src: add comment support when adding tables

Adds userdata building logic if a comment is specified when creating a
new table. Adds netlink userdata parsing callback function.

Relies on kernel supporting userdata for nft_table.

Example:

> nft add table ip x { comment "test"\; }
> nft list ruleset

table ip x {
	comment "test"
}

Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/src/netlink.c b/src/netlink.c
index 0db5e175..a107f492 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -537,10 +537,32 @@ struct chain *netlink_delinearize_chain(struct netlink_ctx *ctx,
 	return chain;
 }
 
+static int table_parse_udata_cb(const struct nftnl_udata *attr, void *data)
+{
+	unsigned char *value = nftnl_udata_get(attr);
+	const struct nftnl_udata **tb = data;
+	uint8_t type = nftnl_udata_type(attr);
+	uint8_t len = nftnl_udata_len(attr);
+
+	switch (type) {
+		case NFTNL_UDATA_TABLE_COMMENT:
+			if (value[len - 1] != '\0')
+				return -1;
+			break;
+		default:
+			return 0;
+	}
+	tb[type] = attr;
+	return 0;
+}
+
 struct table *netlink_delinearize_table(struct netlink_ctx *ctx,
 					const struct nftnl_table *nlt)
 {
+	const struct nftnl_udata *ud[NFTNL_UDATA_TABLE_MAX + 1] = {};
 	struct table *table;
+	const char *udata;
+	uint32_t ulen;
 
 	table = table_alloc();
 	table->handle.family = nftnl_table_get_u32(nlt, NFTNL_TABLE_FAMILY);
@@ -548,6 +570,16 @@ struct table *netlink_delinearize_table(struct netlink_ctx *ctx,
 	table->flags	     = nftnl_table_get_u32(nlt, NFTNL_TABLE_FLAGS);
 	table->handle.handle.id = nftnl_table_get_u64(nlt, NFTNL_TABLE_HANDLE);
 
+	if (nftnl_table_is_set(nlt, NFTNL_TABLE_USERDATA)) {
+		udata = nftnl_table_get_data(nlt, NFTNL_TABLE_USERDATA, &ulen);
+		if (nftnl_udata_parse(udata, ulen, table_parse_udata_cb, ud) < 0) {
+			netlink_io_error(ctx, NULL, "Cannot parse userdata");
+			return NULL;
+		}
+		if (ud[NFTNL_UDATA_TABLE_COMMENT])
+			table->comment = xstrdup(nftnl_udata_get(ud[NFTNL_UDATA_TABLE_COMMENT]));
+	}
+
 	return table;
 }