From: Tejun Heo <tj@kernel.org>
Date: Mon, 1 Nov 2010 10:39:19 +0000 (+0100)
Subject: libata: fix NULL sdev dereference race in atapi_qc_complete()
X-Git-Tag: firefly_0821_release~7613^2~3443^2~2
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=2a5f07b5ec098edc69e05fdd2f35d3fbb1235723;p=firefly-linux-kernel-4.4.55.git

libata: fix NULL sdev dereference race in atapi_qc_complete()

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@kernel.org>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
---

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index d050e073e570..3f91c01c217f 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -2552,8 +2552,11 @@ static void atapi_qc_complete(struct ata_queued_cmd *qc)
 		 *
 		 * 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;