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

[Daehyeon Ko <4ncienth@gmail.com>]

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