diving into how these TCP request socket timeouts are handled, and it seems like a few functions are central to this process. I see that `reqsk_timer_handler` directly calls `tcp_reqsk_timeout`. Interesting. Also, `tcp_check_req` also calls `tcp_reqsk_timeout`, and `tcp_fastopen_synack_timer` calls `tcp_reqsk_timeout_sk`. Seems like a pattern here, with multiple paths leading to these timeout functions.

I'm particularly interested in a few key symbols: `do_tcp_setsockopt`, `tcp_retransmit_timer`, `reqsk_timer_handler`, and `tcp_check_req`. I need to understand how these pieces fit together.

Now, let's see if there are any specific configurations that I need to be aware of related to the timeout behavior. I quickly scanned for any relevant `CONFIG` options. I noticed `CONFIG_SYN_COOKIES` mentioned in `sysctl_net_ipv4.c`, but it appears to be related to another sysctl setting. The one I'm tracking is `tcp_synack_retries`, so I'll keep that in mind. Nothing specific leaps out. So, at least for now, it doesn't look like any special configurations are required for this timeout logic.

Finally, I'll quickly verify if `reqsk_timer_handler` is declared `static` or not. If it's static, I want to find the caller within the same scope. If it's not, I'll broaden my search. Understanding its scope and caller is vital to understanding the full picture of this subsystem.

{
  "Expression": "reqsk_timer_handler"
}

{
  "Output": "net/ipv4/inet_connection_sock.c=1027=void inet_csk_reqsk_queue_drop_and_put(struct sock *sk, struct request_sock *req)\n--\nnet/ipv4/inet_connection_sock.c-1032-\nnet/ipv4/inet_connection_sock.c:1033:static void reqsk_timer_handler(struct timer_list *t)\nnet/ipv4/inet_connection_sock.c-1034-{\n--\nnet/ipv4/inet_connection_sock.c-1059-\t\trefcount_set(\u0026nreq-\u003ersk_refcnt, 2 + 1);\nnet/ipv4/inet_connection_sock.c:1060:\t\ttimer_setup(\u0026nreq-\u003ersk_timer, reqsk_timer_handler, TIMER_PINNED);\nnet/ipv4/inet_connection_sock.c-1061-\t\treqsk_queue_migrated(\u0026inet_csk(nsk)-\u003eicsk_accept_queue, req);\n--\nnet/ipv4/inet_connection_sock.c=1150=static bool reqsk_queue_hash_req(struct request_sock *req)\n--\nnet/ipv4/inet_connection_sock.c-1158-\treq-\u003etimeout = tcp_timeout_init((struct sock *)req);\nnet/ipv4/inet_connection_sock.c:1159:\ttimer_setup(\u0026req-\u003ersk_timer, reqsk_timer_handler, TIMER_PINNED);\nnet/ipv4/inet_connection_sock.c-1160-\n--\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c=54=static struct migrate_reuseport_test_case {\n--\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c-83-\t{\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c:84:\t\t.name = \"IPv4 TCP_NEW_SYN_RECV reqsk_timer_handler\",\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c-85-\t\t.family = AF_INET,\n--\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c-115-\t{\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c:116:\t\t.name = \"IPv6 TCP_NEW_SYN_RECV reqsk_timer_handler\",\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c-117-\t\t.family = AF_INET6,\n--\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c=491=static void run_test(struct migrate_reuseport_test_case *test_case,\n--\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c-547-\t\t/* Wait for SYN+ACK timers to expire so that\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c:548:\t\t * reqsk_timer_handler() migrates TCP_NEW_SYN_RECV requests.\ntools/testing/selftests/bpf/prog_tests/migrate_reuseport.c-549-\t\t */\n"
}

gemini-3.1-pro-preview

null

null

							input: 7673
							output: 19
							thoughts: 36
						

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

**Analyzing the Entry Point and Potential Cross-File Dependencies**

Alright, I'm looking at `reqsk_timer_handler`. Immediately, the "handler" suffix and context clue me in – this is a timer callback. So, it functions as an entry point, and that is important to remember. That means this is where the execution flow begins after a specific timer event. I'll need to keep that in mind when tracing execution.

Now, `tcp_check_req` has me wondering. Is this a function exposed to other parts of the kernel, or is it used across multiple files in this specific module? Knowing the scope of `tcp_check_req` is crucial. Is it an internal function or is it something declared as `EXPORT_SYMBOL`? Understanding its visibility will help me determine the breadth of its impact and how tightly coupled this code is. I need to track down its declaration and usage to understand its scope. It’s important to understand the relationship between this and the timer event. Does the timer affect the result or vice versa?

{
  "Expression": "tcp_check_req"
}

{
  "Output": "include/net/tcp.h=478=enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,\n--\ninclude/net/tcp.h-482-\t\t\t\t\t      enum skb_drop_reason *drop_reason);\ninclude/net/tcp.h:483:struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,\ninclude/net/tcp.h-484-\t\t\t   struct request_sock *req, bool fastopen,\n--\nnet/ipv4/tcp_input.c=7152=tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)\n--\nnet/ipv4/tcp_input.c-7218-\t\tSKB_DR_SET(reason, TCP_FASTOPEN);\nnet/ipv4/tcp_input.c:7219:\t\tif (!tcp_check_req(sk, skb, req, true, \u0026req_stolen, \u0026reason))\nnet/ipv4/tcp_input.c-7220-\t\t\tgoto discard;\n--\nnet/ipv4/tcp_ipv4.c=2070=int tcp_v4_rcv(struct sk_buff *skb)\n--\nnet/ipv4/tcp_ipv4.c-2165-\t\t\ttcp_v4_fill_cb(skb, iph, th);\nnet/ipv4/tcp_ipv4.c:2166:\t\t\tnsk = tcp_check_req(sk, skb, req, false, \u0026req_stolen,\nnet/ipv4/tcp_ipv4.c-2167-\t\t\t\t\t    \u0026drop_reason);\n--\nnet/ipv4/tcp_minisocks.c=546=struct sock *tcp_create_openreq_child(const struct sock *sk,\n--\nnet/ipv4/tcp_minisocks.c-686-\nnet/ipv4/tcp_minisocks.c:687:struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,\nnet/ipv4/tcp_minisocks.c-688-\t\t\t   struct request_sock *req,\n--\nnet/ipv6/tcp_ipv6.c=1730=INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)\n--\nnet/ipv6/tcp_ipv6.c-1821-\t\t\ttcp_v6_fill_cb(skb, hdr, th);\nnet/ipv6/tcp_ipv6.c:1822:\t\t\tnsk = tcp_check_req(sk, skb, req, false, \u0026req_stolen,\nnet/ipv6/tcp_ipv6.c-1823-\t\t\t\t\t    \u0026drop_reason);\n"
}

gemini-3.1-pro-preview

null

null

							input: 8669
							output: 20
							thoughts: 89
						

Here's my analysis of this code snippet:

**Diving into TCP Connection Handling**

Okay, so I'm looking at how TCP connection requests are validated, and where to focus my attention. It's pretty clear that `tcp_check_req` is the key function being called from both IPv4 and IPv6 reception paths (`tcp_v4_rcv` and `tcp_v6_rcv`). Those receiver functions are definitely good starting points to understand the broader context, but, knowing the architecture, I need to remember those are incredibly hot code paths – every packet goes through them, which means they are likely optimized. So, a deeper dive there will be costly in terms of understanding. Therefore, `tcp_check_req` itself seems like a better, less noisy, focus symbol. This is where I should concentrate my initial efforts.

Now, let's pivot. Since we're dealing with connection validation and potential retransmissions, `tcp_retransmit_timer` is another symbol that requires investigation. Let's see what that has to offer.

{
  "Expression": "tcp_retransmit_timer"
}

{
  "Output": "include/net/inet_connection_sock.h=193=static inline unsigned long tcp_timeout_expires(const struct sock *sk)\ninclude/net/inet_connection_sock.h-194-{\ninclude/net/inet_connection_sock.h:195:\treturn READ_ONCE(sk-\u003etcp_retransmit_timer.expires);\ninclude/net/inet_connection_sock.h-196-}\n--\ninclude/net/inet_connection_sock.h=204=static inline void inet_csk_clear_xmit_timer(struct sock *sk, const int what)\n--\ninclude/net/inet_connection_sock.h-210-#ifdef INET_CSK_CLEAR_TIMERS\ninclude/net/inet_connection_sock.h:211:\t\tsk_stop_timer(sk, \u0026sk-\u003etcp_retransmit_timer);\ninclude/net/inet_connection_sock.h-212-#endif\n--\ninclude/net/inet_connection_sock.h=227=static inline void inet_csk_reset_xmit_timer(struct sock *sk, const int what,\n--\ninclude/net/inet_connection_sock.h-242-\t\tsmp_store_release(\u0026icsk-\u003eicsk_pending, what);\ninclude/net/inet_connection_sock.h:243:\t\tsk_reset_timer(sk, \u0026sk-\u003etcp_retransmit_timer, when);\ninclude/net/inet_connection_sock.h-244-\t} else if (what == ICSK_TIME_DACK) {\n--\ninclude/net/sock.h=242=struct sk_filter;\n--\ninclude/net/sock.h-312-  *\t@sk_timer: sock cleanup timer\ninclude/net/sock.h:313:  *\t@tcp_retransmit_timer: tcp retransmit timer\ninclude/net/sock.h:314:  *\t@mptcp_retransmit_timer: mptcp retransmit timer\ninclude/net/sock.h-315-  *\t@sk_stamp: time stamp of last packet received\n--\ninclude/net/sock.h=365=struct sock {\n--\ninclude/net/sock.h-494-\t\tstruct timer_list\tsk_timer;\ninclude/net/sock.h:495:\t\tstruct timer_list\ttcp_retransmit_timer;\ninclude/net/sock.h:496:\t\tstruct timer_list\tmptcp_retransmit_timer;\ninclude/net/sock.h-497-\t};\n--\ninclude/net/tcp.h=753=int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs);\ninclude/net/tcp.h:754:void tcp_retransmit_timer(struct sock *sk);\ninclude/net/tcp.h-755-void tcp_xmit_retransmit_queue(struct sock *);\n--\nnet/ipv4/inet_connection_sock.c=718=void inet_csk_init_xmit_timers(struct sock *sk,\n--\nnet/ipv4/inet_connection_sock.c-724-\nnet/ipv4/inet_connection_sock.c:725:\ttimer_setup(\u0026sk-\u003etcp_retransmit_timer, retransmit_handler, 0);\nnet/ipv4/inet_connection_sock.c-726-\ttimer_setup(\u0026icsk-\u003eicsk_delack_timer, delack_handler, 0);\n--\nnet/ipv4/inet_connection_sock.c=731=void inet_csk_clear_xmit_timers(struct sock *sk)\n--\nnet/ipv4/inet_connection_sock.c-737-\nnet/ipv4/inet_connection_sock.c:738:\tsk_stop_timer(sk, \u0026sk-\u003etcp_retransmit_timer);\nnet/ipv4/inet_connection_sock.c-739-\tsk_stop_timer(sk, \u0026icsk-\u003eicsk_delack_timer);\n--\nnet/ipv4/inet_connection_sock.c=743=void inet_csk_clear_xmit_timers_sync(struct sock *sk)\n--\nnet/ipv4/inet_connection_sock.c-752-\nnet/ipv4/inet_connection_sock.c:753:\tsk_stop_timer_sync(sk, \u0026sk-\u003etcp_retransmit_timer);\nnet/ipv4/inet_connection_sock.c-754-\tsk_stop_timer_sync(sk, \u0026icsk-\u003eicsk_delack_timer);\n--\nnet/ipv4/tcp_ipv4.c=438=void tcp_ld_RTO_revert(struct sock *sk, u32 seq)\n--\nnet/ipv4/tcp_ipv4.c-470-\t\t */\nnet/ipv4/tcp_ipv4.c:471:\t\ttcp_retransmit_timer(sk);\nnet/ipv4/tcp_ipv4.c-472-\t}\n--\nnet/ipv4/tcp_timer.c=389=static void tcp_probe_timer(struct sock *sk)\n--\nnet/ipv4/tcp_timer.c-407-\t * corresponding system limit. We also implement similar policy when\nnet/ipv4/tcp_timer.c:408:\t * we use RTO to probe window in tcp_retransmit_timer().\nnet/ipv4/tcp_timer.c-409-\t */\n--\nnet/ipv4/tcp_timer.c=496=static bool tcp_rtx_probe0_timed_out(const struct sock *sk,\n--\nnet/ipv4/tcp_timer.c-526-/**\nnet/ipv4/tcp_timer.c:527: *  tcp_retransmit_timer() - The TCP retransmit timeout handler\nnet/ipv4/tcp_timer.c-528- *  @sk:  Pointer to the current socket.