On Fri, Jul 08, 2016 at 04:48:38PM -0400, Kees Cook wrote: > On Fri, Jul 8, 2016 at 1:41 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > On Fri, Jul 8, 2016 at 12:20 PM, Christoph Lameter <cl@xxxxxxxxx> wrote: > >> On Fri, 8 Jul 2016, Kees Cook wrote: > >> > >>> Is check_valid_pointer() making sure the pointer is within the usable > >>> size? It seemed like it was checking that it was within the slub > >>> object (checks against s->size, wants it above base after moving > >>> pointer to include redzone, etc). > >> > >> check_valid_pointer verifies that a pointer is pointing to the start of an > >> object. It is used to verify the internal points that SLUB used and > >> should not be modified to do anything different. > > > > Yup, no worries -- I won't touch it. :) I just wanted to verify my > > understanding. > > > > And after playing a bit more, I see that the only thing to the left is > > padding and redzone. SLUB layout, from what I saw: > > > > offset: what's there > > ------- > > start: padding, redzone > > red_left_pad: object itself > > inuse: rest of metadata > > size: start of next slub object > > > > (and object_size == inuse - red_left_pad) > > > > i.e. a pointer must be between red_left_pad and inuse, which is the > > same as pointer - ref_left_pad being less than object_size. > > > > So, as found already, the position in the usercopy check needs to be > > bumped down by red_left_pad, which is what Michael's fix does, so I'll > > include it in the next version. > > Actually, after some offline chats, I think this is better, since it > makes sure the ptr doesn't end up somewhere weird before we start the > calculations. This leaves the pointer as-is, but explicitly handles > the redzone on the offset instead, with no wrapping, etc: > > /* Find offset within object. */ > offset = (ptr - page_address(page)) % s->size; > > + /* Adjust for redzone and reject if within the redzone. */ > + if (s->flags & SLAB_RED_ZONE) { > + if (offset < s->red_left_pad) > + return s->name; > + offset -= s->red_left_pad; > + } > + > /* Allow address range falling entirely within object size. */ > if (offset <= s->object_size && n <= s->object_size - offset) > return NULL; > As Christoph saids, please use slab_ksize() rather than s->object_size. Otherwise, looks good to me. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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