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If > RTM_NEWNEXTHOP replaces a group with fewer paths between those loads, > fib_info_nhc() returns NULL and fib_nexthop_nlmsg_size() dereferences > it. > > Stop sizing when the indexed path is absent. Nexthop groups are > dense, so the current snapshot has no later path. > > Fixes: 680aea08e78c ("net: ipv4: Emit notification when fib hardware flags are changed") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> Reviewed-by: Ido Schimmel A group can also grow between fib_nlmsg_size() and fib_dump_info(), leading to the latter returning -EMSGSIZE and triggering the warning. It requires nexthop_compat_mode being set, which I assume most operators disable nowadays if they are using the nexthop API. Fix with [1]. If v3 is required, include it as patch #4. Otherwise, wait for this series to be applied before sending the fix (to prevent sashiko from flagging the issues being fixed here). diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 6ab95e19b3cf..ef3b1ac08ff9 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; }