AI Trajectory

null

{
  "EnableConfigs": null,
  "FocusSymbols": [
    "ip_fib_metrics_init",
    "fib_create_info",
    "ip6_route_add"
  ],
  "Reasoning": "The patch adds a functional check to `ip_metrics_convert` to ensure that the `RTAX_ADVMSS` metric is either 0 or greater than or equal to `TCP_MIN_MSS`. This code is reachable when configuring IPv4 or IPv6 routes with metrics via netlink (e.g., `RTM_NEWROUTE`). Since it modifies core networking logic that is reachable from user space, it is worth fuzzing.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit eb683b83bd12aba52fb7176c6a64e3ed804598b2\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Wed Jul 29 00:56:00 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/net/ipv4/metrics.c b/net/ipv4/metrics.c\nindex ad40762a8b383..b9b97a0a5126b 100644\n--- a/net/ipv4/metrics.c\n+++ b/net/ipv4/metrics.c\n@@ -44,6 +44,12 @@ static int ip_metrics_convert(struct nlattr *fc_mx,\n \t\t\t}\n \t\t\tval = nla_get_u32(nla);\n \t\t}\n+\t\tif (type == RTAX_ADVMSS \u0026\u0026 val \u0026\u0026 val \u003c TCP_MIN_MSS) {\n+\t\t\tNL_SET_ERR_MSG_ATTR_FMT(extack, nla,\n+\t\t\t\t\t\t\"Invalid advmss, must be 0 or \u003e= %u\",\n+\t\t\t\t\t\tTCP_MIN_MSS);\n+\t\t\treturn -EINVAL;\n+\t\t}\n \t\tif (type == RTAX_ADVMSS \u0026\u0026 val \u003e 65535 - 40)\n \t\t\tval = 65535 - 40;\n \t\tif (type == RTAX_MTU \u0026\u0026 val \u003e 65535 - 15)\n"
}

best-expensive

null

{
  "EnableConfigs": null,
  "FocusSymbols": [
    "ip_fib_metrics_init",
    "fib_create_info",
    "ip6_route_add"
  ],
  "Reasoning": "The patch adds a functional check to `ip_metrics_convert` to ensure that the `RTAX_ADVMSS` metric is either 0 or greater than or equal to `TCP_MIN_MSS`. This code is reachable when configuring IPv4 or IPv6 routes with metrics via netlink (e.g., `RTM_NEWROUTE`). Since it modifies core networking logic that is reachable from user space, it is worth fuzzing.",
  "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 eb683b83bd12aba52fb7176c6a64e3ed804598b2
Author: syz-cluster <triage@syzkaller.com>
Date:   Wed Jul 29 00:56:00 2026 +0000

    syz-cluster: applied patch under review

diff --git a/net/ipv4/metrics.c b/net/ipv4/metrics.c
index ad40762a8b383..b9b97a0a5126b 100644
--- a/net/ipv4/metrics.c
+++ b/net/ipv4/metrics.c
@@ -44,6 +44,12 @@ static int ip_metrics_convert(struct nlattr *fc_mx,
 			}
 			val = nla_get_u32(nla);
 		}
+		if (type == RTAX_ADVMSS && val && val < TCP_MIN_MSS) {
+			NL_SET_ERR_MSG_ATTR_FMT(extack, nla,
+						"Invalid advmss, must be 0 or >= %u",
+						TCP_MIN_MSS);
+			return -EINVAL;
+		}
 		if (type == RTAX_ADVMSS && val > 65535 - 40)
 			val = 65535 - 40;
 		if (type == RTAX_MTU && val > 65535 - 15)

gemini-3.1-pro-preview

null

null

							input: 2129
							output: 30
							thoughts: 201
						

**Analyzing the New IP Metric Patch**

Okay, so I'm looking at this patch that's been proposed for `net/ipv4/metrics.c`, specifically within the `ip_metrics_convert` function. Seems like it's a straightforward functional change – they're adding a validation check for the `RTAX_ADVMSS` metric. Essentially, if someone tries to set an `advmss` value less than `TCP_MIN_MSS` (and it's not zero), the function now throws a `-EINVAL` error. That's good, prevents those out-of-spec values from potentially causing issues down the line. We wouldn't want those setting their MTU down too low.

Right, so `ip_metrics_convert` is used when we're setting IP metrics through netlink – think routing table updates, that sort of thing. I want to make sure this validation doesn't introduce any unforeseen regressions or compatibility issues, especially with existing configurations. The code looks correct on the surface, but I always want to be thorough. Now, let me dig into where this `ip_metrics_convert` function gets called from. That will give me a more complete picture of the potential impact.

{
  "Expression": "ip_metrics_convert",
  "PathPrefix": "net/ipv4/"
}

{
  "Output": "net/ipv4/metrics.c-9-\nnet/ipv4/metrics.c:10:static int ip_metrics_convert(struct nlattr *fc_mx,\nnet/ipv4/metrics.c-11-\t\t\t      int fc_mx_len, u32 *metrics,\n--\nnet/ipv4/metrics.c=72=struct dst_metrics *ip_fib_metrics_init(struct nlattr *fc_mx,\n--\nnet/ipv4/metrics.c-85-\nnet/ipv4/metrics.c:86:\terr = ip_metrics_convert(fc_mx, fc_mx_len, fib_metrics-\u003emetrics,\nnet/ipv4/metrics.c-87-\t\t\t\t extack);\n"
}

gemini-3.1-pro-preview

null

null

							input: 2806
							output: 32
							thoughts: 35
						

Okay, here's my interpretation of that thought process, as if I were thinking it myself, and tailored for an expert audience:

**Analyzing the `ip_fib_metrics_init` Function**

Right, `ip_fib_metrics_init` has to be initializing something. The code directly calls `ip_metrics_convert`, which is a decent clue. My immediate thought is, let's trace this back. Where's this `ip_fib_metrics_init` routine being invoked? Knowing the call sites will give me crucial context. Understanding the purpose of that function is key to making this code make sense, so I'm going to find all calls to this routine to better understand the code and context. That'll guide my subsequent analysis.

