linux-kernel - Re: [SCSI] NULL pointer dereference in sym53c8xx (bisected)

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Date:	Sun, 04 Dec 2011 02:11:33 +0200
From:	Stratos Psomadakis <psomas@...too.org>
To:	Steffen Maier <maier@...ux.vnet.ibm.com>
CC:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	gregkh@...e.de, linux-scsi@...r.kernel.org,
	JBottomley@...allels.com, matthew@....cx, Martin.vGagern@....net,
	kernel@...too.org
Subject: Re: [SCSI] NULL pointer dereference in sym53c8xx (bisected)

On 12/03/2011 11:07 PM, Steffen Maier wrote:
> On 12/02/2011 04:26 PM, Stratos Psomadakis wrote:
>> After upstream commit 4e6c82b3614a18740ef63109d58743a359266daf ([SCSI]
>> fix WARNING: at drivers/scsi/scsi_lib.c:1704), which is also included in
>> 3.0-stable and 3.1-stable kernels, the kernel fails to boot (NULL
>> pointer dereference in sym53c8xx_slave_destroy).
>>
>> Bug report at the Gentoo Bugzilla (reported and bisected by Martin von
>> Gagern). [1]  (stack trace [2])
>>
>> I think that the problem is that (after commit 4e6c82b)
>> __scsi_remove_device() is called if slave_alloc() in scsi_alloc_sdev()
>> fails. But __scsi_remove_device() calls slave_destroy(), which (I think)
>> doesn't make much sense (ie to call slave_destroy() when slave_alloc()
>> fails).
>>
>> For sym53c8xx, this results in a NULL pointer dereference (struct
>> sym_lcb pointer) in slave_destroy().
>>
>> [1] https://bugs.gentoo.org/show_bug.cgi?id=392567
>> [2] https://392567.bugs.gentoo.org/attachment.cgi?id=294381
>
> To me this looks like the same thing we encountered in the zfcp LLD:
> http://www.spinics.net/lists/linux-scsi/msg55575.html
> James explained the pairing of slave_alloc and slave_destroy even if
> slave_alloc returned early in which case slave_destroy needs to cope
> with that:
> http://www.spinics.net/lists/linux-scsi/msg55449.html
>
Indeed.

I'll follow-up with a patch similar to the one you sent for zfcp. I
think that returning if sym_lcb is NULL should be ok.

> HTH
> Steffen
>
> Linux on System z Development
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-- 
Stratos Psomadakis
<psomas@...too.org>



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