[Buildroot] [PATCH v2 3/7] support/scripts/cpedb.py: new CPE XML helper

On 31/01/2021 14:38, Thomas Petazzoni wrote:

 Note that instead of all these cpe.set calls, you can also do:

        cpes.attrib = {
            'xmlns:ns6': "http://scap.nist.gov/schema/scap-core/0.1",
            ...
        }

which IMO is more readable. But that's just nitpick.

 In fact, I think you can do it in the constructor:

        cpes = Element('cpe-list', attrib = { ...

but that is probably less readable.

+        cpes.set('xmlns:ns6', "http://scap.nist.gov/schema/scap-core/0.1")
+        cpes.set('xmlns:scap-core', "http://scap.nist.gov/schema/scap-core/0.3")
+        cpes.set('xmlns:config', "http://scap.nist.gov/schema/configuration/0.1")
+        cpes.set('xmlns:xsi', "http://www.w3.org/2001/XMLSchema-instance")
+        cpes.set('xmlns:meta', "http://scap.nist.gov/schema/cpe-dictionary-metadata/0.2")
+        cpes.set('xsi:schemaLocation', " ".join(["http://scap.nist.gov/schema/cpe-extension/2.3",
+                                                 "https://scap.nist.gov/schema/cpe/2.3/cpe-dictionary-extension_2.3.xsd",

 And here instead of join you can use:

        cpes.set('xsi:schemaLocation',
"http://scap.nist.gov/schema/cpe-extension/2.3 "
                                       "http://cpe.mitre.org/dictionary/2.0 "


(Python has string concatenation like C).

+                                                 "http://cpe.mitre.org/dictionary/2.0",
+                                                 "https://scap.nist.gov/schema/cpe/2.3/cpe-dictionary_2.3.xsd",
+                                                 "http://scap.nist.gov/schema/cpe-dictionary-metadata/0.2",
+                                                 "https://scap.nist.gov/schema/cpe/2.1/cpe-dictionary-metadata_0.2.xsd",
+                                                 "http://scap.nist.gov/schema/scap-core/0.3",
+                                                 "https://scap.nist.gov/schema/nvd/scap-core_0.3.xsd",
+                                                 "http://scap.nist.gov/schema/configuration/0.1",
+                                                 "https://scap.nist.gov/schema/nvd/configuration_0.1.xsd",
+                                                 "http://scap.nist.gov/schema/scap-core/0.1",
+                                                 "https://scap.nist.gov/schema/nvd/scap-core_0.1.xsd"]))
+        item = SubElement(cpes, 'cpe-item')
+        cpe_short_name = CPE.short_name(self.cpe_str)
+        cpe_new_ver = CPE.version_update(self.cpe_str)
+
+        item.set('name', 'cpe:/' + cpe_short_name)
+        self.titles[0].text.replace(self.cpe_cur_ver, cpe_new_ver)
+        for title in self.titles:
+            item.append(title)
+        if self.references:
+            item.append(self.references)
+        cpe23item = SubElement(item, 'cpe-23:cpe23-item')
+        cpe23item.set('name', self.cpe_str)
+
+        # Generate the XML as a string
+        xmlstr = ET.tostring(cpes)
+
+        # And use minidom to pretty print the XML
+        return minidom.parseString(xmlstr).toprettyxml(encoding="utf-8").decode("utf-8")
+
+    @staticmethod
+    def version(cpe):
+        return cpe.split(":")[5]
+
+    @staticmethod
+    def product(cpe):
+        return cpe.split(":")[4]
+
+    @staticmethod
+    def short_name(cpe):
+        return ":".join(cpe.split(":")[2:6])
+
+    @staticmethod
+    def version_update(cpe):

 It's weird to make this a staticmethod if the only caller takes self.cpe_str as
an argument, but OK.

+        return ":".join(cpe.split(":")[5:6])
+
+    @staticmethod
+    def no_version(cpe):
+        return ":".join(cpe.split(":")[:5])
+
+
+class CPEDB:
+    def __init__(self, nvd_path):
+        self.all_cpes = dict()
+        self.all_cpes_no_version = dict()
+        self.nvd_path = nvd_path
+
+    def gen_cached_cpedb(self, cpedb, cache_all_cpes, cache_all_cpes_no_version):
+        print("CPE: Unzipping xml manifest...")
+        nist_cpe_file = gzip.GzipFile(fileobj=open(cpedb, 'rb'))
+        print("CPE: Converting xml manifest to dict...")
+        tree = ET.parse(nist_cpe_file)
+        all_cpedb = tree.getroot()
+        self.parse_dict(all_cpedb)
+
+        print("CPE: Caching dictionary")
+        cpes_file = open(cache_all_cpes, 'wb')
+        pickle.dump(self.all_cpes, cpes_file)
+        cpes_file.close()
+        cpes_file = open(cache_all_cpes_no_version, 'wb')
+        pickle.dump(self.all_cpes_no_version, cpes_file)
+        cpes_file.close()
+
+    def get_xml_dict(self):
+        print("CPE: Setting up NIST dictionary")
+        if not os.path.exists(os.path.join(self.nvd_path, "cpe")):
+            os.makedirs(os.path.join(self.nvd_path, "cpe"))
+
+        cpe_dict_local = os.path.join(self.nvd_path, "cpe", os.path.basename(CPEDB_URL))
+        if not os.path.exists(cpe_dict_local) or os.stat(cpe_dict_local).st_mtime < time.time() - 86400:

 This should be a parameter@the beginning of the file rather than a constant
here. Ideally expressed in hours, with *3600 here.

