netfilter: nft_dup: do not use sreg_dev if the user doesn't specify it

The NFTA_DUP_SREG_DEV attribute is not a must option, so we should use it
in routing lookup only when the user specify it.

Fixes: d877f07112f1 ("netfilter: nf_tables: add nft_dup expression")
Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/nft_dup_ipv4.c

@@ -28,7 +28,7 @@ static void nft_dup_ipv4_eval(const struct nft_expr *expr,
 	struct in_addr gw = {
 		.s_addr = (__force __be32)regs->data[priv->sreg_addr],
 	};
-	int oif = regs->data[priv->sreg_dev];
+	int oif = priv->sreg_dev ? regs->data[priv->sreg_dev] : -1;
 
 	nf_dup_ipv4(pkt->net, pkt->skb, pkt->hook, &gw, oif);
 }
@@ -59,7 +59,9 @@ static int nft_dup_ipv4_dump(struct sk_buff *skb, const struct nft_expr *expr)
 {
 	struct nft_dup_ipv4 *priv = nft_expr_priv(expr);
 
-	if (nft_dump_register(skb, NFTA_DUP_SREG_ADDR, priv->sreg_addr) ||
+	if (nft_dump_register(skb, NFTA_DUP_SREG_ADDR, priv->sreg_addr))
+		goto nla_put_failure;
+	if (priv->sreg_dev &&
 	    nft_dump_register(skb, NFTA_DUP_SREG_DEV, priv->sreg_dev))
 		goto nla_put_failure;
 

net/ipv6/netfilter/nft_dup_ipv6.c

@@ -26,7 +26,7 @@ static void nft_dup_ipv6_eval(const struct nft_expr *expr,
 {
 	struct nft_dup_ipv6 *priv = nft_expr_priv(expr);
 	struct in6_addr *gw = (struct in6_addr *)&regs->data[priv->sreg_addr];
-	int oif = regs->data[priv->sreg_dev];
+	int oif = priv->sreg_dev ? regs->data[priv->sreg_dev] : -1;
 
 	nf_dup_ipv6(pkt->net, pkt->skb, pkt->hook, gw, oif);
 }
@@ -57,7 +57,9 @@ static int nft_dup_ipv6_dump(struct sk_buff *skb, const struct nft_expr *expr)
 {
 	struct nft_dup_ipv6 *priv = nft_expr_priv(expr);
 
-	if (nft_dump_register(skb, NFTA_DUP_SREG_ADDR, priv->sreg_addr) ||
+	if (nft_dump_register(skb, NFTA_DUP_SREG_ADDR, priv->sreg_addr))
+		goto nla_put_failure;
+	if (priv->sreg_dev &&
 	    nft_dump_register(skb, NFTA_DUP_SREG_DEV, priv->sreg_dev))
 		goto nla_put_failure;