AI Trajectory

null

{
  "EnableConfigs": [
    "IP_VS"
  ],
  "FocusSymbols": [
    "ip_vs_in_icmp"
  ],
  "Reasoning": "The patch modifies the MTU calculation logic for ICMP packets in IPVS by including the UDP/GRE header length (`ulen`). This is a functional change in the network packet processing path that should be fuzzed.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 90b99cd2fe9665cb72d159cbffaef284f4de141a\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Wed Jul 1 12:14:45 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c\nindex d40b404c1bf646..906f2c36167638 100644\n--- a/net/netfilter/ipvs/ip_vs_core.c\n+++ b/net/netfilter/ipvs/ip_vs_core.c\n@@ -1767,6 +1767,7 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff *skb, int *related,\n \tbool tunnel, new_cp = false;\n \tunion nf_inet_addr *raddr;\n \tchar *outer_proto = \"IPIP\";\n+\tint ulen = 0;\n \n \t*related = 1;\n \n@@ -1831,7 +1832,6 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff *skb, int *related,\n \t\t   /* Error for our tunnel must arrive at LOCAL_IN */\n \t\t   (skb_rtable(skb)-\u003ert_flags \u0026 RTCF_LOCAL)) {\n \t\t__u8 iproto;\n-\t\tint ulen;\n \n \t\t/* Non-first fragment has no UDP/GRE header */\n \t\tif (unlikely(cih-\u003efrag_off \u0026 htons(IP_OFFSET)))\n@@ -1936,8 +1936,8 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff *skb, int *related,\n \t\t\t\tif (dest_dst)\n \t\t\t\t\tmtu = dst_mtu(dest_dst-\u003edst_cache);\n \t\t\t}\n-\t\t\tif (mtu \u003e 68 + sizeof(struct iphdr))\n-\t\t\t\tmtu -= sizeof(struct iphdr);\n+\t\t\tif (mtu \u003e 68 + sizeof(struct iphdr) + ulen)\n+\t\t\t\tmtu -= sizeof(struct iphdr) + ulen;\n \t\t\tinfo = htonl(mtu);\n \t\t}\n \t\t/* Strip outer IP, ICMP and IPIP/UDP/GRE, go to IP header of\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "IP_VS"
  ],
  "FocusSymbols": [
    "ip_vs_in_icmp"
  ],
  "Reasoning": "The patch modifies the MTU calculation logic for ICMP packets in IPVS by including the UDP/GRE header length (`ulen`). This is a functional change in the network packet processing path that 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).

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.
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.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. 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 90b99cd2fe9665cb72d159cbffaef284f4de141a
Author: syz-cluster <triage@syzkaller.com>
Date:   Wed Jul 1 12:14:45 2026 +0000

    syz-cluster: applied patch under review

diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index d40b404c1bf646..906f2c36167638 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -1767,6 +1767,7 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff *skb, int *related,
 	bool tunnel, new_cp = false;
 	union nf_inet_addr *raddr;
 	char *outer_proto = "IPIP";
+	int ulen = 0;
 
 	*related = 1;
 
@@ -1831,7 +1832,6 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff *skb, int *related,
 		   /* Error for our tunnel must arrive at LOCAL_IN */
 		   (skb_rtable(skb)->rt_flags & RTCF_LOCAL)) {
 		__u8 iproto;
-		int ulen;
 
 		/* Non-first fragment has no UDP/GRE header */
 		if (unlikely(cih->frag_off & htons(IP_OFFSET)))
@@ -1936,8 +1936,8 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff *skb, int *related,
 				if (dest_dst)
 					mtu = dst_mtu(dest_dst->dst_cache);
 			}
-			if (mtu > 68 + sizeof(struct iphdr))
-				mtu -= sizeof(struct iphdr);
+			if (mtu > 68 + sizeof(struct iphdr) + ulen)
+				mtu -= sizeof(struct iphdr) + ulen;
 			info = htonl(mtu);
 		}
 		/* Strip outer IP, ICMP and IPIP/UDP/GRE, go to IP header of

gemini-3.1-pro-preview

null

null

							input: 2162
							output: 42
							thoughts: 174
						

**Analyzing the IPVS ICMP Handling Patch**

Okay, so I'm looking at this patch for `ip_vs_core.c` in the netfilter/ipvs module. The core of it seems straightforward: it's moving the `int ulen = 0;` declaration to a wider scope within the function, which then affects the `ip_vs_in_icmp` function. The key line change is this:

```c
-			if (mtu > 68 + sizeof(struct iphdr))
-				mtu -= sizeof(struct iphdr);
+			if (mtu > 68 + sizeof(struct iphdr) + ulen)
+				mtu -= sizeof(struct iphdr) + ulen;
```

