[PATCH 3.19 2/7] route: Use ipv4_mtu instead of raw rt_pmtu

From: Greg Kroah-Hartman
Date: Fri May 08 2015 - 07:12:52 EST

3.19-stable review patch. If anyone has any objections, please let me know.


From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit cb6ccf09d6b94bec4def1ac5cf4678d12b216474 ]

The commit 3cdaa5be9e81a914e633a6be7b7d2ef75b528562 ("ipv4: Don't
increase PMTU with Datagram Too Big message") broke PMTU in cases
where the rt_pmtu value has expired but is smaller than the new
PMTU value.

This obsolete rt_pmtu then prevents the new PMTU value from being

Fixes: 3cdaa5be9e81 ("ipv4: Don't increase PMTU with Datagram Too Big message")
Reported-by: Gerd v. Egidy <gerd.von.egidy@xxxxxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/ipv4/route.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -963,10 +963,7 @@ static void __ip_rt_update_pmtu(struct r
if (dst_metric_locked(dst, RTAX_MTU))

- if (dst->dev->mtu < mtu)
- return;
- if (rt->rt_pmtu && rt->rt_pmtu < mtu)
+ if (ipv4_mtu(dst) < mtu)

if (mtu < ip_rt_min_pmtu)

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