HID: usbhid: fix use-after-free bug

This patch (as1592) fixes an obscure problem in the usbhid driver.
Under some circumstances, a control or interrupt-OUT URB can be
submitted twice.  This will happen if the first submission fails; the
queue pointers aren't updated, so the next time the queue is restarted
the same URB will be submitted again.

The problem is that raw_report gets deallocated during the first
submission.  The second submission will then dereference and try to
free an already-freed region of memory.  The patch fixes the problem
by setting raw_report to NULL when it is deallocated and checking for
NULL before dereferencing it.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/usbhid/hid-core.c

@@ -331,9 +331,12 @@ static int hid_submit_out(struct hid_device *hid)
 	usbhid->urbout->transfer_buffer_length = ((report->size - 1) >> 3) +
 						 1 + (report->id > 0);
 	usbhid->urbout->dev = hid_to_usb_dev(hid);
-	memcpy(usbhid->outbuf, raw_report,
-	       usbhid->urbout->transfer_buffer_length);
-	kfree(raw_report);
+	if (raw_report) {
+		memcpy(usbhid->outbuf, raw_report,
+				usbhid->urbout->transfer_buffer_length);
+		kfree(raw_report);
+		usbhid->out[usbhid->outtail].raw_report = NULL;
+	}
 
 	dbg_hid("submitting out urb\n");
 
@@ -362,8 +365,11 @@ static int hid_submit_ctrl(struct hid_device *hid)
 	if (dir == USB_DIR_OUT) {
 		usbhid->urbctrl->pipe = usb_sndctrlpipe(hid_to_usb_dev(hid), 0);
 		usbhid->urbctrl->transfer_buffer_length = len;
-		memcpy(usbhid->ctrlbuf, raw_report, len);
-		kfree(raw_report);
+		if (raw_report) {
+			memcpy(usbhid->ctrlbuf, raw_report, len);
+			kfree(raw_report);
+			usbhid->ctrl[usbhid->ctrltail].raw_report = NULL;
+		}
 	} else {
 		int maxpacket, padlen;