USB: gadgetfs: fix copy_to_user while holding spinlock

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>
CC: <stable@vger.kernel.org>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 684900fcfe24..956b3dc7c3a4 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -983,11 +983,14 @@ 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 */
                         }