[PATCH RFC nft] src: avoid re-initing core library when a second context struct is allocated

[Florian Westphal <fw@strlen.de>]

Calling nft_ctx_new() a second time leaks memory, and calling
nft_ctx_free a second time -- on a different context -- causes
double-free.

This patch won't work in case we assume libnftables should be
thread-safe, in such case we either need a mutex or move all resources
under nft_ctx scope.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/libnftables.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/libnftables.c b/src/libnftables.c
index 4a139c58b2b3..880fd4284555 100644
--- a/src/libnftables.c
+++ b/src/libnftables.c
@@ -17,6 +17,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+static unsigned int context_count;
+
 static int nft_netlink(struct nft_ctx *nft,
 		       struct list_head *cmds, struct list_head *msgs,
 		       struct mnl_socket *nf_sock)
@@ -86,6 +88,9 @@ out:
 
 static void nft_init(void)
 {
+	if (context_count++)
+		return;
+
 	mark_table_init();
 	realm_table_rt_init();
 	devgroup_table_init();
@@ -99,6 +104,9 @@ static void nft_init(void)
 
 static void nft_exit(void)
 {
+	if (--context_count)
+		return;
+
 	ct_label_table_exit();
 	realm_table_rt_exit();
 	devgroup_table_exit();
-- 
2.21.0