netfilter: nft_fwd_netdev: validate family and chain type

Make sure the forward action is only used from ingress.

Fixes: 39e6dea ("netfilter: nf_tables: add forward expression to the netdev family")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: ummakynes

net/netfilter/nft_fwd_netdev.c

@@ -190,13 +190,21 @@ static int nft_fwd_neigh_dump(struct sk_buff *skb, const struct nft_expr *expr)
 	return -1;
 }
 
+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));
+}
+
 static struct nft_expr_type nft_fwd_netdev_type;
 static const struct nft_expr_ops nft_fwd_neigh_netdev_ops = {
 	.type		= &nft_fwd_netdev_type,
 	.size		= NFT_EXPR_SIZE(sizeof(struct nft_fwd_neigh)),
 	.eval		= nft_fwd_neigh_eval,
 	.init		= nft_fwd_neigh_init,
 	.dump		= nft_fwd_neigh_dump,
+	.validate	= nft_fwd_validate,
 };
 
 static const struct nft_expr_ops nft_fwd_netdev_ops = {
@@ -205,6 +213,7 @@ static const struct nft_expr_ops nft_fwd_netdev_ops = {
 	.eval		= nft_fwd_netdev_eval,
 	.init		= nft_fwd_netdev_init,
 	.dump		= nft_fwd_netdev_dump,
+	.validate	= nft_fwd_validate,
 	.offload	= nft_fwd_netdev_offload,
 };