{
  "Expression": "ip_fib_metrics_init",
  "PathPrefix": "net/ipv4/"
}

{
  "Output": "net/ipv4/fib_semantics.c=1345=struct fib_info *fib_create_info(struct fib_config *cfg,\n--\nnet/ipv4/fib_semantics.c-1403-\nnet/ipv4/fib_semantics.c:1404:\tfi-\u003efib_metrics = ip_fib_metrics_init(cfg-\u003efc_mx, cfg-\u003efc_mx_len, extack);\nnet/ipv4/fib_semantics.c-1405-\tif (IS_ERR(fi-\u003efib_metrics)) {\n--\nnet/ipv4/metrics.c=10=static int ip_metrics_convert(struct nlattr *fc_mx,\n--\nnet/ipv4/metrics.c-71-\nnet/ipv4/metrics.c:72:struct dst_metrics *ip_fib_metrics_init(struct nlattr *fc_mx,\nnet/ipv4/metrics.c-73-\t\t\t\t\tint fc_mx_len,\n"
}

gemini-3.1-pro-preview

null

null

							input: 3280
							output: 35
							thoughts: 108
						

**Analyzing the FIB Metric Initialization**

Okay, so `fib_create_info` calls `ip_fib_metrics_init`. That's the key starting point. I know from experience that this is absolutely triggered during a netlink route addition, specifically a `RTM_NEWROUTE` message. Now, the `ip_metrics_convert` function is static. Excellent. That means I can narrow my focus; it's either going to be in `ip_fib_metrics_init` or `fib_create_info`. Wait...is `ip_fib_metrics_init` exported or just not static? I need to quickly confirm its visibility. Right, let's just double-check the `net/ipv4/metrics.c` source file and see what's actually going on.

{
  "Expression": "ip_fib_metrics_init",
  "PathPrefix": "net/ipv4/metrics.c"
}

{
  "Output": "net/ipv4/metrics.c=10=static int ip_metrics_convert(struct nlattr *fc_mx,\n--\nnet/ipv4/metrics.c-71-\nnet/ipv4/metrics.c:72:struct dst_metrics *ip_fib_metrics_init(struct nlattr *fc_mx,\nnet/ipv4/metrics.c-73-\t\t\t\t\tint fc_mx_len,\n"
}

gemini-3.1-pro-preview

null

null

							input: 3704
							output: 39
							thoughts: 17
						

Okay, let's see. Here's how I'd approach this, considering I know my way around the kernel:

**Checking for Exported Symbol: `ip_fib_metrics_init`**

Alright, the first thing I need to do is verify if this `ip_fib_metrics_init` symbol is actually exported. I've encountered this kind of situation before, where a function's visibility can impact its availability, especially in the context of modules. So, I need to check the symbol table somehow. Is it defined in the correct header? I'll probably start with a quick `grep` through the relevant source files or use a tool like `nm` or `objdump` on the kernel image or module object files. It’s likely that it needs to be exported with `EXPORT_SYMBOL` or something similar, or it may be within a static context. Knowing where it's *supposed* to be used is also useful context, that would refine the search. This is the obvious starting point. If it's not exported, then it's a no-go for direct access. From there, I'll need to dig deeper and see if there are other access methods.

no matches

{
  "Expression": "EXPORT_SYMBOL.*ip_fib_metrics_init",
  "PathPrefix": "net/ipv4/metrics.c"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 4029
							output: 30
							thoughts: 26
						

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

**Analyzing the Variable's Properties**

Alright, so the variable in question isn't explicitly exported, which is the first thing I notice. However, the fact that it's *not* static is a significant point. That implies some form of external visibility or, at the very least, linkage potential within the current scope or potentially inherited scopes. This lack of static designation suggests it could be modified or accessed in ways that are crucial to understanding its function in the larger system. My next step? Let's immediately dive into `fib_create_info`. I need to understand its relationship to that variable. The call context and properties of `fib_create_info` are almost certainly going to illuminate the use cases for our unnamed variable. Its probably passed there, or affects the arguments passed. This is where the story will really start to unfold.

{
  "Expression": "fib_create_info",
  "PathPrefix": "net/ipv4/"
}

{
  "Output": "net/ipv4/fib_lookup.h=38=void fib_release_info(struct fib_info *);\nnet/ipv4/fib_lookup.h:39:struct fib_info *fib_create_info(struct fib_config *cfg,\nnet/ipv4/fib_lookup.h-40-\t\t\t\t struct netlink_ext_ack *extack);\n--\nnet/ipv4/fib_semantics.c=1321=static bool fib_valid_prefsrc(struct fib_config *cfg, __be32 fib_prefsrc)\n--\nnet/ipv4/fib_semantics.c-1344-\nnet/ipv4/fib_semantics.c:1345:struct fib_info *fib_create_info(struct fib_config *cfg,\nnet/ipv4/fib_semantics.c-1346-\t\t\t\t struct netlink_ext_ack *extack)\n--\nnet/ipv4/fib_trie.c=1194=int fib_table_insert(struct net *net, struct fib_table *tb,\n--\nnet/ipv4/fib_trie.c-1211-\nnet/ipv4/fib_trie.c:1212:\tfi = fib_create_info(cfg, extack);\nnet/ipv4/fib_trie.c-1213-\tif (IS_ERR(fi)) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 4629
							output: 29
							thoughts: 199
						

**Analyzing the Route Insertion Process**

Okay, so I'm digging into how routing information gets added, and it looks like `fib_table_insert` is a key function here. It's called by `inet_rtm_newroute`, which is interesting because that's our entry point. And `fib_table_insert` itself calls `fib_create_info`, which is important for understanding the data creation process.

