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

Kees Cook kees at ubuntu.com
Thu Mar 8 22:11:57 UTC 2012


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.

-- 
Kees Cook



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