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

[Kees Cook]

On Thu, Mar 08, 2012 at 02:21:19PM -0800, John Johansen wrote:
> 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

Oh, right _f_read. Ignore me entirely. If fread returns greater than
nmemb arg, there are much more serious problems. Original patch is
fine. I need lunch. :P

-Kees

-- 
Kees Cook