Bluetooth: hci_sync: don't drain cmd_sync backlog on unregister

hci_unregister_dev() disables cmd_work and cmd_timer, then calls
hci_cmd_sync_clear(), whose cancel_work_sync() waits for
hci_cmd_sync_work() to return. That worker dequeues and runs every
entry on cmd_sync_work_list. With cmd_work disabled nothing reaches
the controller, so each queued HCI command waits the full
HCI_CMD_TIMEOUT (2s).

The backlog has no bound. Userspace can keep queuing MGMT commands
such as MGMT_OP_GET_CLOCK_INFO against a controller that doesn't
answer. Closing /dev/vhci then blocks in vhci_release() for
backlog * 2s:

  INFO: task syz-executor:5749 blocked for more than 143 seconds.
   cancel_work_sync
   hci_cmd_sync_clear
   hci_unregister_dev
   vhci_release

In a local reproduction the backlog held more than 5000 entries,
which comes to hours of hang.

Stop the worker from taking new entries once HCI_UNREGISTER is set,
and wake any request still waiting with -ENODEV before cancelling
the work. The entries left over are destroyed with -ECANCELED by the
existing sweep in hci_cmd_sync_clear(). They stay on the list until
the work has stopped, so hci_cmd_sync_dequeue() and friends still see
them. A callback already running may still issue another command,
which delays unregister by at most one timeout per remaining command,
not by the whole backlog.

Fixes: 008ee9eb8a11 ("Bluetooth: hci_sync: Fix not processing all entries on cmd_sync_work")
Reported-by: syzbot+217e3f1283cafe80586e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=217e3f1283cafe80586e
Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

0 files changed, 0 insertions, 0 deletions