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From: Rich Felker <dalias@libc.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: musl@lists.openwall.com, Michael Forney <mforney@mforney.org>,
	ALSA Development Mailing List <alsa-devel@alsa-project.org>,
	Takashi Iwai <tiwai@suse.com>,
	Baolin Wang <baolin.wang@linaro.org>,
	y2038 Mailman List <y2038@lists.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Mark Brown <broonie@kernel.org>,
	Baolin Wang <baolin.wang7@gmail.com>
Subject: Re: [musl] Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control
Date: Fri, 8 Oct 2021 13:20:10 -0400	[thread overview]
Message-ID: <20211008172010.GG7074@brightrain.aerifal.cx> (raw)
In-Reply-To: <CAK8P3a2=X5tPppmcV4x9=pyodiPfoq=tA5jVKuMwA1nKJe=_bA@mail.gmail.com>

On Fri, Oct 08, 2021 at 02:37:12PM +0200, Arnd Bergmann wrote:
> On Fri, Oct 8, 2021 at 2:06 PM Rich Felker <dalias@libc.org> wrote:
> > On Fri, Oct 08, 2021 at 11:24:39AM +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?
> >
> > If the attempted 64-bit ioctl is missing (ENOTTY), it does the
> > conversion to the legacy 32-bit one and retries with that, then
> > converts the results back to the 64-bit form.
> 
> I understand that it tries to do that.
> 
> The part that I'm not sure about is which of the two possible
> 64-bit forms it's using -- the broken one we have defined in the
> kernel headers, or the one we were trying to define but failed.

It's attempting to convert the intended format, not the one that the
uapi headers defined. That is, it's taking padded-to-64-bit values at
offsets 0 and 8 in __snd_pcm_mmap_control64, putting them at offsets 0
and 4 in the 32-bit struct, and padding them back to 64-bit in the
result.

Since applications would have been compiled with the buggy
(unintended) version of the uapi headers, this will not match the
application's layout of the struct. I haven't worked through what all
the consequences of that are, but I think some fix is needed here in
musl regardless of what happens on the kernel side.

Rich

WARNING: multiple messages have this Message-ID (diff)
From: Rich Felker <dalias@libc.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: ALSA Development Mailing List <alsa-devel@alsa-project.org>,
	Baolin Wang <baolin.wang@linaro.org>,
	y2038 Mailman List <y2038@lists.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	musl@lists.openwall.com, Takashi Iwai <tiwai@suse.com>,
	Michael Forney <mforney@mforney.org>,
	Mark Brown <broonie@kernel.org>,
	Baolin Wang <baolin.wang7@gmail.com>
Subject: Re: [musl] Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control
Date: Fri, 8 Oct 2021 13:20:10 -0400	[thread overview]
Message-ID: <20211008172010.GG7074@brightrain.aerifal.cx> (raw)
In-Reply-To: <CAK8P3a2=X5tPppmcV4x9=pyodiPfoq=tA5jVKuMwA1nKJe=_bA@mail.gmail.com>

On Fri, Oct 08, 2021 at 02:37:12PM +0200, Arnd Bergmann wrote:
> On Fri, Oct 8, 2021 at 2:06 PM Rich Felker <dalias@libc.org> wrote:
> > On Fri, Oct 08, 2021 at 11:24:39AM +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?
> >
> > If the attempted 64-bit ioctl is missing (ENOTTY), it does the
> > conversion to the legacy 32-bit one and retries with that, then
> > converts the results back to the 64-bit form.
> 
> I understand that it tries to do that.
> 
> The part that I'm not sure about is which of the two possible
> 64-bit forms it's using -- the broken one we have defined in the
> kernel headers, or the one we were trying to define but failed.

It's attempting to convert the intended format, not the one that the
uapi headers defined. That is, it's taking padded-to-64-bit values at
offsets 0 and 8 in __snd_pcm_mmap_control64, putting them at offsets 0
and 4 in the 32-bit struct, and padding them back to 64-bit in the
result.

Since applications would have been compiled with the buggy
(unintended) version of the uapi headers, this will not match the
application's layout of the struct. I haven't worked through what all
the consequences of that are, but I think some fix is needed here in
musl regardless of what happens on the kernel side.

Rich

  reply	other threads:[~2021-10-08 17:20 UTC|newest]

