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

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Date:	Tue, 30 Sep 2008 11:23:21 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Stephen Smalley <sds@...ho.nsa.gov>
Cc:	Kentaro Takeda <takedakn@...data.co.jp>,
	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 Stephen Smalley (sds@...ho.nsa.gov):
> 
> On Tue, 2008-09-30 at 10:45 -0500, Serge E. Hallyn wrote:
> > Quoting Kentaro Takeda (takedakn@...data.co.jp):
> > > Serge E. Hallyn wrote:
> > > > Unfortunately I think that is a shortcoming in the security_path_*
> > > > patchset.  Unfortunate bc that is going to be a pain to work out.
> > > Thanks for your constructive and tough suggestion. ;-)
> > > 
> > > > So for starters,
> > > > both vfs_mknod and vfs_create do may_create, so just pull that
> > > > into the callers.
> > > Do you mean that we should move DAC code to all the caller of vfs_* ? 
> > 
> > That's not reasonable, is it.
> > 
> > The rule thus far has been 'DAC before MAC'.  Question to all:  do we
> > insist on keeping it that way?
> 
> It isn't a hard rule; there are already some hooks that occur before the
> DAC checking, e.g. setattr, because the DAC checking happens in the fs
> code as part of the inode op.  But when possible, we prefer DAC before
> MAC for SELinux so that we don't get noise in the audit logs from

Since SELinux won't be using the security_path hooks, it won't be
affected by this, though, right?

Though if we start down the path of mixing dac+mac with _path hooks then
it may get harder to continue to keep that order for other hooks...

> harmless application/library probing that would be denied by DAC anyway.
> Same issue would seemingly apply for learning modes of TOMOYO or
> AppArmor.

Good point.  Kentaro, is that an issue for you?

> > If the answer is yes, then the security_path_hooks patch is inherently
> > wrong.
> > 
> > If the answer is no, then Kentaro doesn't need to resort to this
> > ugliness to try and get may_delete() called before his MAC code, only to
> > have may_delete() called a second time from the vfs_* functions.
> 
> -- 
> Stephen Smalley
> National Security Agency
> 
> --
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