[PATCH] ALSA: pcm: fix divide error in snd_pcm_lib_ioctl

[Takashi Iwai]

On Fri, 27 Aug 2021 02:48:21 +0200,
Zubin Mithra wrote:
> 
> Syzkaller reported a divide error in snd_pcm_lib_ioctl. fifo_size
> is of type snd_pcm_uframes_t(unsigned long). If frame_size
> is 0x100000000, the error occurs.
> 
> Fixes: a9960e6a293e ("ALSA: pcm: fix fifo_size frame calculation")
> Signed-off-by: Zubin Mithra <zsm at chromium.org>
> ---
>  sound/core/pcm_lib.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> index 7d5883432085..e41b4e01aa37 100644
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -1746,7 +1746,7 @@ static int snd_pcm_lib_ioctl_fifo_size(struct snd_pcm_substream *substream,
>  		channels = params_channels(params);
>  		frame_size = snd_pcm_format_size(format, channels);
>  		if (frame_size > 0)
> -			params->fifo_size /= (unsigned)frame_size;
> +			params->fifo_size /= (unsigned long)frame_size;

I guess we can drop the cast completely, instead?
It'd be less ugliness.


Thanks!

Takashi