Essentially, the patch is changing how the Maximum Transmission Unit (MTU) is adjusted when handling ICMP packets. Previously, it simply subtracted the size of the IP header (`sizeof(struct iphdr)`). Now, it also subtracts `ulen` which was previously initialized to 0. It must be intended for `ulen` to change, however. This seems like a functional change, a bit more than just a refactoring. I need to understand what `ulen` represents and how this affects the MTU calculation. The introduction of `ulen` into this equation implies some sort of offset or length adjustment is being added into the consideration of MTU sizes of ICMP packets, and I need to figure out the context of that adjustment. Let's delve into the context of `ip_vs_in_icmp` to understand the rationale behind this modification and the role `ulen` plays in the overall IPVS design. I'm going to look at the surrounding code to determine how `ulen` is set and what value it takes.

{
  "Expression": "ip_vs_in_icmp",
  "PathPrefix": "net/netfilter/ipvs/ip_vs_core.c"
}

{
  "Output": "net/netfilter/ipvs/ip_vs_core.c=1755=static int\nnet/netfilter/ipvs/ip_vs_core.c:1756:ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff *skb, int *related,\nnet/netfilter/ipvs/ip_vs_core.c-1757-\t      unsigned int hooknum)\n--\nnet/netfilter/ipvs/ip_vs_core.c-1978-#ifdef CONFIG_IP_VS_IPV6\nnet/netfilter/ipvs/ip_vs_core.c:1979:static int ip_vs_in_icmp_v6(struct netns_ipvs *ipvs, struct sk_buff *skb,\nnet/netfilter/ipvs/ip_vs_core.c-1980-\t\t\t    int *related, unsigned int hooknum,\n--\nnet/netfilter/ipvs/ip_vs_core.c=2086=ip_vs_in_hook(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)\n--\nnet/netfilter/ipvs/ip_vs_core.c-2135-\t\t\tint related;\nnet/netfilter/ipvs/ip_vs_core.c:2136:\t\t\tint verdict = ip_vs_in_icmp_v6(ipvs, skb, \u0026related,\nnet/netfilter/ipvs/ip_vs_core.c-2137-\t\t\t\t\t\t       hooknum, \u0026iph);\n--\nnet/netfilter/ipvs/ip_vs_core.c-2145-\t\t\tint related;\nnet/netfilter/ipvs/ip_vs_core.c:2146:\t\t\tint verdict = ip_vs_in_icmp(ipvs, skb, \u0026related,\nnet/netfilter/ipvs/ip_vs_core.c-2147-\t\t\t\t\t\t    hooknum);\n--\nnet/netfilter/ipvs/ip_vs_core.c-2274- *      but ICMP destined for 0.0.0.0/0 cannot not be easily marked and\nnet/netfilter/ipvs/ip_vs_core.c:2275: *      sent to ip_vs_in_icmp. So, catch them at the NF_INET_FORWARD chain\nnet/netfilter/ipvs/ip_vs_core.c:2276: *      and send them to ip_vs_in_icmp.\nnet/netfilter/ipvs/ip_vs_core.c-2277- */\n--\nnet/netfilter/ipvs/ip_vs_core.c=2279=ip_vs_forward_icmp(void *priv, struct sk_buff *skb,\n--\nnet/netfilter/ipvs/ip_vs_core.c-2300-\nnet/netfilter/ipvs/ip_vs_core.c:2301:\t\treturn ip_vs_in_icmp_v6(ipvs, skb, \u0026r, state-\u003ehook, \u0026iphdr);\nnet/netfilter/ipvs/ip_vs_core.c-2302-#endif\n--\nnet/netfilter/ipvs/ip_vs_core.c-2304-\nnet/netfilter/ipvs/ip_vs_core.c:2305:\treturn ip_vs_in_icmp(ipvs, skb, \u0026r, state-\u003ehook);\nnet/netfilter/ipvs/ip_vs_core.c-2306-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 3630
							output: 34
							thoughts: 26
						

