Re: [Cerowrt-devel] dnsmasq CVEs

[dpreed@reed.com]

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Sooner or later it dawns on all security professionals that the idea of a "provably secure system" is a pipedream. Same with systems designers working on fault tolerance who are tasked with making their systems "NonStop" as the Tandem claim used to go.
 
What we see here in most of the examples is a failure of design, especially of modularity.
 
Modularity is there to tame complexity, that's really its only reason to exist.
 
One thing that helps enforce modularity is end-to-end encryption, though there are other such concepts. The baseband processor shouldn't have the encryption keys - it has no "need to know".
 
The bigger problem is that those who design these "modules" don't understand the way to make systems containing them modular. A module, for example, performs a function that can be described abstractly, without knowing what is inside it. And it should hide information about "how" and "what" it does to the largest extent possible (Parnas' Information Hiding Principle). There are other time-tested notions of modular design that help.
 
But what we see often are what we used to describe in software as "taking the listing and breaking it into files by tearing on page boundaries".  The tendency is toward throwing a grab bag of functions on a chip that have no consistent and modular functionality. (e.g. the so-called "chipsets" that accompany new Intel CPU releases).
 
I don't know what can be done, other than to design systems that have modular structure where we can.
The one remaining thing we can do is limit the bad things that can happen in a design, by compartmentalizing failure and security risk using fairly strong and redundant approaches. Defense in depth. Don't assume that your firewall will prevent errors from creeping in.
 


On Monday, October 9, 2017 4:32am, "Mikael Abrahamsson" <swmike@swm.pp.se> said:



> On Sat, 7 Oct 2017, valdis.kletnieks@vt.edu wrote:
> 
> > Know how x86 people complain that SSM mode introduces jitter? That's
> > just the tip of the iceberg. Believe it or not, there's an entire
> > IPv4/IPv6 stack *and a webserver* hiding in there...
> >
> > https://schd.ws/hosted_files/ossna2017/91/Linuxcon%202017%20NERF.pdf
> >
> > Gaak. Have some strong adult beverage handy, you'll be needing it....
> 
> Also see the wifi processor remote exploit that Apple devices (and others
> I presume) had problems with.
> 
> Mobile baseband processors behave in the same way, and also have their own
> stack. I have talked to mobile developers who discovered all of a sudden
> the baseband would just silently "steal" a bunch of UDP ports from the
> host OS and just grab these packets. At least with IPv6, the baseband can
> have its own IPv6 address, separated from the host stack IPv6 addreses.
> 
> Just to illustrate (incompletely) what might be going on when you're
> tethering through a mobile phone.
> 
> Packet comes in on the 4G interface. It now hits the baseband processor
> (that runs code), which might send the packet to either the host OS, or
> via an packet accelerator path (which the host OS might or not have a
> control plane into), and this accelerator runs code, and then it hits the
> wifi chip, which also runs code.
> 
> So while the host OS programmer might see their host OS doing something,
> in real life the packet potentially hits at least three other things that
> run code using their own firmware. Also, these components are manufactured
> in factories, how do we verify that these actually do what they were
> intended to do, and not modified between design and production? How do we
> know the firmware we load is actually loaded and it's not intercepted and
> real time patched before execution? Oh, also, the OS is loaded from
> permanent storage, that is also running code. There are several talks
> about people modifying the storage controller (which also runs code of
> coutse) to return different things depending on usage pattern. So it's not
> safe for the OS to read data, check that it passes integrity checks, and
> then read it again, and execute. The storage might return different things
> the second time.
> 
> I don't know that we as humanity know how to do this securely. I've
> discussed this with vendors in different sectors, and there's a lot of
> people who aren't even aware of the problem.
> 
> I'd say the typical smartphone today probably has 10 things or more
> running code/firmware, all susceptable to bugs, all of them risked of even
> with exposed security problems, they're never going to be patched.
> 
> So the IoT problem isn't only for "smart meters" etc, it's for everything.
> We've created devices that are impossible to verify without destroying
> them (sanding down ICs and looking at billions of gates), and in order to
> verify them, you need equipment and skills that are not available to most
> people.
> 
> --
> Mikael Abrahamsson email: swmike@swm.pp.se
> 

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