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Duoming Zhou
67600ccfc4
The original code relies on cancel_delayed_work() in tb_dp_dprx_stop(),
which does not ensure that the delayed work item tunnel->dprx_work has
fully completed if it was already running. This leads to use-after-free
scenarios where tb_tunnel is deallocated by tb_tunnel_put(), while
tunnel->dprx_work remains active and attempts to dereference tb_tunnel
in tb_dp_dprx_work().
A typical race condition is illustrated below:
CPU 0 | CPU 1
tb_dp_tunnel_active() |
tb_deactivate_and_free_tunnel()| tb_dp_dprx_start()
tb_tunnel_deactivate() | queue_delayed_work()
tb_dp_activate() |
tb_dp_dprx_stop() | tb_dp_dprx_work() //delayed worker
cancel_delayed_work() |
tb_tunnel_put(tunnel); |
| tunnel = container_of(...); //UAF
| tunnel-> //UAF
Replacing cancel_delayed_work() with cancel_delayed_work_sync() is
not feasible as it would introduce a deadlock: both tb_dp_dprx_work()
and the cleanup path acquire tb->lock, and cancel_delayed_work_sync()
would wait indefinitely for the work item that cannot proceed.
Instead, implement proper reference counting:
- If cancel_delayed_work() returns true (work is pending), we release
the reference in the stop function.
- If it returns false (work is executing or already completed), the
reference is released in delayed work function itself.
This ensures the tb_tunnel remains valid during work item execution
while preventing memory leaks.
This bug was found by static analysis.
Fixes: d6d458d42e ("thunderbolt: Handle DisplayPort tunnel activation asynchronously")
Cc: stable@vger.kernel.org
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
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 reStructuredText 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.