netfilter: nf_tables: restrict nat/masq expressions to nat chain type

This adds the missing validation code to avoid the use of nat/masq from
non-nat chains. The validation assumes two possible configuration
scenarios:

1) Use of nat from base chain that is not of nat type. Reject this
   configuration from the nft_*_init() path of the expression.

2) Use of nat from non-base chain. In this case, we have to wait until
   the non-base chain is referenced by at least one base chain via
   jump/goto. This is resolved from the nft_*_validate() path which is
   called from nf_tables_check_loops().

The user gets an -EOPNOTSUPP in both cases.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/net/netfilter/nft_masq.c b/net/netfilter/nft_masq.c
index 6637bab00567..d1ffd5eb3a9b 100644
--- a/net/netfilter/nft_masq.c
+++ b/net/netfilter/nft_masq.c
@@ -26,6 +26,11 @@ int nft_masq_init(const struct nft_ctx *ctx,
 		  const struct nlattr * const tb[])
 {
 	struct nft_masq *priv = nft_expr_priv(expr);
+	int err;
+
+	err = nft_chain_validate_dependency(ctx->chain, NFT_CHAIN_T_NAT);
+	if (err < 0)
+		return err;
 
 	if (tb[NFTA_MASQ_FLAGS] == NULL)
 		return 0;
@@ -55,5 +60,12 @@ nla_put_failure:
 }
 EXPORT_SYMBOL_GPL(nft_masq_dump);
 
+int nft_masq_validate(const struct nft_ctx *ctx, const struct nft_expr *expr,
+		      const struct nft_data **data)
+{
+	return nft_chain_validate_dependency(ctx->chain, NFT_CHAIN_T_NAT);
+}
+EXPORT_SYMBOL_GPL(nft_masq_validate);
+
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>");