linux-kernel - Re: [musl] Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap

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Message-ID: <CAK8P3a0kg0NQoxC7_cUJfFZkoheAE2A_fQLTGKqgz0wq3L0rvw@mail.gmail.com>
Date:   Fri, 8 Oct 2021 14:13:16 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     musl@...ts.openwall.com
Cc:     Arnd Bergmann <arnd@...db.de>, Rich Felker <dalias@...c.org>,
        Michael Forney <mforney@...rney.org>,
        ALSA Development Mailing List <alsa-devel@...a-project.org>,
        Takashi Iwai <tiwai@...e.com>,
        Baolin Wang <baolin.wang@...aro.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Baolin Wang <baolin.wang7@...il.com>
Subject: Re: [musl] 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 <tiwai@...e.de> wrote:
> On Fri, 08 Oct 2021 13:45:45 +0200, Arnd Bergmann wrote:
> > On Fri, Oct 8, 2021 at 1:11 PM Takashi Iwai <tiwai@...e.de> 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.

         Arnd