linux-hardening - Re: Per-process flag set via prctl() to deny module loading?

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Message-ID: <ZDQQ0B35NcYwQMyy@tycho.pizza>
Date:   Mon, 10 Apr 2023 07:36:16 -0600
From:   Tycho Andersen <tycho@...ho.pizza>
To:     Topi Miettinen <toiwoton@...il.com>
Cc:     linux-modules <linux-modules@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Per-process flag set via prctl() to deny module loading?

On Mon, Apr 10, 2023 at 01:06:00PM +0300, Topi Miettinen wrote:
> I'd propose to add a per-process flag to irrevocably deny any loading of
> kernel modules for the process and its children. The flag could be set (but
> not unset) via prctl() and for unprivileged processes, only when
> NoNewPrivileges is also set. This would be similar to CAP_SYS_MODULE, but
> unlike capabilities, there would be no issues with namespaces since the flag
> isn't namespaced.
> 
> The implementation should be very simple.
> 
> Preferably the flag, when configured, would be set by systemd, Firejail and
> maybe also container managers. The expectation would be that the permission
> to load modules would be retained only by udev and where SUID needs to be
> allowed (NoNewPrivileges unset).

You can do something like this today via STATIC_USERMODEHELPER without
the need for kernel patches. It is a bit heavyweight for a
general-purpose system though.

Tycho