CVE-2026-89732

/// Technical description

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

usb: gadget: f_fs: Prevent deadlock during ep0 read loop

Currently, ffs_ep0_read() holds ffs->mutex when it prepares to go to

sleep waiting for an event. When no setup events are pending, it calls

wait_event_interruptible_exclusive_locked_irq() with the mutex still

held. The wait macro deliberately drops the waitqueue spinlock before

sleeping but does not drop the mutex.

If a userspace daemon is polling ep0 via read() and the gadget is

asynchronously torn down via configfs (e.g., echo "" > UDC), a

deadlock can occur:

1. The configfs teardown calls functionfs_unbind(), which queues a

FUNCTIONFS_UNBIND event.

2. The daemon wakes up, consumes the event, and drops the mutex.

3. However, if the daemon loops and immediately issues another read()

before exiting, it reacquires ffs->mutex and again goes into an

interruptible sleep.

4. Meanwhile, functionfs_unbind() continues execution and attempts to

acquire ffs

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References