netfilter: nft_ct: fix l3num expectations with inet pseudo family

Following is rejected but should be allowed:

table inet t {
ct expectation exp1 {
[..]
l3proto ip

Valid combos are:
table ip t, l3proto ip
table ip6 t, l3proto ip6
table inet t, l3proto ip OR l3proto ip6

Disallow inet pseudeo family, the l3num must be a on-wire protocol known
to conntrack.

Retain NFPROTO_INET case to make it clear its rejected
intentionally rather as oversight.

Fixes: 8059918a1377 ("netfilter: nft_ct: sanitize layer 3 and 4 protocol number in custom expectations")
Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nft_ct.c

···
 	switch (priv->l3num) {
 	case NFPROTO_IPV4:
 	case NFPROTO_IPV6:
-		if (priv->l3num != ctx->family)
-			return -EINVAL;
+		if (priv->l3num == ctx->family || ctx->family == NFPROTO_INET)
+			break;
 
-		fallthrough;
-	case NFPROTO_INET:
-		break;
+		return -EINVAL;
+	case NFPROTO_INET: /* tuple.src.l3num supports NFPROTO_IPV4/6 only */
 	default:
-		return -EOPNOTSUPP;
+		return -EAFNOSUPPORT;
 	}
 
 	priv->l4proto = nla_get_u8(tb[NFTA_CT_EXPECT_L4PROTO]);