In the Linux kernel, the following vulnerability has been resolved:
HID: uclogic: fix use-after-free of inrange_timer on remove
uclogic_remove() cancels the pen in-range timer and then stops the
device:
<pre>
timer_delete_sync(&drvdata->inrange_timer);
hid_hw_stop(hdev);
</pre>
timer_delete_sync() only guarantees the timer is idle at that instant.
uclogic_raw_event_pen() keeps delivering pen reports until hid_hw_stop()
stops the transport several lines later, and every report with
pen->inrange == UCLOGIC_PARAMS_PEN_INRANGE_NONE re-arms the timer:
<pre>
mod_timer(&drvdata->inrange_timer, jiffies + msecs_to_jiffies(100));
</pre>
A report landing between the timer_delete_sync() call and the transport
teardown in hid_hw_stop() re-arms inrange_timer after it was cancelled.
uclogic_remove() then returns and the devm drvdata is freed, while
hid_hw_stop() has already freed the input device drvdata->pen_input
points at, so when the timer fires ~100 ms later
uclogic_inrange_timeout() dereferences freed memory -- a use-after-free
in timer-softirq context.
Swapping the two calls is not a fix: stopping the device first frees
drvdata->pen_input via hidinput_disconnect() while the timer may still
be pending, so a timer already armed before removal fires on the freed
input device in the window before timer_delete_sync() runs.
Use timer_shutdown_sync() before hid_hw_stop() instead. It cancels the
timer, waits for a running callback while pen_input is still valid, and
prevents any further re-arming -- a later mod_timer() from an in-flight
report is silently ignored -- so the timer is provably dead before
hid_hw_stop() frees the inputs. This is the ordering the timer core
documents for this "timer re-armed from another path" teardown case.