From c780a049f9bf442314335372c9abc4548bfe3e44 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
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 <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/ipv4/route.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
(limited to 'net/ipv4')
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)
--
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