[PATCH 3.2 180/185] net: flow_dissector: fail on evil iph->ihl

[Ben Hutchings]

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

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

From: Jason Wang <jasowang@xxxxxxxxxx>

commit 6f092343855a71e03b8d209815d8c45bf3a27fcd upstream.

We don't validate iph->ihl which may lead a dead loop if we meet a IPIP
skb whose iph->ihl is zero. Fix this by failing immediately when iph->ihl
is evil (less than 5).

This issue were introduced by commit ec5efe7946280d1e84603389a1030ccec0a767ae
(rps: support IPIP encapsulation).

Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Petr Matousek <pmatouse@xxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Daniel Borkmann <dborkman@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.2: the affected code is in __skb_get_rxhash()]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/core/flow_dissector.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2609,6 +2609,8 @@ ip:
 			goto done;
 
 		ip = (const struct iphdr *) (skb->data + nhoff);
+		if (ip->ihl < 5)
+			goto done;
 		if (ip_is_fragment(ip))
 			ip_proto = 0;
 		else

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