linux-kernel - Re: [RFC PATCH RESEND] vfs: Move security_inode

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Date:	Wed, 21 Jan 2015 10:17:29 +1100 (AEDT)
From:	James Morris <jmorris@...ei.org>
To:	Ben Hutchings <ben@...adent.org.uk>
cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, 770492@...s.debian.org,
	Ben Harris <bjh21@....ac.uk>, oss-security@...ts.openwall.com,
	John Johansen <john.johansen@...onical.com>,
	Paul Moore <paul@...l-moore.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC PATCH RESEND] vfs: Move security_inode_killpriv() after
 permission checks

On Sat, 17 Jan 2015, Ben Hutchings wrote:

> chown() and write() should clear all privilege attributes on
> a file - setuid, setgid, setcap and any other extended
> privilege attributes.
> 
> However, any attributes beyond setuid and setgid are managed by the
> LSM and not directly by the filesystem, so they cannot be set along
> with the other attributes.
> 
> Currently we call security_inode_killpriv() in notify_change(),
> but in case of a chown() this is too early - we have not called
> inode_change_ok() or made any filesystem-specific permission/sanity
> checks.
> 
> Add a new function setattr_killpriv() which calls
> security_inode_killpriv() if necessary, and change the setattr()
> implementation to call this in each filesystem that supports xattrs.
> This assumes that extended privilege attributes are always stored in
> xattrs.

It'd be useful to get some input from LSM module maintainers on this. 

e.g. doesn't SELinux already handle this via policy directives?


-- 
James Morris
<jmorris@...ei.org>

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