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

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Message-ID: <CAG48ez3v4dpCGBUc16FQDbGEAXtnDDvTq2GQpVax0rLgHEM3_g@mail.gmail.com>
Date:   Mon, 7 Oct 2019 14:40:13 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Salvatore Mesoraca <s.mesoraca16@...il.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

On Sun, Oct 6, 2019 at 6:49 PM Salvatore Mesoraca
<s.mesoraca16@...il.com> wrote:
> 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?

While I think that it would be nicer not to have yet another
implementation of the same thing, I don't feel strongly about it.