netdev - [PATCH] ip6_tunnel: Clear IP6CB(skb)->frag_max_size in ip4ip6_tnl

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Date:   Mon, 24 Oct 2016 23:07:12 +0800
From:   Eli Cooper <elicooper@....com>
To:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>
Subject: [PATCH] ip6_tunnel: Clear IP6CB(skb)->frag_max_size in ip4ip6_tnl_xmit()

skb->cb may contain data from previous layers, as shown in 5146d1f1511
("tunnel: Clear IPCB(skb)->opt before dst_link_failure called").
However, for ipip6 tunnels, clearing IPCB(skb)->opt alone is not enough,
because skb->cb is later misinterpreted as IP6CB(skb)->frag_max_size.

In the observed scenario, the garbage data made the max fragment size so
so small that packets sent through the tunnel are mistakenly fragmented.

This patch clears IP6CB(skb)->frag_max_size for ipip6 tunnels.

Signed-off-by: Eli Cooper <elicooper@....com>
---
 net/ipv6/ip6_tunnel.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 202d16a..4110562 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1205,6 +1205,7 @@ ip4ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
 	int err;

 	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
+	IP6CB(skb)->frag_max_size = 0;

 	tproto = ACCESS_ONCE(t->parms.proto);
 	if (tproto != IPPROTO_IPIP && tproto != 0)
-- 
2.10.1