On 1/6/2011 5:32 PM, Sven Vermeulen wrote:
I've been working on bringing the SELinux handbook as currently available on
http://www.gentoo.org/proj/en/hardened/selinux/selinux-handbook.xml more
up2date. It's somewhat of a rewrite, but with all elements of the original
SELinux handbook still inside it (apart from the troubleshooting as I guess
those are quite outdated, being from 2006 and older).
The troubleshooting is not outdated, though there could be a few additions.
The draft is currently available in the hardened-docs.git repository. In
http://git.overlays.gentoo.org/gitweb/?p=proj/hardened-docs.git;a=tree;f=html/selinux;hb=HEAD
you should be able to select individual chapters (HTML format) in the "raw"
tree to view them somewhat like they would on the Gentoo site, but for your
convenience there's also a PDF available at
http://git.overlays.gentoo.org/gitweb/?p=proj/hardened-docs.git;a=tree;f=pdf;hb=HEAD
I looked through section 1 and 2 of the pdf version, and here are my
notes so far:
1.2.1 The best way to look at security is by defining your security
goals. An example would be protecting critical system files, such as
the kernel image, shadow passwords, and SELinux policy binary from being
written except by trusted processes.
1.2.2 I don't understand the point of this section
1.2.3 I'd say this is not appropriate for this document.
1.2.4 This has problems; authentication is related to access control,
but not part of it. Also, "discretionary" in the sense of access
control means that users can change the policy. Contrast that with
mandatory access control, where the security admin sets the policy.
1.3.1 SELinux has been included in the kernel for years, we can drop the
"kernel patch" part.
2.2.1 This should be users, roles, and types. "Domain" used in SELinux
refers to a type that labels a process. The amount of access to
unlabeled processes is defined by the policy, not by the SELinux
mechanisms. I also think that the newrole example is out of scope for
this section.
2.2.2 "Contexts for permission rules" doesn't make sense. "Rules" or
"Access control policy" or something similar makes more sense. You also
jump into rules with no discussion of object classes. The part where
you say that if access is denied by DAC, then SELinux isn't checked
should be earlier in the intro.
2.3.1 same thing about domain vs. type. A type is not a state, it is a
security attribute.
2.3.2 I think discussion of the specific rules required for a successful
domain transition are not relevant for this part of the doc.
2.4.1 You say what can be technically done by using a role, but you
don't discuss what the concept of a role is.
2.4.2 Technically, the only default role is object_r. The remainder are
just common ones that you see if you use refpolicy.
2.4.3 The key reason for having a SELinux user id that is separate from
the Linux user id is that the seuser doesn't change during a login
session, but the Linux uid can be changed, eg by setuid or su.
2.5.1 The purpose of MLS is to provide a hierarchical confidentiality
policy. "This allows administrators to ensure that
information flow is more closely governed" is incorrect. MLS can be
implemented in TE, but it causes an explosion of types, so its easier to
have an additional mechanism.
2.6.1 The discussion on why an access is allowed or denied always starts
with TE. In this case, user_t can't alter the clock, nor can it reach
the hwclock_t domain since there is no domain transition.
--
Chris PeBenito
<pebenito@gentoo.org>
Developer,
Hardened Gentoo Linux
SELinux documentation draft
