On Mon, Oct 13, 2025 at 07:57:56AM +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.
Good analysis.
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
drivers/usb/gadget/udc/core.c | 18 +++++++++++++++++- include/linux/usb/gadget.h | 6 ++++++ 2 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c index d709e24c1fd4..c4268b76d747 100644 --- a/drivers/usb/gadget/udc/core.c +++ b/drivers/usb/gadget/udc/core.c
@@ -1357,6 +1362,9 @@ 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)) {
- /* For race-free teardown */
- spin_lock_init(&gadget->state_lock);
- gadget->teardown = false; INIT_WORK(&gadget->work, usb_gadget_state_work); gadget->dev.parent = parent;
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h index 0f28c5512fcb..8302aeaea82e 100644 --- a/include/linux/usb/gadget.h +++ b/include/linux/usb/gadget.h
@@ -426,6 +429,9 @@ struct usb_gadget { enum usb_ssp_rate max_ssp_rate; enum usb_device_state state;
- /* For race-free teardown and state management */
The comments here and above merely repeat information that's already given in the kerneldoc. They aren't needed.
Alan Stern