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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89732
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:20:03 UTC
Updated2026-09-14 13:19:22 UTC
DescriptionIn 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->mutex to tear down ep0req. 5. The kernel deadlocks because the configfs thread is stuck in an uninterruptible sleep waiting for the mutex, while the userspace daemon is in an interruptible sleep holding the mutex forever because no more events will arrive. To fix this, we drop both the waitqueue spinlock and ffs->mutex before going to sleep, and use wait_event_interruptible_exclusive() instead. Upon waking up, we jump back to the `retry` label to safely reacquire the mutex and re-evaluate the state machine. By not sleeping with ffs->mutex held, we natively decouple gadget teardowns (which require the mutex) from userspace polling.

Risk And Classification

EPSS: 0.002150000 probability, percentile 0.119600000 (date 2026-09-14)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected ddf8abd2599491cbad959c700b90ba72a5dce8d0 fbe3db4b650c284df8eb4cb68eebcf270cf861b5 git Not specified
CNA Linux Linux affected ddf8abd2599491cbad959c700b90ba72a5dce8d0 30430509c156e1df2bdafd5f1cadb160e53db5d6 git Not specified
CNA Linux Linux affected ddf8abd2599491cbad959c700b90ba72a5dce8d0 bafddd0f20b5228760be303aa69c58502e92309c git Not specified
CNA Linux Linux affected ddf8abd2599491cbad959c700b90ba72a5dce8d0 b0a6bfac0c3c3edf5b2ecaee87a09234601fe78d git Not specified
CNA Linux Linux affected ddf8abd2599491cbad959c700b90ba72a5dce8d0 fd20cc68bbdb5620696ac108e8f2efd180fe2c1a git Not specified
CNA Linux Linux affected ddf8abd2599491cbad959c700b90ba72a5dce8d0 34e88f53614640b59039a46717fb6142e9871022 git Not specified
CNA Linux Linux affected ddf8abd2599491cbad959c700b90ba72a5dce8d0 eac233e63f9db82ba874e3cccafaafab162999e0 git Not specified
CNA Linux Linux affected ddf8abd2599491cbad959c700b90ba72a5dce8d0 569dd7e5dcffe1e1c6b26ca2cd3be57eb433e082 git Not specified
CNA Linux Linux affected 2.6.35 Not specified
CNA Linux Linux unaffected 2.6.35 semver Not specified
CNA Linux Linux unaffected 5.10.270 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.221 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.188 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.157 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.109 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.50 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/fbe3db4b650c284df8eb4cb68eebcf270cf861b5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/30430509c156e1df2bdafd5f1cadb160e53db5d6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/569dd7e5dcffe1e1c6b26ca2cd3be57eb433e082 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/34e88f53614640b59039a46717fb6142e9871022 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b0a6bfac0c3c3edf5b2ecaee87a09234601fe78d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/eac233e63f9db82ba874e3cccafaafab162999e0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/fd20cc68bbdb5620696ac108e8f2efd180fe2c1a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/bafddd0f20b5228760be303aa69c58502e92309c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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