CVE-2026-89738usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed

Official description

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed In polled-VBUS mode (board.vbus_pin && board.vbus_polled), probe arms a self-restarting cycle: at91_vbus_timer() schedules vbus_timer_work, and at91_vbus_timer_work() calls at91_vbus_update() and re-arms the timer via mod_timer(). Both recover the same udc through container_of and dereference it on every iteration. Neither teardown path cancels this cycle. udc is devm-allocated, so it is freed after at91udc_remove() returns, and is likewise freed when probe fails and devres runs. A timer callback or work item that is pending or running at either point dereferences the freed udc. Add at91_udc_shutdown_vbus_timer() and call it from at91udc_remove() and from the usb_add_gadget_udc() failure path in probe; the remaining probe error paths fail before the timer is armed. timer_shutdown_sync() waits for a running callback and clears timer->function, which makes the work handler's mod_timer() a permanent no-op; cancel_work_sync() then drains any pending or running work whose re-arm attempt now does nothing. The timer must be shut down first, since cancelling the work alone would let the timer re-queue it. The guard mirrors probe: in IRQ mode the timer and work_struct are never initialized. This does not require a fault; a normal driver unbind can interleave with an already queued work item. This issue was found by an in-house static analysis tool.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2440ce54b8c4c8aa6963c181eb56164a466fbe1c
• https://git.kernel.org/stable/c/1674e34fe61ad3f5585dc833ba6bb6522912e6a5
• https://git.kernel.org/stable/c/723d73b245843d4fff4c3f42e857c78c2b2d414e
• https://git.kernel.org/stable/c/a2a602cb1e28d76a5398cec3fa21b0110385f501
• https://git.kernel.org/stable/c/51a311eb97e91ce1aed3005cb71ccb2e30f8cce8
• https://git.kernel.org/stable/c/557ef547d49ff5e6026a4d39bdd3113bd81d7688
• https://git.kernel.org/stable/c/c27d13ce4bab80fbdf6523928071b6c24b37606c