@@ -903,6 +903,21 @@ static int dummy_pullup(struct usb_gadget *_gadget, int value)
spin_lock_irqsave(&dum->lock, flags);
dum->pullup = (value != 0);
set_link_state(dum_hcd);
+ if (value == 0) {
+ /*
+ * Emulate synchronize_irq(): wait for callbacks to finish.
+ * This seems to be the best place to emulate the call to
+ * synchronize_irq() that's in usb_gadget_remove_driver().
+ * Doing it in dummy_udc_stop() would be too late since it
+ * is called after the unbind callback and unbind shouldn't
+ * be invoked until all the other callbacks are finished.
+ */
+ while (dum->callback_usage > 0) {
+ spin_unlock_irqrestore(&dum->lock, flags);
+ usleep_range(1000, 2000);
+ spin_lock_irqsave(&dum->lock, flags);
+ }
+ }
spin_unlock_irqrestore(&dum->lock, flags);
usb_hcd_poll_rh_status(dummy_hcd_to_hcd(dum_hcd));
@@ -1004,14 +1019,6 @@ static int dummy_udc_stop(struct usb_gadget *g)
spin_lock_irq(&dum->lock);
dum->ints_enabled = 0;
stop_activity(dum);
-
- /* emulate synchronize_irq(): wait for callbacks to finish */
- while (dum->callback_usage > 0) {
- spin_unlock_irq(&dum->lock);
- usleep_range(1000, 2000);
- spin_lock_irq(&dum->lock);
- }
-
dum->driver = NULL;
spin_unlock_irq(&dum->lock);
Fix a general protection fault reported by syzbot due to a race between gadget_setup() and gadget_unbind() in raw_gadget. The gadget core is supposed to guarantee that there won't be any more callbacks to the gadget driver once the driver's unbind routine is called. That guarantee is enforced in usb_gadget_remove_driver as follows: usb_gadget_disconnect(udc->gadget); if (udc->gadget->irq) synchronize_irq(udc->gadget->irq); udc->driver->unbind(udc->gadget); usb_gadget_udc_stop(udc); usb_gadget_disconnect turns off the pullup resistor, telling the host that the gadget is no longer connected and preventing the transmission of any more USB packets. Any packets that have already been received are sure to processed by the UDC driver's interrupt handler by the time synchronize_irq returns. But this doesn't work with dummy_hcd, because dummy_hcd doesn't use interrupts; it uses a timer instead. It does have code to emulate the effect of synchronize_irq, but that code doesn't get invoked at the right time -- it currently runs in usb_gadget_udc_stop, after the unbind callback instead of before. Indeed, there's no way for usb_gadget_remove_driver to invoke this code before the unbind callback. To fix this, move the synchronize_irq() emulation code to dummy_pullup so that it runs before unbind. Also, add a comment explaining why it is necessary to have it there. Suggested-by: Alan Stern <stern@rowland.harvard.edu> Reported-by: syzbot+eb4674092e6cc8d9e0bd@syzkaller.appspotmail.com Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com> --- Changes in v2: Improvements in the comment as suggested by Alan Stern. v1: https://lore.kernel.org/lkml/20210417125212.6274-1-mail@anirudhrb.com/ --- drivers/usb/gadget/udc/dummy_hcd.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-)