linux-kernel - [PATCH 3.2 071/126] ip6_tunnel: Clear IP6CB in ip6tunnel

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Date:   Wed, 15 Feb 2017 22:41:34 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
        "Eli Cooper" <elicooper@....com>
Subject: [PATCH 3.2 071/126] ip6_tunnel: Clear IP6CB in ip6tunnel_xmit()

3.2.85-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 3.2: apply to ip6_tnl_xmit2()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/ipv6/ip6_tunnel.c | 1 +
 1 file changed, 1 insertion(+)

--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -983,6 +983,7 @@ static int ip6_tnl_xmit2(struct sk_buff
 	ipv6_addr_copy(&ipv6h->saddr, &fl6->saddr);
 	ipv6_addr_copy(&ipv6h->daddr, &fl6->daddr);
 	nf_reset(skb);
+	memset(skb->cb, 0, sizeof(struct inet6_skb_parm));
 	pkt_len = skb->len;
 	err = ip6_local_out(skb);