[4.2.y-ckt stable] Patch "usb: gadget: f_fs: Fix use-after-free" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 4c89f70b4513df2a6d40509c0cd14dea223cb09e Mon Sep 17 00:00:00 2001
From: Lars-Peter Clausen <lars at metafoo.de>
Date: Thu, 14 Apr 2016 17:01:17 +0200
Subject: usb: gadget: f_fs: Fix use-after-free

commit 38740a5b87d53ceb89eb2c970150f6e94e00373a upstream.

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")
Signed-off-by: Lars-Peter Clausen <lars at metafoo.de>
Signed-off-by: Felipe Balbi <felipe.balbi at linux.intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/usb/gadget/function/f_fs.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 6e7be91..82240db 100644
--- 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);
--
2.7.4