linux-kernel - Re: [PATCH v3 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount property

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Message-ID: <alpine.LRH.2.21.2005011357290.29679@namei.org>
Date:   Fri, 1 May 2020 14:02:16 +1000 (AEST)
From:   James Morris <jmorris@...ei.org>
To:     Mickaël Salaün <mic@...ikod.net>
cc:     linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Heimes <christian@...hon.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Deven Bowers <deven.desai@...ux.microsoft.com>,
        Eric Chiang <ericchiang@...gle.com>,
        Florian Weimer <fweimer@...hat.com>, Jan Kara <jack@...e.cz>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Matthew Garrett <mjg59@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Mickaël Salaün <mickael.salaun@....gouv.fr>,
        Mimi Zohar <zohar@...ux.ibm.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>,
        Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
        Vincent Strubel <vincent.strubel@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec
 mount property

On Tue, 28 Apr 2020, Mickaël Salaün wrote:

> An LSM doesn't get path information related to an access request to open
> an inode.  This new (internal) MAY_EXECMOUNT flag enables an LSM to
> check if the underlying mount point of an inode is marked as executable.
> This is useful to implement a security policy taking advantage of the
> noexec mount option.
> 
> This flag is set according to path_noexec(), which checks if a mount
> point is mounted with MNT_NOEXEC or if the underlying superblock is
> SB_I_NOEXEC.
> 
> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> Reviewed-by: Philippe Trébuchet <philippe.trebuchet@....gouv.fr>
> Reviewed-by: Thibaut Sautereau <thibaut.sautereau@....gouv.fr>
> Cc: Aleksa Sarai <cyphar@...har.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Kees Cook <keescook@...omium.org>

Are there any existing LSMs which plan to use this aspect?

-- 
James Morris
<jmorris@...ei.org>