gadgetfs: use-after-free in ->aio_read()

commit f01d35a1 upstream.

AIO_PREAD requests call ->aio_read() with iovec on caller's stack, so if
we are going to access it asynchronously, we'd better get ourselves
a copy - the one on kernel stack of aio_run_iocb() won't be there
anymore.  function/f_fs.c take care of doing that, legacy/inode.c
doesn't...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[bwh: Backported to 3.2:
 - Adjust filename, context
 - Add kfree(priv->iv) to one additional failure path]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/gadget/inode.c

@@ -570,6 +570,7 @@ static ssize_t ep_aio_read_retry(struct kiocb *iocb)
 			break;
 	}
 	kfree(priv->buf);
+	kfree(priv->iv);
 	kfree(priv);
 	return len;
 }
@@ -591,6 +592,7 @@ static void ep_aio_complete(struct usb_ep *ep, struct usb_request *req)
 	 */
 	if (priv->iv == NULL || unlikely(req->actual == 0)) {
 		kfree(req->buf);
+		kfree(priv->iv);
 		kfree(priv);
 		iocb->private = NULL;
 		/* aio_complete() reports bytes-transferred _and_ faults */
@@ -626,7 +628,7 @@ ep_aio_rwtail(
 	struct usb_request	*req;
 	ssize_t			value;
 
-	priv = kmalloc(sizeof *priv, GFP_KERNEL);
+	priv = kzalloc(sizeof *priv, GFP_KERNEL);
 	if (!priv) {
 		value = -ENOMEM;
 fail:
@@ -634,7 +636,14 @@ ep_aio_rwtail(
 		return value;
 	}
 	iocb->private = priv;
-	priv->iv = iv;
+	if (iv) {
+		priv->iv = kmemdup(iv, nr_segs * sizeof(struct iovec),
+				   GFP_KERNEL);
+		if (!priv->iv) {
+			kfree(priv);
+			goto fail;
+		}
+	}
 	priv->nr_segs = nr_segs;
 
 	value = get_ready_ep(iocb->ki_filp->f_flags, epdata);
@@ -672,6 +681,7 @@ ep_aio_rwtail(
 	mutex_unlock(&epdata->lock);
 
 	if (unlikely(value)) {
+		kfree(priv->iv);
 		kfree(priv);
 		put_ep(epdata);
 	} else