usb: gadget: f_fs: Fix use-after-free

When using asynchronous read or write operations on the USB endpoints the
issuer of the IO request is notified by calling the ki_complete() callback
of the submitted kiocb when the URB has been completed.

Calling this ki_complete() callback will free kiocb. Make sure that the
structure is no longer accessed beyond that point, otherwise undefined
behaviour might occur.

Fixes: 2e4c7553cd6f ("usb: gadget: f_fs: add aio support")
Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index e21ca2bd6839eb6a8b73f6d1e2061dd36939bc65..15b648cbc75c4141bb5c51bd03c2c6e5b5f6c821 100644 (file)
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -646,6 +646,7 @@ static void ffs_user_copy_worker(struct work_struct *work)
                                                   work);
        int ret = io_data->req->status ? io_data->req->status :
                                         io_data->req->actual;
+       bool kiocb_has_eventfd = io_data->kiocb->ki_flags & IOCB_EVENTFD;
 
        if (io_data->read && ret > 0) {
                use_mm(io_data->mm);
@@ -657,13 +658,11 @@ static void ffs_user_copy_worker(struct work_struct *work)
 
        io_data->kiocb->ki_complete(io_data->kiocb, ret, ret);
 
-       if (io_data->ffs->ffs_eventfd &&
-           !(io_data->kiocb->ki_flags & IOCB_EVENTFD))
+       if (io_data->ffs->ffs_eventfd && !kiocb_has_eventfd)
                eventfd_signal(io_data->ffs->ffs_eventfd, 1);
 
        usb_ep_free_request(io_data->ep, io_data->req);
 
-       io_data->kiocb->private = NULL;
        if (io_data->read)
                kfree(io_data->to_free);
        kfree(io_data->buf);