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Date: Mon, 21 Sep 2020 06:28:15 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag
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References: <20200918124533.3487701-1-hch@lst.de> <20200918124533.3487701-2-hch@lst.de> <20200920151510.GS32101@casper.infradead.org> <20200920180742.GN3421308@ZenIV.linux.org.uk> <CALCETrWHW4wHG+Z-mxsY-kvjSi+S6gRUQ+LHd9syPcm5bhi3cw@mail.gmail.com>
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To: Andy Lutomirski <luto@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Matthew Wilcox <willy@infradead.org>, Christoph Hellwig <hch@lst.de>, Andrew Morton <akpm@linux-foundation.org>, Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>, David Howells <dhowells@redhat.com>, linux-arm-kernel <linux-arm-kernel@lists.infradead.org>, X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>, "open list:MIPS" <linux-mips@vger.kernel.org>, Parisc List <linux-parisc@vger.kernel.org>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, linux-s390 <linux-s390@vger.kernel.org>, sparclinux <sparclinux@vger.kernel.org>, linux-block <linux-block@vger.kernel.org>, Linux SCSI List <linux-scsi@vger.kernel.org>, Linux FS Devel <linux-fsdevel@vger.kernel.org>, linux-aio <linux-aio@kvack.org>, io-uring@vger.kernel.org, linux-arch <linux-arch@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, Network Development <netdev@vger.kernel.org>, keyrings@vger.kernel.org, LSM List <linux-security-module@vger.kernel.org>

On Sun, Sep 20, 2020 at 12:14:49PM -0700, Andy Lutomirski wrote:
> I wonder if this is really quite cast in stone.  We could also have
> FMODE_SHITTY_COMPAT and set that when a file like this is *opened* in
> compat mode.  Then that particular struct file would be read and
> written using the compat data format.  The change would be
> user-visible, but the user that would see it would be very strange
> indeed.
> 
> I don't have a strong opinion as to whether that is better or worse
> than denying io_uring access to these things, but at least it moves
> the special case out of io_uring.

open could have happened through an io_uring thread a well, so I don't
see how this would do anything but move the problem to a different
place.

> 
> --Andy
---end quoted text---