net: ipv4: fix regression in local-broadcast routes

Commit 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
introduced a regression where local-broadcast packets would have their
gateway set in __mkroute_output, which was caused by fi = NULL being
removed.

Fix this by resetting the fib_info for local-broadcast packets. This
preserves the intended changes for directed-broadcast packets.

Cc: stable@vger.kernel.org
Fixes: 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
Reported-by: Brett A C Sheffield <bacs@librecast.net>
Closes: https://lore.kernel.org/regressions/20250822165231.4353-4-bacs@librecast.net
Signed-off-by: Oscar Maes <oscmaes92@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250827062322.4807-1-oscmaes92@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index f639a2ae881ac50584e20f067dd83a6a4b3d4989..baa43e5966b19bf0ffd03f733b5aaf55ba5a8d9e 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2575,12 +2575,16 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
                    !netif_is_l3_master(dev_out))
                        return ERR_PTR(-EINVAL);
 
-       if (ipv4_is_lbcast(fl4->daddr))
+       if (ipv4_is_lbcast(fl4->daddr)) {
                type = RTN_BROADCAST;
-       else if (ipv4_is_multicast(fl4->daddr))
+
+               /* reset fi to prevent gateway resolution */
+               fi = NULL;
+       } else if (ipv4_is_multicast(fl4->daddr)) {
                type = RTN_MULTICAST;
-       else if (ipv4_is_zeronet(fl4->daddr))
+       } else if (ipv4_is_zeronet(fl4->daddr)) {
                return ERR_PTR(-EINVAL);
+       }
 
        if (dev_out->flags & IFF_LOOPBACK)
                flags |= RTCF_LOCAL;