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

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Message-ID: <20190821235534.GA9511@lst.de>
Date:   Thu, 22 Aug 2019 01:55:34 +0200
From:   Christoph Hellwig <hch@....de>
To:     Guillem Jover <guillem@...rons.org>
Cc:     linux-aio@...ck.org, Christoph Hellwig <hch@....de>,
        Jeff Moyer <jmoyer@...hat.com>,
        Benjamin LaHaise <bcrl@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] aio: Fix io_pgetevents() struct __compat_aio_sigset
 layout

On Wed, Aug 21, 2019 at 05:38:20AM +0200, Guillem Jover 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 members 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: 7a074e96 ("aio: implement io_pgetevents")
> Signed-off-by: Guillem Jover <guillem@...rons.org>

Looks good,

Reviewed-by: Christoph Hellwig <hch@....de>