[PATCH net-next] nfc: digital: fix use-after-free in nfc_digital_unregister_device()

[Weiming Shi <bestswngs@gmail.com>]

nfc_digital_unregister_device() cancels cmd_work and cmd_complete_work
once each and then frees the command queue.  The two works re-arm each
other: digital_wq_cmd_complete() ends with schedule_work(&ddev->cmd_work),
and digital_wq_cmd() hands a command to the driver whose asynchronous
completion schedules cmd_complete_work.  cancel_work_sync() only waits for
the instance it cancels; it does not stop the work from being queued again.
A work re-armed after its cancel_work_sync() therefore runs concurrently
with the cmd_queue cleanup and dereferences a digital_cmd the cleanup has
already freed.  digital_wq_cmd() widens the window by dropping cmd_lock
before using the command it took from the queue, while the cleanup loop
frees the commands without holding cmd_lock.

It is reproducible with the software NFC simulator (CONFIG_NFC_SIM): start
an NFC-DEP exchange between the two nfcsim devices and unload the module
while it is running.

 BUG: KASAN: slab-use-after-free in digital_wq_cmd (net/nfc/digital_core.c:174)
 Read of size 1 by task kworker/1:5
 Workqueue: events digital_wq_cmd
  digital_wq_cmd (net/nfc/digital_core.c:174)
  process_one_work
  worker_thread
  kthread

 Allocated by task 5124:
  digital_send_cmd (net/nfc/digital_core.c:234)
  digital_in_send_sdd_req
  digital_in_recv_sens_res
  digital_wq_cmd_complete (net/nfc/digital_core.c:134)

 Freed by task 4994:
  kfree
  nfc_digital_unregister_device (net/nfc/digital_core.c:859)
  nfcsim_device_free [nfcsim]
  nfcsim_exit [nfcsim]
  __do_sys_delete_module

Use disable_work_sync() instead of cancel_work_sync() for the two command
works.  disable_work_sync() cancels the work and disables it, so any later
schedule_work() -- whether from the sibling work re-arming it or from the
driver's completion callback -- becomes a no-op.  Once both works are
disabled no work can run, and the cleanup loop frees the queue with no work
able to reach a freed command.

Fixes: 59ee2361c924 ("NFC Digital: Implement driver commands mechanism")
Reported-by: Xiang Mei <xmei5@asu.edu>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 net/nfc/digital_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/nfc/digital_core.c b/net/nfc/digital_core.c
index 7cb1e6aaae90..6def5132a4a6 100644
--- a/net/nfc/digital_core.c
+++ b/net/nfc/digital_core.c
@@ -843,8 +843,8 @@ void nfc_digital_unregister_device(struct nfc_digital_dev *ddev)
 	mutex_unlock(&ddev->poll_lock);
 
 	cancel_delayed_work_sync(&ddev->poll_work);
-	cancel_work_sync(&ddev->cmd_work);
-	cancel_work_sync(&ddev->cmd_complete_work);
+	disable_work_sync(&ddev->cmd_work);
+	disable_work_sync(&ddev->cmd_complete_work);
 
 	list_for_each_entry_safe(cmd, n, &ddev->cmd_queue, queue) {
 		list_del(&cmd->queue);

base-commit: d4932951a19a5f1ec93200260b85e1a4c080ff77
-- 
2.43.0