CVE-2026-43327
Received Received - Intake

Race Condition in Linux Kernel USB Gadget Core

Publication date: 2026-05-08

Last updated on: 2026-05-08

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: USB: dummy-hcd: Fix locking/synchronization error Syzbot testing was able to provoke an addressing exception and crash in the usb_gadget_udc_reset() routine in drivers/usb/gadgets/udc/core.c, resulting from the fact that the routine was called with a second ("driver") argument of NULL. The bad caller was set_link_state() in dummy_hcd.c, and the problem arose because of a race between a USB reset and driver unbind. These sorts of races were not supposed to be possible; commit 7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change"), along with a few followup commits, was written specifically to prevent them. As it turns out, there are (at least) two errors remaining in the code. Another patch will address the second error; this one is concerned with the first. The error responsible for the syzbot crash occurred because the stop_activity() routine will sometimes drop and then re-acquire the dum->lock spinlock. A call to stop_activity() occurs in set_link_state() when handling an emulated USB reset, after the test of dum->ints_enabled and before the increment of dum->callback_usage. This allowed another thread (doing a driver unbind) to sneak in and grab the spinlock, and then clear dum->ints_enabled and dum->driver. Normally this other thread would have to wait for dum->callback_usage to go down to 0 before it would clear dum->driver, but in this case it didn't have to wait since dum->callback_usage had not yet been incremented. The fix is to increment dum->callback_usage _before_ calling stop_activity() instead of after. Then the thread doing the unbind will not clear dum->driver until after the call to usb_gadget_udc_reset() safely returns and dum->callback_usage has been decremented again.

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Meta Information

Published
2026-05-08
Last Modified
2026-05-08
Generated
2026-07-29
AI Q&A
2026-05-08
EPSS Evaluated
2026-07-28
NVD
CVE-2026-43327
EUVD
EUVD-2026-28611

Affected Vendors & Products

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

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability exists in the Linux kernel's USB dummy host controller driver (dummy-hcd). It is caused by a race condition in the usb_gadget_udc_reset() function, where the function is called with a NULL driver argument due to improper synchronization.

The root cause is that the stop_activity() routine sometimes releases and then re-acquires a spinlock (dum->lock), allowing another thread performing a driver unbind to intervene and clear important flags and pointers prematurely. This happens because the callback usage counter (dum->callback_usage) is incremented too late, allowing the unbind thread to proceed without waiting.

The fix involves incrementing dum->callback_usage before calling stop_activity(), ensuring that the unbind thread cannot clear the driver pointer until after usb_gadget_udc_reset() completes safely.

Impact Analysis

This vulnerability can cause the Linux kernel to crash due to an addressing exception triggered by the race condition in the USB dummy host controller driver.

A kernel crash can lead to system instability, denial of service, and potential loss of data or interruption of services relying on USB gadget functionality.

Mitigation Strategies

The vulnerability is a synchronization error in the Linux kernel's USB dummy host controller driver (dummy-hcd) that can cause a crash due to a race condition during USB reset and driver unbind.

To mitigate this vulnerability, you should update your Linux kernel to a version that includes the fix which increments the callback usage counter before calling stop_activity(), preventing the race condition.

Since this is a kernel-level issue, applying the official kernel patch or upgrading to a patched kernel release is the immediate and recommended step.

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