xtables-compat: check if nft ruleset is compatible

This patch adds a verification of the compatibility between the nft
ruleset and iptables. Nft tables, chains and rules are checked to be
compatible with iptables. If something is not compatible, the execution
stops and an error message is displayed to the user.

This checking is triggered by xtables-compat -L and xtables-compat-save
commands.

Signed-off-by: Pablo M. Bermudo Garay <pablombg@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

4 files changed, 206 insertions, 0 deletions

diff --git a/iptables/nft.c b/iptables/nft.c
index 247a60aa..f1f0d9d6 100644
--- a/iptables/nft.c
+++ b/iptables/nft.c
@@ -2698,3 +2698,197 @@ uint32_t nft_invflags2cmp(uint32_t invflags, uint32_t flag)
 
 	return NFT_CMP_EQ;
 }
+
+#define NFT_COMPAT_EXPR_MAX     8
+
+static const char *supported_exprs[NFT_COMPAT_EXPR_MAX] = {
+	"match",
+	"target",
+	"payload",
+	"meta",
+	"cmp",
+	"bitwise",
+	"counter",
+	"immediate"
+};
+
+
+static int nft_is_expr_compatible(const char *name)
+{
+	int i;
+
+	for (i = 0; i < NFT_COMPAT_EXPR_MAX; i++) {
+		if (strcmp(supported_exprs[i], name) == 0)
+			return 0;
+	}
+
+	return 1;
+}
+
+static int nft_is_rule_compatible(struct nftnl_rule *rule)
+{
+	struct nftnl_expr_iter *iter;
+	struct nftnl_expr *expr;
+	int ret = 0;
+
+	iter = nftnl_expr_iter_create(rule);
+	if (iter == NULL)
+		return -1;
+
+	expr = nftnl_expr_iter_next(iter);
+	while (expr != NULL) {
+		const char *name = nftnl_expr_get_str(expr, NFTNL_EXPR_NAME);
+
+		if (nft_is_expr_compatible(name) == 0) {
+			expr = nftnl_expr_iter_next(iter);
+			continue;
+		}
+
+		ret = 1;
+		break;
+	}
+
+	nftnl_expr_iter_destroy(iter);
+	return ret;
+}
+
+static int nft_is_chain_compatible(const char *table, const char *chain)
+{
+	const char *cur_table;
+	struct builtin_chain *chains;
+	int i, j;
+
+	for (i = 0; i < TABLES_MAX; i++) {
+		cur_table = xtables_ipv4[i].name;
+		chains = xtables_ipv4[i].chains;
+
+		if (strcmp(table, cur_table) != 0)
+			continue;
+
+		for (j = 0; j < NF_INET_NUMHOOKS && chains[j].name; j++) {
+			if (strcmp(chain, chains[j].name) == 0)
+				return 0;
+		}
+	}
+
+	return 1;
+}
+
+static int nft_are_chains_compatible(struct nft_handle *h)
+{
+	struct nftnl_chain_list *list;
+	struct nftnl_chain_list_iter *iter;
+	struct nftnl_chain *chain;
+	int ret = 0;
+
+	list = nftnl_chain_list_get(h);
+	if (list == NULL)
+		return -1;
+
+	iter = nftnl_chain_list_iter_create(list);
+	if (iter == NULL)
+		return -1;
+
+	chain = nftnl_chain_list_iter_next(iter);
+	while (chain != NULL) {
+		if (!nft_chain_builtin(chain))
+			goto next;
+
+		const char *table = nftnl_chain_get(chain, NFTNL_CHAIN_TABLE);
+		const char *name = nftnl_chain_get(chain, NFTNL_CHAIN_NAME);
+
+		if (nft_is_chain_compatible(table, name) == 1) {
+			ret = 1;
+			break;
+		}
+
+next:
+		chain = nftnl_chain_list_iter_next(iter);
+	}
+
+	nftnl_chain_list_iter_destroy(iter);
+	nftnl_chain_list_free(list);
+	return ret;
+}
+
+static int nft_is_table_compatible(const char *name)
+{
+	int i;
+
+	for (i = 0; i < TABLES_MAX; i++) {
+		if (strcmp(xtables_ipv4[i].name, name) == 0)
+			return 0;
+	}
+
+	return 1;
+}
+
+static int nft_are_tables_compatible(struct nft_handle *h)
+{
+	struct nftnl_table_list *list;
+	struct nftnl_table_list_iter *iter;
+	struct nftnl_table *table;
+	int ret = 0;
+
+	list = nftnl_table_list_get(h);
+	if (list == NULL)
+		return -1;
+
+	iter = nftnl_table_list_iter_create(list);
+	if (iter == NULL)
+		return -1;
+
+	table = nftnl_table_list_iter_next(iter);
+	while (table != NULL) {
+		const char *name = nftnl_table_get(table, NFTNL_TABLE_NAME);
+
+		if (nft_is_table_compatible(name) == 0) {
+			table = nftnl_table_list_iter_next(iter);
+			continue;
+		}
+
+		ret = 1;
+		break;
+	}
+
+	nftnl_table_list_iter_destroy(iter);
+	nftnl_table_list_free(list);
+	return ret;
+}
+
+int nft_is_ruleset_compatible(struct nft_handle *h)
+{
+
+	struct nftnl_rule_list *list;
+	struct nftnl_rule_list_iter *iter;
+	struct nftnl_rule *rule;
+	int ret = 0;
+
+	ret = nft_are_tables_compatible(h);
+	if (ret != 0)
+		return ret;
+
+	ret = nft_are_chains_compatible(h);
+	if (ret != 0)
+		return ret;
+
+	list = nft_rule_list_get(h);
+	if (list == NULL)
+		return -1;
+
+	iter = nftnl_rule_list_iter_create(list);
+	if (iter == NULL)
+		return -1;
+
+	rule = nftnl_rule_list_iter_next(iter);
+	while (rule != NULL) {
+		ret = nft_is_rule_compatible(rule);
+		if (ret != 0)
+			break;
+
+		rule = nftnl_rule_list_iter_next(iter);
+	}
+
+	nftnl_rule_list_iter_destroy(iter);
+	return ret;
+}
diff --git a/iptables/nft.h b/iptables/nft.h
index bcabf42b..f5449db4 100644
--- a/iptables/nft.h
+++ b/iptables/nft.h
@@ -181,4 +181,6 @@ int nft_arp_rule_insert(struct nft_handle *h, const char *chain,
 
