linux-kernel - Re: IMA policy search speedup

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Message-ID: <20120919044651.GY13973@ZenIV.linux.org.uk>
Date:	Wed, 19 Sep 2012 05:46:51 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	James Morris <jmorris@...ei.org>
Cc:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org,
	linux-security-module <linux-security-module@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Subject: Re: IMA policy search speedup

On Wed, Sep 19, 2012 at 02:21:56PM +1000, James Morris wrote:
> On Tue, 18 Sep 2012, Kasatkin, Dmitry wrote:
> 
> > I looked to <linux/fs.h> and found that there is a possibility to to
> > add additional flag for sb->s_flags.
> > For example
> > 
> > #define MS_NOT_IMA              (1<<25) /* NOT_IMA */
> > #define IS_I_NOT_IMA(inode)   __IS_FLG(inode, MS_NOT_IMA)
> > 
> > 
> > Another way is to add additional dedicated integrity related member to
> > the sb structure.
> > struct super_block {
> > ...
> > #ifdef CONFIG_INTEGRITY
> >       int s_integrity;
> > #endif
> > };
> > 
> > Obviously there are only few super blocks in the system and few bytes
> > will not harm.
> 
> The flag seems better than adding a new struct member.  Why would you need 
> an int for this?

Per-superblock bit would be a bit better, but I really hate the way we have
them mixed up between superblock ->s_flags bits and mount(2) action weirdly
encoded into flags thing.  If we are going to touch that thing, how about
separate S_... bits, with MS_... crap left only for mount(2) decoding?  Mapped
to S_... when needed.

The really messy part is that right now we silently ignore all the unknown
bits in mount(2) flags argument ;-/  It's *not* a widely used syscall, but
still - changing that in a non-trivial way is potential userland breakage.
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