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Date:   Fri, 1 Dec 2017 16:22:00 +0100
From:   Marcus Meissner <>
To:     Theodore Ts'o <>, Kees Cook <>,
        Linus Torvalds <>,
        Djalal Harouni <>,
        Jonathan Corbet <>,
        James Morris <>,
        LSM List <>,
        Linux Kernel Mailing List <>,
        Geo Kozey <>
Subject: Re: [kernel-hardening] Re: [PATCH v5 next 5/5] net: modules: use
 request_module_cap() to load 'netdev-%s' modules

On Tue, Nov 28, 2017 at 06:49:20PM -0500, Theodore Ts'o wrote:
> On Tue, Nov 28, 2017 at 03:29:01PM -0800, Kees Cook wrote:
> > > So in these two cases, if the kernel was built w/o modules, and HDLC
> > > and DCCP was built-in, you'd be screwed, then?
> > 
> > Sure, but that's not the common situation.
> > 
> > > Is the goal here to protect people using distro kernels which build
> > > the world as modules, including dodgy pieces of kernel code that are
> > > bug-ridden?
> > 
> > The bulk of the risk comes from distro kernels, yes. (Though "bug
> > ridden" is a strong statement. There are and will be bugs, scattered
> > across a wide portion of the kernel, it's just that modules tend to
> > cover most of that attack surface.)
> OK, but if the goal is to protect users who are running distro
> kernels, then a kernel config that breaks some percentage of users is
> ****highly**** unlikely to be enabled by Red Hat and SuSE, right?  And
> many of these users either can't (from a skills perspective) or won't
> (because they lose all support from the enterprise distro's help desk)
> recompile their kernel to enable an "might break 3% of all users ---
> oh, well" config option.

Yes, breaking customers is not seen lightly.

I also (not related to this thread here, more to SLAB hardening
have a hard time getting performance losses caused by hardening features approved.
> Which argues for being extremely conservative about making something
> that has an extremely low probability of breaking users, and it points
> out why Geo Kozey's "who cares about breaking users; security is
> IMPORTANT" argument is so wrong-headed.
> If the goal is to protect distro kernels, but a sloppy approach
> guarantees that distro kernels will never enable it, is it really
> worth it?
> 	   	       	       	    	  	 - Ted
> P.S.  This is where it might be useful to get some input from the Red
> Hat and SuSE support teams.  How many angry user calls to their help
> desk are they willing to field before they'll just turn off the kernel
> config option for their kernels?

Speaking for SUSE ... If something that worked for people before and
it breaks, we do get feedback. If no one used it however, we won't.

For our last major product we went over the network module list and 
disabled some for building. e.g. DCCP is no longer built. We did
not receive any complaints about missing DCCP to my knowledge.

We also seperate our modules into "regular supported" and "unsupported"
in different RPMs. The "unsupported" module packages are not shipped on
the Server product. They were shipped on the desktop as some of the WiFi
drivers were requested by customers but were considered not supportable.

We do review this supportable list between kernel version jumps.

Ciao, Marcus

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