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

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Date:	Thu, 18 Jun 2009 16:39:40 +0200
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Rainer Weikusat <rweikusat@...gmbh.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

Hi,

we we're just debugging this and I was about to send the patches
tomorrow but you beat me to it :).

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."

please fix.

> Upon
> calling ide_complete_rq a second time, it is attempted to de-reference
> this null pointer, resulting in a kernel crash.
>
> Signed-Off-By: Rainer Weikusat <rweikusat@...gmbh.com>
>
> ---
>
> 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?

> but a patch
> against 2.6.30 AFAIK doesn't exist (and I didn't find the
> corresponding thread before digging through all of this ...).
> --- drivers/ide/ide-cd.c.orig   2009-06-18 15:10:24.000000000 +0200
> +++ drivers/ide/ide-cd.c        2009-06-18 14:10:16.000000000 +0200
> @@ -758,7 +758,7 @@ out_end:
>                                rq->errors = -EIO;
>                }
>
> -               if (uptodate == 0)
> +               if (uptodate == 0 && rq->bio)
>                        ide_cd_error_cmd(drive, cmd);
>
>                /* make sure it's fully ended */
>

-- 
Regards/Gruss,
Boris
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