linux-kernel - Re: Q, slab, kmemleak

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: <4B160A16.90703@cs.helsinki.fi>
Date:	Wed, 02 Dec 2009 08:32:54 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	hooanon05@...oo.co.jp, linux-kernel@...r.kernel.org
Subject: Re: Q, slab, kmemleak_erase() and redzone?

Pekka Enberg kirjoitti:
> Catalin Marinas kirjoitti:
>> On Tue, 2009-12-01 at 11:49 +0000, Pekka Enberg wrote:
>>> hooanon05@...oo.co.jp kirjoitti:
>>>> Pekka Enberg:
>>>>> We are setting an element in the per CPU array to NULL so the the
>>>>> kmemleak code in ____cache_alloc() is safe. Red-zoning is done at the
>>>>> _object_ which is not touched by kmemleak. Looking at the oops, it
>>>>> does seem likely that you have a bug in your module (or in some other
>>>>> part of the kernel).
>>>> Thanks for reply.
>>>> In ____cache_alloc(), the variable 'ac' is assigned before
>>>> cache_alloc_refill() call, and it is used for the parameter of
>>>> kmemleak_erase(). The value may be changed by cache_alloc_refill(),
>>>> isn't it?
>>> No. The pointer returned by cpu_cache_get() is not changed by
>>> cache_alloc_refill(). The contents of the array might change, yes. That
>>> said, we should check if objp is NULL before calling kmemleak_erase().
>>
>> Possibly but I don't understand why that's needed. The kmemleak_erase()
>> call just sets the ac->entry[ac->avail] to NULL. If ac->avail is 0, it
>> doesn't cause any harm.
> 
> No, you are absolutely correct. Can you please send an updated patch to 
> Catalin that adds a comment on top of the cpu_cache_get() call that 
> explains why we need it there?

Doh, this was supposed to be a reply to Okajima's email :-).

			Pekka
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/