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Message-ID: <87ziprny3i.fsf@@concordia.ellerman.id.au>
Date: Sat, 09 Jul 2016 16:07:29 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Kees Cook <keescook@...omium.org>, Christoph Lameter <cl@...ux.com>
Cc: "kernel-hardening\@lists.openwall.com" <kernel-hardening@...ts.openwall.com>, Jan Kara <jack@...e.cz>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Linux-MM <linux-mm@...ck.org>, sparclinux <sparclinux@...r.kernel.org>, linux-ia64@...r.kernel.org, Andrea Arcangeli <aarcange@...hat.com>, linux-arch <linux-arch@...r.kernel.org>, "x86\@kernel.org" <x86@...nel.org>, Russell King <linux@...linux.org.uk>, PaX Team <pageexec@...email.hu>, Borislav Petkov <bp@...e.de>, Mathias Krause <minipli@...glemail.com>, Fenghua Yu <fenghua.yu@...el.com>, Rik van Riel <riel@...hat.com>, David Rientjes <rientjes@...gle.com>, Tony Luck <tony.luck@...el.com>, Andy Lutomirski <luto@...nel.org>, Joonsoo Kim <iamjoonsoo.kim@....com>, Dmitry Vyukov <dvyukov@...gle.com>, Laura Abbott <labbott@...oraproject.org>, Brad Spengler <spender@...ecurity.net>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, LKML <linux-kernel@...r.kernel.org>, Pekka Enberg <penberg@...nel.org>, Case y Sc
hauf ler <casey@...aufler-ca.com>, Andrew Morton <akpm@...ux-foundation.org>, "linuxppc-dev\@lists.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, "David S. Miller" <davem@...emloft.net>, "linux-arm-kernel\@lists.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Re: [PATCH 9/9] mm: SLUB hardened usercopy support
Michael Ellerman <mpe@...erman.id.au> writes:
> Kees Cook <keescook@...omium.org> writes:
>
>> On Fri, Jul 8, 2016 at 1:41 PM, Kees Cook <keescook@...omium.org> wrote:
>>> 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;
>
> That fixes the case for me in kstrndup(), which allows the system to boot.
Ugh, no it doesn't, booted the wrong kernel.
I don't see the oops in strndup_user(), but instead get:
usercopy: kernel memory overwrite attempt detected to d000000003610028 (cfq_io_cq) (88 bytes)
CPU: 11 PID: 1 Comm: systemd Not tainted 4.7.0-rc3-00098-g09d9556ae5d1-dirty #65
Call Trace:
[c0000001fb087bf0] [c0000000009bdbe8] dump_stack+0xb0/0xf0 (unreliable)
[c0000001fb087c30] [c00000000029cf44] __check_object_size+0x74/0x320
[c0000001fb087cb0] [c00000000005d4d0] copy_from_user+0x60/0xd4
[c0000001fb087cf0] [c0000000008b38f4] __get_filter+0x74/0x160
[c0000001fb087d30] [c0000000008b408c] sk_attach_filter+0x2c/0xc0
[c0000001fb087d60] [c000000000871c34] sock_setsockopt+0x954/0xc00
[c0000001fb087dd0] [c00000000086ac44] SyS_setsockopt+0x134/0x150
[c0000001fb087e30] [c000000000009260] system_call+0x38/0x108
Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
cheers
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