5.4-stable review patch. If anyone has any objections, please let me know.
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From: Oscar Maes oscmaes92@gmail.com
[ Upstream commit 9e30ecf23b1b8f091f7d08b27968dea83aae7908 ]
Currently, __mkroute_output overrules the MTU value configured for broadcast routes.
This buggy behaviour can be reproduced with:
ip link set dev eth1 mtu 9000 ip route del broadcast 192.168.0.255 dev eth1 proto kernel scope link src 192.168.0.2 ip route add broadcast 192.168.0.255 dev eth1 proto kernel scope link src 192.168.0.2 mtu 1500
The maximum packet size should be 1500, but it is actually 8000:
ping -b 192.168.0.255 -s 8000
Fix __mkroute_output to allow MTU values to be configured for for broadcast routes (to support a mixed-MTU local-area-network).
Signed-off-by: Oscar Maes oscmaes92@gmail.com Link: https://patch.msgid.link/20250710142714.12986-1-oscmaes92@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/route.c | 1 - 1 file changed, 1 deletion(-)
diff --git a/net/ipv4/route.c b/net/ipv4/route.c index d173234503f9..80612f73ff53 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -2378,7 +2378,6 @@ static struct rtable *__mkroute_output(const struct fib_result *res, do_cache = true; if (type == RTN_BROADCAST) { flags |= RTCF_BROADCAST | RTCF_LOCAL; - fi = NULL; } else if (type == RTN_MULTICAST) { flags |= RTCF_MULTICAST | RTCF_LOCAL; if (!ip_check_mc_rcu(in_dev, fl4->daddr, fl4->saddr,