[PATCH net v2 0/2] ipv4/ipv6: do not warn on route notification size races

[PATCH net v2 0/2] ipv4/ipv6: do not warn on route notification size races

[Daehyeon Ko]

A nexthop group can grow between route notification sizing and filling.
Both IPv4 and IPv6 can then legitimately return -EMSGSIZE, so remove the
stale warnings while preserving their existing error paths.

Patch 1 is unchanged from v1.  Patch 2 adds the IPv6 counterpart requested
by Ido.  No new build or runtime test was run; both changes only delete the
stale comment and WARN_ON().

---
v2:
- Add the IPv6 counterpart.

v1: <20261007045410.3806739-1-4ncienth@gmail.com>

Daehyeon Ko (2):
  ipv4: do not warn on route notification size race
  ipv6: do not warn on route notification size race

 net/ipv4/fib_trie.c | 2 --
 net/ipv6/route.c    | 2 --
 2 files changed, 4 deletions(-)


base-commit: 23609bce9e1de525d1d0e73fc68c6e7971d0b49e
-- 
2.55.0

[PATCH net v2 1/2] ipv4: do not warn on route notification size race

[Daehyeon Ko]

Commit 680aea08e78c ("net: ipv4: Emit notification when fib hardware
flags are changed") added asynchronous route notifications for hardware
flag changes.

fib_alias_hw_flags_set() sizes the skb with fib_nlmsg_size() and later
fills it with fib_dump_info() while holding only RCU.  With nexthop
compatibility mode enabled, a concurrent replacement can grow the group
between these independent snapshots.  fib_dump_info() can then
legitimately return -EMSGSIZE, so the warning does not prove a sizing bug.

Remove the warning.  The existing error path still frees the skb and
reports the error to listeners.

Fixes: 680aea08e78c ("net: ipv4: Emit notification when fib hardware flags are changed")
Reported-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/netdev/20261004082043.GB92032@shredder/
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
---
 net/ipv4/fib_trie.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index acb1e43859143e..248514dce0cdd5 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -1079,8 +1079,6 @@ void fib_alias_hw_flags_set(struct net *net, const struct fib_rt_info *fri)
 
 	err = fib_dump_info(skb, 0, 0, RTM_NEWROUTE, fri, 0);
 	if (err < 0) {
-		/* -EMSGSIZE implies BUG in fib_nlmsg_size() */
-		WARN_ON(err == -EMSGSIZE);
 		kfree_skb(skb);
 		goto errout;
 	}
-- 
2.55.0

[PATCH net v2 2/2] ipv6: do not warn on route notification size race

[Daehyeon Ko]

fib6_info_hw_flags_set() sizes the skb with rt6_nlmsg_size() and later
fills it with rt6_fill_node().  With nexthop compatibility mode enabled,
a concurrent replacement can grow the group between these independent
snapshots.  rt6_fill_node() can then legitimately return -EMSGSIZE, so
the warning does not prove a sizing bug.

Remove the warning.  The existing error path still frees the skb and
reports the error to listeners.

Fixes: 907eea486888 ("net: ipv6: Emit notification when fib hardware flags are changed")
Reported-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/netdev/20261007114003.GA1011260@shredder/
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
---
 net/ipv6/route.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 153ce16628c1e1..a5e955e56e794f 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -6509,8 +6509,6 @@ void fib6_info_hw_flags_set(struct net *net, struct fib6_info *f6i,
 	err = rt6_fill_node(net, skb, f6i, NULL, NULL, NULL, 0, RTM_NEWROUTE, 0,
 			    0, 0, RT_DEL_REASON_UNSPEC);
 	if (err < 0) {
-		/* -EMSGSIZE implies BUG in rt6_nlmsg_size() */
-		WARN_ON(err == -EMSGSIZE);
 		kfree_skb(skb);
 		goto errout;
 	}
-- 
2.55.0

Re: [PATCH net v2 0/2] ipv4/ipv6: do not warn on route notification size races

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - Whether the issue was actually triggered, or is only theoretical
   (e.g. found by code inspection). If it was triggered please include
   the symptoms, like the stack trace or error messages.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.

Re: [PATCH net v2 0/2] ipv4/ipv6: do not warn on route notification size races

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu,  8 Oct 2026 14:29:21 +0900 you wrote:
> A nexthop group can grow between route notification sizing and filling.
> Both IPv4 and IPv6 can then legitimately return -EMSGSIZE, so remove the
> stale warnings while preserving their existing error paths.
> 
> Patch 1 is unchanged from v1.  Patch 2 adds the IPv6 counterpart requested
> by Ido.  No new build or runtime test was run; both changes only delete the
> stale comment and WARN_ON().
> 
> [...]

Here is the summary with links:
  - [net,v2,1/2] ipv4: do not warn on route notification size race
    https://git.kernel.org/netdev/net/c/e02a5b658816
  - [net,v2,2/2] ipv6: do not warn on route notification size race
    https://git.kernel.org/netdev/net/c/c97426ec649d

You are awesome, thank you!
-- 
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