linux-kernel - Re: [PATCH] ide-cd: prevent null pointer deref via cdrom_newpc

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Date:	Thu, 18 Jun 2009 16:52:57 +0200
From:	Rainer Weikusat <rweikusat@...gmbh.com>
To:	Borislav Petkov <petkovbb@...glemail.com>
Cc:	linux-kernel@...r.kernel.org,
	Linux IDE mailing list <linux-ide@...r.kernel.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Subject: Re: [PATCH] ide-cd: prevent null pointer deref via cdrom_newpc_intr

Borislav Petkov <petkovbb@...glemail.com> writes:
> On Thu, Jun 18, 2009 at 3:48 PM, Rainer Weikusat<rweikusat@...gmbh.com> wrote:
>> From: Rainer Weikusat <rweikusat@...gmbh.com>
>>
>> With 2.6.30, the error handling code in cdrom_newpc_intr was changed
>> to deal with partial request failures by normally completing the 'good'
>> parts of a request and only 'error' the last (and presumably,
>> incompletely transferred) bio associated with a particular
>> request. This doesn't work for requests which don't have bios
>> associated with them ('GPCMD_READ_DISC_INFO'), because the first call
>> to ide_end_rq, done via ide_complete_rq in order to do the
>> partial completion part, returns with a code of zero for all non-bio
>> requests, causing the drive->hwif->rq pointer to be set to NULL.
>
> This is a bit misleading, it should be more like: "ide_complete_rq is
> called over ide_cd_error_cmd() to partially complete the rq but the rq
> is without a bio and the block layer does partial completion only for
> requests with bio's so this request is completed as a whole and the rq
> freed."

Technically, this is not quite correct (assuming I haven't overlooked
something), because ide_cd_queue_pc still has a reference to the rq.

> please fix.

I will send a modified 'patch e-mail' soon.

Something I would like to add: The DVD-ROM mentioned below has exactly
the same 32/30 issue w/ READ DISC INFO. This used to just be an
unnoticed failure in older kernels.

[...]

>> This is fixed in the linux-ide tree since at about 2009/06/10 [Bug
>> 13399, also happens w/ TSSTcorpDVD-ROM SH-D162C],
>
> really, because I can't find it in Bart's trees. Do you have a commit
> id?

No, I just assumed that, since I found the bio-check among beginnings
of code intended to deal with the 32/30 issue.
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