Re: [PATCH v5 04/12] S.A.R.A.: generic DFA for string matching

From: Salvatore Mesoraca <s.mesoraca16@gmail.com>
To: Jann Horn <jannh@google.com>
Cc: kernel list <linux-kernel@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Linux-MM <linux-mm@kvack.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Brad Spengler <spender@grsecurity.net>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Christoph Hellwig <hch@infradead.org>,
	Kees Cook <keescook@chromium.org>,
	PaX Team <pageexec@freemail.hu>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	James Morris <jmorris@namei.org>,
	John Johansen <john.johansen@canonical.com>
Subject: Re: [PATCH v5 04/12] S.A.R.A.: generic DFA for string matching
Date: Sun, 7 Jul 2019 18:01:31 +0200	[thread overview]
Message-ID: <CAJHCu1+35GhGJY8jDMPEU8meYhJTVgvzY5sJgVCuLrxCoGgHEg@mail.gmail.com> (raw)
In-Reply-To: <CAG48ez35oJhey5WNzMQR14ko6RPJUJp+nCuAHVUJqX7EPPPokA@mail.gmail.com>

Jann Horn <jannh@google.com> wrote:
>
> On Sat, Jul 6, 2019 at 12:55 PM Salvatore Mesoraca
> <s.mesoraca16@gmail.com> wrote:
> > Creation of a generic Discrete Finite Automata implementation
> > for string matching. The transition tables have to be produced
> > in user-space.
> > This allows us to possibly support advanced string matching
> > patterns like regular expressions, but they need to be supported
> > by user-space tools.
>
> AppArmor already has a DFA implementation that takes a DFA machine
> from userspace and runs it against file paths; see e.g.
> aa_dfa_match(). Did you look into whether you could move their DFA to
> some place like lib/ and reuse it instead of adding yet another
> generic rule interface to the kernel?

Yes, using AppArmor DFA cloud be a possibility.
Though, I didn't know how AppArmor's maintainers feel about this.
I thought that was easier to just implement my own.
Anyway I understand that re-using that code would be the optimal solution.
I'm adding in CC AppArmor's maintainers, let's see what they think about this.

> > +++ b/security/sara/dfa.c
> > @@ -0,0 +1,335 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/*
> > + * S.A.R.A. Linux Security Module
> > + *
> > + * Copyright (C) 2017 Salvatore Mesoraca <s.mesoraca16@gmail.com>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2, as
> > + * published by the Free Software Foundation.
>
> Throughout the series, you are adding files that both add an SPDX
> identifier and have a description of the license in the comment block
> at the top. The SPDX identifier already identifies the license.

I added the license description because I thought it was required anyway.
IANAL, if you tell me that SPDX it's enough I'll remove the description.

Thank you for your comments.