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Date: Sun, 17 May 2020 19:57:51 +0300
From: "Lev R. Oshvang ." <levonshe@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: Mickaël Salaün <mic@...ikod.net>,
linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>,
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Jonathan Corbet <corbet@....net>, Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>,
Michael Kerrisk <mtk.manpages@...il.com>, Mickaël Salaün <mickael.salaun@....gouv.fr>,
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Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
Vincent Strubel <vincent.strubel@....gouv.fr>, kernel-hardening@...ts.openwall.com,
linux-api@...r.kernel.org, linux-integrity@...r.kernel.org,
LSM List <linux-security-module@...r.kernel.org>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 2/6] fs: Add a MAY_EXECMOUNT flag to infer the noexec
mount property
On Thu, May 14, 2020 at 6:48 PM Kees Cook <keescook@...omium.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
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