So, I should focus on a few key symbols: `ip_fib_metrics_init`, `fib_create_info`, `fib_table_insert`, and definitely `inet_rtm_newroute`. I think `inet_rtm_newroute` is a solid starting point to trace the call chain. `ip_fib_metrics_init` also seems promising.

Now, I'm going to check `net/ipv4/metrics.c` to see what's going on with `ip_fib_metrics_init`. Good, it's a non-static function, meaning it's visible outside of the module.

I'll quickly check if there are any config dependencies that might affect its presence. Let's see... looking at the code, it looks like it's *not* contingent on `CONFIG_IP_ROUTE_CLASSID`. I'm guessing it's probably compiled in for IPv4 regardless. Just to be sure, I'll quickly check the `net/ipv4/Makefile` to confirm the compilation conditions.

{
  "Expression": "metrics.o",
  "PathPrefix": "net/ipv4/Makefile"
}

{
  "Output": "net/ipv4/Makefile=6=obj-y     := route.o inetpeer.o protocol.o \\\n--\nnet/ipv4/Makefile-10-\t     tcp.o tcp_input.o tcp_output.o tcp_timer.o tcp_ipv4.o \\\nnet/ipv4/Makefile:11:\t     tcp_minisocks.o tcp_cong.o tcp_metrics.o tcp_fastopen.o \\\nnet/ipv4/Makefile-12-\t     tcp_recovery.o tcp_ulp.o \\\n--\nnet/ipv4/Makefile-16-\t     inet_fragment.o ping.o ip_tunnel_core.o gre_offload.o \\\nnet/ipv4/Makefile:17:\t     metrics.o netlink.o nexthop.o udp_tunnel_stub.o\nnet/ipv4/Makefile-18-\n"
}

gemini-3.1-pro-preview

null

null

							input: 5396
							output: 27
							thoughts: 49
						

**Analyzing the Inclusion of metrics.o**

Okay, so `metrics.o` is definitely getting compiled because it's listed under `obj-y`. That means it's unconditionally included as long as the parent configuration is active. Now, the parent of `metrics.o` is IPv4.

Right, IPv4 is brought in by `CONFIG_INET`. I need to figure out how `CONFIG_INET` affects the rest of the configuration. It seems like the inclusion of `metrics.o` is directly tied to the presence of `CONFIG_INET`. So, now I should look at `TCP_MIN_MSS` to figure out the larger implications here.

{
  "Expression": "TCP_MIN_MSS",
  "PathPrefix": "include/"
}

{
  "Output": "include/net/tcp.h=68=void tcp_time_wait(struct sock *sk, int state, int timeo);\n--\ninclude/net/tcp.h-81-/* Minimal accepted MSS. It is (60+60+8) - (20+20). */\ninclude/net/tcp.h:82:#define TCP_MIN_MSS\t\t88U\ninclude/net/tcp.h-83-\n"
}

gemini-3.1-pro-preview

null

null

							input: 5729
							output: 35
							thoughts: 88
						

**IP Metric Update: A Quick Review**

Okay, so this patch seems straightforward enough. It introduces a check for the `RTAX_ADVMSS` value when IP metrics are being set. That's good practice – we want to be robust in handling potential variations. Functionally, this is definitely doing something and I can see where this code path is reached. Let's see the context.

I see the key symbols are `ip_fib_metrics_init` and `fib_create_info`. I don't see any weird dependencies here; looks like we don't need to enable any specific configurations beyond `INET`, which is pretty much assumed these days.

Just to be absolutely certain, I'm going to quickly glance at `ip_metrics_convert` in `net/ipv4/metrics.c` to refresh my memory on the surrounding code. Gotta make sure this addition is playing nicely with everything else in that file. That's the important bit for me.

