linux-ext4 - Re: [PATCH v2 1/2] xfs: fix tmpfile/selinux deadlock and initialize security/acl

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Date:	Tue, 15 Apr 2014 21:31:02 +0200 (CEST)
From:	Andreas Gruenbacher <andreas.gruenbacher@...bit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Brian Foster <bfoster@...hat.com>, linux-man@...r.kernel.org,
	xfs@....sgi.com, linux-security-module@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2 1/2] xfs: fix tmpfile/selinux deadlock and initialize
 security/acl

Christoph,

On Tue, Apr 15, 2014 at 10:52:28AM -0700, Christoph Hellwig wrote:
> So any opinions from other fs / security people on how O_TMPFILE files
> should behave for ACL inheritance / labeling?

from how O_TMPFILE is documented right now [*], creating such a file and
then linking it into the namespace is one of the obvious use cases.  The
intent seems to be to make it seem like the file was created and populated
atomically, possibly with inherited permissions and all.  I think this
behavior require that the O_TMPFILE file inherits from the directory it
was "created" in.

Adding code to achieve the effect of create-time inheritance at link
time, only for O_TMPFILE files or files without any links, doesn't seem 
reasonable to me: it would duplicate create code in the link code path,
and it would make it harder to override inherited permissions or labels.

(Trying to fake inheritance by reimplementing it in user space seems like
a much worse idea still.)

[*] http://man7.org/linux/man-pages/man2/open.2.html

Thanks,
Andreas
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