\n--\nnet/ipv4/tcp_timer.c-536- */\nnet/ipv4/tcp_timer.c:537:void tcp_retransmit_timer(struct sock *sk)\nnet/ipv4/tcp_timer.c-538-{\n--\nnet/ipv4/tcp_timer.c=697=void tcp_write_timer_handler(struct sock *sk)\n--\nnet/ipv4/tcp_timer.c-706-\tif (time_after(tcp_timeout_expires(sk), jiffies)) {\nnet/ipv4/tcp_timer.c:707:\t\tsk_reset_timer(sk, \u0026sk-\u003etcp_retransmit_timer,\nnet/ipv4/tcp_timer.c-708-\t\t\t       tcp_timeout_expires(sk));\n--\nnet/ipv4/tcp_timer.c-722-\t\tsmp_store_release(\u0026icsk-\u003eicsk_pending, 0);\nnet/ipv4/tcp_timer.c:723:\t\ttcp_retransmit_timer(sk);\nnet/ipv4/tcp_timer.c-724-\t\tbreak;\n--\nnet/ipv4/tcp_timer.c=732=static void tcp_write_timer(struct timer_list *t)\nnet/ipv4/tcp_timer.c-733-{\nnet/ipv4/tcp_timer.c:734:\tstruct sock *sk = timer_container_of(sk, t, tcp_retransmit_timer);\nnet/ipv4/tcp_timer.c-735-\n--\nnet/mptcp/protocol.c=428=static void mptcp_stop_rtx_timer(struct sock *sk)\nnet/mptcp/protocol.c-429-{\nnet/mptcp/protocol.c:430:\tsk_stop_timer(sk, \u0026sk-\u003emptcp_retransmit_timer);\nnet/mptcp/protocol.c-431-\tmptcp_sk(sk)-\u003etimer_ival = 0;\n--\nnet/mptcp/protocol.c=997=static bool mptcp_rtx_timer_pending(struct sock *sk)\nnet/mptcp/protocol.c-998-{\nnet/mptcp/protocol.c:999:\treturn timer_pending(\u0026sk-\u003emptcp_retransmit_timer);\nnet/mptcp/protocol.c-1000-}\n--\nnet/mptcp/protocol.c=1002=static void mptcp_reset_rtx_timer(struct sock *sk)\n--\nnet/mptcp/protocol.c-1010-\ttout = mptcp_sk(sk)-\u003etimer_ival;\nnet/mptcp/protocol.c:1011:\tsk_reset_timer(sk, \u0026sk-\u003emptcp_retransmit_timer, jiffies + tout);\nnet/mptcp/protocol.c-1012-}\n--\nnet/mptcp/protocol.c=2313=static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,\n--\nnet/mptcp/protocol.c-2424-\nnet/mptcp/protocol.c:2425:static void mptcp_retransmit_timer(struct timer_list *t)\nnet/mptcp/protocol.c-2426-{\nnet/mptcp/protocol.c:2427:\tstruct sock *sk = timer_container_of(sk, t, mptcp_retransmit_timer);\nnet/mptcp/protocol.c-2428-\tstruct mptcp_sock *msk = mptcp_sk(sk);\n--\nnet/mptcp/protocol.c=3044=static void __mptcp_init_sock(struct sock *sk)\n--\nnet/mptcp/protocol.c-3074-\t/* re-use the csk retrans timer for MPTCP-level retrans */\nnet/mptcp/protocol.c:3075:\ttimer_setup(\u0026sk-\u003emptcp_retransmit_timer, mptcp_retransmit_timer, 0);\nnet/mptcp/protocol.c-3076-\ttimer_setup(\u0026msk-\u003esk.mptcp_tout_timer, mptcp_tout_timer, 0);\n--\ntools/testing/selftests/bpf/progs/bpf_iter_tcp4.c=74=static int dump_tcp_sock(struct seq_file *seq, struct tcp_sock *tp,\n--\ntools/testing/selftests/bpf/progs/bpf_iter_tcp4.c-101-\t\ttimer_active = 1;\ntools/testing/selftests/bpf/progs/bpf_iter_tcp4.c:102:\t\ttimer_expires = sp-\u003etcp_retransmit_timer.expires;\ntools/testing/selftests/bpf/progs/bpf_iter_tcp4.c-103-\t} else if (icsk-\u003eicsk_pending == ICSK_TIME_PROBE0) {\ntools/testing/selftests/bpf/progs/bpf_iter_tcp4.c-104-\t\ttimer_active = 4;\ntools/testing/selftests/bpf/progs/bpf_iter_tcp4.c:105:\t\ttimer_expires = sp-\u003etcp_retransmit_timer.expires;\ntools/testing/selftests/bpf/progs/bpf_iter_tcp4.c-106-\t} else if (timer_pending(\u0026icsk-\u003eicsk_keepalive_timer)) {\n--\ntools/testing/selftests/bpf/progs/bpf_iter_tcp6.c=74=static int dump_tcp6_sock(struct seq_file *seq, struct tcp6_sock *tp,\n--\ntools/testing/selftests/bpf/progs/bpf_iter_tcp6.c-101-\t\ttimer_active = 1;\ntools/testing/selftests/bpf/progs/bpf_iter_tcp6.c:102:\t\ttimer_expires = sp-\u003etcp_retransmit_timer.expires;\ntools/testing/selftests/bpf/progs/bpf_iter_tcp6.c-103-\t} else if (icsk-\u003eicsk_pending == ICSK_TIME_PROBE0) {\ntools/testing/selftests/bpf/progs/bpf_iter_tcp6.c-104-\t\ttimer_active = 4;\ntools/testing/selftests/bpf/progs/bpf_iter_tcp6.c:105:\t\ttimer_expires = sp-\u003etcp_retransmit_timer.expires;\ntools/testing/selftests/bpf/progs/bpf_iter_tcp6.c-106-\t} else if (timer_pending(\u0026icsk-\u003eicsk_keepalive_timer)) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 12198
							output: 127
							thoughts: 731
						