{
  "File": "net/ipv4/metrics.c",
  "FirstLine": 1,
  "LineCount": 100
}

{
  "Contents": "   1:\t// SPDX-License-Identifier: GPL-2.0-only\n   2:\t#include \u003clinux/netlink.h\u003e\n   3:\t#include \u003clinux/nospec.h\u003e\n   4:\t#include \u003clinux/rtnetlink.h\u003e\n   5:\t#include \u003clinux/types.h\u003e\n   6:\t#include \u003cnet/ip.h\u003e\n   7:\t#include \u003cnet/net_namespace.h\u003e\n   8:\t#include \u003cnet/tcp.h\u003e\n   9:\t\n  10:\tstatic int ip_metrics_convert(struct nlattr *fc_mx,\n  11:\t\t\t\t      int fc_mx_len, u32 *metrics,\n  12:\t\t\t\t      struct netlink_ext_ack *extack)\n  13:\t{\n  14:\t\tbool ecn_ca = false;\n  15:\t\tstruct nlattr *nla;\n  16:\t\tint remaining;\n  17:\t\n  18:\t\tnla_for_each_attr(nla, fc_mx, fc_mx_len, remaining) {\n  19:\t\t\tint type = nla_type(nla);\n  20:\t\t\tu32 val;\n  21:\t\n  22:\t\t\tif (!type)\n  23:\t\t\t\tcontinue;\n  24:\t\t\tif (type \u003e RTAX_MAX) {\n  25:\t\t\t\tNL_SET_ERR_MSG(extack, \"Invalid metric type\");\n  26:\t\t\t\treturn -EINVAL;\n  27:\t\t\t}\n  28:\t\n  29:\t\t\ttype = array_index_nospec(type, RTAX_MAX + 1);\n  30:\t\t\tif (type == RTAX_CC_ALGO) {\n  31:\t\t\t\tchar tmp[TCP_CA_NAME_MAX];\n  32:\t\n  33:\t\t\t\tnla_strscpy(tmp, nla, sizeof(tmp));\n  34:\t\t\t\tval = tcp_ca_get_key_by_name(tmp, \u0026ecn_ca);\n  35:\t\t\t\tif (val == TCP_CA_UNSPEC) {\n  36:\t\t\t\t\tNL_SET_ERR_MSG(extack, \"Unknown tcp congestion algorithm\");\n  37:\t\t\t\t\treturn -EINVAL;\n  38:\t\t\t\t}\n  39:\t\t\t} else {\n  40:\t\t\t\tif (nla_len(nla) != sizeof(u32)) {\n  41:\t\t\t\t\tNL_SET_ERR_MSG_ATTR(extack, nla,\n  42:\t\t\t\t\t\t\t    \"Invalid attribute in metrics\");\n  43:\t\t\t\t\treturn -EINVAL;\n  44:\t\t\t\t}\n  45:\t\t\t\tval = nla_get_u32(nla);\n  46:\t\t\t}\n  47:\t\t\tif (type == RTAX_ADVMSS \u0026\u0026 val \u0026\u0026 val \u003c TCP_MIN_MSS) {\n  48:\t\t\t\tNL_SET_ERR_MSG_ATTR_FMT(extack, nla,\n  49:\t\t\t\t\t\t\t\"Invalid advmss, must be 0 or \u003e= %u\",\n  50:\t\t\t\t\t\t\tTCP_MIN_MSS);\n  51:\t\t\t\treturn -EINVAL;\n  52:\t\t\t}\n  53:\t\t\tif (type == RTAX_ADVMSS \u0026\u0026 val \u003e 65535 - 40)\n  54:\t\t\t\tval = 65535 - 40;\n  55:\t\t\tif (type == RTAX_MTU \u0026\u0026 val \u003e 65535 - 15)\n  56:\t\t\t\tval = 65535 - 15;\n  57:\t\t\tif (type == RTAX_HOPLIMIT \u0026\u0026 val \u003e 255)\n  58:\t\t\t\tval = 255;\n  59:\t\t\tif (type == RTAX_FEATURES \u0026\u0026 (val \u0026 ~RTAX_FEATURE_MASK)) {\n  60:\t\t\t\tNL_SET_ERR_MSG(extack, \"Unknown flag set in feature mask in metrics attribute\");\n  61:\t\t\t\treturn -EINVAL;\n  62:\t\t\t}\n  63:\t\t\tmetrics[type - 1] = val;\n  64:\t\t}\n  65:\t\n  66:\t\tif (ecn_ca)\n  67:\t\t\tmetrics[RTAX_FEATURES - 1] |= DST_FEATURE_ECN_CA;\n  68:\t\n  69:\t\treturn 0;\n  70:\t}\n  71:\t\n  72:\tstruct dst_metrics *ip_fib_metrics_init(struct nlattr *fc_mx,\n  73:\t\t\t\t\t\tint fc_mx_len,\n  74:\t\t\t\t\t\tstruct netlink_ext_ack *extack)\n  75:\t{\n  76:\t\tstruct dst_metrics *fib_metrics;\n  77:\t\tint err;\n  78:\t\n  79:\t\tif (!fc_mx)\n  80:\t\t\treturn (struct dst_metrics *)\u0026dst_default_metrics;\n  81:\t\n  82:\t\tfib_metrics = kzalloc_obj(*fib_metrics);\n  83:\t\tif (unlikely(!fib_metrics))\n  84:\t\t\treturn ERR_PTR(-ENOMEM);\n  85:\t\n  86:\t\terr = ip_metrics_convert(fc_mx, fc_mx_len, fib_metrics-\u003emetrics,\n  87:\t\t\t\t\t extack);\n  88:\t\tif (!err) {\n  89:\t\t\trefcount_set(\u0026fib_metrics-\u003erefcnt, 1);\n  90:\t\t} else {\n  91:\t\t\tkfree(fib_metrics);\n  92:\t\t\tfib_metrics = ERR_PTR(err);\n  93:\t\t}\n  94:\t\n  95:\t\treturn fib_metrics;\n  96:\t}\n"
}

gemini-3.1-pro-preview

null

null

							input: 7476
							output: 31
							thoughts: 120
						

**Investigating IP FIB Metrics Initialization**

Okay, so `ip_fib_metrics_init` is the entry point, the non-static one. That feels right. And, yeah, `fib_create_info` in `net/ipv4/fib_semantics.c` looks like a key symbol to dig into.

Alright, let's just confirm that `ip_fib_metrics_init` is exported. Nope, not exported, but it *isn't* static. That's a point to make, it means it's accessible.

Okay, is there anything else calling `ip_metrics_convert`? Nope, nothing. Interesting.

Now, let's switch gears and check if there are any similar changes in `net/ipv6/route.c`. Need to see if IPv6 is handled similarly.

no matches

{
  "Expression": "RTAX_ADVMSS",
  "PathPrefix": "net/ipv6/"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 7820
							output: 30
							thoughts: 50
						

Okay, let's see...

**Investigating the Absence of RTAX_ADVMSS in net/ipv6/route.c**

Hmm, hold on a second. I was under the impression that the IPv6 routing implementation in `net/ipv6/route.c` would utilize `RTAX_ADVMSS`, but that doesn't seem to be the case. That's a bit unexpected. I need to understand why. Perhaps it's handled differently or not supported at all in this particular area? Let's take a closer look. My first step is to search within the `net/ipv6/route.c` file itself for a function like `ip_metrics_convert` or anything with a similar naming convention that might be involved in handling or translating routing metrics. This should illuminate how the code manages this kind of information, or potentially why it's ignored.

no matches

{
  "Expression": "ip_metrics_convert",
  "PathPrefix": "net/ipv6/"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 8102
							output: 28
							thoughts: 18
						

Okay, here's my attempt at summarizing that thought process, keeping in mind I'm dealing with someone who understands these networking details:

**Digging into IPv6 Routing and Metrics**

Right, so I'm thinking about IPv6, specifically the routing side of things. I'm wondering if the system I'm working with, or perhaps a system I'm analyzing, uses `ip6_route_info_create`. That function name looks familiar...and the thought then triggers: could this be where routing metrics might be parsed or even configured? It’s a good starting point for understanding how the system handles route prioritization and selection based on those metrics, be they cost, hop count, or whatever the implementation uses. I'll need to go look into the code, and this function name is a useful pointer.

