From: Kees Cook <keescook@chromium.org>
To: Christoph Lameter <cl@linux.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>, Jan Kara <jack@suse.cz>,
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sparclinux <sparclinux@vger.kernel.org>,
linux-ia64@vger.kernel.org,
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lin <ux-arm-kernel@lists.infradead.org>,
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Brad Spengler <spender@grsecurity.net>,
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LKML <linux-kernel@vger.kernel.org>,
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"David S. Miller" <davem@davemloft.net>
Subject: Re: [kernel-hardening] Re: [PATCH 9/9] mm: SLUB hardened usercopy support
Date: Fri, 8 Jul 2016 12:07:54 -0400 [thread overview]
Message-ID: <CAGXu5jKE=h32tHVLsDeaPN1GfC+BB3YbFvC+5TE5TK1oR-xU3A@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1607080844370.3379@east.gentwo.org>
On Fri, Jul 8, 2016 at 9:45 AM, Christoph Lameter <cl@linux.com> 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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next prev parent reply other threads:[~2016-07-08 16:07 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <577f7e55.4668420a.84f17.5cb9SMTPIN_ADDED_MISSING@mx.google.com>
2016-07-08 13:45 ` [kernel-hardening] Re: [PATCH 9/9] mm: SLUB hardened usercopy support Christoph Lameter
2016-07-08 16:07 ` Kees Cook [this message]
2016-07-08 16:20 ` Christoph Lameter
2016-07-08 17:41 ` Kees Cook
2016-07-08 20:48 ` Kees Cook
2016-07-09 5:58 ` Michael Ellerman
2016-07-09 5:58 ` [kernel-hardening] " Michael Ellerman
2016-07-09 5:58 ` Michael Ellerman
2016-07-09 5:58 ` Michael Ellerman
2016-07-09 5:58 ` Michael Ellerman
[not found] ` <8737njpd37.fsf@@concordia.ellerman.id.au>
2016-07-09 6:07 ` Michael Ellerman
2016-07-09 6:07 ` Michael Ellerman
2016-07-09 6:07 ` Michael Ellerman
2016-07-09 6:07 ` Michael Ellerman
2016-07-09 6:07 ` Michael Ellerman
[not found] ` <57809299.84b3370a.5390c.ffff9e58SMTPIN_ADDED_BROKEN@mx.google.com>
2016-07-09 6:17 ` [kernel-hardening] " Valdis.Kletnieks
2016-07-09 17:07 ` Kees Cook
2016-07-11 6:08 ` Joonsoo Kim
2016-07-06 22:25 [PATCH 0/9] mm: Hardened usercopy Kees Cook
2016-07-06 22:25 ` [PATCH 9/9] mm: SLUB hardened usercopy support Kees Cook
[not found] ` <577ddc18.d351190a.1fa54.ffffbe79SMTPIN_ADDED_BROKEN@mx.google.com>
2016-07-07 18:56 ` [kernel-hardening] " Kees Cook
2016-07-08 10:19 ` Michael Ellerman
2016-07-08 10:19 ` Michael Ellerman
2016-07-08 10:19 ` Michael Ellerman
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