**My Analysis of TCP Timer and Socket Option Entry Points**

Okay, let's break this down. My goal is to identify the key entry points into the relevant TCP logic, keeping in mind the preference for non-static, non-inlined functions as the "cleanest" way to access the code. I need to trace how the `tcp_retransmit_timer`, `reqsk_timer_handler`, `tcp_check_req`, and `do_tcp_setsockopt` functions relate to each other.

First, I see that `tcp_retransmit_timer` is triggered from `tcp_write_timer_handler`, which itself is a callback from the `tcp_write_timer`. That's a clear chain. The list I'm working with is:

*   `do_tcp_setsockopt`
*   `tcp_retransmit_timer`
*   `reqsk_timer_handler`
*   `tcp_check_req`

Wait, `reqsk_timer_handler` is marked as `static`. That means it's not directly exported. However, it *is* a timer callback, so its address is taken and passed to `timer_setup`. Therefore, it's safe to use it, even if it's static, since it won't be inlined. The other three look good: `tcp_check_req`, `do_tcp_setsockopt`, and `tcp_retransmit_timer` are all non-static.

Now, I'm digging deeper to see which of these are the best entry points. Looking at the call chains:

*   `do_tcp_setsockopt` is directly connected to `secs_to_retrans` when setting `TCP_DEFER_ACCEPT`. Seems like a good entry point.
*   `tcp_retransmit_timer` directly calls `tcp_fastopen_synack_timer`. Makes sense as an entry point.
*   `reqsk_timer_handler` directly calls `tcp_reqsk_timeout`. Confirms this is a good entry point.
*   `tcp_check_req` also calls `tcp_reqsk_timeout`. Confirms this is a good entry point as well.

So, I have a good handle on where the logic starts. There are no configuration options I need to worry about here.

Based on this analysis, the patch focuses on modifying TCP SYNACK retries and timeout calculation, specifically to address potential overflow issues and limit `tcp_synack_retries` to 127. These changes touch core connection establishment and retransmission logic. This logic is accessible through socket options and timer callbacks involved in connection handling.

