[PATCH] media: usbvision: Fix a use after free in v4l2_release()

Dan Carpenter
2020-01-24T14:14:42Z

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@syzkaller.appspotmail.com
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.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