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. Thanks! -Kees -- Kees Cook Chrome OS & Brillo Security -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