{
  "EnableConfigs": [],
  "FocusSymbols": [
    "do_tcp_setsockopt",
    "tcp_retransmit_timer",
    "reqsk_timer_handler",
    "tcp_check_req"
  ],
  "Reasoning": "The patch modifies TCP SYNACK retries limits and timeout calculation logic to prevent shift overflows and bounds `tcp_synack_retries` to 127. These changes affect core TCP connection establishment and retransmission logic. The modifications are reachable via TCP socket options and timer callbacks during connection handling.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": null,
  "FocusSymbols": [
    "do_tcp_setsockopt",
    "tcp_retransmit_timer",
    "reqsk_timer_handler",
    "tcp_check_req"
  ],
  "Reasoning": "The patch modifies TCP SYNACK retries limits and timeout calculation logic to prevent shift overflows and bounds `tcp_synack_retries` to 127. These changes affect core TCP connection establishment and retransmission logic. The modifications are reachable via TCP socket options and timer callbacks during connection handling.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

best-expensive

null

{
  "KMSANReasoning": "The patch fixes an integer overflow and out-of-bounds shift in TCP timeout calculation (`req-\u003etimeout \u003c\u003c req-\u003enum_timeout`) by capping the maximum number of SYNACK retries to 127 and adding overflow checks in `tcp_reqsk_timeout_sk`. It does not introduce any new memory allocations, uninitialized variables, or data copied to userspace. Standard KASAN and UBSAN are sufficient to detect memory corruption or undefined behavior related to this code. KMSAN is not applicable.",
  "NeedsKMSAN": false
}

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

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

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

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

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

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

Use your code access tools to inspect the surrounding code if necessary, then provide
detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 806434ca0328309a350aeafd7b616e304128681d
Author: syz-cluster <triage@syzkaller.com>
Date:   Wed Aug 12 15:39:47 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 208f46967ee59..fd5038b6cab9f 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -954,7 +954,7 @@ tcp_stdurg - BOOLEAN
 
 tcp_synack_retries - INTEGER
 	Number of times SYNACKs for a passive TCP connection attempt will
-	be retransmitted. Should not be higher than 255. Default value
+	be retransmitted. Should not be higher than 127. Default value
 	is 5, which corresponds to 31seconds till the last retransmission
 	with the current initial RTO of 1second. With this the final timeout
 	for a passive TCP connection will happen after 63seconds.
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 2c5b889530b55..8ab2fd368ed3b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -183,6 +183,8 @@ static_assert((1 << ATO_BITS) > TCP_DELACK_MAX);
 #define MAX_TCP_KEEPINTVL	32767
 #define MAX_TCP_KEEPCNT		127
 #define MAX_TCP_SYNCNT		127
+/* request_sock::num_timeout is a 7-bit field. */
+#define MAX_TCP_SYNACK_RETRIES	127
 
 /* Ensure that TCP PAWS checks are relaxed after ~2147 seconds
  * to avoid overflows. This assumes a clock smaller than 1 Mhz.
@@ -882,12 +884,22 @@ static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
 	return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
 }
 
-static inline unsigned long tcp_reqsk_timeout(struct request_sock *req)
+static inline unsigned long tcp_reqsk_timeout_sk(const struct sock *sk,
+						 struct request_sock *req)
 {
-	u64 timeout = (u64)req->timeout << req->num_timeout;
+	u32 rto_max = tcp_rto_max(sk);
+	u64 timeout = req->timeout;
+
+	if (req->num_timeout >= BITS_PER_TYPE(timeout) ||
+	    timeout > U64_MAX >> req->num_timeout)
+		return rto_max;
+
+	return (unsigned long)min_t(u64, timeout << req->num_timeout, rto_max);
+}
 
-	return (unsigned long)min_t(u64, timeout,
-				    tcp_rto_max(req->rsk_listener));
+static inline unsigned long tcp_reqsk_timeout(struct request_sock *req)
+{
+	return tcp_reqsk_timeout_sk(req->rsk_listener, req);
 }
 
 u32 tcp_delack_max(const struct sock *sk);
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index ca1180dba1dea..fc5152dfa3c86 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -35,6 +35,7 @@ static int ip_ttl_min = 1;
 static int ip_ttl_max = 255;
 static int tcp_syn_retries_min = 1;
 static int tcp_syn_retries_max = MAX_TCP_SYNCNT;
+static int tcp_synack_retries_max = MAX_TCP_SYNACK_RETRIES;
 static int tcp_syn_linear_timeouts_max = MAX_TCP_SYNCNT;
 static unsigned long ip_ping_group_range_min[] = { 0, 0 };
 static unsigned long ip_ping_group_range_max[] = { GID_T_MAX, GID_T_MAX };
@@ -1034,6 +1035,7 @@ static struct ctl_table ipv4_net_table[] = {
 		.maxlen		= sizeof(u8),
 		.mode		= 0644,
 		.proc_handler	= proc_dou8vec_minmax,
+		.extra2		= &tcp_synack_retries_max,
 	},
 #ifdef CONFIG_SYN_COOKIES
 	{
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 455441f1b6949..24896fa08a5d8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -357,7 +357,7 @@ static u8 secs_to_retrans(int seconds, int timeout, int rto_max)
 		int period = timeout;
 