+            print("CPE: Fetching xml manifest from [" + CPEDB_URL + "]")
+            cpe_dict = requests.get(CPEDB_URL)
+            open(cpe_dict_local, "wb").write(cpe_dict.content)
+
+        cache_all_cpes = os.path.join(self.nvd_path, "cpe", "all_cpes.pkl")
+        cache_all_cpes_no_version = os.path.join(self.nvd_path, "cpe", "all_cpes_no_version.pkl")
+
+        if not os.path.exists(cache_all_cpes) or \
+           not os.path.exists(cache_all_cpes_no_version) or \
+           os.stat(cache_all_cpes).st_mtime < os.stat(cpe_dict_local).st_mtime or \
+           os.stat(cache_all_cpes_no_version).st_mtime < os.stat(cpe_dict_local).st_mtime:
+            self.gen_cached_cpedb(cpe_dict_local,
+                                  cache_all_cpes,
+                                  cache_all_cpes_no_version)
+
+        print("CPE: Loading CACHED dictionary")
+        cpe_file = open(cache_all_cpes, 'rb')
+        self.all_cpes = pickle.load(cpe_file)
+        cpe_file.close()

 The above is better done as

        with open(cache_all_cpes, 'rb') as cpe_file:
            self.all_cpes = pickle.load(cpe_file)

This do things properly in case of exception.

 However, I'm not so sure if the pickled cache is really worth it. I gave it a
go, and the ET.parse + parse_dict took roughly 20 seconds, while just loading
the pickle file also took about 20 seconds...

+        cpe_file = open(cache_all_cpes_no_version, 'rb')
+        self.all_cpes_no_version = pickle.load(cpe_file)
+        cpe_file.close()
+
+    def parse_dict(self, all_cpedb):
+        # Cycle through the dict and build two dict to be used for custom
+        # lookups of partial and complete CPE objects
+        # The objects are then used to create new proposed XML updates if
+        # if is determined one is required
+        # Out of the different language titles, select English

 This could have been a docstring.

 Actually, all "public" functions should really have a docstring.



 So, I accidentally applied this patch... So all the above comments are just
informational - feel free to send follow-up patches, or ignore my feedback.

 Regards,
 Arnout

+        for cpe in all_cpedb.findall(".//{http://cpe.mitre.org/dictionary/2.0}cpe-item"):
+            cpe_titles = []
+            for title in cpe.findall('.//{http://cpe.mitre.org/dictionary/2.0}title[@xml:lang="en-US"]', ns):
+                title.tail = None
+                cpe_titles.append(title)
+
+            # Some older CPE don't include references, if they do, make
+            # sure we handle the case of one ref needing to be packed
+            # in a list
+            cpe_ref = cpe.find(".//{http://cpe.mitre.org/dictionary/2.0}references")
+            if cpe_ref:
+                for ref in cpe_ref.findall(".//{http://cpe.mitre.org/dictionary/2.0}reference"):
+                    ref.tail = None
+                    ref.text = ref.text.upper()
+                    if ref.text not in VALID_REFS:
+                        ref.text = ref.text + "-- UPDATE this entry, here are some examples and just one word should be used -- " + ' '.join(VALID_REFS) # noqa E501
+                cpe_ref.tail = None
+                cpe_ref.text = None
+
+            cpe_str = cpe.find(".//{http://scap.nist.gov/schema/cpe-extension/2.3}cpe23-item").get('name')
+            item = CPE(cpe_str, cpe_titles, cpe_ref)
+            cpe_str_no_version = CPE.no_version(cpe_str)
+            # This dict must have a unique key for every CPE version
+            # which allows matching to the specific obj data of that
+            # NIST dict entry
+            self.all_cpes.update({cpe_str: item})
+            # This dict has one entry for every CPE (w/o version) to allow
+            # partial match (no valid version) check (the obj is saved and
+            # used as seed for suggested xml updates. By updating the same
+            # non-version'd entry, it assumes the last update here is the
+            # latest version in the NIST dict)
+            self.all_cpes_no_version.update({cpe_str_no_version: item})
+
+    def find_partial(self, cpe_str):
+        cpe_str_no_version = CPE.no_version(cpe_str)
+        if cpe_str_no_version in self.all_cpes_no_version:
+            return cpe_str_no_version
+
+    def find_partial_obj(self, cpe_str):
+        cpe_str_no_version = CPE.no_version(cpe_str)
+        if cpe_str_no_version in self.all_cpes_no_version:
+            return self.all_cpes_no_version[cpe_str_no_version]
+
+    def find_partial_latest_version(self, cpe_str_partial):
+        cpe_obj = self.find_partial_obj(cpe_str_partial)
+        return cpe_obj.cpe_cur_ver
+
+    def find(self, cpe_str):
+        if self.find_partial(cpe_str):
+            if cpe_str in self.all_cpes:
+                return cpe_str
+
+    def gen_update_xml(self, cpe_str):
+        cpe = self.find_partial_obj(cpe_str)
+        return cpe.update_xml_dict()