linux-kernel - Re: [PATCH v2] aio: Fix io_pgetevents() struct __compat_aio

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Message-ID: <CAK8P3a1OOz2fSgn1YMGxdL+_ZSb5Wc0sAcROfaX=xfJANKpxjQ@mail.gmail.com>
Date:   Tue, 22 Oct 2019 14:45:07 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Guillem Jover <guillem@...rons.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
        linux-aio <linux-aio@...ck.org>, Christoph Hellwig <hch@....de>,
        Jeff Moyer <jmoyer@...hat.com>,
        Benjamin LaHaise <bcrl@...ck.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] aio: Fix io_pgetevents() struct __compat_aio_sigset layout

On Tue, Oct 22, 2019 at 12:49 AM Guillem Jover <guillem@...rons.org> wrote:
>
> This type is used to pass the sigset_t from userland to the kernel,
> but it was using the kernel native pointer type for the member
> representing the compat userland pointer to the userland sigset_t.
>
> This messes up the layout, and makes the kernel eat up both the
> userland pointer and the size into the kernel pointer, and then
> reads garbage into the kernel sigsetsize. Which makes the sigset_t
> size consistency check fail, and consequently the syscall always
> returns -EINVAL.
>
> This breaks both libaio and strace on 32-bit userland running on 64-bit
> kernels. And there are apparently no users in the wild of the current
> broken layout (at least according to codesearch.debian.org and a brief
> check over github.com search). So it looks safe to fix this directly
> in the kernel, instead of either letting userland deal with this
> permanently with the additional overhead or trying to make the syscall
> infer what layout userland used, even though this is also being worked
> around in libaio to temporarily cope with kernels that have not yet
> been fixed.
>
> We use a proper compat_uptr_t instead of a compat_sigset_t pointer.
>
> Fixes: 7a074e96dee6 ("aio: implement io_pgetevents")
> Signed-off-by: Guillem Jover <guillem@...rons.org>

When resending a patch that has already been reviewed, please
add the tags you received so they get picked up into the final
changeset as well:

Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Jeff Moyer <jmoyer@...hat.com>

Let's make sure this also gets added to stable kernels

Cc: <stable@...r.kernel.org> # v4.18+

Finally (if you like)
Reviewed-by: Arnd Bergmann <arnd@...db.de>

     Arnd