Re: [PATCH rt-tests v0 1/4] pmqtest: Increase buffer to avoid overflow

[Daniel Wagner <wagi@monom.org>]

On 8/16/19 5:41 PM, Sebastian Andrzej Siewior wrote:
> On 2019-08-16 08:42:01 [+0200], Daniel Wagner wrote:
>> Increase the size of the char buffer. gcc 9.1.1 reports:
>>
>> src/pmqtest/pmqtest.c: In function ‘main’:
>> src/pmqtest/pmqtest.c:46:21: warning: ‘%d’ directive writing between 1 and 10 bytes into a region of size 8 [-Wformat-overflow=]
>>     46 | #define SYNCMQ_NAME "/syncmsg%d"
>>        |                     ^~~~~~~~~~~~
>>
>> src/pmqtest/pmqtest.c:445:3: note: ‘sprintf’ output between 10 and 19 bytes into a destination of size 16
>>    445 |   sprintf(mqname, SYNCMQ_NAME, i);
>>        |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Signed-off-by: Daniel Wagner <wagi@monom.org>
>> ---
>>   src/pmqtest/pmqtest.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/pmqtest/pmqtest.c b/src/pmqtest/pmqtest.c
>> index a04fc49872bf..20164c8d547f 100644
>> --- a/src/pmqtest/pmqtest.c
>> +++ b/src/pmqtest/pmqtest.c
>> @@ -440,7 +440,7 @@ int main(int argc, char *argv[])
>>   		goto nomem;
>>   
>>   	for (i = 0; i < num_threads; i++) {
>> -		char mqname[16];
>> +		char mqname[32];
> 
> The compiler says, based on SYNCMQ_NAME's size and maximum possible %d
> we will have 19 bytes max. Why do you change it to 32? Why it is not
> wrong, one might ask what the extra storage is for.

I was taking the 16 bytes value as reference and doubled it. Indeed, 19 
bytes would be a better choice. Let me refresh the series.