netfilter: nft_compat: relax chain type validation

Check for nat chain dependency only, which is the one that can
actually crash the kernel. Don't care if mangle, filter and security
specific match and targets are used out of their scope, they are
harmless.

This restores iptables-compat with mangle specific match/target when
used out of the OUTPUT chain, that are actually emulated through filter
chains, which broke when performing strict validation.

Fixes: f3f5dded ("netfilter: nft_compat: validate chain type in match/target")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_compat.c

@@ -21,45 +21,17 @@
 #include <linux/netfilter_ipv6/ip6_tables.h>
 #include <net/netfilter/nf_tables.h>
 
-static const struct {
-       const char	*name;
-       u8		type;
-} table_to_chaintype[] = {
-       { "filter",     NFT_CHAIN_T_DEFAULT },
-       { "raw",        NFT_CHAIN_T_DEFAULT },
-       { "security",   NFT_CHAIN_T_DEFAULT },
-       { "mangle",     NFT_CHAIN_T_ROUTE },
-       { "nat",        NFT_CHAIN_T_NAT },
-       { },
-};
-
-static int nft_compat_table_to_chaintype(const char *table)
-{
-	int i;
-
-	for (i = 0; table_to_chaintype[i].name != NULL; i++) {
-		if (strcmp(table_to_chaintype[i].name, table) == 0)
-			return table_to_chaintype[i].type;
-	}
-
-	return -1;
-}
-
 static int nft_compat_chain_validate_dependency(const char *tablename,
 						const struct nft_chain *chain)
 {
-	enum nft_chain_type type;
 	const struct nft_base_chain *basechain;
 
 	if (!tablename || !(chain->flags & NFT_BASE_CHAIN))
 		return 0;
 
-	type = nft_compat_table_to_chaintype(tablename);
-	if (type < 0)
-		return -EINVAL;
-
 	basechain = nft_base_chain(chain);
-	if (basechain->type->type != type)
+	if (strcmp(tablename, "nat") == 0 &&
+	    basechain->type->type != NFT_CHAIN_T_NAT)
 		return -EINVAL;
 
 	return 0;