platform/chrome: cros_ec_debugfs: detach log reader wq from devm
Debugfs console_log uses devm memory (e.g. debug_info in cros_ec_console_log_poll()). However, lifecycles of device and debugfs are independent. An use-after-free issue is observed if userland program operates the debugfs after the memory has been freed. The call trace: do_raw_spin_lock _raw_spin_lock_irqsave remove_wait_queue ep_unregister_pollwait ep_remove do_epoll_ctl A Python example to reproduce the issue: ... import select ... p = select.epoll() ... f = open('/sys/kernel/debug/cros_scp/console_log') ... p.register(f, select.POLLIN) ... p.poll(1) [(4, 1)] # 4=fd, 1=select.POLLIN [ shutdown cros_scp at the point ] ... p.poll(1) [(4, 16)] # 4=fd, 16=select.POLLHUP ... p.unregister(f) An use-after-free issue raises here. It called epoll_ctl with EPOLL_CTL_DEL which in turn to use the workqueue in the devm (i.e. log_wq). Detaches log reader's workqueue from devm to make sure it is persistent even if the device has been removed. Signed-off-by:Tzung-Bi Shih <tzungbi@google.com> Reviewed-by:
Guenter Roeck <groeck@google.com> Link: https://lore.kernel.org/r/20220209051130.386175-1-tzungbi@google.com Signed-off-by:
Benson Leung <bleung@chromium.org>
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