Joshua Brindle wrote:
Andy Warner wrote:
Please don't take my lack of asking for new object classes as anything
other than ignorance as to how things "work" in the open source
community. All of our previous work has been on proprietary MLS systems.
The idea of asking an OS vendor or community to add features for my
needs was foreign to me. Plus, my time constraints on the project may
not have allowed it. I have found this community to be very open and
helpful and always planned to give some input as to the need for these
object classes after my project was finished (which is now).
Fair enough. I'm happy to see additional efforts in this arena, regardless.
So, internally, the access checks on the database and catalog are
performed when those objects are opened. During the actual create table
operation we have two calls to avc_has_perm, the first checks the
client's context, schema's context for dir {search add_name} and the
second checks the client's context, table's context for db_table {create}
Could you elaborate on what you mean by "I don't think it is a good idea
to muddle the object
class ownership concept by doing checks for classes which are owned by
another
object manager" ? In what way is an object class *owned* by an object
manager? I'm a newbie in this area and would appreciate some
constructive criticism.
So, overloading object classes leads to confusion and other issues. For example,
if an actual directory got labeled what the internal catalog was labeled then
the client would have access to that, even if that wasn't the intention. There
also may be conflicting type_transition rules because you end up wanting one
object label transition to be different from another when used on the different
kinds of objects.
Yep, I can see that as an issue. Practically speaking, I would think the
new object classes will be added before any such real issue arose. But,
isn't there a similar issue, say, between a system with a sepostres
policy and a Trusted RUBIX installation on the same platform? I have
already bumped up against some of the type_transition rules for sepostgres.
The flask architecture was originally implemented in a microkernel where object
managers were services that enforced access per the security servers decision.
In that architecture an object manager would be responsible for the object class
it was enforcing access on. Stephen can correct me here if I'm wrong but I
object to object class overloading based on these issues.
You shouldn't really bump in to each other since the dbms domain and objects
should all be labeled differently, what have you seen happen?
KaiGai and I talked about this a bit already, and I'll preface my
response by saying that my memory of it is poor. Also, this issue was
one of my first practical introductions to selinux, so I'm sure I was
shooting in the dark. But, the main issue revolved around the type
transition rule for the database object. It seems to me, what makes it
special is that it has no parent object. It seems equivalent to writing
a type transition rule for creating the OS root directory, except in
our DBMS case we can have more than one type (each dbms has their own).
A rule for sepostgres is:
type_transition sepgsql_client_type sepgsql_client_type : db_database
sepgsql_db_t;
Where I believe the standard user_t and such had the
sepgsql_client_type attribute. So, with that rule in place I think it
was impossible for rubix to have a similar rule, if our client_type's
overlapped. Which seems likely, as the user_t is a likely candidate for
a client. For instance, if I did this:
type_transition rubix_client_type rubix_client_type : db_database
rubix_db_t; (where rubix_client_type contained user_t)
I think it would not compile because its ambiguous, right? So, what I
did was write a rule like this:
type_transition rubix_client_type rubix_t : db_database rubix_db_t;
and hard-coded the rubix_t into the avc_compute_create call. The
rubix_t is actually the type of our server process. Prior to doing
that, I could not find a way to not have a database be created with a
sepgsql_t type.
I see (now) that the reference policy also has the rule:
type_transition postgresql_t postgresql_t : db_database sepgsql_db_t;
Obviously, the above would never conflict with another dbms's rules. If
that single type transition rule satisfied all of seposgresql's needs,
then that would eliminate the need for the conflicting rule. Though, I
assume thats dependent on the internals of seposgresql.
In your terminology, because rubix is enforcing the policy, would it be
considered an object manager? And, if so, wouldn't seposgres also be
considered one? where they both enforce access to the same set of object
classes?
Yes, both rubix and sepostgres are object managers. abstract object classes
where there isn't a single owner are interesting, I'd expect different object
labeling in most cases so it doesn't matter. In the case of the data in both
being equivalent from a security POV maybe it actually does make sense for them
to share labels and object classes (especially true if the database is primarily
enforcing an MLS policy)
Were the db object classes incomplete for you so you needed to use filesystem
object classes? I'm trying to get a feeling for what the motivation was behind
these checks.
Yes, if the db object classes supported schema and catalog I would not
use the dir. I'm not sure what to say for motivation, other than I felt
it important and useful to have security checks on our catalog and
schemata. And, since these objects function very closely to an OS
directory, and there was no support for the catalog and schema objects
in the selinux policy, and I decided not to modify the targeted/mls
policies as part of our release, I chose to use the dir object class.
Actually, I think I got the idea from an old post on this newsgroup. The
options presented in that post were to either modify the policy's object
class and permissions or overload a pre-existing object class. I chose
the latter. It was the lesser of two evils. I didn't want to have to
keep up with updates to the targeted/mls policies.
See above, you brought up another issue here where permissions being overloaded
may not have the same read/write mappings and therefore may be difficult to work
around with respect to the MLS policy. Approaching the community to work on a
common set of object classes/perms and getting them merged in to upstream
refpolicy is definitely the right answer.
I agree completely.
Is Trusted RUBIX with these SELinux checks actually released, are the access
checks set in stone? I'd like to see as much consistency between dbms object
models as possible so that policy won't be dramatically different between them.
Yes, Trusted RUBIX with these security checks is released. But no, they
are not set in stone. The minute a new policy is released supporting the
db_schema and db_catalog object classes will be the time I change our
product to use them, and stop using the dir object class.
Good. Hopefully we can get this worked out between you guys and have a
consistent (and documented) set of permissions that make it easy to write policy
that works on both systems (as much as possible)
I think that is well on its way. One question out of curiosity. Would
you anticipate that I should or would use the seposgres TE rules that
already exist in the targeted/mls policy? I ask that from your comment
about writing policy that that works on both systems. With current state
of things this seems very difficult, though, I think a higher level
interface set, like the one we created for the object set, could be made
that, for the most part, worked for both systems.
Yes, I don't mean they'd be using an identical policy but shared
templates/interfaces that worked with both would certainly make it easier to
target both systems without really needing to know the intricacies of each
systems enforcement.
Sounds like a good goal.
To my knowledge there are only two DBMS's that integrate SELinux into
its product, SEPostgresql and Trusted RUBIX. I'm not so sure I would say
our DBMS object models are dramatically different. SEPostgresql does
not have a catalog object and chose not to have selinux control over
their schema object. From looking at KaiGai's work and posts I think in
the future they will support the schema object, in much the same way I
tried to in our current release.
They chose not to for now, the initial set of permissions used by SEPostgres
looks like it is going to be minimal, unfortunately, but should evolve into
something more comprehensive.
I may be missing it but do you support 'domain-like' type_transitions for stored
procedures? This was one of the more interesting features in the initial
sepostgres patches IMHO because it allowed for trusted stored procedures that
can read tables the client couldn't necessarily read, and could do operations on
them before handing over the data (eg., fuzzing of coordinates)
We do not implement stored procedures at all, though this is a near
future possibility. As I said before, our background is MLS and often in
the EAL-5+ type (old B3). The group-think was always that stored
procedures were too insecure for such assurance levels. But, I have been
pushing the possibility in a EAL-4 type mode, for exactly the reasons
you mentioned above. With the selinux domain transition concept a stored
procedure becomes very interesting.
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