linux-kernel - Re: [RFC 0/28] Patches to pass vfsmount to LSM inode security hooks

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Date:	Tue, 06 Feb 2007 07:55:39 -0500
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	Andreas Gruenbacher <agruen@...e.de>
Cc:	Christoph Hellwig <hch@...radead.org>, Tony Jones <tonyj@...e.de>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	chrisw@...s-sol.org, linux-security-module@...r.kernel.org,
	viro@...iv.linux.org.uk
Subject: Re: [RFC 0/28] Patches to pass vfsmount to LSM inode security hooks

On Mon, 2007-02-05 at 18:13 -0800, Andreas Gruenbacher wrote:
> On Monday 05 February 2007 10:44, Christoph Hellwig wrote:
> > Looking at the actual patches I see you're lazy in a lot of places.
> > Please make sure that when you introduce a vfsmount argument somewhere
> > that it is _always_ passed and not just when it's conveniant.  Yes, that's
> > more work, but then again if you're not consistant anyone half-serious
> > will laught at a security model using this infrasturcture.
> 
> It may appear like laziness, but it's not. Let's look at where we're passing 
> NULL at the moment:
> 
> fs/hpfs/namei.c
> 
> 	In hpfs_unlink, hpfs truncates one of its own inodes through
> 	notify_change(). You definitely don't want any lsms to interfere here,
> 	pathname based or not; hpfs should probably truncate its inode itself
> 	instead. But given that hpfs goes via the vfs, we at least pass NULL
> 	to indicate that this file really has no meaningful paths to it
> 	anymore. (In addition, we don't really have a vfsmount at this
> 	point anymore, and neither would it make sense to pass it there.)
> 
> 	To play more nicely with other lsms, hpfs could mark the inode as
> 	private before attempting the truncate.
> 
> fs/reiserfs/xattr.c
> 
> 	The directories an files that reiserfs uses internally to store xattrs
> 	are hanging off ".reiserfs_priv/xattrs" in the filesystem. This part
> 	of the namespace is not accessible or visible from user space though
> 	except through the xattr syscalls.
> 
> 	Reiserfs should probably just mark all its xattr inodes as private in order
> 	to play nicely with other lsms. As far as pathname based lsms are concerned,
> 	pathnames to those fs-internal objects are meaningless though, and so we
> 	pass NULL here.

That should be handled by the current marking of reiserfs xattr inodes
with S_PRIVATE and the tests for IS_PRIVATE in include/linux/security.h
(and in one instance, within SELinux itself).

-- 
Stephen Smalley
National Security Agency

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