netfilter: do not propagate nf_queue errors in nf_hook_slow

commit f1585086
(netfilter: nfnetlink_queue: return error number to caller)
erronously assigns the return value of nf_queue() to the "ret" value.

This can cause bogus return values if we encounter QUEUE verdict
when bypassing is enabled, the listener does not exist and the
next hook returns NF_STOLEN.

In this case nf_hook_slow returned -ESRCH instead of 0.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/core.c

@@ -180,17 +180,16 @@ int nf_hook_slow(u_int8_t pf, unsigned int hook, struct sk_buff *skb,
 		if (ret == 0)
 			ret = -EPERM;
 	} else if ((verdict & NF_VERDICT_MASK) == NF_QUEUE) {
-		ret = nf_queue(skb, elem, pf, hook, indev, outdev, okfn,
+		int err = nf_queue(skb, elem, pf, hook, indev, outdev, okfn,
 						verdict >> NF_VERDICT_QBITS);
-		if (ret < 0) {
-			if (ret == -ECANCELED)
+		if (err < 0) {
+			if (err == -ECANCELED)
 				goto next_hook;
-			if (ret == -ESRCH &&
+			if (err == -ESRCH &&
 			   (verdict & NF_VERDICT_FLAG_QUEUE_BYPASS))
 				goto next_hook;
 			kfree_skb(skb);
 		}
-		ret = 0;
 	}
 	rcu_read_unlock();
 	return ret;