linux-kernel - Re: [PATCH v5 0/3] close

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Date:   Wed, 3 Jun 2020 01:33:55 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kyle Evans <self@...e-evans.net>,
        Victor Stinner <victor.stinner@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Jann Horn <jannh@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Shuah Khan <shuah@...nel.org>,
        David Howells <dhowells@...hat.com>,
        "Dmitry V. Levin" <ldv@...linux.org>
Subject: Re: [PATCH v5 0/3] close_range()

On Tue, Jun 02, 2020 at 02:03:09PM -0700, Linus Torvalds wrote:
> On Tue, Jun 2, 2020 at 1:42 PM Christian Brauner
> <christian.brauner@...ntu.com> wrote:
> >
> > This is a resend of the close_range() syscall, as discussed in [1]. There weren't any outstanding
> > discussions anymore and this was in mergeable shape. I simply hadn't gotten around to moving this
> > into my for-next the last few cycles and then forgot about it. Thanks to Kyle and the Python people,
> > and others for consistenly reminding me before every merge window and mea culpa for not moving on
> > this sooner. I plan on moving this into for-next after v5.8-rc1 has been released and targeting the
> > v5.9 merge window.
> 
> Btw, I did have one reaction that I can't find in the original thread,
> which probably means that it got lost.
> 
> If one of the designed uses for this is for dropping file descriptors
> just before execve(), it's possible that we'd want to have the option
> to say "unshare my fd array" as part of close_range().
> 
> Yes, yes, you can do
> 
>         unshare(CLONE_FILES);
>         close_range(3,~0u);
> 
> to do it as two operations (and you had that as the example typical
> use), but it would actually be better to be able to do
> 
>         close_range(3, ~0ul, CLOSE_RANGE_UNSHARE);
> 
> instead. Because otherwise we just waste time copying the file
> descriptors first in the unshare, and then closing them after.. Double
> the work..
> 
> And maybe this _did_ get mentioned last time, and I just don't find
> it. I also don't see anything like that in the patches, although the
> flags argument is there.

I spent some good time digging and I couldn't find this mentioned
anywhere so maybe it just never got sent to the list?
It sounds pretty useful, so yeah let me add a patch for this tomorrow.

Christian