{
  "Expression": "RTAX_",
  "PathPrefix": "net/ipv6/"
}

{
  "Output": "net/ipv6/ip6_fib.c=1089=static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,\n--\nnet/ipv6/ip6_fib.c-1156-\t\t\t\tif (rt-\u003efib6_pmtu)\nnet/ipv6/ip6_fib.c:1157:\t\t\t\t\tfib6_metric_set(iter, RTAX_MTU,\nnet/ipv6/ip6_fib.c-1158-\t\t\t\t\t\t\trt-\u003efib6_pmtu);\n--\nnet/ipv6/ip6_output.c=262=int ip6_dst_hoplimit(struct dst_entry *dst)\nnet/ipv6/ip6_output.c-263-{\nnet/ipv6/ip6_output.c:264:\tint hoplimit = dst_metric_raw(dst, RTAX_HOPLIMIT);\nnet/ipv6/ip6_output.c-265-\n--\nnet/ipv6/ndisc.c=1231=static enum skb_drop_reason ndisc_router_discovery(struct sk_buff *skb)\n--\nnet/ipv6/ndisc.c-1416-\t\t\t\t   ra_msg-\u003eicmph.icmp6_hop_limit);\nnet/ipv6/ndisc.c:1417:\t\t\tfib6_metric_set(rt, RTAX_HOPLIMIT,\nnet/ipv6/ndisc.c-1418-\t\t\t\t\tra_msg-\u003eicmph.icmp6_hop_limit);\n--\nnet/ipv6/ndisc.c-1568-\t\t\tWRITE_ONCE(in6_dev-\u003ecnf.mtu6, mtu);\nnet/ipv6/ndisc.c:1569:\t\t\tfib6_metric_set(rt, RTAX_MTU, mtu);\nnet/ipv6/ndisc.c-1570-\t\t\trt6_mtu_change(skb-\u003edev, mtu);\n--\nnet/ipv6/route.c=268=static struct dst_ops ip6_dst_blackhole_ops = {\n--\nnet/ipv6/route.c-279-\nnet/ipv6/route.c:280:static const u32 ip6_template_metrics[RTAX_MAX] = {\nnet/ipv6/route.c:281:\t[RTAX_HOPLIMIT - 1] = 0,\nnet/ipv6/route.c-282-};\n--\nnet/ipv6/route.c=1718=static int rt6_insert_exception(struct rt6_info *nrt,\n--\nnet/ipv6/route.c-1760-\t */\nnet/ipv6/route.c:1761:\tif (dst_metric_raw(\u0026nrt-\u003edst, RTAX_MTU) \u003e= fib6_mtu(res)) {\nnet/ipv6/route.c-1762-\t\terr = -EINVAL;\n--\nnet/ipv6/route.c=2082=static void rt6_exceptions_update_pmtu(struct inet6_dev *idev,\n--\nnet/ipv6/route.c-2100-\t\t\t */\nnet/ipv6/route.c:2101:\t\t\tif (dst_metric_raw(\u0026entry-\u003edst, RTAX_MTU) \u0026\u0026\nnet/ipv6/route.c-2102-\t\t\t    rt6_mtu_change_route_allowed(idev, entry, mtu))\nnet/ipv6/route.c:2103:\t\t\t\tdst_metric_set(\u0026entry-\u003edst, RTAX_MTU, mtu);\nnet/ipv6/route.c-2104-\t\t}\n--\nnet/ipv6/route.c=2907=static void rt6_do_update_pmtu(struct rt6_info *rt, u32 mtu)\n--\nnet/ipv6/route.c-2910-\nnet/ipv6/route.c:2911:\tdst_metric_set(\u0026rt-\u003edst, RTAX_MTU, mtu);\nnet/ipv6/route.c-2912-\trt-\u003ert6i_flags |= RTF_MODIFIED;\n--\nnet/ipv6/route.c=2922=static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,\n--\nnet/ipv6/route.c-2928-\nnet/ipv6/route.c:2929:\t/* Note: do *NOT* check dst_metric_locked(dst, RTAX_MTU)\nnet/ipv6/route.c-2930-\t * IPv6 pmtu discovery isn't optional, so 'mtu lock' cannot disable it.\n--\nnet/ipv6/route.c=3302=u32 ip6_mtu_from_fib6(const struct fib6_result *res,\n--\nnet/ipv6/route.c-3311-\nnet/ipv6/route.c:3312:\tif (unlikely(fib6_metric_locked(f6i, RTAX_MTU))) {\nnet/ipv6/route.c-3313-\t\tmtu = f6i-\u003efib6_pmtu;\n--\nnet/ipv6/route.c-3319-\tif (unlikely(rt)) {\nnet/ipv6/route.c:3320:\t\tmtu = dst_metric_raw(\u0026rt-\u003edst, RTAX_MTU);\nnet/ipv6/route.c-3321-\t} else {\n--\nnet/ipv6/route.c=3335=struct dst_entry *icmp6_dst_alloc(struct net_device *dev,\n--\nnet/ipv6/route.c-3358-\trt-\u003ert6i_idev     = idev;\nnet/ipv6/route.c:3359:\tdst_metric_set(\u0026rt-\u003edst, RTAX_HOPLIMIT, 0);\nnet/ipv6/route.c-3360-\n--\nnet/ipv6/route.c=5044=static int fib6_nh_mtu_change(struct fib6_nh *nh, void *_arg)\n--\nnet/ipv6/route.c-5062-\t\t    (mtu \u003c arg-\u003emtu \u0026\u0026 mtu == idev-\u003ecnf.mtu6))\nnet/ipv6/route.c:5063:\t\t\tfib6_metric_set(f6i, RTAX_MTU, arg-\u003emtu);\nnet/ipv6/route.c-5064-\n--\nnet/ipv6/route.c=5073=static int rt6_mtu_change_route(struct fib6_info *f6i, void *p_arg)\n--\nnet/ipv6/route.c-5078-\t/* In IPv6 pmtu discovery is not optional,\nnet/ipv6/route.c:5079:\t   so that RTAX_MTU lock cannot disable it.\nnet/ipv6/route.c-5080-\t   We still use this lock to block changes\n--\nnet/ipv6/route.c-5087-\nnet/ipv6/route.c:5088:\tif (fib6_metric_locked(f6i, RTAX_MTU))\nnet/ipv6/route.c-5089-\t\treturn 0;\n--\nnet/ipv6/route.c=5699=static size_t rt6_nlmsg_size(struct fib6_info *f6i)\n--\nnet/ipv6/route.c-5737-\t       + nla_total_size(4) /* RTA_PRIORITY */\nnet/ipv6/route.c:5738:\t       + RTAX_MAX * nla_total_size(4) /* RTA_METRICS */\nnet/ipv6/route.c-5739-\t       + nla_total_size(sizeof(struct rta_cacheinfo))\nnet/ipv6/route.c:5740:\t       + nla_total_size(TCP_CA_NAME_MAX) /* RTAX_CC_ALGO */\nnet/ipv6/route.c-5741-\t       + nla_total_size(1) /* RTA_PREF */\n--\nnet/ipv6/syncookies.c=174=struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)\n--\nnet/ipv6/syncookies.c-256-\nnet/ipv6/syncookies.c:257:\treq-\u003ersk_window_clamp = READ_ONCE(tp-\u003ewindow_clamp) ? :dst_metric(dst, RTAX_WINDOW);\nnet/ipv6/syncookies.c-258-\t/* limit the window selection if the user enforce a smaller rx buffer */\n--\nnet/ipv6/syncookies.c-266-\t\t\t\t  ireq-\u003ewscale_ok, \u0026rcv_wscale,\nnet/ipv6/syncookies.c:267:\t\t\t\t  dst_metric(dst, RTAX_INITRWND));\nnet/ipv6/syncookies.c-268-\n"
}

