640397afdf
[ Upstream commit b8cedb7093b2d1394cae9b86494cba4b62d3a30a ] When removing the pn533 device (i2c or USB), there is a logic error. The original code first cancels the worker (flush_delayed_work) and then destroys the workqueue (destroy_workqueue), leaving the timer the last one to be deleted (del_timer). This result in a possible race condition in a multi-core preempt-able kernel. That is, if the cleanup (pn53x_common_clean) is concurrently run with the timer handler (pn533_listen_mode_timer), the timer can queue the poll_work to the already destroyed workqueue, causing use-after-free. This patch reorder the cleanup: it uses the del_timer_sync to make sure the handler is finished before the routine will destroy the workqueue. Note that the timer cannot be activated by the worker again. static void pn533_wq_poll(struct work_struct *work) ... rc = pn533_send_poll_frame(dev); if (rc) return; if (cur_mod->len == 0 && dev->poll_mod_count > 1) mod_timer(&dev->listen_timer, ...); That is, the mod_timer can be called only when pn533_send_poll_frame() returns no error, which is impossible because the device is detaching and the lower driver should return ENODEV code. Signed-off-by: Lin Ma <linma@zju.edu.cn> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.