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.

Fixes: 5702f75375aa9 ("usb: gadget: udc-core: move sysfs_notify() to a workqueue") Signed-off-by: Jimmy Hu hhhuuu@google.com Cc: stable@vger.kernel.org

---

Reviewed-by: Alan Stern stern@rowland.harvard.edu

drivers/usb/gadget/udc/core.c | 17 ++++++++++++++++- include/linux/usb/gadget.h | 5 +++++ 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c index d709e24c1fd4..66d2428835da 100644 --- a/drivers/usb/gadget/udc/core.c +++ b/drivers/usb/gadget/udc/core.c @@ -1123,8 +1123,13 @@ static void usb_gadget_state_work(struct work_struct *work) void usb_gadget_set_state(struct usb_gadget *gadget, enum usb_device_state state) {

• unsigned long flags;
• spin_lock_irqsave(&gadget->state_lock, flags); gadget->state = state;

• schedule_work(&gadget->work);

• if (!gadget->teardown)

• schedule_work(&gadget->work);
  

• spin_unlock_irqrestore(&gadget->state_lock, flags);

} EXPORT_SYMBOL_GPL(usb_gadget_set_state); @@ -1357,6 +1362,8 @@ static void usb_udc_nop_release(struct device *dev) void usb_initialize_gadget(struct device *parent, struct usb_gadget *gadget, void (*release)(struct device *dev)) {

• spin_lock_init(&gadget->state_lock);
• gadget->teardown = false; INIT_WORK(&gadget->work, usb_gadget_state_work); gadget->dev.parent = parent;

@@ -1531,6 +1538,7 @@ EXPORT_SYMBOL_GPL(usb_add_gadget_udc); void usb_del_gadget(struct usb_gadget *gadget) { struct usb_udc *udc = gadget->udc;

• unsigned long flags;

if (!udc) return; @@ -1544,6 +1552,13 @@ void usb_del_gadget(struct usb_gadget *gadget) kobject_uevent(&udc->dev.kobj, KOBJ_REMOVE); sysfs_remove_link(&udc->dev.kobj, "gadget"); device_del(&gadget->dev);

• /*

• * Set the teardown flag before flushing the work to prevent new work
  

• * from being scheduled while we are cleaning up.
  

• */
  

• spin_lock_irqsave(&gadget->state_lock, flags);
• gadget->teardown = true;
• spin_unlock_irqrestore(&gadget->state_lock, flags); flush_work(&gadget->work); ida_free(&gadget_id_numbers, gadget->id_number); cancel_work_sync(&udc->vbus_work);

diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h index 0f28c5512fcb..8b5e593f7966 100644 --- a/include/linux/usb/gadget.h +++ b/include/linux/usb/gadget.h @@ -351,6 +351,9 @@ struct usb_gadget_ops {

• can handle. The UDC must support this and all slower speeds and lower
• number of lanes.
• @state: the state we are now (attached, suspended, configured, etc)

• • @state_lock: Spinlock protecting the `state` and `teardown` members.
• • @teardown: True if the device is undergoing teardown, used to prevent
• • new work from being scheduled during cleanup.
  • @name: Identifies the controller hardware type. Used in diagnostics
  • and sometimes configuration.
  • @dev: Driver model state for this abstract device.

@@ -426,6 +429,8 @@ struct usb_gadget { enum usb_ssp_rate max_ssp_rate; enum usb_device_state state;

• spinlock_t state_lock;
• bool teardown; const char *name; struct device dev; unsigned isoch_delay;

-- 2.51.0.760.g7b8bcc2412-goog