linux-kernel - [PATCH 3.16 200/306] ip6_tunnel: Clear IP6CB in ip6tunnel

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Message-ID: <lsq.1487198500.153536260@decadent.org.uk>
Date:   Wed, 15 Feb 2017 22:41:40 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Eli Cooper" <elicooper@....com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 200/306] ip6_tunnel: Clear IP6CB in ip6tunnel_xmit()

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Eli Cooper <elicooper@....com>

commit 23f4ffedb7d751c7e298732ba91ca75d224bc1a6 upstream.

skb->cb may contain data from previous layers. In the observed scenario,
the garbage data were misinterpreted as IP6CB(skb)->frag_max_size, so
that small packets sent through the tunnel are mistakenly fragmented.

This patch unconditionally clears the control buffer in ip6tunnel_xmit(),
which affects ip6_tunnel, ip6_udp_tunnel and ip6_gre. Currently none of
these tunnels set IP6CB(skb)->flags, otherwise it needs to be done earlier.

Signed-off-by: Eli Cooper <elicooper@....com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/net/ip6_tunnel.h | 1 +
 1 file changed, 1 insertion(+)

--- a/include/net/ip6_tunnel.h
+++ b/include/net/ip6_tunnel.h
@@ -75,6 +75,7 @@ static inline void ip6tunnel_xmit(struct
 	struct net_device_stats *stats = &dev->stats;
 	int pkt_len, err;

+	memset(skb->cb, 0, sizeof(struct inet6_skb_parm));
 	pkt_len = skb->len;
 	err = ip6_local_out(skb);