linux-kernel - Re: [TOMOYO #9 (2.6.27-rc7-mm1) 1/6] LSM adapter functions.

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Date:	Mon, 6 Oct 2008 11:54:46 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Kentaro Takeda <takedakn@...data.co.jp>
Cc:	Valdis.Kletnieks@...edu, Casey Schaufler <casey@...aufler-ca.com>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, haradats@...data.co.jp,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [TOMOYO #9 (2.6.27-rc7-mm1) 1/6] LSM adapter functions.

Quoting Kentaro Takeda (takedakn@...data.co.jp):
> Serge E. Hallyn wrote:
> > Why can't you just clear the value during security_inode_foo()?
> We need a new hook for clearing the value since security_inode_*() 
> are not always called after security_path_*() .

Heh, obviously you're right :)

So I'd recommend floating your security_path_clear() patch with a clear
description about the DAC-before-MAC property which you are maintaining.
Someone may come up with a better overall solution, but we're unlikely
to hear it until you try to push your patch.

-serge

> > Note I'm seeing this as a way for Tomoyo to temporarily (maybe) work
> > around the mis-placement of the security_path_foo() hooks.  I don't want
> > to add security_path_clear() hooks to "legitimize" the workaround.  I'd
> > rather Tomoyo and Apparmor folks keep looking for a better way to get
> > real DAC-before-MAC.
> Hmm, I can understand your opinion. The best way for AppArmor and 
> TOMOYO is to pass vfsmount to vfs_*() and security_inode_*() . This 
> approach has no DAC-before-MAC problem. However, it is clearly 
> opposed by Al because of layering. So, we are going forward 
> security_path_*() approach, which Al advised us.
> 
> Since vfsmount is only available outside vfs_*() (and vfs_*() perform 
> DAC), we cannot conceive another place now... Where do you think the 
> right place to introduce security_path_*() hooks is?
> 
> Regards,
> 
> --
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