[PATCH 3.16 025/148] media: usbvision: Fix invalid accesses after device disconnect

Ben Hutchings
2020-02-08T18:38:46Z

From: Alan Stern <stern@rowland.harvard.edu>

commit c7a191464078262bf799136317c95824e26a222b upstream.

The syzbot fuzzer found two invalid-access bugs in the usbvision
driver. These bugs occur when userspace keeps the device file open
after the device has been disconnected and usbvision_disconnect() has
set usbvision->dev to NULL:

When the device file is closed, usbvision_radio_close() tries
to issue a usb_set_interface() call, passing the NULL pointer
as its first argument.

If userspace performs a querycap ioctl call, vidioc_querycap()
calls usb_make_path() with the same NULL pointer.

This patch fixes the problems by making the appropriate tests
beforehand. Note that vidioc_querycap() is protected by
usbvision->v4l2_lock, acquired in a higher layer of the V4L2
subsystem.

Reported-and-tested-by: syzbot+7fa38a608b1075dfd634@syzkaller.appspotmail.com

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/media/usb/usbvision/usbvision-video.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/media/usb/usbvision/usbvision-video.c
+++ b/drivers/media/usb/usbvision/usbvision-video.c
@@ -482,6 +482,9 @@ static int vidioc_querycap(struct file *
{
struct usb_usbvision *usbvision = video_drvdata(file);

+ if (!usbvision->dev)
+ return -ENODEV;
+
strlcpy(vc->driver, "USBVision", sizeof(vc->driver));
strlcpy(vc->card,
usbvision_device_data[usbvision->dev_model].model_string,
@@ -1169,8 +1172,9 @@ static int usbvision_radio_close(struct
mutex_lock(&usbvision->v4l2_lock);
/* Set packet size to 0 */
usbvision->iface_alt = 0;
- err_code = usb_set_interface(usbvision->dev, usbvision->iface,
- usbvision->iface_alt);
+ if (usbvision->dev)
+ err_code = usb_set_interface(usbvision->dev, usbvision->iface,
+ usbvision->iface_alt);

usbvision_audio_off(usbvision);
usbvision->radio = 0;