[SCSI] don't reference freed command in scsi_init_sgtable

Patch

commit 04796336
Author: Christoph Hellwig <hch@infradead.org>
Date:   Thu Feb 20 14:20:55 2014 -0800

    [SCSI] do not manipulate device reference counts in scsi_get/put_command

Introduced a use after free: when scsi_init_io fails we have to release our
device reference, but we do this trying to reference the just freed command.
Add a local scsi_device pointer to fix this.

Fixes: 04796336Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/scsi_lib.c

@@ -1044,6 +1044,7 @@ static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer *sdb,
  */
 int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
 {
+	struct scsi_device *sdev = cmd->device;
 	struct request *rq = cmd->request;
 
 	int error = scsi_init_sgtable(rq, &cmd->sdb, gfp_mask);
@@ -1091,7 +1092,7 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
 	scsi_release_buffers(cmd);
 	cmd->request->special = NULL;
 	scsi_put_command(cmd);
-	put_device(&cmd->device->sdev_gendev);
+	put_device(&sdev->sdev_gendev);
 	return error;
 }
 EXPORT_SYMBOL(scsi_init_io);