net: flow_dissector: fail on evil iph->ihl

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>

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 8d7d0dd..143b6fd 100644 (file)
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -40,7 +40,7 @@ again:
                struct iphdr _iph;
 ip:
                iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph);
-               if (!iph)
+               if (!iph || iph->ihl < 5)
                        return false;
 
                if (ip_is_fragment(iph))