ipv4: Don't create nh exeption when the device mtu is smaller than the reported pmtu

When a local tool like tracepath tries to send packets bigger than
the device mtu, we create a nh exeption and set the pmtu to device
mtu. The device mtu does not expire, so check if the device mtu is
smaller than the reported pmtu and don't crerate a nh exeption in
that case.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.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 90ba8358a892..741df67a81ec 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -909,6 +909,9 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
         struct dst_entry *dst = &rt->dst;
         struct fib_result res;
 
+        if (dst->dev->mtu < mtu)
+                return;
+
         if (mtu < ip_rt_min_pmtu)
                 mtu = ip_rt_min_pmtu;