AI Trajectory


Trajectory: (Expand/Collapse All)
Seq Timestamp Type Name Duration
0/0 2026/08/25 08:05 flow patch-triage
0m Args: 
null

Results: 
{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "KMSANReasoning": "",
  "NeedsKMSAN": false,
  "Reasoning": "The patch only introduces a new skb drop reason (SKB_DROP_REASON_IP_TTL_EXCEEDED) and updates several call sites to use it instead of generic drop reasons or kfree_skb(). Drop reasons are used for tracing and observability, and these changes do not functionally alter the execution flow of the kernel.",
  "WorthFuzzing": false
}
1/1 2026/08/25 08:05 action read-patch-diff
0m Args: 
null

Results: 
{
  "PatchDiff": "commit 6aa8c188994550bf2f4694c8e48df6c488fecdf4\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Tue Aug 25 08:05:09 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h\nindex 2f312d1f67d69..3046a2699479d 100644\n--- a/include/net/dropreason-core.h\n+++ b/include/net/dropreason-core.h\n@@ -128,6 +128,7 @@\n \tFN(PSP_INPUT)\t\t\t\\\n \tFN(PSP_OUTPUT)\t\t\t\\\n \tFN(RECURSION_LIMIT)\t\t\\\n+\tFN(IP_TTL_EXCEEDED)\t\t\\\n \tFNe(MAX)\n \n /**\n@@ -606,6 +607,11 @@ enum skb_drop_reason {\n \tSKB_DROP_REASON_PSP_OUTPUT,\n \t/** @SKB_DROP_REASON_RECURSION_LIMIT: Dead loop on virtual device. */\n \tSKB_DROP_REASON_RECURSION_LIMIT,\n+\t/**\n+\t * @SKB_DROP_REASON_IP_TTL_EXCEEDED: IPv4 TTL or IPv6 hop limit hit\n+\t * zero on a packet being forwarded (see IPSTATS_MIB_INHDRERRORS)\n+\t */\n+\tSKB_DROP_REASON_IP_TTL_EXCEEDED,\n \t/**\n \t * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which\n \t * shouldn't be used as a real 'reason' - only for tracing code gen\ndiff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c\nindex 8b65f12583eb6..b242561d37e73 100644\n--- a/net/ipv4/ip_forward.c\n+++ b/net/ipv4/ip_forward.c\n@@ -174,7 +174,7 @@ int ip_forward(struct sk_buff *skb)\n \t/* Tell the sender its packet died... */\n \t__IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);\n \ticmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);\n-\tSKB_DR_SET(reason, IP_INHDR);\n+\tSKB_DR_SET(reason, IP_TTL_EXCEEDED);\n drop:\n \tkfree_skb_reason(skb, reason);\n \treturn NET_RX_DROP;\ndiff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c\nindex 9c677eb1d1a61..b9103b02e8c74 100644\n--- a/net/ipv6/exthdrs.c\n+++ b/net/ipv6/exthdrs.c\n@@ -471,7 +471,7 @@ static int ipv6_srh_rcv(struct sk_buff *skb)\n \t\t\t__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);\n \t\t\ticmpv6_send(skb, ICMPV6_TIME_EXCEED,\n \t\t\t\t    ICMPV6_EXC_HOPLIMIT, 0);\n-\t\t\tkfree_skb(skb);\n+\t\t\tkfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED);\n \t\t\treturn -1;\n \t\t}\n \t\tipv6_hdr(skb)-\u003ehop_limit--;\n@@ -633,7 +633,7 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)\n \t\t\t__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);\n \t\t\ticmpv6_send(skb, ICMPV6_TIME_EXCEED,\n \t\t\t\t    ICMPV6_EXC_HOPLIMIT, 0);\n-\t\t\tkfree_skb(skb);\n+\t\t\tkfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED);\n \t\t\treturn -1;\n \t\t}\n \t\tipv6_hdr(skb)-\u003ehop_limit--;\n@@ -821,7 +821,7 @@ static int ipv6_rthdr_rcv(struct sk_buff *skb)\n \t\t\t__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);\n \t\t\ticmpv6_send(skb, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT,\n \t\t\t\t    0);\n-\t\t\tkfree_skb(skb);\n+\t\t\tkfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED);\n \t\t\treturn -1;\n \t\t}\n \t\tipv6_hdr(skb)-\u003ehop_limit--;\ndiff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c\nindex 8fc4766c8da90..0b6d78c8b6be4 100644\n--- a/net/ipv6/ip6_output.c\n+++ b/net/ipv6/ip6_output.c\n@@ -577,7 +577,7 @@ int ip6_forward(struct sk_buff *skb)\n \t\ticmpv6_send(skb, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT, 0);\n \t\t__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);\n \n-\t\tkfree_skb_reason(skb, SKB_DROP_REASON_IP_INHDR);\n+\t\tkfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED);\n \t\treturn -ETIMEDOUT;\n \t}\n \n"
}
2/1 2026/08/25 08:05 agent patch-evaluator
0m Model: 
best-expensive

