linux-kernel - [PATCH 4.20 02/80] ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation

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Date:   Mon,  4 Feb 2019 11:36:22 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yohei Kanemaru <yohei.kanemaru@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.20 02/80] ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation

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

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

From: Yohei Kanemaru <yohei.kanemaru@...il.com>

[ Upstream commit ef489749aae508e6f17886775c075f12ff919fb1 ]

skb->cb may contain data from previous layers (in an observed case
IPv4 with L3 Master Device). In the observed scenario, the data in
IPCB(skb)->frags was misinterpreted as IP6CB(skb)->frag_max_size,
eventually caused an unexpected IPv6 fragmentation in ip6_fragment()
through ip6_finish_output().

This patch clears IP6CB(skb), which potentially contains garbage data,
on the SRH ip4ip6 encapsulation.

Fixes: 32d99d0b6702 ("ipv6: sr: add support for ip4ip6 encapsulation")
Signed-off-by: Yohei Kanemaru <yohei.kanemaru@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv6/seg6_iptunnel.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/ipv6/seg6_iptunnel.c
+++ b/net/ipv6/seg6_iptunnel.c
@@ -146,6 +146,8 @@ int seg6_do_srh_encap(struct sk_buff *sk
 	} else {
 		ip6_flow_hdr(hdr, 0, flowlabel);
 		hdr->hop_limit = ip6_dst_hoplimit(skb_dst(skb));
+
+		memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
 	}
 
 	hdr->nexthdr = NEXTHDR_ROUTING;