linux-kernel - Re: [PATCH v2] usb: gadget: udc: fix race condition in usb_del

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Message-ID: <2025102212-selected-ovary-6259@gregkh>
Date: Wed, 22 Oct 2025 10:02:45 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Jimmy Hu <hhhuuu@...gle.com>
Cc: linux-usb@...r.kernel.org, badhri@...gle.com, stern@...land.harvard.edu,
	royluo@...gle.com, Thinh.Nguyen@...opsys.com, balbi@...com,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] usb: gadget: udc: fix race condition in usb_del_gadget

On Tue, Oct 14, 2025 at 08:51:56AM +0000, Jimmy Hu wrote:
> A race condition during gadget teardown can lead to a use-after-free
> in usb_gadget_state_work(), as reported by KASAN:
> 
>   BUG: KASAN: invalid-access in sysfs_notify+0_x_2c/0_x_d0
>   Workqueue: events usb_gadget_state_work
> 
> The fundamental race occurs because a concurrent event (e.g., an
> interrupt) can call usb_gadget_set_state() and schedule gadget->work
> at any time during the cleanup process in usb_del_gadget().
> 
> Commit 399a45e5237c ("usb: gadget: core: flush gadget workqueue after
> device removal") attempted to fix this by moving flush_work() to after
> device_del(). However, this does not fully solve the race, as a new
> work item can still be scheduled *after* flush_work() completes but
> before the gadget's memory is freed, leading to the same use-after-free.
> 
> This patch fixes the race condition robustly by introducing a 'teardown'
> flag and a 'state_lock' spinlock to the usb_gadget struct. The flag is
> set during cleanup in usb_del_gadget() *before* calling flush_work() to
> prevent any new work from being scheduled once cleanup has commenced.
> The scheduling site, usb_gadget_set_state(), now checks this flag under
> the lock before queueing the work, thus safely closing the race window.
> 
> Changes in v2:
>   - Removed redundant inline comments as suggested by Alan Stern.

This goes below the --- line.

> 2.51.0.760.g7b8bcc2412-goog

This does not apply to my usb-linus branch, what kernel was it made
against?  Can you rebase and resubmit it based on that one?