linux-kernel - Re: [PATCH v25 10/12] LRNG

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Date:   Thu, 21 Nov 2019 00:57:31 +0500
From:   "Alexander E. Patrakov" <patrakov@...il.com>
To:     Stephan Müller <smueller@...onox.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>,
        Florian Weimer <fweimer@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Nicolai Stange <nstange@...e.de>,
        "Peter, Matthias" <matthias.peter@....bund.de>,
        Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        Roman Drahtmueller <draht@...altsekun.de>,
        Neil Horman <nhorman@...hat.com>
Subject: Re: [PATCH v25 10/12] LRNG - add TRNG support

21.11.2019 00:51, Stephan Müller пишет:
> Am Mittwoch, 20. November 2019, 14:29:18 CET schrieb Greg Kroah-Hartman:
> 
> Hi Greg,
> 
>> On Wed, Nov 20, 2019 at 09:58:35AM +0100, Stephan Müller wrote:
>>> Am Dienstag, 19. November 2019, 13:41:50 CET schrieb Greg Kroah-Hartman:
>>>
>>> Hi Greg,
>>>
>>>> On Tue, Nov 19, 2019 at 02:07:40AM -0800, Andy Lutomirski wrote:
>>>>>> As this would introduce a new device file now, is there a special
>>>>>> process that I need to follow or do I need to copy? Which
>>>>>> major/minor
>>>>>> number should I use?
>>>>>>
>>>>>> Looking into static const struct memdev devlist[] I see
>>>>>>
>>>>>>           [8] = { "random", 0666, &random_fops, 0 },
>>>>>>           [9] = { "urandom", 0666, &urandom_fops, 0 },
>>>>>>
>>>>>> Shall a true_random be added here with [10]?
>>>>>
>>>>> I am not at all an expert on chardevs, but this sounds generally
>>>>> reasonable.  gregkh is probably the real authority here.
>>>>
>>>> [10] is the aio char device node, so you better not try to overlap it or
>>>> bad things will happen :(
>>>
>>> Thanks for your insights.
>>>
>>> Which device minor number could we use?
>>
>> Get your own dynamic one by using a misc device if you _REALLY_ want to
>> add yet-another-char-node-for-random-data.
>>
>> But I would have thought that we all realize that this is not the way to
>> do things.  Let's not have "random", "urandom", and "true_random" be
>> something we want to totally confuse userspace with, that way is insane.
>>
>> Please just make the existing userspace api "just work", don't add to
>> the mess.
> 
> Thank you, I think we should follow that advise.
> 
> With that and considering Alexander's rightful remark we have a challenge. So,
> changing the syscall may not be the right way unless we find a way to restrict
> the permissions somehow (capability? LSM? None of that seems to be a good
> fit).
> 
> What about providing a /sys file? I.e. adding a file that:
> 
> a) has permissions 440 per default and maybe the ownership of root:root
> 
> b) allow user space to perform a chown/chgrp
> 
> c) only supports reading of data from user space
> 
> But then, how could we provide a common interface for the existing random.c
> and the LRNG?
> 
> Or should we use a proc file for that? If yes, I guess it should not be a
> sysctl, but a "regular" proc file that should allow a chown(2) operation. On
> the other hand, is proc the right place to provide a user space interface for
> exporting data to user?
> 
> Thanks a lot.
> 
> Ciao
> Stephan
> 
> 

I'd say that a sys or proc file is worse than a device node, because the 
wanted semantics are exactly those of a device node. Besides, a chown of 
a sysfs file is something not friendly to containers. We may need 
different uids in different containers to be able to access true random 
data.

-- 
Alexander E. Patrakov


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