[SNAP]: Check packet length before reading

The snap_rcv code reads 5 bytes so we should make sure that
we have 5 bytes in the head before proceeding.

Based on diagnosis and fix by Evgeniy Polyakov, reported by
Alan J. Wylie.

Patch also kills the skb->sk assignment before kfree_skb
since it's redundant.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 5 deletions

diff --git a/net/802/psnap.c b/net/802/psnap.c
index 04ee43e7538f..31128cb92a23 100644
--- a/net/802/psnap.c
+++ b/net/802/psnap.c
@@ -55,6 +55,9 @@ static int snap_rcv(struct sk_buff *skb, struct net_device *dev,
                 .type = __constant_htons(ETH_P_SNAP),
         };
 
+        if (unlikely(!pskb_may_pull(skb, 5)))
+                goto drop;
+
         rcu_read_lock();
         proto = find_snap_client(skb_transport_header(skb));
         if (proto) {
@@ -62,14 +65,18 @@ static int snap_rcv(struct sk_buff *skb, struct net_device *dev,
                 skb->transport_header += 5;
                 skb_pull_rcsum(skb, 5);
                 rc = proto->rcvfunc(skb, dev, &snap_packet_type, orig_dev);
-        } else {
-                skb->sk = NULL;
-                kfree_skb(skb);
-                rc = 1;
         }
-
         rcu_read_unlock();
+
+        if (unlikely(!proto))
+                goto drop;
+
+out:
         return rc;
+
+drop:
+        kfree_skb(skb);
+        goto out;
 }
 
 /*