netfilter: xt_mangle: only check verdict part of return value

These checks assume that the caller only returns NF_DROP without
any errno embedded in the upper bits.

This is fine right now, but followup patches will start to propagate
such errors to allow kfree_skb_drop_reason() in the called functions,
those would then indicate 'errno << 8 | NF_STOLEN'.

To not break things we have to mask those parts out.
Signed-off-by: Florian Westphal <fw@strlen.de>

net/ipv4/netfilter/iptable_mangle.c

@@ -36,12 +36,12 @@ static const struct xt_table packet_mangler = {
 static unsigned int
 ipt_mangle_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
 {
-	unsigned int ret;
+	unsigned int ret, verdict;
 	const struct iphdr *iph;
-	u_int8_t tos;
 	__be32 saddr, daddr;
-	u_int32_t mark;
+	u32 mark;
 	int err;
+	u8 tos;
 
 	/* Save things which could affect route */
 	mark = skb->mark;
@@ -51,8 +51,9 @@ ipt_mangle_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *stat
 	tos = iph->tos;
 
 	ret = ipt_do_table(priv, skb, state);
+	verdict = ret & NF_VERDICT_MASK;
 	/* Reroute for ANY change. */
-	if (ret != NF_DROP && ret != NF_STOLEN) {
+	if (verdict != NF_DROP && verdict != NF_STOLEN) {
 		iph = ip_hdr(skb);
 
 		if (iph->saddr != saddr ||

net/ipv6/netfilter/ip6table_mangle.c

@@ -31,10 +31,10 @@ static const struct xt_table packet_mangler = {
 static unsigned int
 ip6t_mangle_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
 {
-	unsigned int ret;
 	struct in6_addr saddr, daddr;
-	u_int8_t hop_limit;
-	u_int32_t flowlabel, mark;
+	unsigned int ret, verdict;
+	u32 flowlabel, mark;
+	u8 hop_limit;
 	int err;
 
 	/* save source/dest address, mark, hoplimit, flowlabel, priority,  */
@@ -47,8 +47,9 @@ ip6t_mangle_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *sta
 	flowlabel = *((u_int32_t *)ipv6_hdr(skb));
 
 	ret = ip6t_do_table(priv, skb, state);
+	verdict = ret & NF_VERDICT_MASK;
 
-	if (ret != NF_DROP && ret != NF_STOLEN &&
+	if (verdict != NF_DROP && verdict != NF_STOLEN &&
 	    (!ipv6_addr_equal(&ipv6_hdr(skb)->saddr, &saddr) ||
 	     !ipv6_addr_equal(&ipv6_hdr(skb)->daddr, &daddr) ||
 	     skb->mark != mark ||