Thread overview: 94+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-11 21:20 [PATCH v7 0/8] Fix year 2038 issue for sound subsystem Arnd Bergmann
2019-12-11 21:20 ` [alsa-devel] " Arnd Bergmann
2019-12-11 21:20 ` [PATCH v7 1/9] ALSA: Replace timespec with timespec64 Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2019-12-11 21:20 ` [PATCH v7 2/9] ALSA: Avoid using timespec for struct snd_timer_status Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2019-12-11 21:20 ` [PATCH v7 3/9] ALSA: Avoid using timespec for struct snd_ctl_elem_value Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2019-12-11 21:20 ` [PATCH v7 4/9] ALSA: Avoid using timespec for struct snd_pcm_status Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2019-12-11 21:20 ` [PATCH v7 5/9] ALSA: Avoid using timespec for struct snd_rawmidi_status Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2019-12-11 21:20 ` [PATCH v7 6/9] ALSA: Avoid using timespec for struct snd_timer_tread Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2019-12-12  0:14   ` [Y2038] " Ben Hutchings
2019-12-12  0:14     ` [alsa-devel] " Ben Hutchings
2019-12-12  9:57     ` Arnd Bergmann
2019-12-12  9:57       ` [alsa-devel] " Arnd Bergmann
2019-12-12 14:27       ` Ben Hutchings
2019-12-12 14:27         ` [alsa-devel] " Ben Hutchings
2019-12-13 10:25         ` Arnd Bergmann
2019-12-13 10:25           ` [alsa-devel] " Arnd Bergmann
2019-12-11 21:20 ` [PATCH v7 7/9] ALSA: move snd_pcm_ioctl_sync_ptr_compat into pcm_native.c Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2019-12-11 21:20 ` [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2021-10-06 17:49   ` Michael Forney
2021-10-06 17:49     ` Michael Forney
2021-10-07 10:52     ` Takashi Iwai
2021-10-07 10:52       ` Takashi Iwai
2021-10-07 11:48       ` Arnd Bergmann
2021-10-07 11:48         ` Arnd Bergmann
2021-10-07 12:43         ` Takashi Iwai
2021-10-07 12:43           ` Takashi Iwai
2021-10-07 13:02           ` Takashi Iwai
2021-10-07 13:02             ` Takashi Iwai
2021-10-07 13:11           ` Arnd Bergmann
2021-10-07 13:11             ` Arnd Bergmann
2021-10-07 15:33             ` Takashi Iwai
2021-10-07 15:33               ` Takashi Iwai
2021-10-07 16:06               ` [musl] " Rich Felker
2021-10-07 16:06                 ` Rich Felker
2021-10-07 16:18                 ` Takashi Iwai
2021-10-07 16:18                   ` Takashi Iwai
2021-10-07 16:51                   ` Rich Felker
2021-10-07 16:51                     ` Rich Felker
2021-10-08  8:43                     ` Takashi Iwai
2021-10-08  8:43                       ` Takashi Iwai
2021-10-08  8:44                       ` Takashi Iwai
2021-10-08  8:44                         ` Takashi Iwai
2021-10-08  9:24                       ` Arnd Bergmann
2021-10-08  9:24                         ` Arnd Bergmann
2021-10-08 11:11                         ` Takashi Iwai
2021-10-08 11:11                           ` Takashi Iwai
2021-10-08 11:45                           ` Arnd Bergmann
2021-10-08 11:45                             ` Arnd Bergmann
2021-10-08 11:53                             ` Takashi Iwai
2021-10-08 11:53                               ` Takashi Iwai
2021-10-08 12:13                               ` Arnd Bergmann
2021-10-08 12:13                                 ` Arnd Bergmann
2021-10-08 12:07                           ` Rich Felker
2021-10-08 12:07                             ` Rich Felker
2021-10-10  7:53                             ` Takashi Iwai
2021-10-10  7:53                               ` Takashi Iwai
2021-10-18 14:43                               ` Rich Felker
2021-10-18 14:43                                 ` Rich Felker
2021-10-18 14:58                                 ` Takashi Iwai
2021-10-18 14:58                                   ` Takashi Iwai
2021-10-18 15:08                                   ` Rich Felker
2021-10-18 15:08                                     ` Rich Felker
2021-10-18 15:26                                     ` Arnd Bergmann
2021-10-18 15:26                                       ` Arnd Bergmann
2021-10-18 20:42                                       ` Rich Felker
2021-10-18 20:42                                         ` Rich Felker
2021-10-19 14:16                                         ` Rich Felker
2021-10-19 14:16                                           ` Rich Felker
2021-10-19 14:23                                           ` Arnd Bergmann
2021-10-19 14:23                                             ` Arnd Bergmann
2021-10-08 12:06                         ` Rich Felker
2021-10-08 12:06                           ` Rich Felker
2021-10-08 12:37                           ` Arnd Bergmann
2021-10-08 12:37                             ` Arnd Bergmann
2021-10-08 17:20                             ` Rich Felker [this message]
2021-10-08 17:20                               ` Rich Felker
2019-12-11 21:20 ` [PATCH v7 9/9] ALSA: bump uapi version numbers Arnd Bergmann
2019-12-11 21:20   ` [alsa-devel] " Arnd Bergmann
2019-12-17 10:42 ` [PATCH v7 0/8] Fix year 2038 issue for sound subsystem Takashi Iwai
2019-12-17 10:42   ` [alsa-devel] " Takashi Iwai
2019-12-17 21:15   ` Arnd Bergmann
2019-12-17 21:15     ` [alsa-devel] " Arnd Bergmann
2019-12-17 21:16     ` [GIT PULL, v8] " Arnd Bergmann
2019-12-17 21:16       ` [alsa-devel] " Arnd Bergmann
2019-12-17 22:22     ` [PATCH v7 0/8] " Takashi Iwai
2019-12-17 22:22       ` [alsa-devel] " Takashi Iwai

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