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

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Date:	Thu, 18 Jun 2009 17:04:00 +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

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. In order to do this, ide_complete_rq is called over
ide_cd_error_cmd() to partially complete the rq. The block layer
does partial completion only for requests with bio's and if the
rq doesn't have one (eg 'GPCMD_READ_DISC_INFO') the request is
completed as a whole and the drive->hwif->rq pointer set to NULL
afterwards. When calling ide_complete_rq again to report
the error, this null pointer is derefenced, resulting in a kernel
crash.

Signed-Off-By: Rainer Weikusat <rweikusat@...gmbh.com>

---

--- 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 */
--
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