net: flow_dissector: fail on evil iph->ihl

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@google.com>
Cc: Petr Matousek <pmatouse@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: the affected code is in __skb_get_rxhash()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/core/dev.c b/net/core/dev.c
index ecf5ea2..7bcf37d 100644 (file)
--- 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