From c780a049f9bf442314335372c9abc4548bfe3e44 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 16 Aug 2017 11:09:12 -0700 Subject: ipv4: better IP_MAX_MTU enforcement While working on yet another syzkaller report, I found that our IP_MAX_MTU enforcements were not properly done. gcc seems to reload dev->mtu for min(dev->mtu, IP_MAX_MTU), and final result can be bigger than IP_MAX_MTU :/ This is a problem because device mtu can be changed on other cpus or threads. While this patch does not fix the issue I am working on, it is probably worth addressing it. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/route.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net') diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 7effa62beed3..fe877a4a72b1 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1267,7 +1267,7 @@ static unsigned int ipv4_mtu(const struct dst_entry *dst) if (mtu) return mtu; - mtu = dst->dev->mtu; + mtu = READ_ONCE(dst->dev->mtu); if (unlikely(dst_metric_locked(dst, RTAX_MTU))) { if (rt->rt_uses_gateway && mtu > 576) -- cgit v1.2.3-59-g8ed1b