Here's my take on the changes:

**Analyzing the IPVS Configuration**

Okay, so the `ip_vs_in_icmp` function has been touched. My immediate thought is, "What's changed, and how does it relate to the broader IP Virtual Server setup?" I need to understand the context of these modifications. I'll start by diving into the config options for IPVS. I want to quickly ascertain what flags or settings influence the behavior of `ip_vs_in_icmp`, or related functions and data structures. I need to understand if these changes imply a modification to default behavior, or if these changes are now configurable via an added option. Are there any new options introduced? Did the dependencies change?

{
  "Expression": "config IP_VS",
  "PathPrefix": "net/netfilter/ipvs/Kconfig"
}

{
  "Output": "net/netfilter/ipvs/Kconfig-4-#\nnet/netfilter/ipvs/Kconfig:5:menuconfig IP_VS\nnet/netfilter/ipvs/Kconfig-6-\ttristate \"IP virtual server support\"\n--\nnet/netfilter/ipvs/Kconfig=286=comment 'IPVS SH scheduler'\nnet/netfilter/ipvs/Kconfig-287-\nnet/netfilter/ipvs/Kconfig:288:config IP_VS_SH_TAB_BITS\nnet/netfilter/ipvs/Kconfig-289-\tint \"IPVS source hashing table size (the Nth power of 2)\"\n--\nnet/netfilter/ipvs/Kconfig=301=comment 'IPVS MH scheduler'\nnet/netfilter/ipvs/Kconfig-302-\nnet/netfilter/ipvs/Kconfig:303:config IP_VS_MH_TAB_INDEX\nnet/netfilter/ipvs/Kconfig-304-\tint \"IPVS maglev hashing table index of size (the prime numbers)\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 4112
							output: 32
							thoughts: 18
						

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

**Investigating the Configuration Landscape**

Okay, so the current configuration setting is `IP_VS`. My immediate thought is, "Is this the only configuration we're working with here?" Before I delve too deeply into the implications of `IP_VS`, I need to establish the scope. I need to make sure I haven't missed any other related configurations that might be in play, or that could influence how `IP_VS` is operating. It's best practice to rule out any potential conflicting or complementary settings early on. A thorough scan will save time and potential headaches down the line. I'll need to know the bigger picture.

{
  "Expression": "config IP_VS",
  "PathPrefix": "net/netfilter/ipvs/"
}

{
  "Output": "net/netfilter/ipvs/Kconfig-4-#\nnet/netfilter/ipvs/Kconfig:5:menuconfig IP_VS\nnet/netfilter/ipvs/Kconfig-6-\ttristate \"IP virtual server support\"\n--\nnet/netfilter/ipvs/Kconfig=286=comment 'IPVS SH scheduler'\nnet/netfilter/ipvs/Kconfig-287-\nnet/netfilter/ipvs/Kconfig:288:config IP_VS_SH_TAB_BITS\nnet/netfilter/ipvs/Kconfig-289-\tint \"IPVS source hashing table size (the Nth power of 2)\"\n--\nnet/netfilter/ipvs/Kconfig=301=comment 'IPVS MH scheduler'\nnet/netfilter/ipvs/Kconfig-302-\nnet/netfilter/ipvs/Kconfig:303:config IP_VS_MH_TAB_INDEX\nnet/netfilter/ipvs/Kconfig-304-\tint \"IPVS maglev hashing table index of size (the prime numbers)\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 4583
							output: 40
							thoughts: 83
						

Here's my thought process, as it stands:

**Reaching `ip_vs_in_icmp`**

Okay, so I need to figure out how `ip_vs_in_icmp` is being called. Let's see... Aha! It looks like it's called from both `ip_vs_in_hook` and `ip_vs_forward_icmp`. That's a good starting point. Now, the plot thickens... `ip_vs_in_hook` is registered as a netfilter hook. That definitely warrants a closer look. I need to understand the flow and context of that hook to fully grasp the execution path.

