[PATCH] hmp: fix memory leak in qom_composition_compare()

[Li Qiang <liq3ea@163.com>]

While 'make chekc', I got following error:

root@ubuntu:~/qemu# ./tests/qtest/device-introspect-test
/x86_64/device/introspect/list: OK
/x86_64/device/introspect/list-fields: OK
/x86_64/device/introspect/none:
=================================================================
==53741==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 212 byte(s) in 20 object(s) allocated from:
    #0 0x7f3b6319cb40 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdeb40)
    #1 0x7f3b62805ab8 in g_malloc (/usr/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x51ab8)

SUMMARY: AddressSanitizer: 212 byte(s) leaked in 20 allocation(s).
tests/qtest/libqtest.c:166: kill_qemu() tried to terminate QEMU process but encountered exit status 1 (expected 0)
Aborted (core dumped)

This is because the 'info qom-tree' path has a memory leak and qemu
exit 1. The leak is in 'qom_composition_compare'. This patch fixes this.

Fixes: e8c9e65816f("qom: Make "info qom-tree" show children sorted")
Signed-off-by: Li Qiang <liq3ea@163.com>
---
 qom/qom-hmp-cmds.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/qom/qom-hmp-cmds.c b/qom/qom-hmp-cmds.c
index 9ed8bb1c9f..3547d5ba4e 100644
--- a/qom/qom-hmp-cmds.c
+++ b/qom/qom-hmp-cmds.c
@@ -96,8 +96,10 @@ static void print_qom_composition(Monitor *mon, Object *obj, int indent);
 
 static int qom_composition_compare(const void *a, const void *b, void *ignore)
 {
-    return g_strcmp0(a ? object_get_canonical_path_component(a) : NULL,
-                     b ? object_get_canonical_path_component(b) : NULL);
+    g_autofree char *t1 = a ? object_get_canonical_path_component(a) : NULL;
+    g_autofree char *t2 = b ? object_get_canonical_path_component(b) : NULL;
+
+    return g_strcmp0(t1, t2);
 }
 
 static int insert_qom_composition_child(Object *obj, void *opaque)
-- 
2.17.1