AZL-108818

In the Linux kernel, the following vulnerability has been resolved:

HID: multitouch: stop the release timer from being rearmed on remove

mt_remove() quiesces the sticky-finger timer before stopping the hardware:

timer_delete_sync(&td->release_timer);

sysfs_remove_group(&hdev->dev.kobj, &mt_attribute_group);
hid_hw_stop(hdev);

timer_delete_sync() waits for a running callback and dequeues the timer, but it does not stop the timer from being armed again. The transport is still delivering reports at that point, and the report path rearms it:

if (app->quirks & MT_QUIRK_STICKY_FINGERS) {
    if (td->mt_io_flags & MT_IO_SLOTS_MASK)
        mod_timer(&td->release_timer,
                  jiffies + msecs_to_jiffies(100));

A report that arrives after timer_delete_sync() has returned therefore leaves the timer queued. td is allocated with devm_kzalloc() against hdev->dev, so it is freed when the driver is unbound, after mt_remove() returns. When the timer fires afterwards, mt_expired_timeout() dereferences the freed td:

struct mt_device *td = timer_container_of(td, t, release_timer);
struct hid_device *hdev = td->hdev;

if (test_and_set_bit_lock(MT_IO_FLAGS_RUNNING, &td->mt_io_flags))

Simply moving the teardown after hid_hw_stop() does not fix this on its own, because mt_expired_timeout() calls mt_release_contacts(), which walks hdev->inputs; the timer still has to be quiesced before hid_hw_stop() tears the input devices down.

Use timer_shutdown_sync() instead, which additionally makes any later mod_timer() a no-op, so neither ordering constraint has to be traded off against the other. This is the final-teardown pattern the function was introduced for, and hid-wiimote already uses it for the same reason.