gemini-3.1-pro-preview

null

null

							input: 10598
							output: 30
							thoughts: 54
						

**IPv6 Routing Metrics Conundrum**

Okay, hold on a second. I was under the impression that the standard `ip_metrics_convert` function was universally used for handling route metrics across both IPv4 and IPv6. But the code for `net/ipv6/route.c` doesn't seem to be calling it. That’s unexpected. It throws a wrench in my mental model of the commonalities between the two implementations.

So, how exactly does the IPv6 route parsing deal with these metrics? I need to figure out where the conversion or interpretation of those metrics is happening within the IPv6 routing context. Alright, let’s go directly to `net/ipv6/route.c` and specifically search for how the code handles `RTA_METRICS` to clarify things. This should illuminate the logic that is being used, or explain *why* something else is used.

{
  "Expression": "RTA_METRICS",
  "PathPrefix": "net/ipv6/"
}

{
  "Output": "net/ipv6/route.c=5111=static const struct nla_policy rtm_ipv6_policy[RTA_MAX+1] = {\n--\nnet/ipv6/route.c-5117-\t[RTA_PRIORITY]          = { .type = NLA_U32 },\nnet/ipv6/route.c:5118:\t[RTA_METRICS]           = { .type = NLA_NESTED },\nnet/ipv6/route.c-5119-\t[RTA_MULTIPATH]\t\t= { .len = sizeof(struct rtnexthop) },\n--\nnet/ipv6/route.c=5181=static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,\n--\nnet/ipv6/route.c-5283-\nnet/ipv6/route.c:5284:\tif (tb[RTA_METRICS]) {\nnet/ipv6/route.c:5285:\t\tcfg-\u003efc_mx = nla_data(tb[RTA_METRICS]);\nnet/ipv6/route.c:5286:\t\tcfg-\u003efc_mx_len = nla_len(tb[RTA_METRICS]);\nnet/ipv6/route.c-5287-\t}\n--\nnet/ipv6/route.c=5699=static size_t rt6_nlmsg_size(struct fib6_info *f6i)\n--\nnet/ipv6/route.c-5737-\t       + nla_total_size(4) /* RTA_PRIORITY */\nnet/ipv6/route.c:5738:\t       + RTAX_MAX * nla_total_size(4) /* RTA_METRICS */\nnet/ipv6/route.c-5739-\t       + nla_total_size(sizeof(struct rta_cacheinfo))\n"
}

gemini-3.1-pro-preview

null

null

							input: 11360
							output: 31
							thoughts: 36
						

Here's my take on the process, thinking through it as an expert would:

**Digging into the IPv6 Route Configuration**

Okay, so `rtm_to_fib6_config` is the function that's setting the `cfg->fc_mx` field, huh? That's the crucial step. Now, I need to remember what's involved with that particular structure, and what it relates to in the routing process.

Ah, right, so `cfg->fc_mx` is obviously something that gets fed to the configuration routines. Then, `ip6_route_info_create` parses all of this. I bet it takes `cfg->fc_mx` and extracts the relevant information for the route, maybe setting the various fib entry flags or route attributes. I should look into the source for `ip6_route_info_create` and double check. Knowing where that configuration information originates is key to understanding how these routes get installed. This should be interesting to verify against the configuration logic and any potential caveats.

