In the Linux kernel, the following vulnerability has been resolved:
thunderbolt: Fix use-after-free in tb_dp_dprx_work
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
- If it returns false (work is executing or already completed), the
This ensures the tb_tunnel remains valid during work item execution while preventing memory leaks.
This bug was found by static analysis.