Provide necessary forward declarations or includes.

Implement the register/deregister/evaluation API for secmodel(9). It
allows registration of callbacks that can be used later for
cross-secmodel "safe" communication.

When a secmodel wishes to know a property maintained by another
secmodel, it has to submit a request to it so the other secmodel can
proceed to evaluating the request. This is done through the
secmodel_eval(9) call; example:

bool isroot;
error = secmodel_eval("org.netbsd.secmodel.suser", "is-root",
cred, &isroot);
if (error == 0 && !isroot)
result = KAUTH_RESULT_DENY;

This one asks the suser module if the credentials are assumed to be root
when evaluated by suser module. If the module is present, it will
respond. If absent, the call will return an error.

Args and command are arbitrarily defined; it's up to the secmodel(9) to
document what it expects.

Typical example is securelevel testing: when someone wants to know
whether securelevel is raised above a certain level or not, the caller
has to request this property to the secmodel_securelevel(9) module.
Given that securelevel module may be absent from system's context (thus
making access to the global "securelevel" variable impossible or
unsafe), this API can cope with this absence and return an error.

We are using secmodel_eval(9) to implement a secmodel_extensions(9)
module, which plugs with the bsd44, suser and securelevel secmodels
to provide the logic behind curtain, usermount and user_set_cpu_affinity
modes, without adding hooks to traditional secmodels. This solves a
real issue with the current secmodel(9) code, as usermount or
user_set_cpu_affinity are not really tied to secmodel_suser(9).

The secmodel_eval(9) is also used to restrict security.models settings
when securelevel is above 0, through the "is-securelevel-above"
evaluation:
- curtain can be enabled any time, but cannot be disabled if
securelevel is above 0.
- usermount/user_set_cpu_affinity can be disabled any time, but cannot
be enabled if securelevel is above 0.

Regarding sysctl(7) entries:
curtain and usermount are now found under security.models.extensions
tree. The security.curtain and vfs.generic.usermount are still
accessible for backwards compat.

Documentation is incoming, I am proof-reading my writings.

Written by elad@, reviewed and tested (anita test + interact for rights
tests) by me. ok elad@.

See also
http://mail-index.netbsd.org/tech-security/2011/11/29/msg000422.html

XXX might consider va0 mapping too.

XXX Having a secmodel(9) specific printf (like aprint_*) for reporting
secmodel(9) errors might be a good idea, but I am not sure on how
to design such a function right now.

branches: 1.3.10; 1.3.14;
Remove secmodel.h, forgotten in previous commit:

http://mail-index.netbsd.org/source-changes/2009/10/02/msg001437.html

branches: 1.2.44;
Remove advertising clause from all of my stuff.

branches: 1.1.2; 1.1.6; 1.1.10;
First take at security model abstraction.

- Add a few scopes to the kernel: system, network, and machdep.

- Add a few more actions/sub-actions (requests), and start using them as
opposed to the KAUTH_GENERIC_ISSUSER place-holders.

- Introduce a basic set of listeners that implement our "traditional"
security model, called "bsd44". This is the default (and only) model we
have at the moment.

- Update all relevant documentation.

- Add some code and docs to help folks who want to actually use this stuff:

* There's a sample overlay model, sitting on-top of "bsd44", for
fast experimenting with tweaking just a subset of an existing model.

This is pretty cool because it's *really* straightforward to do stuff
you had to use ugly hacks for until now...

* And of course, documentation describing how to do the above for quick
reference, including code samples.

All of these changes were tested for regressions using a Python-based
testsuite that will be (I hope) available soon via pkgsrc. Information
about the tests, and how to write new ones, can be found on:

http://kauth.linbsd.org/kauthwiki

NOTE FOR DEVELOPERS: *PLEASE* don't add any code that does any of the
following:

- Uses a KAUTH_GENERIC_ISSUSER kauth(9) request,
- Checks 'securelevel' directly,
- Checks a uid/gid directly.

(or if you feel you have to, contact me first)

This is still work in progress; It's far from being done, but now it'll
be a lot easier.

Relevant mailing list threads:

http://mail-index.netbsd.org/tech-security/2006/01/25/0011.html
http://mail-index.netbsd.org/tech-security/2006/03/24/0001.html
http://mail-index.netbsd.org/tech-security/2006/04/18/0000.html
http://mail-index.netbsd.org/tech-security/2006/05/15/0000.html
http://mail-index.netbsd.org/tech-security/2006/08/01/0000.html
http://mail-index.netbsd.org/tech-security/2006/08/25/0000.html

Many thanks to YAMAMOTO Takashi, Matt Thomas, and Christos Zoulas for help
stablizing kauth(9).

Full credit for the regression tests, making sure these changes didn't break
anything, goes to Matt Fleming and Jaime Fournier.

Happy birthday Randi! :)