Re: [PATCH 1/2] rtnetlink: gate MAC address with an LSM hook

[David Miller <davem@davemloft.net>]

From: Jeff Vander Stoep <jeffv@google.com>
Date: Wed, 21 Aug 2019 15:45:47 +0200

> MAC addresses are often considered sensitive because they are
> usually unique and can be used to identify/track a device or
> user [1].
> 
> The MAC address is accessible via the RTM_NEWLINK message type of a
> netlink route socket[2]. Ideally we could grant/deny access to the
> MAC address on a case-by-case basis without blocking the entire
> RTM_NEWLINK message type which contains a lot of other useful
> information. This can be achieved using a new LSM hook on the netlink
> message receive path. Using this new hook, individual LSMs can select
> which processes are allowed access to the real MAC, otherwise a
> default value of zeros is returned. Offloading access control
> decisions like this to an LSM is convenient because it preserves the
> status quo for most Linux users while giving the various LSMs
> flexibility to make finer grained decisions on access to sensitive
> data based on policy.
> 
> [1] https://adamdrake.com/mac-addresses-udids-and-privacy.html
> [2] Other access vectors like ioctl(SIOCGIFHWADDR) are already covered
> by existing LSM hooks.
> 
> Signed-off-by: Jeff Vander Stoep <jeffv@google.com>

I'm sure the MAC address will escape into userspace via other means,
dumping pieces of networking config in other contexts, etc.  I mean,
if I can get a link dump, I can dump the neighbor table as well.

I kinda think this is all very silly whack-a-mole kind of stuff, to
be quite honest.

And like others have said, tomorrow you'll be like "oh crap, we should
block X too" and we'll get another hook, another config knob, another
rulset update, etc.