[PATCH] qtest/libqtest.c: fix heap-buffer-overflow in qtest_cb_for_every_machine()

[Gan Qixin]

When the length of mname is less than 5, memcpy ("xenfv", mname, 5) will cause
heap buffer overflow. Therefore, use strcmp to avoid this problem.

The asan showed stack:

ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60200000f2f4 at
pc 0x7f65d8cc2225 bp 0x7ffe93cc5a60 sp 0x7ffe93cc5208 READ of size 5 at
0x60200000f2f4 thread T0
    #0 0x7f65d8cc2224 in memcmp (/lib64/libasan.so.5+0xdf224)
    #1 0x5632c20be95b in qtest_cb_for_every_machine tests/qtest/libqtest.c:1282
    #2 0x5632c20b7995 in main tests/qtest/test-hmp.c:160
    #3 0x7f65d88fed42 in __libc_start_main (/lib64/libc.so.6+0x26d42)
    #4 0x5632c20b72cd in _start (build/tests/qtest/test-hmp+0x542cd)

Reported-by: Euler Robot <euler.ro...@huawei.com>
Signed-off-by: Gan Qixin <ganqi...@huawei.com>
---
Cc: Thomas Huth <th...@redhat.com>
Cc: Laurent Vivier <lviv...@redhat.com>
---
 tests/qtest/libqtest.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/qtest/libqtest.c b/tests/qtest/libqtest.c
index e49f3a1e45..e8179a3509 100644
--- a/tests/qtest/libqtest.c
+++ b/tests/qtest/libqtest.c
@@ -1281,7 +1281,7 @@ void qtest_cb_for_every_machine(void (*cb)(const char 
*machine),
         g_assert(qstr);
         mname = qstring_get_str(qstr);
         /* Ignore machines that cannot be used for qtests */
-        if (!memcmp("xenfv", mname, 5) || g_str_equal("xenpv", mname)) {
+        if (!strcmp("xenfv", mname) || g_str_equal("xenpv", mname)) {
             continue;
         }
         if (!skip_old_versioned || !qtest_is_old_versioned_machine(mname)) {
-- 
2.23.0