{
  "Expression": "fc_mx",
  "PathPrefix": "net/ipv6/route.c"
}

{
  "Output": "net/ipv6/route.c=3809=static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg,\n--\nnet/ipv6/route.c-3838-\nnet/ipv6/route.c:3839:\trt-\u003efib6_metrics = ip_fib_metrics_init(cfg-\u003efc_mx, cfg-\u003efc_mx_len,\nnet/ipv6/route.c-3840-\t\t\t\t\t       extack);\n--\nnet/ipv6/route.c=5181=static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,\n--\nnet/ipv6/route.c-5284-\tif (tb[RTA_METRICS]) {\nnet/ipv6/route.c:5285:\t\tcfg-\u003efc_mx = nla_data(tb[RTA_METRICS]);\nnet/ipv6/route.c:5286:\t\tcfg-\u003efc_mx_len = nla_len(tb[RTA_METRICS]);\nnet/ipv6/route.c-5287-\t}\n"
}

gemini-3.1-pro-preview

null

null

							input: 11943
							output: 29
							thoughts: 58
						

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

**Diving into the IPv6 Routing Setup**

Right, `ip6_route_info_create` calls `ip_fib_metrics_init`. That's the key. I need to understand how those metrics are being initialized for IPv6 routes. The crucial question is, is `ip_fib_metrics_init` a globally accessible function, or is it declared somewhere internal? Is it exported or visible via a header file?

My immediate instinct is to look in the standard places, probably within `include/net/ip.h` or somewhere equally obvious within the network stack's include directory. That's usually where these initialization routines live. Let's see if I can find a definition or declaration in there to confirm.

{
  "Expression": "ip_fib_metrics_init",
  "PathPrefix": "include/"
}

{
  "Output": "include/net/ip.h=509=static inline unsigned int ip_skb_dst_mtu(struct sock *sk,\n--\ninclude/net/ip.h-524-\ninclude/net/ip.h:525:struct dst_metrics *ip_fib_metrics_init(struct nlattr *fc_mx, int fc_mx_len,\ninclude/net/ip.h-526-\t\t\t\t\tstruct netlink_ext_ack *extack);\n"
}

gemini-3.1-pro-preview

null

null

							input: 12333
							output: 36
							thoughts: 434
						

**My Analysis of the Fuzzing Target**

Okay, so `ip_fib_metrics_init` is the core function we're looking at, and it's neatly defined in `include/net/ip.h`. The fact that it's called by both IPv4 and IPv6 makes it a prime candidate for fuzzing. Excellent!

Let's broaden the scope. Beyond `ip_fib_metrics_init`, I should also be considering other related functions to fuzz. Based on my quick review, `fib_create_info` (for IPv4) and `ip6_route_info_create` (for IPv6) look like worthwhile targets as well, especially since they are related to the FIB setup.

Okay, let me revisit `ip_fib_metrics_init` and get a finer grained view. It takes `fc_mx` and `fc_mx_len` as inputs and, importantly, calls `ip_metrics_convert`. The patch documentation clearly indicates a modification to `ip_metrics_convert` within `net/ipv4/metrics.c`. This is key.

Therefore, my final list of focus symbols will be:
*   `ip_fib_metrics_init`
*   `fib_create_info`
*   `ip6_route_info_create`

Now, let's consider the build environment. Are there any specific configuration options I need to worry about? Nope, `CONFIG_INET` is sufficient. That simplifies things.

Time to dive back into the patch itself.

```c
		if (type == RTAX_ADVMSS && val && val < TCP_MIN_MSS) {
			NL_SET_ERR_MSG_ATTR_FMT(extack, nla,
						"Invalid advmss, must be 0 or >= %u",
						TCP_MIN_MSS);
			return -EINVAL;
		}
```

This is a functional change, an important check! It's preventing the assignment of `advmss` to invalid values between 1 and `TCP_MIN_MSS - 1`, reachable through netlink route configuration. This is definitely fuzzable because it introduces a new constraint, so I need to explore the boundaries of this check thoroughly. The fuzzing should specifically target the `RTAX_ADVMSS` handling.

To be clear on the focus symbols for fuzzing, again the final list is:
*   `ip_fib_metrics_init`
*   `fib_create_info`
*   `ip6_route_info_create`

I should just double check if `ip6_route_info_create` is declared as static.

