usb: f_fs: fix memory leak when ep changes during transfer

In the ffs_epfile_io function, data buffer is allocated for non-halt
requests.  Later, after grabing a mutex, the function checks that
epfile->ep is still ep and if it’s not, it set ret to -ESHUTDOWN and
follow a path including spin_unlock_irq (just after ‘ret = -ESHUTDOWN’),
mutex_unlock (after if-else-if-else chain) and returns ret.  Noticeably,
this does not include freeing of the data buffer.

Fix by introducing a goto which moves control flow to the the end of the
function where spin_unlock_irq, mutex_unlock and kfree are all called.
Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/gadget/function/f_fs.c

@@ -763,7 +763,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 	if (epfile->ep != ep) {
 		/* In the meantime, endpoint got disabled or changed. */
 		ret = -ESHUTDOWN;
-		spin_unlock_irq(&epfile->ffs->eps_lock);
+		goto error_lock;
 	} else if (halt) {
 		/* Halt */
 		if (likely(epfile->ep == ep) && !WARN_ON(!ep->ep))