 		res = 1;
-		while (seconds > period && res < 255) {
+		while (seconds > period && res < MAX_TCP_SYNACK_RETRIES) {
 			res++;
 			timeout <<= 1;
 			if (timeout > rto_max)
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index bf171b5e1eb30..daa4eac072dd9 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -462,11 +462,13 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 
 	tcp_syn_ack_timeout(req);
 
-	/* Add one more retry for fastopen.
+	/* Add one more retry for fastopen when the timeout counter can
+	 * represent it.
 	 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()
 	 */
 	max_retries = READ_ONCE(icsk->icsk_syn_retries) ? :
 		READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;
+	max_retries = min_t(int, max_retries, MAX_TCP_SYNACK_RETRIES);
 
 	if (req->num_timeout >= max_retries) {
 		tcp_write_err(sk);
@@ -488,7 +490,7 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 	if (!tp->retrans_stamp)
 		tp->retrans_stamp = tcp_time_stamp_ts(tp);
 	tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-			  req->timeout << req->num_timeout, false);
+			     tcp_reqsk_timeout_sk(sk, req), false);
 }
 
 static bool tcp_rtx_probe0_timed_out(const struct sock *sk,

gemini-3.1-pro-preview

null

null

							input: 3662
							output: 131
							thoughts: 528
						

**KMSAN Fuzzing Session Assessment**

Okay, let's break this down. My initial assessment is that this patch, which modifies the TCP SYNACK retry logic, likely *doesn't* warrant a dedicated KMSAN fuzzing session. The core change here involves adjusting the maximum value of `tcp_synack_retries` from 255 to 127 and implementing `tcp_reqsk_timeout_sk` to prevent potential integer overflows during the timeout calculation. The `req->num_timeout` field being 7-bits is a key point, because that makes shifting by more than 63 a problem. However, the existing and new code carefully checks for potential overflows and limits retry counts.

My primary concern is always uninitialized memory, but this patch doesn't seem to introduce any new fields, nor does it copy data to userspace. In fact, it seems to *resolve* a potential overflow issue, specifically with that shift operation, by including a check on the timeout value. It's essentially a logic bug related to an out-of-bounds shift. While it could trigger undefined behavior, that is not directly related to uninitialized memory. We're talking about a shift that goes beyond a defined bit length. UBSAN or KASAN would be sufficient to detect that. I've double-checked that `req->num_timeout` is indeed a 7-bit field, and the overflow check makes sense.

Given all of that, I can confidently say that `NeedsKMSAN` is `false`. Standard KASAN and UBSAN should be adequate to catch any potential issues introduced by this patch. KMSAN is not necessary here.

{
  "KMSANReasoning": "The patch fixes an integer overflow and out-of-bounds shift in TCP timeout calculation (`req-\u003etimeout \u003c\u003c req-\u003enum_timeout`) by capping the maximum number of SYNACK retries to 127 and adding overflow checks in `tcp_reqsk_timeout_sk`. It does not introduce any new memory allocations, uninitialized variables, or data copied to userspace. Standard KASAN and UBSAN are sufficient to detect memory corruption or undefined behavior related to this code. KMSAN is not applicable.",
  "NeedsKMSAN": false
}

{
  "KMSANReasoning": "The patch fixes an integer overflow and out-of-bounds shift in TCP timeout calculation (`req-\u003etimeout \u003c\u003c req-\u003enum_timeout`) by capping the maximum number of SYNACK retries to 127 and adding overflow checks in `tcp_reqsk_timeout_sk`. It does not introduce any new memory allocations, uninitialized variables, or data copied to userspace. Standard KASAN and UBSAN are sufficient to detect memory corruption or undefined behavior related to this code. KMSAN is not applicable.",
  "NeedsKMSAN": false
}