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Message-ID: <46e2d4b9-94a4-76e3-be25-144f26f74fb6@linux.com>
Date: Mon, 17 Jul 2017 21:23:44 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
keescook@...omium.org
Subject: Re: [PATCH 1/1] mm/slub.c: add a naive detection of double free or
corruption
On 17.07.2017 20:54, Matthew Wilcox wrote:
> On Mon, Jul 17, 2017 at 07:45:07PM +0300, Alexander Popov wrote:
>> Add an assertion similar to "fasttop" check in GNU C Library allocator:
>> an object added to a singly linked freelist should not point to itself.
>> That helps to detect some double free errors (e.g. CVE-2017-2636) without
>> slub_debug and KASAN. Testing with hackbench doesn't show any noticeable
>> performance penalty.
>
>> {
>> + BUG_ON(object == fp); /* naive detection of double free or corruption */
>> *(void **)(object + s->offset) = fp;
>> }
>
> Is BUG() the best response to this situation? If it's a corruption, then
> yes, but if we spot a double-free, then surely we should WARN() and return
> without doing anything?
Hello Matthew,
Double-free leads to the memory corruption too, since the next two kmalloc()
calls return the same address to their callers. And we can spot it early here.
--
Alexander
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