linux-kernel - [189/289] libata: fix NULL sdev dereference race in atapi_qc

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Message-Id: <20101208005740.387428982@clark.site>
Date:	Tue, 07 Dec 2010 16:59:26 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Tejun Heo <tj@...nel.org>, Jeff Garzik <jgarzik@...hat.com>
Subject: [189/289] libata: fix NULL sdev dereference race in atapi_qc_complete()

2.6.36-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Tejun Heo <tj@...nel.org>

commit 2a5f07b5ec098edc69e05fdd2f35d3fbb1235723 upstream.

SCSI commands may be issued between __scsi_add_device() and dev->sdev
assignment, so it's unsafe for ata_qc_complete() to dereference
dev->sdev->locked without checking whether it's NULL or not.  Fix it.

Signed-off-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Jeff Garzik <jgarzik@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/ata/libata-scsi.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -2577,8 +2577,11 @@ static void atapi_qc_complete(struct ata
 		 *
 		 * If door lock fails, always clear sdev->locked to
 		 * avoid this infinite loop.
+		 *
+		 * This may happen before SCSI scan is complete.  Make
+		 * sure qc->dev->sdev isn't NULL before dereferencing.
 		 */
-		if (qc->cdb[0] == ALLOW_MEDIUM_REMOVAL)
+		if (qc->cdb[0] == ALLOW_MEDIUM_REMOVAL && qc->dev->sdev)
 			qc->dev->sdev->locked = 0;
 
 		qc->scsicmd->result = SAM_STAT_CHECK_CONDITION;


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