[for-2.7] qtest.c: Allow zero size in memset qtest commands

Some tests use the qtest protocol "memset" command with a zero
size, expecting it to do nothing. However in the current code this
will result in calling memset() with a NULL pointer, which is
undefined behaviour. Detect and specially handle zero sizes to
avoid this.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Looking at the code for the other commands that take a size
('read', 'write', 'b64read' and 'b64write' they all assume a
non-zero size. I've left those alone though, somebody else can
make them do nothing on zero size if they feel it's important.)

 qtest.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

Ping?

(Now that 2.7 is out it would be nice to get rid of the clang
warnings cluttering up my build logs :-))

thanks
-- PMM

On 5 August 2016 at 11:43, Peter Maydell <peter.maydell@linaro.org> wrote:
> Some tests use the qtest protocol "memset" command with a zero
> size, expecting it to do nothing. However in the current code this
> will result in calling memset() with a NULL pointer, which is
> undefined behaviour. Detect and specially handle zero sizes to
> avoid this.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> Looking at the code for the other commands that take a size
> ('read', 'write', 'b64read' and 'b64write' they all assume a
> non-zero size. I've left those alone though, somebody else can
> make them do nothing on zero size if they feel it's important.)
>
>  qtest.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/qtest.c b/qtest.c
> index da4826c..ce4c6db 100644
> --- a/qtest.c
> +++ b/qtest.c
> @@ -133,6 +133,7 @@ static bool qtest_opened;
>   *  < OK
>   *
>   * ADDR, SIZE, VALUE are all integers parsed with strtoul() with a base of 0.
> + * For 'memset' a zero size is permitted and does nothing.
>   *
>   * DATA is an arbitrarily long hex number prefixed with '0x'.  If it's smaller
>   * than the expected size, the value will be zero filled at the end of the data
> @@ -493,10 +494,12 @@ static void qtest_process_command(CharDriverState *chr, gchar **words)
>          len = strtoull(words[2], NULL, 0);
>          pattern = strtoull(words[3], NULL, 0);
>
> -        data = g_malloc(len);
> -        memset(data, pattern, len);
> -        cpu_physical_memory_write(addr, data, len);
> -        g_free(data);
> +        if (len) {
> +            data = g_malloc(len);
> +            memset(data, pattern, len);
> +            cpu_physical_memory_write(addr, data, len);
> +            g_free(data);
> +        }
>
>          qtest_send_prefix(chr);
>          qtest_send(chr, "OK\n");
> --
> 2.7.4

On 08/05/2016 05:43 AM, Peter Maydell wrote:
> Some tests use the qtest protocol "memset" command with a zero
> size, expecting it to do nothing. However in the current code this
> will result in calling memset() with a NULL pointer, which is
> undefined behaviour. Detect and specially handle zero sizes to
> avoid this.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> Looking at the code for the other commands that take a size
> ('read', 'write', 'b64read' and 'b64write' they all assume a
> non-zero size. I've left those alone though, somebody else can
> make them do nothing on zero size if they feel it's important.)

I obviously missed reviewing this in time for 2.7, but looks reasonable
to me.

Reviewed-by: Eric Blake <eblake@redhat.com>

On 8 September 2016 at 15:37, Eric Blake <eblake@redhat.com> wrote:
> On 08/05/2016 05:43 AM, Peter Maydell wrote:
>> Some tests use the qtest protocol "memset" command with a zero
>> size, expecting it to do nothing. However in the current code this
>> will result in calling memset() with a NULL pointer, which is
>> undefined behaviour. Detect and specially handle zero sizes to
>> avoid this.
>>
>> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>> ---
>> Looking at the code for the other commands that take a size
>> ('read', 'write', 'b64read' and 'b64write' they all assume a
>> non-zero size. I've left those alone though, somebody else can
>> make them do nothing on zero size if they feel it's important.)
>
> I obviously missed reviewing this in time for 2.7, but looks reasonable
> to me.
>
> Reviewed-by: Eric Blake <eblake@redhat.com>

Applied to master, thanks.

-- PMM