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Date:   Fri, 24 Jan 2020 17:13:56 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Hans Verkuil <hverkuil@...all.nl>,
        syzbot <syzbot+75287f75e2fedd69d680@...kaller.appspotmail.com>,
        Hillf Danton <hdanton@...a.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Souptick Joarder <jrdr.linux@...il.com>, andreyknvl@...gle.com,
        bnvandana@...il.com, laurent.pinchart@...asonboard.com,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-usb@...r.kernel.org, mchehab@...nel.org,
        syzkaller-bugs@...glegroups.com
Subject: [PATCH] media: usbvision: Fix a use after free in v4l2_release()

Syzbot triggered a use after free in v5.5-rc6:

BUG: KASAN: use-after-free in v4l2_release+0x2f1/0x390 drivers/media/v4l2-core/v4l2-dev.c:459

Allocated by task 94:
 usbvision_alloc drivers/media/usb/usbvision/usbvision-video.c:1315 [inline]
 usbvision_probe.cold+0x5c5/0x1f21 drivers/media/usb/usbvision/usbvision-video.c:1469

Freed by task 1913:
 kfree+0xd5/0x300 mm/slub.c:3957
 usbvision_release+0x181/0x1c0 drivers/media/usb/usbvision/usbvision-video.c:1364
 usbvision_radio_close.cold+0x2b/0x74 drivers/media/usb/usbvision/usbvision-video.c:1130
 v4l2_release+0x2e7/0x390 drivers/media/v4l2-core/v4l2-dev.c:455

The problem is that the v4l2_release() calls usbvision_release() which
frees "usbvision" but v4l2_release() still wants to use
"usbvision->vdev".  One solution is to make this devm_ allocated memory
so the memory isn't freed until later.

Reported-by: syzbot+75287f75e2fedd69d680@...kaller.appspotmail.com
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
I copied this idea from a different driver, but I haven't tested it.
I wanted to try the #syz fix command to see if it works.

 drivers/media/usb/usbvision/usbvision-video.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/media/usb/usbvision/usbvision-video.c b/drivers/media/usb/usbvision/usbvision-video.c
index 93d36aab824f..07b4763062c4 100644
--- a/drivers/media/usb/usbvision/usbvision-video.c
+++ b/drivers/media/usb/usbvision/usbvision-video.c
@@ -1312,7 +1312,7 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
 {
 	struct usb_usbvision *usbvision;
 
-	usbvision = kzalloc(sizeof(*usbvision), GFP_KERNEL);
+	usbvision = devm_kzalloc(&dev->dev, sizeof(*usbvision), GFP_KERNEL);
 	if (!usbvision)
 		return NULL;
 
@@ -1336,7 +1336,6 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
 	v4l2_ctrl_handler_free(&usbvision->hdl);
 	v4l2_device_unregister(&usbvision->v4l2_dev);
 err_free:
-	kfree(usbvision);
 	return NULL;
 }
 
@@ -1361,7 +1360,6 @@ static void usbvision_release(struct usb_usbvision *usbvision)
 
 	v4l2_ctrl_handler_free(&usbvision->hdl);
 	v4l2_device_unregister(&usbvision->v4l2_dev);
-	kfree(usbvision);
 
 	PDEBUG(DBG_PROBE, "success");
 }
-- 
2.11.0

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