CVE-2026-80854
Received Received - Intake

USB Gadget f_tcm Port Count Race Condition

Publication date: 2026-09-04

Last updated on: 2026-09-04

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_tcm: keep port count until LUN teardown completes tcm_usbg_drop_nexus() permits session removal once tpg_port_count reaches zero. However, usbg_port_unlink() currently decrements that count from the fabric_pre_unlink() callback, before core_dev_del_lun() waits for active se_lun references to drain. If removal of the last LUN races a nexus removal, the latter can observe a zero port count and call target_remove_session(). This frees sess_cmd_map while an in-flight struct usbg_cmd, including its work item, can still be accessed. Overlapping the last-LUN unlink with nexus removal reproduces this lifetime violation as a DEBUG_OBJECTS "free active" warning for usbg_cmd_work, followed by a target-core BUG/Oops. The generic target-core unlink path has no callback after core_dev_del_lun() completes. Add an optional fabric_post_unlink() callback and use it for the f_tcm port count. The count now remains nonzero until core_dev_del_lun() has finished draining active LUN references, preventing nexus removal from freeing the session during command completion.

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Meta Information

Published
2026-09-04
Last Modified
2026-09-04
Generated
2026-09-25
AI Q&A
2026-09-04
EPSS Evaluated
2026-09-23
NVD
CVE-2026-80854
EUVD
EUVD-2026-71304

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a race condition in the USB gadget function for Target Channel Modules (f_tcm). The issue occurs when the last Logical Unit Number (LUN) is removed while a nexus (a connection between a target and initiator) is also being removed. This can lead to a use-after-free scenario where a command's work item is accessed after the session memory has been freed, causing a system crash or kernel oops.

Detection Guidance

This vulnerability is specific to the Linux kernel's USB gadget target mode (f_tcm) and may not have direct network detection commands. Monitor kernel logs for DEBUG_OBJECTS warnings or target-core BUG/Oops messages related to usbg_cmd_work or session removal. Check for crashes during LUN or nexus removal operations.

Impact Analysis

If exploited, this vulnerability could cause system instability, crashes, or kernel panics, potentially leading to denial of service. It may also expose systems to further security risks if the kernel's memory management is compromised during the race condition.

Compliance Impact

This vulnerability is a kernel-level issue in the Linux USB gadget subsystem that could lead to memory corruption or system crashes. It does not directly relate to data privacy, access controls, or audit logging required by standards like GDPR or HIPAA. Compliance impact would depend on whether the affected system processes sensitive data and if the crash leads to unauthorized access or data loss.

Mitigation Strategies

Apply the latest Linux kernel patches addressing this issue. Avoid removing the last LUN while active I/O operations are in progress. Monitor kernel logs for related errors and update affected systems to a patched kernel version.

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