Re: [PULL v2 17/61] virtio-snd: check for invalid param shift operands

[Volker Rümelin]

> From: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
>
> When setting the parameters of a PCM stream, we compute the bit flag
> with the format and rate values as shift operand to check if they are
> set in supported_formats and supported_rates.
>
> If the guest provides a format/rate value which when shifting 1 results
> in a value bigger than the number of bits in
> supported_formats/supported_rates, we must report an error.
>
> Previously, this ended up triggering the not reached assertions later
> when converting to internal QEMU values.
>
> Reported-by: Zheyu Ma <zheyuma97@gmail.com>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2416
> Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
> Message-Id: <virtio-snd-fuzz-2416-fix-v1-manos.pitsidianakis@linaro.org>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  hw/audio/virtio-snd.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/hw/audio/virtio-snd.c b/hw/audio/virtio-snd.c
> index e6432ac959..e5196aa4bb 100644
> --- a/hw/audio/virtio-snd.c
> +++ b/hw/audio/virtio-snd.c
> @@ -282,11 +282,13 @@ uint32_t virtio_snd_set_pcm_params(VirtIOSound *s,
>          error_report("Number of channels is not supported.");
>          return cpu_to_le32(VIRTIO_SND_S_NOT_SUPP);
>      }
> -    if (!(supported_formats & BIT(params->format))) {

Hi Manos,

this patch doesn't work as intended. I guess you wanted to write

    if (params->format >= sizeof(supported_formats) * BITS_PER_BYTE ||
        !(supported_formats & BIT(params->format))) {

> +    if (BIT(params->format) > sizeof(supported_formats) ||
> +        !(supported_formats & BIT(params->format))) {
>          error_report("Stream format is not supported.");
>          return cpu_to_le32(VIRTIO_SND_S_NOT_SUPP);
>      }
> -    if (!(supported_rates & BIT(params->rate))) {

    if (params->rate >= sizeof(supported_rates) * BITS_PER_BYTE ||
        !(supported_rates & BIT(params->rate))) {

With best regards,
Volker

> +    if (BIT(params->rate) > sizeof(supported_rates) ||
> +        !(supported_rates & BIT(params->rate))) {
>          error_report("Stream rate is not supported.");
>          return cpu_to_le32(VIRTIO_SND_S_NOT_SUPP);
>      }