[PATCH 1/1] usb: gadget: Don't attempt to dequeue requests for a disabled USB endpoint on Freescale hardware

[Simon Haggett <simon.haggett@realvnc.com>]

Some gadget drivers may attempt to dequeue requests for an endpoint that has
already been disabled. For example, in the UVC gadget driver, uvc_function_set_alt()
will call usb_ep_disable() when alt setting 0 is selected. When the userspace
application subsequently issues the VIDIOC_STREAMOFF ioctl, uvc_video_enable()
invokes usb_ep_dequeue() to ensure that all requests have been cancelled.

For the Freescale High Speed Dual-Role USB controller, fsl_ep_dequeue() provides
the implementation of usb_ep_dequeue(). If this is called for a disabled endpoint,
a kernel oops will occur when the ep->ep.desc field is dereferenced (by ep_index()).
fsl_ep_disable() sets this field to NULL, as well as deleting all pending requests
for the endpoint.

This patch adds an additional check to fsl_ep_dequeue() to ensure that the
endpoint has not already been disabled before attempting to dequeue requests.

Signed-off-by: Simon Haggett <simon.haggett@realvnc.com>
---
 drivers/usb/gadget/fsl_udc_core.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/drivers/usb/gadget/fsl_udc_core.c b/drivers/usb/gadget/fsl_udc_core.c
index 6ae70cb..acd513b 100644
--- a/drivers/usb/gadget/fsl_udc_core.c
+++ b/drivers/usb/gadget/fsl_udc_core.c
@@ -955,7 +955,10 @@ static int fsl_ep_dequeue(struct usb_ep *_ep, struct usb_request *_req)
 	int ep_num, stopped, ret = 0;
 	u32 epctrl;
 
-	if (!_ep || !_req)
+	/* Ensure that the ep and request are valid, and the ep is not
+	 * disabled
+	 */
+	if (!_ep || !_req || !ep->ep.desc)
 		return -EINVAL;
 
 	spin_lock_irqsave(&ep->udc->lock, flags);
-- 
1.7.4.1