netfilter: bridge: don't leak skb in error paths

br_nf_dev_queue_xmit must free skb in its error path.
NF_DROP is misleading -- its an okfn, not a netfilter hook.

Fixes: 462fb2af ("bridge : Sanitize skb before it enters the IP stack")
Fixes: efb6de9b ("netfilter: bridge: forward IPv6 fragmented packets")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/bridge/br_netfilter_hooks.c

@@ -744,7 +744,7 @@ static int br_nf_dev_queue_xmit(struct sock *sk, struct sk_buff *skb)
 		struct brnf_frag_data *data;
 
 		if (br_validate_ipv4(skb))
-			return NF_DROP;
+			goto drop;
 
 		IPCB(skb)->frag_max_size = nf_bridge->frag_max_size;
 
@@ -769,7 +769,7 @@ static int br_nf_dev_queue_xmit(struct sock *sk, struct sk_buff *skb)
 		struct brnf_frag_data *data;
 
 		if (br_validate_ipv6(skb))
-			return NF_DROP;
+			goto drop;
 
 		IP6CB(skb)->frag_max_size = nf_bridge->frag_max_size;
 
@@ -784,12 +784,16 @@ static int br_nf_dev_queue_xmit(struct sock *sk, struct sk_buff *skb)
 
 		if (v6ops)
 			return v6ops->fragment(sk, skb, br_nf_push_frag_xmit);
-		else
+
+		kfree_skb(skb);
 		return -EMSGSIZE;
 	}
 #endif
 	nf_bridge_info_free(skb);
 	return br_dev_queue_push_xmit(sk, skb);
+ drop:
+	kfree_skb(skb);
+	return 0;
 }
 
 /* PF_BRIDGE/POST_ROUTING ********************************************/