Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <52301293-0e21-2885-904b-776b82d5a18d@gmail.com>
Date:   Tue, 11 Apr 2023 00:04:31 +0300
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.9.0
Subject: Re: Per-process flag set via prctl() to deny module loading?
Content-Language: en-US
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     linux-modules <linux-modules@vger.kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        "linux-hardening@vger.kernel.org" <linux-hardening@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <640c4327-0b40-f964-0b5b-c978683ac9ba@gmail.com>
 <2023041010-vacation-scribble-ba46@gregkh>
From:   Topi Miettinen <toiwoton@gmail.com>
In-Reply-To: <2023041010-vacation-scribble-ba46@gregkh>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

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