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

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Date:   Sun, 6 Oct 2019 17:49:24 +0100
From:   Salvatore Mesoraca <s.mesoraca16@...il.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux-MM <linux-mm@...ck.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Brad Spengler <spender@...ecurity.net>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        PaX Team <pageexec@...email.hu>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        James Morris <jmorris@...ei.org>,
        John Johansen <john.johansen@...onical.com>
Subject: Re: [PATCH v5 04/12] S.A.R.A.: generic DFA for string matching

Salvatore Mesoraca <s.mesoraca16@...il.com> wrote:
>
> Jann Horn <jannh@...gle.com> wrote:
> >
> > On Sat, Jul 6, 2019 at 12:55 PM Salvatore Mesoraca
> > <s.mesoraca16@...il.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.

I don't want this to prevent SARA from being up-streamed.
Do you think that having another DFA here could be acceptable anyway?
Would it be better if I just drop the DFA an go back to simple string
matching to speed up things?

Thank you,

Salvatore