New subject: On the purpose of cpe_generate.py script (& mainly cpe_variables section within it)

26 Aug 2014


      Hello folks,
within effort to rewrite umask checks (more about the motivation for this
later within its dedicated email thread) encountered the following 
RHEL/6/transforms/cpe_generate.py script related issue.
Use case: Let's consider RHEL/6/input/checks/accounts_umask_etc_profile.xml
OVAL check would have the form as attached (it's not the final form of the
check. The final one will be slightly more complex yet. In any case the attached
form is syntactically correct one & sufficient to demonstrate the issue I would
like to speak below about), then running 'make' in scap-security-guide/RHEL/6
subdirectory returns the following error when trying to generate the datastream
output:
oscap ds sds-compose output/ssg-rhel6-xccdf-1.2.xml output/ssg-rhel6-ds.xml
oscap ds sds-add output/ssg-rhel6-cpe-dictionary.xml output/ssg-rhel6-ds.xml
File 'output/ssg-rhel6-ds.xml' line 32236: Element '{http://oval.mitre.org/XMLSchema/oval-definitions-5%7Dobject_component': No match found for key-sequence ['oval:ssg:obj:111'] of keyref '{http://oval.mitre.org/XMLSchema/oval-definitions-5%7DobjectKeyRef'.
Invalid SCAP Source Datastream content(1.2) in output/ssg-rhel6-ds.xml.
make: *** [content] Error 1
Investigated the problem further, and noticed the problem is content of RHEL/6/output/ssg-rhel6-cpe-oval.xml
file. Namely it contains the content as follows:
...
    </states><variables><local_variable id="oval:ssg:var:110" datatype="int" comment="x" version="1">
      <substring substring_start="1" substring_length="1">
        <object_component item_field="subexpression" object_ref="oval:ssg:obj:111"/>
      </substring>
    </local_variable>
    </variables></oval_definitions>
which after more detailed look explains why 'oval:ssg:obj:111' wouldn't be defined in output/ssg-rhel6-ds.xml
file (the oval:ssg:var:110 local variable references oval:ssg:obj:111, but this object isn't defined
within that ssg-rhel6-cpe-oval.xml file [only in different part of ssg-rhel6-ds.xml file]).
So investigated further to see, which part of the RHEL/6's Makefile generates / includes this variable,
when creating ssg-rhel6-cpe-oval.xml file, and noticed the responsible script being RHEL/6/transforms/cpe_generate.py.
The questions:
1) Can someone more familiar with the implementation of this script clarify it's purpose?
   It requires two input files (OVAL file & CPE file), and one identifier (ssg), and generates
   'ssg-rhel6-cpe-oval.xml' file.
2) Can someone more familiar with the implementation of this script clarify the need for the
   following construct within it?:
82         variables = ovaltree.find("./{%s}variables" % oval_ns)
    83         cpe_variables = extract_referred_nodes(ovaltree, variables, "var_ref")
    84         if cpe_variables:
    85                 variables.clear()
    86                 [variables.append(cpe_variable) for cpe_variable in cpe_variables]
    87         else:
    88                 ovaltree.remove(variables)
Is it there to (when generating ssg.ini object name to object id file) to incorporate
    also OVAL local_variables that might reference another variables via the "var_ref"
    attribute?
The reason why I am asking being that have noticed, when I comment out the following part
    of this file (IOW when the cpe_generate.py script has the following form around the
    critical lines):
82         variables = ovaltree.find("./{%s}variables" % oval_ns)
    83         #cpe_variables = extract_referred_nodes(ovaltree, variables, "var_ref")
    84         #if cpe_variables:
    85         #       variables.clear()
    86         #       [variables.append(cpe_variable) for cpe_variable in cpe_variables]
    87         #else:
    88         ovaltree.remove(variables)
the aforementioned error message:
File 'output/ssg-rhel6-ds.xml' line 32236: Element '{http://oval.mitre.org/XMLSchema/oval-definitions-5%7Dobject_component': No match found for key-sequence ['oval:ssg:obj:111'] of keyref '{http://oval.mitre.org/XMLSchema/oval-definitions-5%7DobjectKeyRef'.
when generating ssg-rhel6-ds.xml isn't reported anymore & the content builds successfully.
Since I wouldn't like to break something, the purpose of this email is to ask someone more familiar
with the implementation of cpe_generate.py script, why the cpe_variables section (lines from #83 up
to #87 need to be present there)?
Is there a chance this behaviour is somehow related with the following commit:
  [1] https://github.com/OpenSCAP/scap-security-guide/commit/59d650ffe140e4ae742dc... ?
For example in the sense the original meaning of 'cpe_variables' part of cpe_generate.py was to include
also variables, that reference other variables via 'var_ref' attribute into final ssg.ini file
(and assign IDs in the form of "oval:ssg:var:..." to them too)? But the change [1] is causing
variable objects having 'var_ref' attribute is now included within relabelids.py script & therefore
the 'cpe_variables' section of the cpe_generate.py script is not needed anymore & can be safely remove
as suggested above (or in the also attached RHEL_6_transforms_cpe_generate_py.diff patch)?
Any hints you can provide wrt to observed cpe_generate.py behaviour & how to possibly fix it
are appreciated.
Thank you && Regards, Jan.
--
Jan iankko Lieskovsky / Red Hat Security Technologies Team
P.S.: If wondering why this problem didn't show earlier, assuming there isn't such construct
      (local_variable referencing another local_variable referencing textfilecontent54_object)
      used in the current content yet. Tried also different approach (encapsulate those local_variables
      into variable_objects & reference those objects instead), but it didn't help (in the sense
      datastream output would be successfully generated).