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

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Message-ID: <4EDA8FA9.8020004@linux.vnet.ibm.com>
Date:	Sat, 03 Dec 2011 22:07:53 +0100
From:	Steffen Maier <maier@...ux.vnet.ibm.com>
To:	Stratos Psomadakis <psomas@...too.org>
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 12/02/2011 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

HTH
Steffen

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