linux-kernel - Re: [RFC PATCH v9 0/3] Add introspect_access(2) (was O

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Date:   Thu, 10 Sep 2020 21:05:43 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Mickaël Salaün <mic@...ikod.net>,
        Mimi Zohar <zohar@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        Aleksa Sarai <cyphar@...har.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Christian Heimes <christian@...hon.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Deven Bowers <deven.desai@...ux.microsoft.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Eric Chiang <ericchiang@...gle.com>,
        Florian Weimer <fweimer@...hat.com>,
        James Morris <jmorris@...ei.org>, Jan Kara <jack@...e.cz>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Philippe Trébuchet 
        <philippe.trebuchet@....gouv.fr>,
        Scott Shell <scottsh@...rosoft.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        Steve Dower <steve.dower@...hon.org>,
        Steve Grubb <sgrubb@...hat.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Thibaut Sautereau <thibaut.sautereau@...p-os.org>,
        Vincent Strubel <vincent.strubel@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH v9 0/3] Add introspect_access(2) (was O_MAYEXEC)

On Thu, Sep 10, 2020 at 09:00:10PM +0100, Al Viro wrote:
> On Thu, Sep 10, 2020 at 07:40:33PM +0100, Matthew Wilcox wrote:
> > On Thu, Sep 10, 2020 at 08:38:21PM +0200, Mickaël Salaün wrote:
> > > There is also the use case of noexec mounts and file permissions. From
> > > user space point of view, it doesn't matter which kernel component is in
> > > charge of defining the policy. The syscall should then not be tied with
> > > a verification/integrity/signature/appraisal vocabulary, but simply an
> > > access control one.
> > 
> > permission()?
> 
> int lsm(int fd, const char *how, char *error, int size);
> 
> Seriously, this is "ask LSM to apply special policy to file"; let's
> _not_ mess with flags, etc. for that; give it decent bandwidth
> and since it's completely opaque for the rest of the kernel,
> just a pass a string to be parsed by LSM as it sees fit.

Hang on, it does have some things which aren't BD^W^WLSM.  It lets
the interpreter honour the mount -o noexec option.  I presume it's
not easily defeated by
	cat /home/salaun/bin/bad.pl | perl -