[PATCH v2] selftests/powerpc: Fix strncpy usage

[Breno Leitao]

On 06/26/2018 02:24 AM, Michael Ellerman wrote:
> Breno Leitao <leitao at debian.org> writes:
> 
>> There is a buffer overflow in dscr_inherit_test.c test. In main(), strncpy()'s
>> third argument is the length of the source, not the size of the destination
>> buffer, which makes strncpy() behaves like strcpy(), causing a buffer overflow
>> if argv[0] is bigger than LEN_MAX (100).
>>
>> This patch allocates 'prog' according to the argv[0] length, avoiding LEN_MAX
>> restriction.
>>
>> CC: Segher Boessenkool <segher at kernel.crashing.org>
>> CC: Anshuman Khandual <khandual at linux.vnet.ibm.com>
>> Signed-off-by: Breno Leitao <leitao at debian.org>
>> ---
>>  tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c | 11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c b/tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c
>> index 08a8b95e3bc1..ecac4900c7dd 100644
>> --- a/tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c
>> +++ b/tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c
>> @@ -19,7 +19,7 @@
>>   */
>>  #include "dscr.h"
>>  
>> -static char prog[LEN_MAX];
>> +static char *prog;
>>  
>>  static void do_exec(unsigned long parent_dscr)
>>  {
>> @@ -104,6 +104,13 @@ int main(int argc, char *argv[])
>>  		exit(1);
>>  	}
>>  
>> -	strncpy(prog, argv[0], strlen(argv[0]));
>> +	prog = malloc(strlen(argv[0]) + 1);
>> +	if (prog == NULL) {
>> +		fprintf(stderr, "Unable to allocate enough memory\n");
>> +		exit(1);
>> +	}
>> +
>> +	strcpy(prog, argv[0]);
> 
> Why do we need to copy it at all?

We do not. Pointing proj to argv[0], as you proposed, should be the best
solution for this problem.

Thanks!