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 d050e07..3f91c01 100644 (file)
--- 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;