[PATCH] usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed

[Fan Wu]

In polled-VBUS mode (board.vbus_pin && board.vbus_polled), probe arms a
self-restarting cycle: at91_vbus_timer() schedules vbus_timer_work, and
at91_vbus_timer_work() calls at91_vbus_update() and re-arms the timer via
mod_timer(). Both recover the same udc through container_of and dereference
it on every iteration.

Neither teardown path cancels this cycle. udc is devm-allocated, so it is
freed after at91udc_remove() returns, and is likewise freed when probe
fails and devres runs. A timer callback or work item that is pending or
running at either point dereferences the freed udc.

Add at91_udc_shutdown_vbus_timer() and call it from at91udc_remove() and
from the usb_add_gadget_udc() failure path in probe; the remaining probe
error paths fail before the timer is armed. timer_shutdown_sync() waits
for a running callback and clears timer->function, which makes the work
handler's mod_timer() a permanent no-op; cancel_work_sync() then drains
any pending or running work whose re-arm attempt now does nothing. The
timer must be shut down first, since cancelling the work alone would let
the timer re-queue it. The guard mirrors probe: in IRQ mode the timer and
work_struct are never initialized.

This does not require a fault; a normal driver unbind can interleave with
an already queued work item.

This issue was found by an in-house static analysis tool.

Fixes: 4037242c4f5f ("ARM: 6209/3: at91_udc: Add vbus polarity and polling mode")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <fanwu01@xxxxxxxxxx>
---
 drivers/usb/gadget/udc/at91_udc.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/udc/at91_udc.c b/drivers/usb/gadget/udc/at91_udc.c
index 5aa360ba4..8e5d7fb71 100644
--- a/drivers/usb/gadget/udc/at91_udc.c
+++ b/drivers/usb/gadget/udc/at91_udc.c
@@ -1794,6 +1794,19 @@ static void at91udc_of_init(struct at91_udc *udc, struct device_node *np)
 		udc->caps = match->data;
 }
 
+/*
+ * The work handler re-arms this timer, so shut the timer down before
+ * draining the work; otherwise it restarts the polling cycle.
+ */
+static void at91_udc_shutdown_vbus_timer(struct at91_udc *udc)
+{
+	if (!(udc->board.vbus_pin && udc->board.vbus_polled))
+		return;
+
+	timer_shutdown_sync(&udc->vbus_timer);
+	cancel_work_sync(&udc->vbus_timer_work);
+}
+
 static int at91udc_probe(struct platform_device *pdev)
 {
 	struct device	*dev = &pdev->dev;
@@ -1907,7 +1920,7 @@ static int at91udc_probe(struct platform_device *pdev)
 	}
 	retval = usb_add_gadget_udc(dev, &udc->gadget);
 	if (retval)
-		goto err_unprepare_iclk;
+		goto err_shutdown_vbus;
 	dev_set_drvdata(dev, udc);
 	device_init_wakeup(dev, 1);
 	create_debug_file(udc);
@@ -1915,6 +1928,8 @@ static int at91udc_probe(struct platform_device *pdev)
 	INFO("%s version %s\n", driver_name, DRIVER_VERSION);
 	return 0;
 
+err_shutdown_vbus:
+	at91_udc_shutdown_vbus_timer(udc);
 err_unprepare_iclk:
 	clk_unprepare(udc->iclk);
 err_unprepare_fclk:
@@ -1933,6 +1948,9 @@ static void at91udc_remove(struct platform_device *pdev)
 	DBG("remove\n");
 
 	usb_del_gadget_udc(&udc->gadget);
+
+	at91_udc_shutdown_vbus_timer(udc);
+
 	if (udc->driver) {
 		dev_err(&pdev->dev,
 			"Driver still in use but removing anyhow\n");
-- 
2.34.1