[189/289] libata: fix NULL sdev dereference race in atapi_qc_complete()

Greg KH
2010-12-08T01:24:31Z

From: Tejun Heo <tj@kernel.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@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.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;