On Sat, Apr 22, 2017 at 1:51 AM, Andy Lutomirski [off-list ref] wrote:
[...]

quoted

quoted

I personally like my implicit_rights idea, and it might be interesting
to prototype it.

I don't like blocking a needed feature behind a large super-feature
that doesn't exist yet. We'd be able to refactor this code into using
such a thing in the future, so I'd prefer to move ahead with this
since it would stop actual exploits.

I don't think the super-feature is so hard, and I think we should not
add the per-task thing the way it's done in this patch.  Let's not add
per-task things where the best argument for their security is "not
sure how it would be exploited".

Actually the XFRM framework CVE-2017-7184 [1] is one real example, of
course there are others. The exploit was used on a generic distro
during a security contest that distro is Ubuntu. That distro will
never provide a module autoloading restriction by default to not harm
it's users. Consumers or containers/sandboxes then can run their
confined apps using such facilities.

These bugs will stay in embedded devices that use these generic
distros for ever.

Anyway, I think the sysctl is really the important bit.  The per-task
setting is icing on the cake IMO.  One upon a time autoload was more
important, but these days modaliases are supposed to do most of the
work.  I bet that modern distros don't need unprivileged autoload at
all.

Actually I think they do and we can't just change that. Users may
depend on it, it is a well established facility.

Now the other problem is CAP_NET_ADMIN which does lot of things, it is
more like the CAP_SYS_ADMIN.

This is a quick list that I got from only the past months, I'm pretty
sure there are more:

* DCCP use after free CVE-2017-6074
* n_hldc CVE-2017-2636
* XFRM framework CVE-2017-7184
* L2TPv3 CVE-2016-10200

Most of these need CAP_NET_ADMIN to be autoloaded, however we also
need CAP_NET_ADMIN for other things... therefore it is better to have
an extra facility that could coexist with CAP_NET_ADMIN and other
sandbox features.


[1] http://www.openwall.com/lists/oss-security/2017/03/29/2


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