My next step is to examine `ip_vs_core.c`. I expect to find the details of how that netfilter hook is set up, specifically the `nf_hook_ops` structure which holds all the hook details. That should clarify the priority, the hook point, and the function being registered. This will give me a clear picture of how `ip_vs_in_icmp` fits into the broader connection tracking and forwarding context.

{
  "Expression": "nf_hook_ops",
  "PathPrefix": "net/netfilter/ipvs/ip_vs_core.c"
}

{
  "Output": "net/netfilter/ipvs/ip_vs_core.c=2279=ip_vs_forward_icmp(void *priv, struct sk_buff *skb,\n--\nnet/netfilter/ipvs/ip_vs_core.c-2307-\nnet/netfilter/ipvs/ip_vs_core.c:2308:static const struct nf_hook_ops ip_vs_ops4[] = {\nnet/netfilter/ipvs/ip_vs_core.c-2309-\t/* After packet filtering, change source only for VS/NAT */\n--\nnet/netfilter/ipvs/ip_vs_core.c-2356-#ifdef CONFIG_IP_VS_IPV6\nnet/netfilter/ipvs/ip_vs_core.c:2357:static const struct nf_hook_ops ip_vs_ops6[] = {\nnet/netfilter/ipvs/ip_vs_core.c-2358-\t/* After packet filtering, change source only for VS/NAT */\n--\nnet/netfilter/ipvs/ip_vs_core.c=2406=int ip_vs_register_hooks(struct netns_ipvs *ipvs, unsigned int af)\nnet/netfilter/ipvs/ip_vs_core.c-2407-{\nnet/netfilter/ipvs/ip_vs_core.c:2408:\tconst struct nf_hook_ops *ops;\nnet/netfilter/ipvs/ip_vs_core.c-2409-\tunsigned int count;\n--\nnet/netfilter/ipvs/ip_vs_core.c=2435=void ip_vs_unregister_hooks(struct netns_ipvs *ipvs, unsigned int af)\nnet/netfilter/ipvs/ip_vs_core.c-2436-{\nnet/netfilter/ipvs/ip_vs_core.c:2437:\tconst struct nf_hook_ops *ops;\nnet/netfilter/ipvs/ip_vs_core.c-2438-\tunsigned int count;\n"
}

gemini-3.1-pro-preview

null

null

							input: 5459
							output: 34
							thoughts: 398
						

**Analyzing the `ip_vs_in_icmp` Vulnerability Patch**

Okay, so I've confirmed that the code path for `ip_vs_in_icmp` is definitely reachable. Now, diving into this patch, it's clear it addresses an MTU calculation issue. The core problem is that `ulen`, which represents the UDP or GRE payload length, was either being used before it was initialized, or the original code wasn't correctly incorporating it into the MTU calculation.

Looking at the original code snippet, it's pretty obvious. `ulen` and `iproto` are declared *inside* a nested `if/else` block based on the IP header. The code reads:

```c
		__u8 iproto;
		int ulen;
```
```c
	if (ip_is_fragment(iph)) {
		...
	} else if (unlikely(cih->frag_off & htons(IP_OFFSET))) {
		/* Non-first fragment has no UDP/GRE header */
		...
	} else {
		...
		if (iproto == IPPROTO_UDP) {
			...
			ulen = ntohs(uh->len);
		} else if (iproto == IPPROTO_GRE) {
			...
			ulen = ...
		}
	}
```

Then, later, the code performs the MTU adjustment using `mtu -= sizeof(struct iphdr);`. The fix changes this MTU adjustment to:

```c
			if (mtu > 68 + sizeof(struct iphdr) + ulen)
				mtu -= sizeof(struct iphdr) + ulen;
```

Crucially, it *also* moves the `ulen` declaration to the outer scope to ensure it's always initialized and considered in the calculation. This is a clear functional change, improving the accuracy of MTU handling for these types of packets. My primary focus here is definitely on `ip_vs_in_icmp`.

