Re: [PATCH v1 1/1] virtio-snd: add max size bounds check in input cb

[Philippe Mathieu-Daudé]

On 8/7/24 09:09, Manos Pitsidianakis wrote:
> When reading input audio in the virtio-snd input callback,
> virtio_snd_pcm_in_cb(), we do not check whether the iov can actually fit
> the data buffer. This is because we use the buffer->size field as a
> total-so-far accumulator instead of byte-size-left like in TX buffers.
>
> This triggers an out of bounds write if the size of the virtio queue
> element is equal to virtio_snd_pcm_status, which makes the available
> space for audio data zero. This commit adds a check for reaching the
> maximum buffer size before attempting any writes.
>
> Reported-by: Zheyu Ma <zheyuma97@gmail.com>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2427
> Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
> ---
>   hw/audio/virtio-snd.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/hw/audio/virtio-snd.c b/hw/audio/virtio-snd.c
> index 5993f4f040..e6432ac959 100644
> --- a/hw/audio/virtio-snd.c
> +++ b/hw/audio/virtio-snd.c
> @@ -1261,7 +1261,7 @@ static void virtio_snd_pcm_in_cb(void *data, int 
> available)
>   {
>       VirtIOSoundPCMStream *stream = data;
>       VirtIOSoundPCMBuffer *buffer;
> -    size_t size;
> +    size_t size, max_size;
>   
>       WITH_QEMU_LOCK_GUARD(&stream->queue_mutex) {
>           while (!QSIMPLEQ_EMPTY(&stream->queue)) {
> @@ -1275,7 +1275,12 @@ static void virtio_snd_pcm_in_cb(void *data, int 
> available)
>                   continue;
>               }
>   
> +            max_size = iov_size(buffer->elem->in_sg, buffer->elem->in_num);
>               for (;;) {
> +                if (buffer->size >= max_size) {
> +                    return_rx_buffer(stream, buffer);

return_rx_buffer() could be renamed
flush_input_stream_to_buffer() for clarity.

I suspect virtio_snd_pcm_in_cb() has a high complexity. Anyhow,

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

> +                    break;
> +                }
>                   size = AUD_read(stream->voice.in,
>                           buffer->data + buffer->size,
>                           MIN(available, (stream->params.period_bytes -
>
> base-commit: b9ee1387e0cf0fba5a73a610d31cb9cead457dc0