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

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Message-ID: <20081001211507.GA28377@us.ibm.com>
Date:	Wed, 1 Oct 2008 16:15:07 -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):
> Valdis.Kletnieks@...edu wrote:
> > On Tue, 30 Sep 2008 19:33:32 PDT, Casey Schaufler said:
> >> I have always believed that MAC should come first, then DAC, because
> >> MAC may care if you can see the mode bits. The current DAC before MAC
> >> is an artifact of the desire for the LSM to behave cleanly as a
> >> strictly additional mechanism. From an ideal security perspective
> >> MAC should be first, but the pragmatic DAC first isn't going to cause
> >> too much grief. If Tomoyo wants to do what I think is the right thing,
> >> well, it's OK with me.
> > I'm OK with the MAC going first as well
> Current implementation is as follows.
> - security_path_*: MAC before DAC
> - security_inode_*: DAC before MAC
> I can understand Casey and Valdis' MAC first approach from the ideal 
> security perspective. However, from the pragmatic perspective, we 
> prefer DAC before MAC approach as SELinux does. This approach doesn't 
> change error code returned to callers if requested access is denied 
> by DAC.
> 
> Regards,

I suppose you could do something like define both _path and _inode,
save away your result from the _path hook but always return 0, there,
then if you'd saved off an error and you make it to the _inode hook,
return the error there...

-serge
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