Args: 
null

Results: 
{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch only introduces a new skb drop reason (SKB_DROP_REASON_IP_TTL_EXCEEDED) and updates several call sites to use it instead of generic drop reasons or kfree_skb(). Drop reasons are used for tracing and observability, and these changes do not functionally alter the execution flow of the kernel.",
  "WorthFuzzing": false
}

Instruction: 
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.

Prompt: 
For your convenience, here is the diff of the changes:
commit 6aa8c188994550bf2f4694c8e48df6c488fecdf4
Author: syz-cluster <triage@syzkaller.com>
Date:   Tue Aug 25 08:05:09 2026 +0000

    syz-cluster: applied patch under review

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index 2f312d1f67d69..3046a2699479d 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -128,6 +128,7 @@
 	FN(PSP_INPUT)			\
 	FN(PSP_OUTPUT)			\
 	FN(RECURSION_LIMIT)		\
+	FN(IP_TTL_EXCEEDED)		\
 	FNe(MAX)
 
 /**
@@ -606,6 +607,11 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_PSP_OUTPUT,
 	/** @SKB_DROP_REASON_RECURSION_LIMIT: Dead loop on virtual device. */
 	SKB_DROP_REASON_RECURSION_LIMIT,
+	/**
+	 * @SKB_DROP_REASON_IP_TTL_EXCEEDED: IPv4 TTL or IPv6 hop limit hit
+	 * zero on a packet being forwarded (see IPSTATS_MIB_INHDRERRORS)
+	 */
+	SKB_DROP_REASON_IP_TTL_EXCEEDED,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
 	 * shouldn't be used as a real 'reason' - only for tracing code gen
diff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c
index 8b65f12583eb6..b242561d37e73 100644
--- a/net/ipv4/ip_forward.c
+++ b/net/ipv4/ip_forward.c
@@ -174,7 +174,7 @@ int ip_forward(struct sk_buff *skb)
 	/* Tell the sender its packet died... */
 	__IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
 	icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
-	SKB_DR_SET(reason, IP_INHDR);
+	SKB_DR_SET(reason, IP_TTL_EXCEEDED);
 drop:
 	kfree_skb_reason(skb, reason);
 	return NET_RX_DROP;
diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 9c677eb1d1a61..b9103b02e8c74 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -471,7 +471,7 @@ static int ipv6_srh_rcv(struct sk_buff *skb)
 			__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
 			icmpv6_send(skb, ICMPV6_TIME_EXCEED,
 				    ICMPV6_EXC_HOPLIMIT, 0);
-			kfree_skb(skb);
+			kfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED);
 			return -1;
 		}
 		ipv6_hdr(skb)->hop_limit--;
@@ -633,7 +633,7 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
 			__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
 			icmpv6_send(skb, ICMPV6_TIME_EXCEED,
 				    ICMPV6_EXC_HOPLIMIT, 0);
-			kfree_skb(skb);
+			kfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED);
 			return -1;
 		}
 		ipv6_hdr(skb)->hop_limit--;
@@ -821,7 +821,7 @@ static int ipv6_rthdr_rcv(struct sk_buff *skb)
 			__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
 			icmpv6_send(skb, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT,
 				    0);
-			kfree_skb(skb);
+			kfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED);
 			return -1;
 		}
 		ipv6_hdr(skb)->hop_limit--;
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 8fc4766c8da90..0b6d78c8b6be4 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -577,7 +577,7 @@ int ip6_forward(struct sk_buff *skb)
 		icmpv6_send(skb, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT, 0);
 		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
 
