Re: [PATCH] libblkid: Avoid strlen if only first char is checked

[Bruce Dubbs <bruce.dubbs@gmail.com>]

Karel Zak wrote:
> On Mon, Oct 03, 2016 at 10:05:03PM +0200, Tobias Stoeckmann wrote:
>> A strlen() call can lead to out of boundary read access if the
>> superblock in question has no nul-bytes after the string. This
>> could be avoided by using strnlen() but the calls in question
>> merely existed to check if the string length is not 0.
>>
>> By changing the calls as proposed with this diff, these files are
>> in sync with other superblock files, which do exactly the same.
>> ---
>>   libblkid/src/superblocks/befs.c  | 2 +-
>>   libblkid/src/superblocks/ext.c   | 2 +-
>>   libblkid/src/superblocks/jfs.c   | 2 +-
>>   libblkid/src/superblocks/nilfs.c | 2 +-
>>   libblkid/src/superblocks/romfs.c | 2 +-
>>   libblkid/src/superblocks/xfs.c   | 2 +-
>>   6 files changed, 6 insertions(+), 6 deletions(-)
>
>   Applied, thanks.
>
>> diff --git a/libblkid/src/superblocks/befs.c b/libblkid/src/superblocks/befs.c
>> index 7e9eaf6..36e079f 100644
>> --- a/libblkid/src/superblocks/befs.c
>> +++ b/libblkid/src/superblocks/befs.c
>> @@ -451,7 +451,7 @@ static int probe_befs(blkid_probe pr, const struct blkid_idmag *mag)
>>   	/*
>>   	 * all checks pass, set LABEL, VERSION and UUID
>>   	 */
>> -	if (strlen(bs->name))
>> +	if (*bs->name != '\0')
>
> Good catch, I hate it too. BTW, you can use
>
>      if (*bs->name)
>
> it's enough.

It is enough for the compiler, but the explicit comparison is more clear 
to a casual reader.  The compiler probably optimizes out the comparison 
anyway.

   -- Bruce