netfilter: nf_tables: disallow jump to implicit chain from set element

Extend struct nft_data_desc to add a flag field that specifies
nft_data_init() is being called for set element data.

Use it to disallow jump to implicit chain from set element, only jump
to chain via immediate expression is allowed.

Fixes: d0e2c7de ("netfilter: nf_tables: add NFT_CHAIN_BINDING")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables.h

@@ -221,10 +221,15 @@ struct nft_ctx {
 	bool				report;
 };
 
+enum nft_data_desc_flags {
+	NFT_DATA_DESC_SETELEM	= (1 << 0),
+};
+
 struct nft_data_desc {
 	enum nft_data_types		type;
 	unsigned int			size;
 	unsigned int			len;
+	unsigned int			flags;
 };
 
 int nft_data_init(const struct nft_ctx *ctx, struct nft_data *data,

net/netfilter/nf_tables_api.c

@@ -5226,6 +5226,7 @@ static int nft_setelem_parse_data(struct nft_ctx *ctx, struct nft_set *set,
 	desc->type = dtype;
 	desc->size = NFT_DATA_VALUE_MAXLEN;
 	desc->len = set->dlen;
+	desc->flags = NFT_DATA_DESC_SETELEM;
 
 	return nft_data_init(ctx, data, desc, attr);
 }
@@ -9665,6 +9666,9 @@ static int nft_verdict_init(const struct nft_ctx *ctx, struct nft_data *data,
 			return PTR_ERR(chain);
 		if (nft_is_base_chain(chain))
 			return -EOPNOTSUPP;
+		if (desc->flags & NFT_DATA_DESC_SETELEM &&
+		    chain->flags & NFT_CHAIN_BINDING)
+			return -EINVAL;
 
 		chain->use++;
 		data->verdict.chain = chain;