stable inclusion
from stable-v5.10.118
commit 0acaf9cacd4feb99c11c2303cb3c04a63a32f048
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L686

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0acaf9cacd4feb99c11c2303cb3c04a63a32f048

--------------------------------

[ Upstream commit 0e8eb5e8 ]

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: NTzung-Bi Shih <tzungbi@google.com>
Reviewed-by: NGuenter Roeck <groeck@google.com>
Link: https://lore.kernel.org/r/20220209051130.386175-1-tzungbi@google.comSigned-off-by: NBenson Leung <bleung@chromium.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>