 void nft_rule_to_arpt_entry(struct nftnl_rule *r, struct arpt_entry *fw);
 
+int nft_is_ruleset_compatible(struct nft_handle *h);
+
 #endif
diff --git a/iptables/xtables-save.c b/iptables/xtables-save.c
index 50b5b5ae..f30867cf 100644
--- a/iptables/xtables-save.c
+++ b/iptables/xtables-save.c
@@ -138,6 +138,11 @@ xtables_save_main(int family, const char *progname, int argc, char *argv[])
 		exit(1);
 	}
 
+	if (nft_is_ruleset_compatible(&h) == 1) {
+		printf("ERROR: You're using nft features that cannot be mapped to iptables, please keep using nft.\n");
+		exit(EXIT_FAILURE);
+	}
+
 	if (dump) {
 		do_output(&h, tablename, show_counters);
 		exit(0);
diff --git a/iptables/xtables.c b/iptables/xtables.c
index 48b9c51c..d222ae99 100644
--- a/iptables/xtables.c
+++ b/iptables/xtables.c
@@ -1253,6 +1253,11 @@ int do_commandx(struct nft_handle *h, int argc, char *argv[], char **table,
 	case CMD_LIST:
 	case CMD_LIST|CMD_ZERO:
 	case CMD_LIST|CMD_ZERO_NUM:
+		if (nft_is_ruleset_compatible(h) == 1) {
+			printf("ERROR: You're using nft features that cannot be mapped to iptables, please keep using nft.\n");
+			exit(EXIT_FAILURE);
+		}
+
 		ret = list_entries(h, p.chain, p.table, p.rulenum,
 				   cs.options & OPT_VERBOSE,
 				   cs.options & OPT_NUMERIC,