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

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Message-ID: <87zlc58xgd.fsf@fever.mssgmbh.com>
Date:	Thu, 18 Jun 2009 15:48:18 +0200
From:	Rainer Weikusat <rweikusat@...gmbh.com>
To:	linux-kernel@...r.kernel.org
Cc:	petkovbb@...il.com
Subject: [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. 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. 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], 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 */
--
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