In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free of a deferred file_lock on double SMB2_CANCEL

A deferred byte-range lock (an SMB2_LOCK that blocks) registers an async work on
conn->async_requests via setup_async_work(), with cancel_fn =
smb2_remove_blocked_lock and cancel_argv[0] pointing at the struct file_lock.

When the request is cancelled, the worker frees the file_lock with
locks_free_lock() and takes the cancelled early-exit, which "goto out"s and never
reaches release_async_work() -- the only site that unlinks the work from
conn->async_requests and clears cancel_fn/cancel_argv. The work therefore stays
matchable on async_requests with a live cancel_fn pointing at the freed file_lock,
until connection teardown finally runs release_async_work().

smb2_cancel() fires cancel_fn unconditionally with no state guard, so a second
SMB2_CANCEL for the same AsyncId, arriving in that window, re-runs
smb2_remove_blocked_lock() on the freed file_lock -- a slab use-after-free:

  BUG: KASAN: slab-use-after-free in __locks_delete_block
    __locks_delete_block
    locks_delete_block
    ksmbd_vfs_posix_lock_unblock
    smb2_remove_blocked_lock
    smb2_cancel                 <- 2nd SMB2_CANCEL fires cancel_fn
    handle_ksmbd_work
  Allocated by ...: locks_alloc_lock <- smb2_lock
  Freed by ...:     locks_free_lock  <- smb2_lock (cancelled branch)
  ... cache file_lock_cache of size 192

Reproduced on mainline with KASAN by an authenticated SMB client.

Skip a work whose state is already KSMBD_WORK_CANCELLED so its cancel callback
cannot be fired a second time.

https://git.kernel.org/stable/c/0da2e073f9cbf4985a0fd9acb71bc5ff599f8afd

https://git.kernel.org/stable/c/14d2eee0193ac3cd1bf3d014373449f0b8d35d6d

https://git.kernel.org/stable/c/2b2eda2821cff1d1b5a423b6ee7d8fc6fbc8e694

https://git.kernel.org/stable/c/89ae9df09d2c1fb4a4eb495c113a7ce1dca34147

https://git.kernel.org/stable/c/b7063c7426ea5a4d15e01b60538718765392f49d

https://git.kernel.org/stable/c/f580d27e8928828693df44ba2db0fffdbe11dfea

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