linux-kernel - Re: [PATCH 0/2] ima: policy search speedup

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Message-ID: <CA+55aFwhY2+UG-VCGrUk=N3KNXvDudA-QHnDqPbWU5pf4Ty5jw@mail.gmail.com>
Date:	Tue, 11 Dec 2012 10:35:57 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	James Morris <jmorris@...ei.org>
Subject: Re: [PATCH 0/2] ima: policy search speedup

On Tue, Dec 11, 2012 at 10:12 AM, Kasatkin, Dmitry
<dmitry.kasatkin@...el.com> wrote:
>
> Actually S_PRIVATE does not work work for normal filesystems which IMA
> might want to ignore.

The reading comprehension here is abysmal.

First you claim that you need the new flag for pseudo-filesystems, and
now that I point out that we have an *old* flag for pseudo-filesystems
you turn around 180 degrees and talk about other filesystems.

And none of that matters for my argument AT ALL.

My argument has not been that we cannot add a new flag.

My argument has been that we already have the logical place for such a
flag, and that adding a totally new field seems so stupid.

Seriously. The i_flags place is where we already do pretty much
*exactly* what you ask for. The fact that it is faster and more
flexible to boot should be a bonus.

Now, there are real reasons to avoid "s_flags", notably the fact that
we're running out of bits there (unlike i_flags), and they are exposed
as generic fields and are generally meant for mount options etc. So I
understand why we might want to avoid that (although the whole
mount-option thing could also be seen as an advantage), but I really
don't see any argument against i_flags, considering that we already
use it for S_IMA and S_PRIVATE, both of which are related to exactly
what you seem to want to do.

The one downside of i_flags may be that any update should own the
inode semaphore. But within the context of a security model, that
should be fine (and normally you'd update it once per lifetime of the
inode).

                  Linus
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