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: d6d458d42e1e ("thunderbolt: Handle DisplayPort tunnel activation asynchronously")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
drivers/thunderbolt/tunnel.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/thunderbolt/tunnel.c b/drivers/thunderbolt/tunnel.c
index d52efe3f658c..89fa0c626d3e 100644
--- a/drivers/thunderbolt/tunnel.c
+++ b/drivers/thunderbolt/tunnel.c
@@ -1073,6 +1073,7 @@ static void tb_dp_dprx_work(struct work_struct *work)
if (tunnel->callback)
tunnel->callback(tunnel, tunnel->callback_data);
+ tb_tunnel_put(tunnel);
}
static int tb_dp_dprx_start(struct tb_tunnel *tunnel)
@@ -1097,11 +1098,14 @@ static int tb_dp_dprx_start(struct tb_tunnel *tunnel)
static void tb_dp_dprx_stop(struct tb_tunnel *tunnel)
{
+ bool ret;
+
if (tunnel->dprx_started) {
tunnel->dprx_started = false;
tunnel->dprx_canceled = true;
- cancel_delayed_work(&tunnel->dprx_work);
- tb_tunnel_put(tunnel);
+ ret = cancel_delayed_work(&tunnel->dprx_work);
+ if (ret)
+ tb_tunnel_put(tunnel);
}
}
--
2.34.1
