linux-kernel - Re: [PATCH (mmotm-2008-12-02-17-08)] Introduce security_path

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Date:	Sat, 6 Dec 2008 08:27:45 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	sds@...ho.nsa.gov, viro@...iv.linux.org.uk, miklos@...redi.hu
Cc:	serue@...ibm.com, jmorris@...ei.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, takedakn@...data.co.jp,
	haradats@...data.co.jp, penguin-kernel@...ove.SAKURA.ne.jp
Subject: Re: [PATCH (mmotm-2008-12-02-17-08)] Introduce security_path_set/clear() hooks.

Hello.

Stephen Smalley wrote:
> > Right. Locations of inserting security_path_set()/security_path_clear() pairs
> > are subset of mnt_want_write()/mnt_drop_write() pairs. Thus, we can insert
> > security_path_set()/security_path_clear() pairs into
> > mnt_want_write()/mnt_drop_write() pairs, if we can tolerate performance
> > regression. According to our rough measurement, there is about 8 - 22% of
> > performance regression. But this approach needs minimum modification to the
> > existing kernel (only two hooks to be inserted).
> 
> I assume you also need separate hooks to cover the read-only open case?

security_dentry_open() receives "struct file *", so I think we don't need
separate hooks for open(O_RDONLY).

> As for your performance, your implementation of mp_* is clearly
> non-optimal, so I'd expect there is plenty of room for improvement
> there.

Yes. Thus, I want to pass a caller identifier to mnt_want_write() so that
we can skip calculating vfsmount's pathname when it is not interested for
a LSM module (e.g. mnt_want_write() called for updating atime/ctime/mtime
checks).
May I add "int caller_id" to mnt_want_write()?

> No #ifdef's within the functions, of course.  That gets handled by
> security.h.
OK.

Regards.
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