USB: gadgetfs: fix copy_to_user while holding spinlock

commit 6e76c01e71551cb221c1f3deacb9dcd9a7346784 upstream.

The gadgetfs driver as a long-outstanding FIXME, regarding a call of
copy_to_user() made while holding a spinlock.  This patch fixes the
issue by dropping the spinlock and using the dev->udc_usage mechanism
introduced by another recent patch to guard against status changes
while the lock isn't held.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/usb/gadget/inode.c b/drivers/usb/gadget/inode.c
index 9307311..b32e386 100644 (file)
--- a/drivers/usb/gadget/inode.c
+++ b/drivers/usb/gadget/inode.c
@@ -1054,11 +1054,14 @@ ep0_read (struct file *fd, char __user *buf, size_t len, loff_t *ptr)
                                retval = -EIO;
                        else {
                                len = min (len, (size_t)dev->req->actual);
-// FIXME don't call this with the spinlock held ...
+                               ++dev->udc_usage;
+                               spin_unlock_irq(&dev->lock);
                                if (copy_to_user (buf, dev->req->buf, len))
                                        retval = -EFAULT;
                                else
                                        retval = len;
+                               spin_lock_irq(&dev->lock);
+                               --dev->udc_usage;
                                clean_req (dev->gadget->ep0, dev->req);
                                /* NOTE userspace can't yet choose to stall */
                        }