Re: [PATCH 2/2] media: dvb-usb: Fix use-after-free access

[Robert Foss]

Hey Takashi,

This patch is generating a checkpatch warning, but I think it is
spurious and can be ignored.

Other than that, this looks good to me.
Reviewed-by: Robert Foss <robert.foss@xxxxxxxxxx>

On Wed, 20 Jan 2021 at 12:51, Takashi Iwai <tiwai@xxxxxxx> wrote:
>
> dvb_usb_device_init() copies the properties to the own data, so that
> the callers can release the original properties later (as done in the
> commit 299c7007e936 "media: dw2102: Fix memleak on sequence of
> probes").  However, it also stores dev->desc pointer that is a
> reference to the original properties data.  Since dev->desc is
> referred later, it may result in use-after-free, in the worst case,
> leading to a kernel Oops as reported.
>
> This patch addresses the problem by allocating and copying the
> properties at first, then get the desc from the copied properties.
>
> Reported-and-tested-by: Stefan Seyfried <seife+kernel@xxxxxxxxxxxxxx>
> BugLink: http://bugzilla.opensuse.org/show_bug.cgi?id=1181104
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> ---
>  drivers/media/usb/dvb-usb/dvb-usb-init.c | 23 +++++++++++++----------
>  1 file changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> index 5befec87f26a..07ff9b4d2f34 100644
> --- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
> +++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> @@ -255,27 +255,30 @@ int dvb_usb_device_init(struct usb_interface *intf,
>         if (du != NULL)
>                 *du = NULL;
>
> -       if ((desc = dvb_usb_find_device(udev, props, &cold)) == NULL) {
> +       d = kzalloc(sizeof(struct dvb_usb_device), GFP_KERNEL);
> +       if (!d) {
> +               err("no memory for 'struct dvb_usb_device'");
> +               return -ENOMEM;
> +       }
> +
> +       memcpy(&d->props, props, sizeof(struct dvb_usb_device_properties));
> +
> +       desc = dvb_usb_find_device(udev, &d->props, &cold);
> +       if (!desc) {
>                 deb_err("something went very wrong, device was not found in current device list - let's see what comes next.\n");
> -               return -ENODEV;
> +               ret = -ENODEV;
> +               goto error;
>         }
>
>         if (cold) {
>                 info("found a '%s' in cold state, will try to load a firmware", desc->name);
>                 ret = dvb_usb_download_firmware(udev, props);
>                 if (!props->no_reconnect || ret != 0)
> -                       return ret;
> +                       goto error;
>         }
>
>         info("found a '%s' in warm state.", desc->name);
> -       d = kzalloc(sizeof(struct dvb_usb_device), GFP_KERNEL);
> -       if (d == NULL) {
> -               err("no memory for 'struct dvb_usb_device'");
> -               return -ENOMEM;
> -       }
> -
>         d->udev = udev;
> -       memcpy(&d->props, props, sizeof(struct dvb_usb_device_properties));
>         d->desc = desc;
>         d->owner = owner;
>
> --
> 2.26.2
>