[PATCH] usb: gadget: f_printer: fix list corruption in printer_soft_reset()

[Liu Chao]

printer_soft_reset() has three loops that drain different lists back to
rx_reqs / tx_reqs.  The second loop's condition tests rx_reqs_active but
its body was copy-pasted from the first loop and still reads from
rx_buffers:

    while (!list_empty(&dev->rx_reqs_active)) {
        req = container_of(dev->rx_buffers.next, ...);  /* BUG */

The first loop already empties rx_buffers, so by the time the second
loop runs, dev->rx_buffers.next points back to the list head itself.
Consequently:

 - list_del_init() treats the list head as an entry and poisons it
 - list_add() splices the rx_buffers head into rx_reqs
 - rx_reqs_active is never drained, so the loop condition stays true
   indefinitely

This results in linked-list corruption and a hang that is trivially
triggered by a USB host sending a SOFT_RESET class request.

Fix by reading from rx_reqs_active.next, matching the loop condition.

Fixes: 856c5e59aa0d ("usb: gadget: f_printer: copy Data Interface instead of using a singleton")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Weibin Liu <liuwb@xxxxxxxxxxxx>
Signed-off-by: Liu Chao <liuc63@xxxxxxxxxxxx>
---
 drivers/usb/gadget/function/f_printer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
index 1857d7861..2305733fe 100644
--- a/drivers/usb/gadget/function/f_printer.c
+++ b/drivers/usb/gadget/function/f_printer.c
@@ -940,7 +940,7 @@ static void printer_soft_reset(struct printer_dev *dev)
 	}
 
 	while (likely(!(list_empty(&dev->rx_reqs_active)))) {
-		req = container_of(dev->rx_buffers.next, struct usb_request,
+		req = container_of(dev->rx_reqs_active.next, struct usb_request,
 				list);
 		list_del_init(&req->list);
 		list_add(&req->list, &dev->rx_reqs);
-- 
2.50.1