From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Linux API <linux-api@vger.kernel.org>,
Linus Walleij <linus.walleij@linaro.org>,
QEMU Developers <qemu-devel@nongnu.org>,
Florian Weimer <fw@deneb.enyo.de>,
Andreas Dilger <adilger.kernel@dilger.ca>,
Andy Lutomirski <luto@kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Ext4 Developers List <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH] fcntl: Add 32bit filesystem mode
Date: Mon, 20 Apr 2020 13:01:31 -0400 [thread overview]
Message-ID: <20200420170131.GD1080594@mit.edu> (raw)
In-Reply-To: <CAFEAcA9BQQah2vVfnwO4-3m4eHv9QtfvjvDpTdw+SmqicsDOMA@mail.gmail.com>
On Mon, Apr 20, 2020 at 04:29:32PM +0100, Peter Maydell wrote:
> On Mon, 20 Apr 2020 at 16:24, Eric Blake <eblake@redhat.com> wrote:
> > It will be interesting to find how much code (wrongly) assumes it can
> > use a blind assignment of fcntl(fd, F_SETFD, 1) and thereby accidentally
> > wipes out other existing flags, when it should have instead been doing a
> > read-modify-write to protect flags other than FD_CLOEXEC.
>
> For instance, a quick grep shows 4 instances of this in QEMU :-)
Fortunately, most applications aren't going to be interested in
forcing 32-bit mode for 64-bit applications, QEMU being the notable
exception. We do need to make sure that for 32-bit applications, we
either make FD_32BIT_MODE a no-op (don't set the bit, and ignore the
bit). We could allow the bit to be visible for 32-bit applications,
but we would want to disallow clearing the the bit for 32-bit
applications if it was visible.
If we did that, then blind assignments of fcntl(fd, F_SETFD, 1) should
be mostly harmless with respect to the FD_32BIT_MODE bit.
- Ted
prev parent reply other threads:[~2020-04-20 17:02 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-31 13:35 [PATCH] fcntl: Add 32bit filesystem mode Linus Walleij
2020-04-20 11:19 ` Peter Maydell
2020-04-20 11:23 ` Florian Weimer
2020-04-20 11:38 ` Peter Maydell
2020-04-20 14:16 ` Peter Maydell
2020-04-20 23:51 ` Andreas Dilger
2020-04-21 13:02 ` Peter Maydell
2020-04-20 15:13 ` Theodore Y. Ts'o
2020-04-20 15:23 ` Eric Blake
2020-04-20 15:29 ` Peter Maydell
2020-04-20 17:01 ` Theodore Y. Ts'o [this message]
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