Date: Fri, 08 Oct 2021 13:53:15 +0200 From: Takashi Iwai <tiwai@...e.de> To: Arnd Bergmann <arnd@...db.de> Cc: musl@...ts.openwall.com, 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: Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control 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: > > > > > > > I've tried to understand this part of musl's convert_ioctl_struct(), but I just > > > can't figure out whether it does the conversion based the on the layout that > > > is currently used in the kernel, or based on the layout we should have been > > > using, and would use with the above fix. Rich, can you help me here? > > > > So, at this moment, I'm not sure whether we should correct the struct > > at all. This will lead to yet more breakage, and basically the struct > > itself *works* -- the only bug is in 32bit compat handling in the > > kernel (again). > > I'm still unsure if the musl fallback code is correct or not. We need to verify the current behavior in anyway... > > 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. thanks, Takashi
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