Modify SELinux to dynamically discover class and permission values
upon policy load, based on the dynamic object class/perm discovery
logic from libselinux. A mapping is created between kernel-private
class and permission indices used outside the security server and the
policy values used within the security server.
The mappings are only applied upon kernel-internal computations;
similar mappings for the private indices of userspace object managers
is handled on a per-object manager basis by the userspace AVC. The
interfaces for compute_av and transition_sid are split for kernel
vs. userspace; the userspace functions are distinguished by a _user
suffix.
The kernel-private class indices are no longer tied to the policy
values and thus do not need to skip indices for userspace classes;
thus the kernel class index values are compressed. The flask.h
definitions were regenerated by deleting the userspace classes from
refpolicy's definitions and then regenerating the headers. Going
forward, we can just maintain the flask.h, av_permissions.h, and
classmap.h definitions separately from policy as they are no longer
tied to the policy values. The next patch introduces a utility to
automate generation of flask.h and av_permissions.h from the
classmap.h definitions.
The older kernel class and permission string tables are removed and
replaced by a single security class mapping table that is walked at
policy load to generate the mapping. The old kernel class validation
logic is completely replaced by the mapping logic.
The handle unknown logic is reworked. reject_unknown=1 is handled
when the mappings are computed at policy load time, similar to the old
handling by the class validation logic. allow_unknown=1 is handled
when computing and mapping decisions - if the permission was not able
to be mapped (i.e. undefined, mapped to zero), then it is
automatically added to the allowed vector. If the class was not able
to be mapped (i.e. undefined, mapped to zero), then all permissions
are allowed for it if allow_unknown=1.
avc_audit leverages the new security class mapping table to lookup the
class and permission names from the kernel-private indices.
The mdp program is updated to use the new table when generating the
class definitions and allow rules for a minimal boot policy for the
kernel. It should be noted that this policy will not include any
userspace classes, nor will its policy index values for the kernel
classes correspond with the ones in refpolicy (they will instead match
the kernel-private indices).
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>
In August 2006 I posted a patch generating a minimal SELinux policy. This
week, David P. Quigley posted an updated version of that as a patch against
the kernel. It also had nice logic for auto-installing the policy.
Following is David's original patch intro (preserved especially
bc it has stats on the generated policies):
se interested in the changes there were only two significant
changes. The first is that the iteration through the list of classes
used NULL as a sentinel value. The problem with this is that the
class_to_string array actually has NULL entries in its table as place
holders for the user space object classes.
The second change was that it would seem at some point the initial sids
table was NULL terminated. This is no longer the case so that iteration
has to be done on array length instead of looking for NULL.
Some statistics on the policy that it generates:
The policy consists of 523 lines which contain no blank lines. Of those
523 lines 453 of them are class, permission, and initial sid
definitions. These lines are usually little to no concern to the policy
developer since they will not be adding object classes or permissions.
Of the remaining 70 lines there is one type, one role, and one user
statement. The remaining lines are broken into three portions. The first
group are TE allow rules which make up 29 of the remaining lines, the
second is assignment of labels to the initial sids which consist of 27
lines, and file system labeling statements which are the remaining 11.
In addition to the policy.conf generated there is a single file_contexts
file containing two lines which labels the entire system with base_t.
This policy generates a policy.23 binary that is 7920 bytes.
(then a few versions later...):
The new policy is 587 lines (stripped of blank lines) with 476 of those
lines being the boilerplate that I mentioned last time. The remaining
111 lines have the 3 lines for type, user, and role, 70 lines for the
allow rules (one for each object class including user space object
classes), 27 lines to assign types to the initial sids, and 11 lines for
file system labeling. The policy binary is 9194 bytes.
Changelog:
Aug 26: Added Documentation/SELinux.txt
Aug 26: Incorporated a set of comments by Stephen Smalley:
1. auto-setup SELINUXTYPE=dummy
2. don't auto-install if selinux is enabled with
non-dummy policy
3. don't re-compute policy version
4. /sbin/setfiles not /usr/sbin/setfiles
Aug 22: As per JMorris comments, made sure make distclean
cleans up the mdp directory.
Removed a check for file_contexts which is now
created in the same file as the check, making it
superfluous.
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: David Quigley <dpquigl@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>
Stephen Smalley