netfilter: nft_tproxy: restrict support to TCP and UDP transport protocols

Add unfront check for TCP and UDP packets before performing further
processing.

Fixes: 4ed8eb65 ("netfilter: nf_tables: Add native tproxy support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_tproxy.c

@@ -30,6 +30,12 @@ static void nft_tproxy_eval_v4(const struct nft_expr *expr,
 	__be16 tport = 0;
 	struct sock *sk;
 
+	if (pkt->tprot != IPPROTO_TCP &&
+	    pkt->tprot != IPPROTO_UDP) {
+		regs->verdict.code = NFT_BREAK;
+		return;
+	}
+
 	hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
 	if (!hp) {
 		regs->verdict.code = NFT_BREAK;
@@ -91,7 +97,8 @@ static void nft_tproxy_eval_v6(const struct nft_expr *expr,
 
 	memset(&taddr, 0, sizeof(taddr));
 
-	if (!pkt->tprot_set) {
+	if (pkt->tprot != IPPROTO_TCP &&
+	    pkt->tprot != IPPROTO_UDP) {
 		regs->verdict.code = NFT_BREAK;
 		return;
 	}