linux-kernel - [PATCH 4.15 47/72] media: usbtv: prevent double free in error case

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Date:   Fri,  6 Apr 2018 15:24:22 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Yavuz, Tuba" <tuba@....ufl.edu>,
        Oliver Neukum <oneukum@...e.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Subject: [PATCH 4.15 47/72] media: usbtv: prevent double free in error case

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oliver Neukum <oneukum@...e.com>

commit 50e7044535537b2a54c7ab798cd34c7f6d900bd2 upstream.

Quoting the original report:

It looks like there is a double-free vulnerability in Linux usbtv driver
on an error path of usbtv_probe function. When audio registration fails,
usbtv_video_free function ends up freeing usbtv data structure, which
gets freed the second time under usbtv_video_fail label.

usbtv_audio_fail:

        usbtv_video_free(usbtv); =>

           v4l2_device_put(&usbtv->v4l2_dev);

              => v4l2_device_put

                  => kref_put

                      => v4l2_device_release

  => usbtv_release (CALLBACK)

                             => kfree(usbtv) (1st time)

usbtv_video_fail:

        usb_set_intfdata(intf, NULL);

        usb_put_dev(usbtv->udev);

        kfree(usbtv); (2nd time)

So, as we have refcounting, use it

Reported-by: Yavuz, Tuba <tuba@....ufl.edu>
Signed-off-by: Oliver Neukum <oneukum@...e.com>
CC: stable@...r.kernel.org
Signed-off-by: Hans Verkuil <hans.verkuil@...co.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@...pensource.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/media/usb/usbtv/usbtv-core.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/media/usb/usbtv/usbtv-core.c
+++ b/drivers/media/usb/usbtv/usbtv-core.c
@@ -112,6 +112,8 @@ static int usbtv_probe(struct usb_interf
 	return 0;
 
 usbtv_audio_fail:
+	/* we must not free at this point */
+	usb_get_dev(usbtv->udev);
 	usbtv_video_free(usbtv);
 
 usbtv_video_fail: