linux-kernel - Re: [PATCH v5 next 1/5] modules:capabilities: add request_module

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Message-ID: <CAGXu5jKgHWNE4NH_xqcM084-BNBPy+HmEVPbTA+w_=K3S6gC=w@mail.gmail.com>
Date:   Tue, 28 Nov 2017 12:11:34 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Djalal Harouni <tixxdz@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        James Morris <james.l.morris@...cle.com>,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        Solar Designer <solar@...nwall.com>,
        Serge Hallyn <serge@...lyn.com>, Jessica Yu <jeyu@...nel.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v5 next 1/5] modules:capabilities: add request_module_cap()

On Tue, Nov 28, 2017 at 11:14 AM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> kmod is just a helper to poke userpsace to load a module, that's it.
>
> The old init_module() and newer finit_module() do the real handy work or
> module loading, and both currently only use may_init_module():
>
> static int may_init_module(void)
> {
>         if (!capable(CAP_SYS_MODULE) || modules_disabled)
>                 return -EPERM;
>
>         return 0;
> }
>
> This begs the question:
>
>   o If userspace just tries to just use raw finit_module() do we want similar
>     checks?
>
> Otherwise, correct me if I'm wrong this all seems pointless.

Hm? That's direct-loading, not auto-loading. This series is only about
auto-loading.

We already have a global sysctl for blocking direct-loading (modules_disabled).

> If we want something similar I think we might need to be processing aliases and
> check for the aliases for their desired restrictions on finit_module(),

We don't need to handle aliases.

-Kees

-- 
Kees Cook
Pixel Security