ipv4: Don't increase PMTU with Datagram Too Big message.

RFC 1191 said, "a host MUST not increase its estimate of the Path
MTU in response to the contents of a Datagram Too Big message."

Signed-off-by: Li Wei <lw@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index d58dd0ec3e53..52e1f2bf0ca2 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -966,6 +966,9 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
         if (dst->dev->mtu < mtu)
                 return;
 
+        if (rt->rt_pmtu && rt->rt_pmtu < mtu)
+                return;
+
         if (mtu < ip_rt_min_pmtu)
                 mtu = ip_rt_min_pmtu;