[PATCH v2] usb: gadget: aspeed_udc: avoid past-the-end iterator in dequeue

[Maoyi Xie]

ast_udc_ep_dequeue() declares the loop cursor `req` outside the
list_for_each_entry(). After the loop it tests `&req->req != _req`
to decide whether the request was found. If the queue holds no
match, `req` is past-the-end. It then aliases
container_of(&ep->queue, struct ast_udc_request, queue) via offset
cancellation. Whether that synthetic address equals `_req` depends
on heap layout. The function can return 0 without dequeueing
anything.

Walk the list with a separate `iter`. Set `req` only when a
request matches. After the loop, `req` is NULL if nothing
matched.

Suggested-by: Alan Stern <stern at rowland.harvard.edu>
Signed-off-by: Maoyi Xie <maoyixie.tju at gmail.com>
---
v2: Switch the loop body to Alan Stern's shape: test inside
    the if, assign `req`, break. Same behaviour as v1.
v1: https://lore.kernel.org/linux-usb/20260518073403.1285339-1-maoyi.xie@ntu.edu.sg/

 drivers/usb/gadget/udc/aspeed_udc.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

--- a/drivers/usb/gadget/udc/aspeed_udc.c	2026-05-19 15:29:28.690931576 +0800
+++ b/drivers/usb/gadget/udc/aspeed_udc.c	2026-05-19 15:29:59.482953528 +0800
@@ -692,26 +692,30 @@
 {
 	struct ast_udc_ep *ep = to_ast_ep(_ep);
 	struct ast_udc_dev *udc = ep->udc;
-	struct ast_udc_request *req;
+	struct ast_udc_request *req = NULL, *iter;
 	unsigned long flags;
 	int rc = 0;
 
 	spin_lock_irqsave(&udc->lock, flags);
 
 	/* make sure it's actually queued on this endpoint */
-	list_for_each_entry(req, &ep->queue, queue) {
-		if (&req->req == _req) {
-			list_del_init(&req->queue);
-			ast_udc_done(ep, req, -ESHUTDOWN);
-			_req->status = -ECONNRESET;
+	list_for_each_entry(iter, &ep->queue, queue) {
+		if (&iter->req == _req) {
+			req = iter;
 			break;
 		}
 	}
 
-	/* dequeue request not found */
-	if (&req->req != _req)
+	if (!req) {
 		rc = -EINVAL;
+		goto out;
+	}
+
+	list_del_init(&req->queue);
+	ast_udc_done(ep, req, -ESHUTDOWN);
+	_req->status = -ECONNRESET;
 
+out:
 	spin_unlock_irqrestore(&udc->lock, flags);
 
 	return rc;

-- 
2.34.1