{
  "Expression": "ip6_route_info_create",
  "PathPrefix": "net/ipv6/route.c"
}

{
  "Output": "net/ipv6/route.c=3762=static int fib6_config_validate(struct fib6_config *cfg,\n--\nnet/ipv6/route.c-3808-\nnet/ipv6/route.c:3809:static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg,\nnet/ipv6/route.c-3810-\t\t\t\t\t       gfp_t gfp_flags,\n--\nnet/ipv6/route.c-3875-\nnet/ipv6/route.c:3876:static int ip6_route_info_create_nh(struct fib6_info *rt,\nnet/ipv6/route.c-3877-\t\t\t\t    struct fib6_config *cfg,\n--\nnet/ipv6/route.c=3952=int ip6_route_add(struct fib6_config *cfg, gfp_t gfp_flags,\n--\nnet/ipv6/route.c-3961-\nnet/ipv6/route.c:3962:\trt = ip6_route_info_create(cfg, gfp_flags, extack);\nnet/ipv6/route.c-3963-\tif (IS_ERR(rt))\n--\nnet/ipv6/route.c-3965-\nnet/ipv6/route.c:3966:\terr = ip6_route_info_create_nh(rt, cfg, gfp_flags, extack);\nnet/ipv6/route.c-3967-\tif (err)\n--\nnet/ipv6/route.c=4675=struct fib6_info *addrconf_f6i_alloc(struct net *net,\n--\nnet/ipv6/route.c-4701-\nnet/ipv6/route.c:4702:\tf6i = ip6_route_info_create(\u0026cfg, gfp_flags, extack);\nnet/ipv6/route.c-4703-\tif (IS_ERR(f6i))\n--\nnet/ipv6/route.c-4705-\nnet/ipv6/route.c:4706:\terr = ip6_route_info_create_nh(f6i, \u0026cfg, gfp_flags, extack);\nnet/ipv6/route.c-4707-\tif (err)\n--\nnet/ipv6/route.c=5415=static int ip6_route_multipath_add(struct fib6_config *cfg,\n--\nnet/ipv6/route.c-5471-\t\tr_cfg.fc_flags |= (rtnh-\u003ertnh_flags \u0026 RTNH_F_ONLINK);\nnet/ipv6/route.c:5472:\t\trt = ip6_route_info_create(\u0026r_cfg, GFP_KERNEL, extack);\nnet/ipv6/route.c-5473-\t\tif (IS_ERR(rt)) {\n--\nnet/ipv6/route.c-5478-\nnet/ipv6/route.c:5479:\t\terr = ip6_route_info_create_nh(rt, \u0026r_cfg, GFP_KERNEL, extack);\nnet/ipv6/route.c-5480-\t\tif (err) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 14205
							output: 34
							thoughts: 34
						

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

**Checking IPv6 Routing Table Functions**

Alright, let me just quickly confirm a couple of things here. I seem to recall that the `ip6_route_info_create` function is a static function. That makes sense, given its usual role. Now, I need to double-check my memory on `ip6_route_add`. I *think* that's a non-static function, and that it's exported for external use. I should probably just confirm that now to make sure nothing has changed recently. Let's see... a quick verification is in order.

{
  "Expression": "ip6_route_add",
  "PathPrefix": "net/ipv6/route.c"
}

{
  "Output": "net/ipv6/route.c=3876=static int ip6_route_info_create_nh(struct fib6_info *rt,\n--\nnet/ipv6/route.c-3951-\nnet/ipv6/route.c:3952:int ip6_route_add(struct fib6_config *cfg, gfp_t gfp_flags,\nnet/ipv6/route.c-3953-\t\t  struct netlink_ext_ack *extack)\n--\nnet/ipv6/route.c=4413=static struct fib6_info *rt6_add_route_info(struct net *net,\n--\nnet/ipv6/route.c-4439-\nnet/ipv6/route.c:4440:\tip6_route_add(\u0026cfg, GFP_ATOMIC, NULL);\nnet/ipv6/route.c-4441-\n--\nnet/ipv6/route.c=4478=struct fib6_info *rt6_add_dflt_router(struct net *net,\n--\nnet/ipv6/route.c-4500-\nnet/ipv6/route.c:4501:\tif (!ip6_route_add(\u0026cfg, GFP_ATOMIC, NULL)) {\nnet/ipv6/route.c-4502-\t\tstruct fib6_table *table;\n--\nnet/ipv6/route.c=4578=int ipv6_route_ioctl(struct net *net, unsigned int cmd, struct in6_rtmsg *rtmsg)\n--\nnet/ipv6/route.c-4594-\t\t\tcfg.fc_metric = IP6_RT_PRIO_USER;\nnet/ipv6/route.c:4595:\t\terr = ip6_route_add(\u0026cfg, GFP_KERNEL, NULL);\nnet/ipv6/route.c-4596-\t\tbreak;\n--\nnet/ipv6/route.c=5661=static int inet6_rtm_newroute(struct sk_buff *skb, struct nlmsghdr *nlh,\n--\nnet/ipv6/route.c-5676-\telse\nnet/ipv6/route.c:5677:\t\treturn ip6_route_add(\u0026cfg, GFP_KERNEL, extack);\nnet/ipv6/route.c-5678-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 15008
							output: 149
							thoughts: 108
						

**My Assessment of the Key Functions**

Okay, so I've been looking at these functions and the non-static nature of `ip6_route_add` immediately caught my eye. That's a good starting point. I also like what I see with `inet6_rtm_newroute`; that's relevant to the topic as well. To further my investigation, I'm going to take a peek at `fib_create_info` within `net/ipv4/fib_semantics.c`. Ah, yes, confirmed: it's also non-static. Excellent, this is solid.

Therefore, the key symbols I need to focus on are: `ip_fib_metrics_init`, `fib_create_info`, and `ip6_route_add`. This set appears to be the right way to achieve my goal. I'm satisfied with this analysis, so I'll set these findings aside for now and move forward.

{
  "EnableConfigs": [],
  "FocusSymbols": [
    "ip_fib_metrics_init",
    "fib_create_info",
    "ip6_route_add"
  ],
  "Reasoning": "The patch adds a functional check to `ip_metrics_convert` to ensure that the `RTAX_ADVMSS` metric is either 0 or greater than or equal to `TCP_MIN_MSS`. This code is reachable when configuring IPv4 or IPv6 routes with metrics via netlink (e.g., `RTM_NEWROUTE`). Since it modifies core networking logic that is reachable from user space, it is worth fuzzing.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": null,
  "FocusSymbols": [
    "ip_fib_metrics_init",
    "fib_create_info",
    "ip6_route_add"
  ],
  "Reasoning": "The patch adds a functional check to `ip_metrics_convert` to ensure that the `RTAX_ADVMSS` metric is either 0 or greater than or equal to `TCP_MIN_MSS`. This code is reachable when configuring IPv4 or IPv6 routes with metrics via netlink (e.g., `RTM_NEWROUTE`). Since it modifies core networking logic that is reachable from user space, it is worth fuzzing.",
  "WorthFuzzing": true
}