CVE-2026-98765: USB: gadget: dummy-hcd: Fix wait for outstanding request completions
In the Linux kernel, the following vulnerability has been resolved:
USB: gadget: dummy-hcd: Fix wait for outstanding request completions
The dummy-hcd driver emulates synchronizeirq() by waiting until its private callbackusage counter drops to 0 (with the private lock not held). This counter is incremented whenever a gadget driver callback occurs (which requires the private lock to be dropped), but not when a request completion handler is called.
This is an oversight. Request completion is triggered by timer interrupts (emulating device IRQs in a real UDC), and the interrupt handlers are supposed to have completed when the synchronizeirq() emulation routine returns -- they aren't supposed to be in the middle of a completion callback. If this happens it can lead to a gadget driver's unbind routine running before all outstanding request completions have finished, maybe even allowing the gadget driver's module to be unloaded while a completion handler is still running.
Fix the oversight by incrementing the callbackusage value across request completion callbacks.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
In the dummy-hcd driver, account for request completion callbacks in the private callback_usage counter and wait for callback_usage to drop to 0 before synchronize_irq() returns, so unbind or module unload cannot occur while a completion handler is still running.