linux-kernel - Re: [RFC][PATCH 0/7] File descriptor labeling

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Message-ID: <4DC18E3B.2000104@schaufler-ca.com>
Date:	Wed, 04 May 2011 10:34:51 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Roberto Sassu <roberto.sassu@...ito.it>
CC:	John Johansen <john.johansen@...onical.com>,
	Tyler Hicks <tyhicks@...ux.vnet.ibm.com>,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	dhowells@...hat.com, jmorris@...ei.org, zohar@...ux.vnet.ibm.com,
	safford@...son.ibm.com, kirkland@...onical.com,
	ecryptfs-devel@...ts.launchpad.net, eparis@...hat.com,
	sds@...ho.nsa.gov, selinux@...ho.nsa.gov, viro@...iv.linux.org.uk,
	apparmor@...ts.ubuntu.com, Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC][PATCH 0/7] File descriptor labeling

On 5/4/2011 1:47 AM, Roberto Sassu wrote:
> On Wednesday, May 04, 2011 01:58:00 AM John Johansen wrote:
>> ....
>> I have to agree with Casey, Generally looping back through the vfs should
>> be using the user's credentials.  This doesn't even stop you opening the
>> lower file with a different set of permissions (eg.  rw while the upper
>> is opened with r).
> Hi Casey and John
>
> my patch set does not modify this behavior:  VFS calls on upper inodes
> made by user processes and VFS calls (read/write) made by eCryptfs
> on lower inodes still use the user's credentials.
>
> In addition, SELinux provide a model for file descriptors. They may be
> opened by another subject (which provided its own credentials) and
> other processes need the 'use' permission for those file descriptors
> other than permissions for related inodes.
>
> This means that, even if eCryptfs opens lower inodes with its own
> credentials, user processes still need permissions to read/write both
> upper and lower inodes.
>
> One benefit of allowing eCryptfs to provide its own credentials is that
> user processes must have granted only strictly required permissions.
>
> Roberto Sassu

My point is that you should be able to achieve all of what you
say you want to do without introducing the LSM changes you are
proposing.

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