Re: [PATCH v2] qtest/libqtest: fix heap-buffer-overflow in qtest_cb_for_every_machine()

[Laurent Vivier <lvivier@redhat.com>]

On 06/01/2021 06:06, Gan Qixin wrote:
> When the length of mname is less than 5, memcpy("xenfv", mname, 5) will cause
> heap buffer overflow. Therefore, use strncmp 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>
> 
> v2:
> Changes suggested by Thomas Huth:
>     Replace memcmp(..., 5) with strncmp(..., 5).
> ---
>  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..e93424ffdd 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 (!strncmp("xenfv", mname, 5) || g_str_equal("xenpv", mname)) {
>              continue;
>          }
>          if (!skip_old_versioned || !qtest_is_old_versioned_machine(mname)) {
> 

Reviewed-by: Laurent Vivier <lvivier@redhat.com>

Problem seem to have been introduced originally by
9a709f06c870 ("piix: fix xenfv regression, add compat machine xenfv-4.2")

Moved here by:
51b3ca975929 ("tests/qtest: Unify the test for the xenfv and xenpv machines"

Thanks,
Laurent