I'm making sure to check the configuration options. The symbol `ip_vs_in_icmp` itself is located in `net/netfilter/ipvs/ip_vs_core.c`. As expected, the code is under `IP_VS`. I need to ensure that `IP_VS` is enabled. A quick check of the `net/netfilter/ipvs/Makefile` confirms there are no specific configuration options tied just to the ICMP side of IPVS, just the general `IP_VS` config. Excellent. That covers the build requirements.

{
  "Expression": "ip_vs_core",
  "PathPrefix": "net/netfilter/ipvs/Makefile"
}

{
  "Output": "net/netfilter/ipvs/Makefile=14=ip_vs-extra_objs-$(CONFIG_IP_VS_NFCT) += ip_vs_nfct.o\nnet/netfilter/ipvs/Makefile-15-\nnet/netfilter/ipvs/Makefile:16:ip_vs-objs :=\tip_vs_conn.o ip_vs_core.o ip_vs_ctl.o ip_vs_sched.o\t   \\\nnet/netfilter/ipvs/Makefile-17-\t\tip_vs_xmit.o ip_vs_app.o ip_vs_sync.o\t   \t\t   \\\n"
}

gemini-3.1-pro-preview

null

null

							input: 5906
							output: 89
							thoughts: 473
						

**My Analysis of the IPVS ICMP Patch**

Okay, so this patch is a straightforward modification within the `ip_vs_in_icmp` function, found in `net/netfilter/ipvs/ip_vs_core.c`. My initial assessment indicates a functional change directly affecting how IPVS handles ICMP packets, specifically in the calculation of MTU.

The core of the change lies in how `ulen` is handled. It's now declared at the function's outer scope and initialized to zero. Crucially, this `ulen` variable is then incorporated into the MTU calculation:

```c
-			if (mtu > 68 + sizeof(struct iphdr))
-				mtu -= sizeof(struct iphdr);
+			if (mtu > 68 + sizeof(struct iphdr) + ulen)
+				mtu -= sizeof(struct iphdr) + ulen;
```

This suggests the code now accounts for potential UDP or GRE header lengths when determining the maximum transmittable unit for ICMP error handling. The issue the patch fixes is that `ulen` was previously scoped within a specific block.

Given the nature of the change, it's essential to understand the broader context. Let's examine the relevant configuration options. `CONFIG_IP_VS` is obviously the primary enabler for IPVS. While `CONFIG_IP_VS_IPV6` might be relevant if this were IPv6-specific, the modified function (`ip_vs_in_icmp`) is definitively IPv4, so IPv6 concerns are secondary for this specific patch. From what I recall, `ip_vs_in_icmp` is called from `ip_vs_in_hook` and `ip_vs_forward_icmp`. I'm going to quickly confirm that the patch only affects `ip_vs_in_icmp`, and yes, it's the only function changed.

Given the impact on ICMP packet handling and the change in MTU calculation, which is a critical aspect of network packet processing, fuzzing this patch is warranted. I will set `WorthFuzzing` to `true`.

I'll focus the fuzzing efforts specifically on `ip_vs_in_icmp`, making it the `FocusSymbols`.

I will set the `EnableConfigs` to `["IP_VS"]`, as it's a prerequisite.

My `Reasoning` will be: "The patch modifies the MTU calculation logic for ICMP packets in IPVS by including the UDP/GRE header length (`ulen`). This is a functional change in the network packet processing path that should be fuzzed."

{
  "EnableConfigs": [
    "IP_VS"
  ],
  "FocusSymbols": [
    "ip_vs_in_icmp"
  ],
  "Reasoning": "The patch modifies the MTU calculation logic for ICMP packets in IPVS by including the UDP/GRE header length (`ulen`). This is a functional change in the network packet processing path that should be fuzzed.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "IP_VS"
  ],
  "FocusSymbols": [
    "ip_vs_in_icmp"
  ],
  "Reasoning": "The patch modifies the MTU calculation logic for ICMP packets in IPVS by including the UDP/GRE header length (`ulen`). This is a functional change in the network packet processing path that should be fuzzed.",
  "WorthFuzzing": true
}