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

[Thomas Huth]

On 04/01/2021 15.10, Gan Qixin wrote:
> 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.robot@huawei.com>
> Signed-off-by: Gan Qixin <ganqixin@huawei.com>
> ---
> Cc: Thomas Huth <thuth@redhat.com>
> Cc: Laurent Vivier <lvivier@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)) {

Using strcmp() is likely wrong here, since we're talking about strings like 
"xenfv-4.2" here ... so I guess strncmp(..., 5) would be the right way to go?

 Thomas