-		kfree_skb_reason(skb, SKB_DROP_REASON_IP_INHDR);
+		kfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED);
 		return -ETIMEDOUT;
 	}

3/2 2026/08/25 08:05 llm patch-evaluator
0m Model: 
gemini-3.1-pro-preview

Args: 
null

Results: 
null

Tokens: 
							input: 3274
							output: 101
							thoughts: 806

Thoughts: 
**Analyzing the Impact of the Proposed Patch**

Okay, so I've got this patch in front of me that introduces a new drop reason, `SKB_DROP_REASON_IP_TTL_EXCEEDED`, and utilizes it in a few key locations within the networking stack. My initial thought is that this *is* a functional change, as it modifies the drop reason and would be observable through drop monitors and tracing. But wait, let's zoom out and consider the larger implications.

The instruction says to determine if this is worth fuzzing, based on some criteria. I need to keep in mind, specifically, that a patch is not to be worthfuzzed if it only contains changes to "purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints."

Right, drop reasons are essentially tracepoints, aren't they? They're used for logging and observability, not for altering the fundamental control flow. I need to refresh my memory on the way this `kfree_skb_reason` works. Hmm, I see that the new drop reason is set with `SKB_DR_SET(reason, IP_TTL_EXCEEDED)`, and it's then passed to `kfree_skb_reason`. Looking at `ipv6_srh_rcv` for example, `kfree_skb(skb)` is changed to `kfree_skb_reason(skb, SKB_DROP_REASON_IP_TTL_EXCEEDED)`. `kfree_skb` is just a wrapper for `kfree_skb_reason` with the default reason.

So, this is purely a change in the *information* being logged or traced, not in how the kernel actually handles the packet. I need to confirm this. Yes, drop reasons are used for the `kfree_skb` tracepoint, which makes them essentially a decorative element. This perfectly aligns with the criteria, specifically "Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints."

Okay, let me quickly summarize the changes: the patch adds the new macro `SKB_DROP_REASON_IP_TTL_EXCEEDED` and then updates a few key locations. Specifically, `net/ipv4/ip_forward.c`, `net/ipv6/exthdrs.c`, and `net/ipv6/ip6_output.c`. Importantly, none of these modifications alter the execution path of the kernel. They are simply changing the reason code passed to the tracepoint when an skb is freed.

Given that this is solely a modification of tracepoint information, and doesn't change execution flow, my expert opinion is that this patch is not worth fuzzing. The final answer is **WorthFuzzing=false**.

4/2 2026/08/25 08:05 tool set-results
0m Args: 
{
  "EnableConfigs": [],
  "FocusSymbols": [],
  "Reasoning": "The patch only introduces a new skb drop reason (SKB_DROP_REASON_IP_TTL_EXCEEDED) and updates several call sites to use it instead of generic drop reasons or kfree_skb(). Drop reasons are used for tracing and observability, and these changes do not functionally alter the execution flow of the kernel.",
  "WorthFuzzing": false
}

Results: 
{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch only introduces a new skb drop reason (SKB_DROP_REASON_IP_TTL_EXCEEDED) and updates several call sites to use it instead of generic drop reasons or kfree_skb(). Drop reasons are used for tracing and observability, and these changes do not functionally alter the execution flow of the kernel.",
  "WorthFuzzing": false
}
5/1 2026/08/25 08:05 action If
0m Args: 
{
  "WorthFuzzing": false
}

Results: 
null
LLM Calls Summary:
Total Calls Total Tokens Avg Tokens Total Duration (Seconds) Avg Duration (Seconds)
Tool Calls Summary:
Total Calls Total Duration (Seconds) Avg Duration (Seconds)