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

[Zubin Mithra]

On Fri, Aug 27, 2021 at 08:05:00AM +0200, Takashi Iwai wrote:
> 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.

Sounds good, thanks, I've sent out a v2.

> 
> 
> Thanks!
> 
> Takashi