scsi: sd: improve TUR handling in sd_check_events

Remove bogus evaluations of retval and sshdr when the device is offline,
and fix a possible NULL pointer dereference by allocating the 8 byte
sized sense header on stack.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sd.c

@@ -1425,7 +1425,6 @@ static unsigned int sd_check_events(struct gendisk *disk, unsigned int clearing)
 {
 	struct scsi_disk *sdkp = scsi_disk_get(disk);
 	struct scsi_device *sdp;
-	struct scsi_sense_hdr *sshdr = NULL;
 	int retval;
 
 	if (!sdkp)
@@ -1454,22 +1453,21 @@ static unsigned int sd_check_events(struct gendisk *disk, unsigned int clearing)
 	 * by sd_spinup_disk() from sd_revalidate_disk(), which happens whenever
 	 * sd_revalidate() is called.
 	 */
-	retval = -ENODEV;
-
 	if (scsi_block_when_processing_errors(sdp)) {
-		sshdr  = kzalloc(sizeof(*sshdr), GFP_KERNEL);
+		struct scsi_sense_hdr sshdr = { 0, };
+
 		retval = scsi_test_unit_ready(sdp, SD_TIMEOUT, SD_MAX_RETRIES,
-					      sshdr);
-	}
+					      &sshdr);
 
-	/* failed to execute TUR, assume media not present */
-	if (host_byte(retval)) {
-		set_media_not_present(sdkp);
-		goto out;
-	}
+		/* failed to execute TUR, assume media not present */
+		if (host_byte(retval)) {
+			set_media_not_present(sdkp);
+			goto out;
+		}
 
-	if (media_not_present(sdkp, sshdr))
-		goto out;
+		if (media_not_present(sdkp, &sshdr))
+			goto out;
+	}
 
 	/*
 	 * For removable scsi disk we have to recognise the presence
@@ -1485,7 +1483,6 @@ out:
 	 *	Medium present state has changed in either direction.
 	 *	Device has indicated UNIT_ATTENTION.
 	 */
-	kfree(sshdr);
 	retval = sdp->changed ? DISK_EVENT_MEDIA_CHANGE : 0;
 	sdp->changed = 0;
 	scsi_disk_put(sdkp);