Re: [PATCH 00/12] Add kdbus implementation

On 2014-10-30 15:47, Greg Kroah-Hartman wrote:

On Thu, Oct 30, 2014 at 11:44:39AM +0100, Karol Lewandowski wrote:

quoted

[ Sorry for breaking thread and resend - gmane rejected my original message
  due to too long list of recipients... ]

On 2014-10-30 00:40, Greg Kroah-Hartman wrote:

quoted

There is a 1815 line documentation file in this series, so we aren't
trying to not provide this type of information here at all.  But yes,
more background, about why this can't be done in userspace (zero copy,
less context switches, proper credential passing, timestamping, availble
at early-boot, LSM hooks for security models to tie into

While you're at it... I did some work on proof-of-concept LSM patches for
kdbus some time ago, see [1][2].  Currently, these are completely of date.

 [1] https://github.com/lmctl/linux/commits/kdbus-lsm-v4.for-systemd-v212
 [2] https://github.com/lmctl/kdbus/commit/aa0885489d19be92fa41c6f0a71df28763228a40

May I ask if you guys have your own plan for LSM or maybe it would be
worth to resurrect [1]?

The core calls are already mediated by LSM today, right?  We don't want
anyone to be parsing the data stream through an LSM, that idea got
rejected a long time ago as something that is really not a good idea.

Parsing data is out of question, of course, but this is not what we were
proposing.

Other than that, I don't know exactly what your patches do, or why they
are needed, care to go into details?

Patches in question were supposed to add few hooks for kdbus-specific
operations that doesn't seem to have compatible semantics with hooks
currently available in LSM.

kdbus' bus introduces quite a few new concepts that we wanted to be able
to limit based on MAC label/context, eg.

 - check flags at HELO stage (say disallow fd passing),

 - restrict ability to acquire name to certain subjects (for system bus),

 - disallow creation of new buses,

 - limit scope of broadcasts,

 - etc.

Please take a look at hook list - I think most of names are self-explanatory:

  https://github.com/lmctl/linux/blob/a9fe4c33b6e5ab25a243e0590df406aabb6add12/include/linux/security.h#L1874

kdbus modifications were pretty light - with most visible change being
addition of opaque security pointer to kdbus_bus and similar structs.

Thanks!
-- 
Karol Lewandowski, Samsung R&D Institute Poland