Virtualization - Nov 2022 - [PATCH v3] vduse: Validate vq_num in vduse_validate_config()

On Mon, Nov 28, 2022 at 11:57 PM Harshit Mogalapalli
<harshit.m.mogalapalli at oracle.com> wrote:
>
> Add a limit to 'config->vq_num' which is user controlled data
which
> comes from an vduse_ioctl to prevent large memory allocations.
>
> Micheal says  - This limit is somewhat arbitrary.
> However, currently virtio pci and ccw are limited to a 16 bit vq number.
> While MMIO isn't it is also isn't used with lots of VQs due to
> current lack of support for per-vq interrupts.
> Thus, the 0xffff limit on number of VQs corresponding
> to a 16-bit VQ number seems sufficient for now.
>
> This is found using static analysis with smatch.
>
> Suggested-by: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli at
oracle.com>
Acked-by: Jason Wang <jasowang at redhat.com>

Thanks
> ---
> v1->v2: Change title of the commit and description, add a limit to
>         vq_num.
>
> v2->v3: Improve commit message to include reason for setting limit to
>         0xffff
>
> Only compile and boot tested.
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c
b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 35dceee3ed56..31017ebc4d7c 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -1440,6 +1440,9 @@ static bool vduse_validate_config(struct
vduse_dev_config *config)
>         if (config->config_size > PAGE_SIZE)
>                 return false;
>
> +       if (config->vq_num > 0xffff)
> +               return false;
> +
>         if (!device_is_allowed(config->device_id))
>                 return false;
>
> --
> 2.38.1
>