Messages in this thread | | | From | Kees Cook <> | Date | Fri, 8 Jul 2016 13:41:20 -0400 | Subject | Re: [kernel-hardening] Re: [PATCH 9/9] mm: SLUB hardened usercopy support |
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On Fri, Jul 8, 2016 at 12:20 PM, Christoph Lameter <cl@linux.com> 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
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