linux-kernel - [ 31/79] gre: Fix MTU sizing check for gretap tunnels

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Message-Id: <20130726204725.184611789@linuxfoundation.org>
Date:	Fri, 26 Jul 2013 13:47:21 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Cong Wang <amwang@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 31/79] gre: Fix MTU sizing check for gretap tunnels

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

------------------

From: Alexander Duyck <alexander.h.duyck@...el.com>

[ Upstream commit 8c91e162e058bb91b7766f26f4d5823a21941026 ]

This change fixes an MTU sizing issue seen with gretap tunnels when non-gso
packets are sent from the interface.

In my case I was able to reproduce the issue by simply sending a ping of
1421 bytes with the gretap interface created on a device with a standard
1500 mtu.

This fix is based on the fact that the tunnel mtu is already adjusted by
dev->hard_header_len so it would make sense that any packets being compared
against that mtu should also be adjusted by hard_header_len and the tunnel
header instead of just the tunnel header.

Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
Reported-by: Cong Wang <amwang@...hat.com>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv4/ip_tunnel.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -490,7 +490,7 @@ static int tnl_update_pmtu(struct net_de
 			    struct rtable *rt, __be16 df)
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
-	int pkt_size = skb->len - tunnel->hlen;
+	int pkt_size = skb->len - tunnel->hlen - dev->hard_header_len;
 	int mtu;
 
 	if (df)


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