netfilter: nft_fwd_netdev: Support egress hook

Allow packet redirection to another interface upon egress.

[lukas: set skb_iif, add commit message, original patch from Pablo. ]
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_fwd_netdev.c

@@ -27,9 +27,11 @@ static void nft_fwd_netdev_eval(const struct nft_expr *expr,
 {
 	struct nft_fwd_netdev *priv = nft_expr_priv(expr);
 	int oif = regs->data[priv->sreg_dev];
+	struct sk_buff *skb = pkt->skb;
 
 	/* This is used by ifb only. */
-	skb_set_redirected(pkt->skb, true);
+	skb->skb_iif = skb->dev->ifindex;
+	skb_set_redirected(skb, nft_hook(pkt) == NF_NETDEV_INGRESS);
 
 	nf_fwd_netdev_egress(pkt, oif);
 	regs->verdict.code = NF_STOLEN;
@@ -198,7 +200,8 @@ static int nft_fwd_validate(const struct nft_ctx *ctx,
 			    const struct nft_expr *expr,
 			    const struct nft_data **data)
 {
-	return nft_chain_validate_hooks(ctx->chain, (1 << NF_NETDEV_INGRESS));
+	return nft_chain_validate_hooks(ctx->chain, (1 << NF_NETDEV_INGRESS) |
+						    (1 << NF_NETDEV_EGRESS));
 }
 
 static struct nft_expr_type nft_fwd_netdev_type;