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

Overview

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

• Linux >= 4037242c4f5ff77afe61bf07ca1e8a99490219e5 < 723d73b245843d4fff4c3f42e857c78c2b2d414e
• Linux >= 4037242c4f5ff77afe61bf07ca1e8a99490219e5 < a2a602cb1e28d76a5398cec3fa21b0110385f501
• Linux >= 4037242c4f5ff77afe61bf07ca1e8a99490219e5 < 51a311eb97e91ce1aed3005cb71ccb2e30f8cce8
• Linux >= 4037242c4f5ff77afe61bf07ca1e8a99490219e5 < 557ef547d49ff5e6026a4d39bdd3113bd81d7688
• Linux >= 4037242c4f5ff77afe61bf07ca1e8a99490219e5 < c27d13ce4bab80fbdf6523928071b6c24b37606c
• Linux 2.6.36

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Moderate · updated 2026-09-21 · vex