linux-kernel - Re: [PATCH 0/6] File Sealing & memfd

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Message-ID: <CALCETrXFJfoD9xrYpu6UjsHF74kYm3_o-xLNKjqh-OF2x-nyFQ@mail.gmail.com>
Date:	Thu, 10 Apr 2014 16:05:34 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Kay Sievers <kay@...y.org>, Daniel Mack <zonque@...il.com>,
	Lennart Poettering <lennart@...ttering.net>,
	John Stultz <john.stultz@...aro.org>,
	Greg Kroah-Hartman <greg@...ah.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ryan Lortie <desrt@...rt.ca>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Subject: Re: [PATCH 0/6] File Sealing & memfd_create()

On Thu, Apr 10, 2014 at 3:57 PM, David Herrmann <dh.herrmann@...il.com> wrote:
> Hi
>
> On Thu, Apr 10, 2014 at 11:16 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> Would it make sense for the initial mode on a memfd inode to be 000?
>> Anyone who finds this to be problematic could use fchmod to fix it.
>
> memfd_create() should be subject to umask() just like anything else.
> That should solve any possible race here, right?

Yes, but how many people will actually think about umask when doing
things that don't really look like creating files?

/proc/pid/fd is a really weird corner case in which the mode of an
inode that doesn't have a name matters.  I suspect that almost no one
will ever want to open one of these things out of /proc/self/fd, and
those who do should be made to think about it.

It also avoids odd screwups where things are secure until someone runs
them with umask 000.

--Andy
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