USB: chaoskey: fail open after removal

USB: chaoskey: fail open after removal

chaoskey_open() takes the lock only to increase the
counter of openings. That means that the mutual exclusion
with chaoskey_disconnect() cannot prevent an increase
of the counter and chaoskey_open() returning a success.

If that race is hit, chaoskey_disconnect() will happily
free all resources associated with the device after
it has dropped the lock, as it has read the counter
as zero.

To prevent this race chaoskey_open() has to check
the presence of the device under the lock.
However, the current per device lock cannot be used,
because it is a part of the data structure to be
freed. Hence an additional global mutex is needed.
The issue is as old as the driver.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Reported-by: syzbot+422188bce66e76020e55@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=422188bce66e76020e55
Fixes: 66e3e591891da ("usb: Add driver for Altus Metrum ChaosKey device (v2)")
Rule: add
Link: https://lore.kernel.org/stable/20241002132201.552578-1-oneukum%40suse.com
Link: https://lore.kernel.org/r/20241002132201.552578-1-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>