CVE-2026-43324

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

USB: dummy-hcd: Fix interrupt synchronization error

This fixes an error in synchronization in the dummy-hcd driver. The error has a somewhat involved history. The synchronization mechanism was introduced by commit 7dbd8f4cabd9 (USB: dummy-hcd: Fix erroneous synchronization change), which added an emulated interrupts enabled flag together with code emulating synchronize_irq() (it waits until all current handler callbacks have returned).

But the emulated interrupt-disable occurred too late, after the driver containing the handler callback routines had been told that it was unbound and no more callbacks would occur. Commit 4a5d797a9f9c (usb: gadget: dummy_hcd: fix gpf in gadget_setup) tried to fix this by moving the synchronize_irq() emulation code from dummy_stop() to dummy_pullup(), which runs before the unbind callback.

There still were races, though, because the emulated interrupt-disable still occurred too late. It couldnt be moved to dummy_pullup(), because that routine can be called for reasons other than an impending unbind. Therefore commits 7dc0c55e9f30 (USB: UDC core: Add udc_async_callbacks gadget op) and 04145a03db9d (USB: UDC: Implement udc_async_callbacks in dummy-hcd) added an API allowing the UDC core to tell dummy-hcd exactly when emulated interrupts and their callbacks should be disabled.

That brings us to the current state of things, which is still wrong because the emulated synchronize_irq() occurs before the emulated interrupt-disable! Thats no good, beause it means that more emulated interrupts can occur after the synchronize_irq() emulation has run, leading to the possibility that a callback handler may be running when the gadget driver is unbound.

To fix this, we have to move the synchronize_irq() emulation code yet again, to the dummy_udc_async_callbacks() routine, which takes care of enabling and disabling emulated interrupt requests. The synchronization will now run immediately after emulated interrupts are disabled, which is where it belongs.

Affected Software

References

• https://git.kernel.org/stable/c/2ca9e46f8f1f5a297eb0ac83f79d35d5b3a02541
• https://git.kernel.org/stable/c/5687a09776069bd915560021c9728ca528440128
• https://git.kernel.org/stable/c/5aa776c8615bea3b1eaeec87b0788375800ead4f
• https://git.kernel.org/stable/c/8bcd80219d8e10e660bf29b20e41bb8beb4e4cb7
• https://git.kernel.org/stable/c/94d4fab1dd9e64f45449bcc7d6a5acf796b13015
• https://git.kernel.org/stable/c/cbf7df5e5d27cd5bea92ee9a75a4b28dbcc718d4
• https://git.kernel.org/stable/c/d847f375b1bcea713143bc02720d13d2d01b012a