[apparmor] [PATCH 10/11] Fix caching when used with a newer kernel with the feature directory

[John Johansen]

On 03/08/2012 02:11 PM, Kees Cook wrote:
> 
> On Thu, Mar 08, 2012 at 01:57:44PM -0800, John Johansen wrote:
>> On 03/08/2012 01:46 PM, Kees Cook wrote:
>>> On Thu, Mar 08, 2012 at 01:40:54PM -0800, John Johansen wrote:
>>>> On 03/08/2012 11:17 AM, Steve Beattie wrote:
>>>>> On Thu, Mar 08, 2012 at 11:15:12AM -0800, Steve Beattie wrote:
>>>>>> On Wed, Mar 07, 2012 at 06:17:29AM -0800, John Johansen wrote:
>>>>>>> On newer kernels the features directory causes the creation of a
>>>>>>> cache/.feature file that contains newline characters.  This causes the
>>>>>>> feature comparison to fail, because get_flags_string() uses fgets
>>>>>>> which stop reading in the feature file after the first newline.
>>>>>>>
>>>>>>> This caches the features comparision to compare a single line of the
>>>>>>> file against the full kernel feature directory resulting in caching
>>>>>>> failure.
>>>>>>>
>>>>>>> Worse this also means the cache won't get updated as the parser doesn't
>>>>>>> change what set gets caches after the .feature file gets created.
>>>>>>>
>>>>>>> Signed-off-by: John Johansen <john.johansen at canonical.com>
>>>>>>
>>>>>> Acked-By: Steve Beattie <sbeattie at ubuntu.com>
>>>>>
>>>>> Actually, fread() doesn't null terminate what it reads like fgets()
>>>>> does. I think you'll need to address that.
>>>>>
>>>> How about with this additional patch on top
>>>>
>>>> diff --git a/parser/parser_main.c b/parser/parser_main.c
>>>> index 67ab231..3f4789b 100644
>>>> --- a/parser/parser_main.c
>>>> +++ b/parser/parser_main.c
>>>> @@ -844,6 +844,7 @@ out:
>>>>  static void get_flags_string(char **flags, char *flags_file) {
>>>>  	char *pos;
>>>>  	FILE *f = NULL;
>>>> +	size_t size;
>>>>  
>>>>  	/* abort if missing or already set */
>>>>  	if (!flags || *flags)
>>>> @@ -857,8 +858,10 @@ static void get_flags_string(char **flags, char *flags_file) {
>>>>  	if (!*flags)
>>>>  		goto fail;
>>>>  
>>>> -	if (!fread(*flags, 1, FLAGS_STRING_SIZE, f))
>>>> +	size = fread(*flags, 1, FLAGS_STRING_SIZE - 1, f);
>>>> +	if (ferror(f))
>>>
>>> How about:
>>>
>>>   if (size < 1 || ferror(f))
>>> ...
>>>
>>>
>>>>  		goto fail;
>>>> +	*flags[size] = 0;
>>>
>>> Then this can't freak out.
>>>
>> hrmmm well it shouldn't freak out if size == 0 and that is the only value less than 1 it
>> could be, but from read fread again, yeah we should be checking for 0
> 
> Ah, yeah, good point. size < 0 should be fine.
> 
err its an unsigned type how about size > FLAGS_STRING_SIZE