json: fix use after free in table_flags_json()

Add `$NFT -j list ruleset` to the end of "tests/shell/testcases/transactions/table_onoff".
Then valgrind will find this issue:

  $ make -j && ./tests/shell/run-tests.sh tests/shell/testcases/transactions/table_onoff -V

Gives:

  ==286== Invalid read of size 4
  ==286==    at 0x49B0261: do_dump (dump.c:211)
  ==286==    by 0x49B08B8: do_dump (dump.c:378)
  ==286==    by 0x49B08B8: do_dump (dump.c:378)
  ==286==    by 0x49B04F7: do_dump (dump.c:273)
  ==286==    by 0x49B08B8: do_dump (dump.c:378)
  ==286==    by 0x49B0E84: json_dump_callback (dump.c:465)
  ==286==    by 0x48AF22A: do_command_list_json (json.c:2016)
  ==286==    by 0x48732F1: do_command_list (rule.c:2335)
  ==286==    by 0x48737F5: do_command (rule.c:2605)
  ==286==    by 0x48A867D: nft_netlink (libnftables.c:42)
  ==286==    by 0x48A92B1: nft_run_cmd_from_buffer (libnftables.c:597)
  ==286==    by 0x402CBA: main (main.c:533)

Fixes: e70354f53e9f ("libnftables: Implement JSON output support")
Signed-off-by: Thomas Haller <thaller@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/json.c b/src/json.c
index 23bd2472..81328ab3 100644
--- a/src/json.c
+++ b/src/json.c
@@ -496,7 +496,7 @@ static json_t *table_flags_json(const struct table *table)
 		json_decref(root);
 		return NULL;
 	case 1:
-		json_unpack(root, "[o]", &tmp);
+		json_unpack(root, "[O]", &tmp);
 		json_decref(root);
 		root = tmp;
 		break;