Wind River Support Network

Description

In the Linux kernel, the following vulnerability has been resolved:  rbd: eliminate a race in lock_dwork draining on unmap  Given how rbd_lock_add_request() and rbd_img_exclusive_lock() are written, lock_dwork may be (re)queued more than it's actually needed: for example in case a new I/O request comes in while we are in the middle of rbd_acquire_lock() on behalf of another I/O request.  This is expected and with rbd_release_lock() preemptively canceling lock_dwork is benign under normal operation.  A more problematic example is maybe_kick_acquire():      if (have_requests || delayed_work_pending(&rbd_dev->lock_dwork)) {             dout("%s rbd_dev %p kicking lock_dwork\n", __func__, rbd_dev);             mod_delayed_work(rbd_dev->task_wq, &rbd_dev->lock_dwork, 0);     }  It's not unrealistic for lock_dwork to get canceled right after delayed_work_pending() returns true and for mod_delayed_work() to requeue it right there anyway.  This is a classic TOCTOU race.  When it comes to unmapping the image, there is an implicit assumption of no self-initiated exclusive lock activity past the point of return from rbd_dev_image_unlock() which unlocks the lock if it happens to be held.  This unlock is assumed to be final and lock_dwork (as well as all other exclusive lock tasks, really) isn't expected to get queued again.  However, lock_dwork is canceled only in cancel_tasks_sync() (i.e. later in the unmap sequence) and on top of that the cancellation can get in effect nullified by maybe_kick_acquire().  This may result in rbd_acquire_lock() executing after rbd_dev_device_release() and rbd_dev_image_release() run and free and/or reset a bunch of things. One of the possible failure modes then is a violated      rbd_assert(rbd_image_format_valid(rbd_dev->image_format));  in rbd_dev_header_info() which is called via rbd_dev_refresh() from rbd_post_acquire_action().  Redo exclusive lock task draining to provide saner semantics and try to meet the assumptions around rbd_dev_image_unlock().