[PATCH net] ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation

[PATCH net] ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation

[Yohei Kanemaru]

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@gmail.com>
---
 net/ipv6/seg6_iptunnel.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
index 8181ee7..ee5403c 100644
--- a/net/ipv6/seg6_iptunnel.c
+++ b/net/ipv6/seg6_iptunnel.c
@@ -146,6 +146,8 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
 	} 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;
-- 
2.10.0

Re: [PATCH net] ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation

[David Miller]

From: Yohei Kanemaru <yohei.kanemaru@gmail.com>
Date: Tue, 29 Jan 2019 15:52:34 +0900

> 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@gmail.com>

Applied, thanks.