Re: [PATCH] libselinux: silence -Wstringop-overflow warning from gcc 10.3.1

[Petr Lautrbach <plautrba@redhat.com>]

Petr Lautrbach <plautrba@redhat.com> writes:

> Nicolas Iooss <nicolas.iooss@m4x.org> writes:
>
>> When building libselinux on Fedora 33 with gcc 10.3.1, the compiler
>> reports:
>>
>>     label_file.c: In function ‘lookup_all.isra’:
>>     label_file.c:940:4: error: ‘strncpy’ specified bound depends on the
>>     length of the source argument [-Werror=stringop-overflow=]
>>       940 |    strncpy(clean_key, key, len - 1);
>>           |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>     label_file.c:927:8: note: length computed here
>>       927 |  len = strlen(key);
>>           |        ^~~~~~~~~~~
>>     cc1: all warnings being treated as errors
>>
>> As clean_key is the result of malloc(len), there is no issue here. But
>> using strncpy can be considered as strange, because the size of the
>> string is already known and the NUL terminator is always added later, in
>> function ‘lookup_all.isra.
>>
>> Replace strncpy with memcpy to silence this gcc false-positive warning.
>>
>> Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
>
> I wasn't able to reproduce it with gcc-11.0.1-0.7.fc35.x86_64, but it's
> indeed reproducible with gcc-10.3.1-1.fc33.x86_64 and this patch fixes
> it.
>
> Acked-by: Petr Lautrbach <plautrba@redhat.com>
>

Merged

>> ---
>>  libselinux/src/label_file.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/libselinux/src/label_file.c b/libselinux/src/label_file.c
>> index 726394ca4332..cfce23e0119e 100644
>> --- a/libselinux/src/label_file.c
>> +++ b/libselinux/src/label_file.c
>> @@ -909,7 +909,7 @@ static const struct spec **lookup_all(struct selabel_handle *rec,
>>  			if (!clean_key)
>>  				goto finish;
>>  
>> -			strncpy(clean_key, key, len - 1);
>> +			memcpy(clean_key, key, len - 1);
>>  		}
>>  
>>  		clean_key[len - 1] = '\0';
>> -- 
>> 2.31.0