linux-kernel - Re: [RFC v1 00/14] Bus1 Kernel Message Bus

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Message-ID: <CA+55aFyDCR1bdzNe+kwuAO-XAzdxhtBjqRNrRnWFuo0Q8-QUmA@mail.gmail.com>
Date:   Wed, 26 Oct 2016 12:39:54 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Herrmann <dh.herrmann@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, Greg KH <greg@...ah.com>,
        Hannes Reinecke <hare@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Arnd Bergmann <arnd@...db.de>, Tom Gundersen <teg@...m.no>,
        Josh Triplett <josh@...htriplett.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC v1 00/14] Bus1 Kernel Message Bus

So the thing that tends to worry me about these is resource management.

If I understood the documentation correctly, this has per-user
resource management, which guarantees that at least the system won't
run out of memory. Good. The act of sending a message transfers the
resource to the receiver end. Fine.

However, the usual problem ends up being that a bad user can basically
DoS a system agent, especially since for obvious performance reasons
the send/receive has to be asynchronous.

So the usual DoS model is that some user just sends a lot of messages
to a system agent, filling up the system agent resource quota, and
basically killing the system. No, it didn't run out of memory, but the
system agent may not be able to do anything more, since it is now out
of resources.

Keeping the resource management with the sender doesn't solve the
problem, it just reverses it: now the attack will be to send a lot of
queries to the system agent, but then just refuse to listen to the
replies - again causing the system agent to run out of resources.

Usually the way this is resolved this is by forcing a
"request-and-reply" resource management model, where the person who
sends out a request is not only the one who is accounted for the
request, but also accounted for the reply buffer. That way the system
agent never runs out of resources, because it's always the requesting
party that has its resources accounted, never the system agent.

You may well have solved this, but can you describe what the solution
is without forcing people to read the code and try to analyze it?

               Linus