linux-kernel - Re: [PATCH] mm,memblock: reset memblock.reserved to system init state to prevent UAF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <7dc943023c620bed4bf49710dbe6facaade203fa.camel@surriel.com>
Date:   Thu, 20 Jul 2023 09:15:25 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH] mm,memblock: reset memblock.reserved to system init
 state to  prevent UAF

On Thu, 2023-07-20 at 08:00 +0300, Mike Rapoport wrote:
> Hi Ric,
> 
> On Wed, Jul 19, 2023 at 03:41:37PM -0400, Rik van Riel wrote:
> > The memblock_discard function frees the memblock.reserved.regions
> > array, which is good.
> > 
> > However, if a subsequent memblock_free (or memblock_phys_free)
> > comes
> > in later, from for example ima_free_kexec_buffer, that will result
> > in
> > a use after free bug in memblock_isolate_range.
> 
> The use of memblock_phys_free() in ima_free_kexec_buffer() is
> entirely
> bogus and must be fixed. It should be memblock_free_late() there.
> 
I'll send in a patch for that code, then. Thank you!

> > When running a kernel with CONFIG_KASAN enabled, this will cause a
> > kernel panic very early in boot. Without CONFIG_KASAN, there is
> > a chance that memblock_isolate_range might scribble on memory
> > that is now in use by somebody else.
>  
> This can't happen because memblock_double_array() uses kmalloc() as
> soon as
> slab_is_available(), so this sentence is misleading.

memblock_discard() freed the array, but did not change
the pointer. That resulted in memblock_isolate_range()
following a stale pointer.

There was no call to memblock_double_array() in the
final call that crashed. I checked that by booting
with memblock=debug.

kind regards,

Rik van Riel
-- 
All Rights Reversed.

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)