Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200505153156.925111-1-mic@digikod.net> <20200505153156.925111-3-mic@digikod.net>
 <202005121407.A339D31A@keescook> <CAP22eLEWW+KjD5rHosZV8vSuBB4YBLh0BQ=4-=kJQt9o=Fx1ig@mail.gmail.com>
 <202005140845.16F1CDC@keescook>
In-Reply-To: <202005140845.16F1CDC@keescook>
From:   "Lev R. Oshvang ." <levonshe@gmail.com>
Date:   Sun, 17 May 2020 19:57:51 +0300
Message-ID: <CAP22eLEy5nc4u6gPHtY56afrvF9oTNBwRwNAc7Le=Y_8V49nqQ@mail.gmail.com>
Subject: Re: [PATCH v5 2/6] fs: Add a MAY_EXECMOUNT flag to infer the noexec
 mount property
To:     Kees Cook <keescook@chromium.org>
Cc:     =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mic@digikod.net>,
        linux-kernel@vger.kernel.org, Aleksa Sarai <cyphar@cyphar.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andy Lutomirski <luto@kernel.org>,
        Christian Heimes <christian@python.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Deven Bowers <deven.desai@linux.microsoft.com>,
        Eric Chiang <ericchiang@google.com>,
        Florian Weimer <fweimer@redhat.com>,
        James Morris <jmorris@namei.org>, Jan Kara <jack@suse.cz>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
        Matthew Garrett <mjg59@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mickael.salaun@ssi.gouv.fr>,
        Mimi Zohar <zohar@linux.ibm.com>,
        =?UTF-8?Q?Philippe_Tr=C3=A9buchet?= 
        <philippe.trebuchet@ssi.gouv.fr>,
        Scott Shell <scottsh@microsoft.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Shuah Khan <shuah@kernel.org>,
        Steve Dower <steve.dower@python.org>,
        Steve Grubb <sgrubb@redhat.com>,
        Thibaut Sautereau <thibaut.sautereau@ssi.gouv.fr>,
        Vincent Strubel <vincent.strubel@ssi.gouv.fr>,
        kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
        linux-integrity@vger.kernel.org,
        LSM List <linux-security-module@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, May 14, 2020 at 6:48 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, May 14, 2020 at 11:14:04AM +0300, Lev R. Oshvang . wrote:
> > New sysctl is indeed required to allow userspace that places scripts
> > or libs under noexec mounts.
>
> But since this is a not-uncommon environment, we must have the sysctl
> otherwise this change would break those systems.
>
 But I proposed sysctl on a line below.

> > fs.mnt_noexec_strict =1 (allow, e) , 1 (deny any file with --x
> > permission), 2 (deny when O_MAYEXEC absent), for any file with ---x
> > permissions)
>
> I don't think we want another mount option -- this is already fully
> expressed with noexec and the system-wide sysctl.
>
> --

The intended use of proposed sysctl is to ebable sysadmin to decide
whar is desired semantics  mount with NO_EXEC option.

fs.mnt_noexec_scope =0 |1|2|3
0  - means old behaviour i.e do nor run executables and scripts (default)
1 - deny any file with --x permissions, i.e executables , script and libs
2 - deny any file when O_MAYEXEC is present.

I think this is enough to handle all use cases and to not break
current sysadmin file mounts setting
I oppose the new O_MAY_EXECMOUNT flag, kernel already has MNT_NO_EXEC,
SB_NOEXEC and SB_I_NOEXEC and I frankly do not understand why so many
variants exist.
Lev