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Date: Wed, 21 Jan 2015 10:17:29 +1100 (AEDT)
From: James Morris <jmorris@namei.org>
To: Ben Hutchings <ben@decadent.org.uk>
cc: Alexander Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org,
        linux-security-module@vger.kernel.org,
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        Paul Moore <paul@paul-moore.com>, Stephen Smalley <sds@tycho.nsa.gov>,
        Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [RFC PATCH RESEND] vfs: Move security_inode_killpriv() after
 permission checks
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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@namei.org>