Re: [kernel-hardening] Re: [PATCH 9/9] mm: SLUB hardened usercopy support
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- To: Christoph Lameter <cl@xxxxxxxxx>
- Subject: Re: [kernel-hardening] Re: [PATCH 9/9] mm: SLUB hardened usercopy support
- From: Kees Cook <keescook@xxxxxxxxxxxx>
- Date: Fri, 8 Jul 2016 12:07:54 -0400
- Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>, "kernel-hardening@xxxxxxxxxxxxxxxxxx" <kernel-hardening@xxxxxxxxxxxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Will Deacon <will.deacon@xxxxxxx>, Linux-MM <linux-mm@xxxxxxxxx>, sparclinux <sparclinux@xxxxxxxxxxxxxxx>, linux-ia64@xxxxxxxxxxxxxxx, Andrea Arcangeli <aarcange@xxxxxxxxxx>, linux-arch <linux-arch@xxxxxxxxxxxxxxx>, "x86@xxxxxxxxxx" <x86@xxxxxxxxxx>, Russell King <linux@xxxxxxxxxxxxxxx>, PaX Team <pageexec@xxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, lin <ux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, Mathias Krause <minipli@xxxxxxxxxxxxxx>, Fenghua Yu <fenghua.yu@xxxxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, David Rientjes <rientjes@xxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>, Dmitry Vyukov <dvyukov@xxxxxxxxxx>, Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>, Brad Spengler <spender@xxxxxxxxxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Pekka Enberg <penberg@xxxxxxxxxx>, Case y Schauf ler <casey@xxxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, "linuxppc-dev@xxxxxxxxxxxxxxxx" <linuxppc-dev@xxxxxxxxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>
- In-reply-to: <alpine.DEB.2.20.1607080844370.3379@east.gentwo.org>
- List-id: <linux-ia64.vger.kernel.org>
- References: <577f7e55.4668420a.84f17.5cb9SMTPIN_ADDED_MISSING@mx.google.com> <alpine.DEB.2.20.1607080844370.3379@east.gentwo.org>
On Fri, Jul 8, 2016 at 9:45 AM, Christoph Lameter <cl@xxxxxxxxx> wrote:
> On Fri, 8 Jul 2016, Michael Ellerman wrote:
>
>> > I wonder if this code should be using size_from_object() instead of s->size?
BTW, I can't reproduce this on x86 yet...
>>
>> Hmm, not sure. Who's SLUB maintainer? :)
>
> Me.
>
> s->size is the size of the whole object including debugging info etc.
> ksize() gives you the actual usable size of an object.
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).
I think a potential problem with Michael's fix is that the ptr in
__check_heap_object() may not point at the _start_ of the usable
object, so doing the red zone shift isn't quite right.
This finds the ptr's offset within the slub object (since s->size is
the slub object size):
offset = (ptr - page_address(page)) % s->size;
But this looks at object_size and doesn't take into account actual size:
if (offset <= s->object_size && n <= s->object_size - offset)
return NULL;
I think offset needs to be adjusted by the size of padding, which the
restore_red_left() call had the same effect, but may not cover all
padding conditions? I'm not sure.
Should it be:
/* Find offset within slab object. */
offset = (ptr - page_address(page)) % s->size;
/* Adjust offset for meta data and padding. */
offset -= s->size - s->object_size;
/* Make sure offset and size are within bounds of the
allocation size. */
if (offset <= s->object_size && n <= s->object_size - offset)
return NULL;
?
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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