[SCSI] sg: checking sdp->detached isn't protected when open

@detached is set under the protection of sg_index_lock. Without getting the
lock, new sfp will be added during sg removal and there is no chance for it
to be picked out. So check with sg_index_lock held in sg_add_sfp().

Signed-off-by: Vaughan Cao <vaughan.cao@oracle.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/sg.c

@@ -295,23 +295,20 @@ sg_open(struct inode *inode, struct file *filp)
  if (flags & O_EXCL)
  sdp->exclude = 1; /* used by release lock */
 
- if (sdp->detached) {
- retval = -ENODEV;
- goto sem_out;
- }
  if (sfds_list_empty(sdp)) { /* no existing opens on this device */
  sdp->sgdebug = 0;
  q = sdp->device->request_queue;
  sdp->sg_tablesize = queue_max_segments(q);
  }
- if ((sfp = sg_add_sfp(sdp, dev)))
+ sfp = sg_add_sfp(sdp, dev);
+ if (!IS_ERR(sfp))
  filp->private_data = sfp;
  /* retval is already provably zero at this point because of the
  * check after retval = scsi_autopm_get_device(sdp->device))
  */
  else {
- retval = -ENOMEM;
-sem_out:
+ retval = PTR_ERR(sfp);
+
  if (flags & O_EXCL) {
  sdp->exclude = 0; /* undo if error */
  up_write(&sdp->o_sem);
@@ -2045,7 +2042,7 @@ sg_add_sfp(Sg_device * sdp, int dev)
 
  sfp = kzalloc(sizeof(*sfp), GFP_ATOMIC | __GFP_NOWARN);
  if (!sfp)
- return NULL;
+ return ERR_PTR(-ENOMEM);
 
  init_waitqueue_head(&sfp->read_wait);
  rwlock_init(&sfp->rq_list_lock);
@@ -2060,6 +2057,10 @@ sg_add_sfp(Sg_device * sdp, int dev)
  sfp->keep_orphan = SG_DEF_KEEP_ORPHAN;
  sfp->parentdp = sdp;
  write_lock_irqsave(&sg_index_lock, iflags);
+ if (sdp->detached) {
+ write_unlock_irqrestore(&sg_index_lock, iflags);
+ return ERR_PTR(-ENODEV);
+ }
  list_add_tail(&sfp->sfd_siblings, &sdp->sfds);
  write_unlock_irqrestore(&sg_index_lock, iflags);
  SCSI_LOG_TIMEOUT(3, printk("sg_add_sfp: sfp=0x%p\n", sfp));