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

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Message-ID: <52301293-0e21-2885-904b-776b82d5a18d@gmail.com>
Date:   Tue, 11 Apr 2023 00:04:31 +0300
From:   Topi Miettinen <toiwoton@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
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 10.4.2023 21.37, Greg KH wrote:
> 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.
> 
> Patches are always welcome to be reviewed.
> 
> But note, please watch out for processes that cause devices to be found,
> and then modules to be loaded that way, it's not going to be as simple
> as you might have imagined...

A very simple version would only add a simple check like 
!current->allow_module_load after every !capable(CAP_SYS_MODULE). It 
wouldn't block all the ways how modules could be caused to be loaded 
indirectly.

I think a less simple version could also do the check at __request_module().

-Topi