nfc: nfcsim: fix use after free during module unload

There is a use after free memory corruption during module exit:
 - nfcsim_exit()
  - nfcsim_device_free(dev0)
    - nfc_digital_unregister_device()
      This iterates over command queue and frees all commands,
    - dev->up = false
    - nfcsim_link_shutdown()
      - nfcsim_link_recv_wake()
        This wakes the sleeping thread nfcsim_link_recv_skb().

 - nfcsim_link_recv_skb()
   Wake from wait_event_interruptible_timeout(),
   call directly the deb->cb callback even though (dev->up == false),
   - digital_send_cmd_complete()
     Dereference of "struct digital_cmd" cmd which was freed earlier by

This causes memory corruption shortly after (with unrelated stack

  nfc nfc0: NFC: nfcsim_recv_wq: Device is down
  llcp: nfc_llcp_recv: err -19
  nfc nfc1: NFC: nfcsim_recv_wq: Device is down
  BUG: unable to handle page fault for address: ffffffffffffffed
  Call Trace:
   ? vfs_write+0x27c/0x390

KASAN report:

  BUG: KASAN: use-after-free in digital_send_cmd_complete+0x16/0x50
  Write of size 8 at addr ffff88800a05f720 by task kworker/0:2/71
  Workqueue: events nfcsim_recv_wq [nfcsim]
  Call Trace:
   ? digital_send_cmd_complete+0x16/0x50
   ? digital_send_cmd_complete+0x16/0x50
   ? digital_send_cmd_complete+0x16/0x50
   ? digital_dep_link_down+0x60/0x60
   nfcsim_recv_wq+0x38f/0x3d5 [nfcsim]
   ? nfcsim_in_send_cmd+0x4a/0x4a [nfcsim]
   ? lock_is_held_type+0x98/0x110
   ? finish_wait+0x110/0x110
   ? rcu_read_lock_sched_held+0x9c/0xd0
   ? rcu_read_lock_bh_held+0xb0/0xb0
   ? lockdep_hardirqs_on_prepare+0x12e/0x1f0

This flow of calling digital_send_cmd_complete() callback on driver exit
is specific to nfcsim which implements reading and sending work queues.
Since the NFC digital device was unregistered, the callback should not
be called.

Fixes: 204bddcb508f ("NFC: nfcsim: Make use of the Digital layer")
Cc: <>
Signed-off-by: Krzysztof Kozlowski <>
Signed-off-by: David S. Miller <>
1 file changed