netdev - [PATCH net 1/2] net: ipv4: fix regression in local-broadcast routes

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Message-Id: <20250825060918.4799-1-oscmaes92@gmail.com>
Date: Mon, 25 Aug 2025 08:09:17 +0200
From: Oscar Maes <oscmaes92@...il.com>
To: bacs@...recast.net,
	brett@...recast.net,
	kuba@...nel.org
Cc: davem@...emloft.net,
	dsahern@...nel.org,
	netdev@...r.kernel.org,
	regressions@...ts.linux.dev,
	stable@...r.kernel.org,
	Oscar Maes <oscmaes92@...il.com>
Subject: [PATCH net 1/2] 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.

Fixes: 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
Reported-by: Brett A C Sheffield <bacs@...recast.net>
Closes: https://lore.kernel.org/regressions/20250822165231.4353-4-bacs@librecast.net
Signed-off-by: Oscar Maes <oscmaes92@...il.com>
---
 net/ipv4/route.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index f639a2ae881a..98d237e3ec04 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2575,9 +2575,12 @@ 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))
 		return ERR_PTR(-EINVAL);
-- 
2.39.5