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Date: Fri, 8 Oct 2021 14:13:16 +0200
From: Arnd Bergmann <>
Cc: Arnd Bergmann <>, Rich Felker <>, Michael Forney <>, 
	ALSA Development Mailing List <>, Takashi Iwai <>, 
	Baolin Wang <>, y2038 Mailman List <>, 
	Linux Kernel Mailing List <>, Mark Brown <>, 
	Baolin Wang <>
Subject: Re: Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit
 layout for snd_pcm_mmap_status/control

On Fri, Oct 8, 2021 at 1:53 PM Takashi Iwai <> wrote:
> On Fri, 08 Oct 2021 13:45:45 +0200, Arnd Bergmann wrote:
> > On Fri, Oct 8, 2021 at 1:11 PM Takashi Iwai <> wrote:
> > > On Fri, 08 Oct 2021 11:24:39 +0200, Arnd Bergmann wrote:
> > > The below is a revised kernel patch (again untested), just correcting
> > > the behavior of 32bit compat mode.  32bit apps on 32bit kernel work
> > > fine as is, as well as 64bit apps on 64bit kernel.
> >
> > Right, this should cover all cases of the ioctl itself misbehaving.
> > In addition, we still need to disallow the mmap() interface on compat
> > kernels then. Strictly speaking, we could allow the snd_pcm_mmap_status
> > but not snd_pcm_mmap_control to be mapped, but I'm not sure if
> > that's better than disallowing both.
> IIRC, the compat mmap is already disallowed even for the
> SNDRV_PCM_MMAP_OFFSET_CONTROL_NEW (in pcm_control_mmap_allowed()), so
> no need to change around that.

Ah, right. I think it was meant to become allowed as part of commit
80fe7430c708 ("ALSA: add new 32-bit layout for snd_pcm_mmap_status/control"),
which did allow the snd_pcm_mmap_status to be mmap()ed, but it appears
to be the rare case where two mistakes cancel out and we don't have to
change the mmap code.


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