azure: Filter list of ssh keys pulled from fabric

The Azure data source is expected to expose a list of
ssh keys for the user-to-be-provisioned in the crawled
metadata. When configured to use the __builtin__ agent
this list is built by the WALinuxAgentShim. The shim
retrieves the full set of certificates and public keys
exposed to the VM from the wireserver, extracts any
ssh keys it can, and returns that list.

This fix reduces that list of ssh keys to just the
ones whose fingerprints appear in the "administrative
user" section of the ovf-env.xml file. The Azure
control plane exposes other ssh keys to the VM for
other reasons, but those should not be added to the
authorized_keys file for the provisioned user.

1 files changed, 78 insertions, 31 deletions

diff --git a/cloudinit/sources/helpers/azure.py b/cloudinit/sources/helpers/azure.py
index e5696b1f..2829dd20 100644
--- a/cloudinit/sources/helpers/azure.py
+++ b/cloudinit/sources/helpers/azure.py
@@ -138,9 +138,36 @@ class OpenSSLManager(object):
             self.certificate = certificate
         LOG.debug('New certificate generated.')
 
-    def parse_certificates(self, certificates_xml):
-        tag = ElementTree.fromstring(certificates_xml).find(
-            './/Data')
+    @staticmethod
+    def _run_x509_action(action, cert):
+        cmd = ['openssl', 'x509', '-noout', action]
+        result, _ = util.subp(cmd, data=cert)
+        return result
+
+    def _get_ssh_key_from_cert(self, certificate):
+        pub_key = self._run_x509_action('-pubkey', certificate)
+        keygen_cmd = ['ssh-keygen', '-i', '-m', 'PKCS8', '-f', '/dev/stdin']
+        ssh_key, _ = util.subp(keygen_cmd, data=pub_key)
+        return ssh_key
+
+    def _get_fingerprint_from_cert(self, certificate):
+        """openssl x509 formats fingerprints as so:
+        'SHA1 Fingerprint=07:3E:19:D1:4D:1C:79:92:24:C6:A0:FD:8D:DA:\
+        B6:A8:BF:27:D4:73\n'
+
+        Azure control plane passes that fingerprint as so:
+        '073E19D14D1C799224C6A0FD8DDAB6A8BF27D473'
+        """
+        raw_fp = self._run_x509_action('-fingerprint', certificate)
+        eq = raw_fp.find('=')
+        octets = raw_fp[eq+1:-1].split(':')
+        return ''.join(octets)
+
+    def _decrypt_certs_from_xml(self, certificates_xml):
+        """Decrypt the certificates XML document using the our private key;
+           return the list of certs and private keys contained in the doc.
+        """
+        tag = ElementTree.fromstring(certificates_xml).find('.//Data')
         certificates_content = tag.text
         lines = [
             b'MIME-Version: 1.0',
@@ -151,32 +178,30 @@ class OpenSSLManager(object):
             certificates_content.encode('utf-8'),
         ]
         with cd(self.tmpdir):
-            with open('Certificates.p7m', 'wb') as f:
-                f.write(b'\n'.join(lines))
             out, _ = util.subp(
-                'openssl cms -decrypt -in Certificates.p7m -inkey'
+                'openssl cms -decrypt -in /dev/stdin -inkey'
                 ' {private_key} -recip {certificate} | openssl pkcs12 -nodes'
                 ' -password pass:'.format(**self.certificate_names),
-                shell=True)
-        private_keys, certificates = [], []
+                shell=True, data=b'\n'.join(lines))
+        return out
+
+    def parse_certificates(self, certificates_xml):
+        """Given the Certificates XML document, return a dictionary of
+           fingerprints and associated SSH keys derived from the certs."""
+        out = self._decrypt_certs_from_xml(certificates_xml)
         current = []
+        keys = {}
         for line in out.splitlines():
             current.append(line)
             if re.match(r'[-]+END .*?KEY[-]+$', line):
-                private_keys.append('\n'.join(current))
+                # ignore private_keys
                 current = []
             elif re.match(r'[-]+END .*?CERTIFICATE[-]+$', line):
-                certificates.append('\n'.join(current))
+                certificate = '\n'.join(current)
+                ssh_key = self._get_ssh_key_from_cert(certificate)
+                fingerprint = self._get_fingerprint_from_cert(certificate)
+                keys[fingerprint] = ssh_key
                 current = []
-        keys = []
-        for certificate in certificates:
-            with cd(self.tmpdir):
-                public_key, _ = util.subp(
-                    'openssl x509 -noout -pubkey |'
-                    'ssh-keygen -i -m PKCS8 -f /dev/stdin',
-                    data=certificate,
-                    shell=True)
-            keys.append(public_key)
         return keys
 
 
@@ -206,7 +231,6 @@ class WALinuxAgentShim(object):
         self.dhcpoptions = dhcp_options
         self._endpoint = None
         self.openssl_manager = None
-        self.values = {}
         self.lease_file = fallback_lease_file
 
     def clean_up(self):
@@ -328,8 +352,9 @@ class WALinuxAgentShim(object):
         LOG.debug('Azure endpoint found at %s', endpoint_ip_address)
         return endpoint_ip_address
 
-    def register_with_azure_and_fetch_data(self):
-        self.openssl_manager = OpenSSLManager()
+    def register_with_azure_and_fetch_data(self, pubkey_info=None):
+        if self.openssl_manager is None:
+            self.openssl_manager = OpenSSLManager()
         http_client = AzureEndpointHttpClient(self.openssl_manager.certificate)
         LOG.info('Registering with Azure...')
         attempts = 0
@@ -347,16 +372,37 @@ class WALinuxAgentShim(object):
             attempts += 1
         LOG.debug('Successfully fetched GoalState XML.')
         goal_state = GoalState(response.contents, http_client)
-        public_keys = []
-        if goal_state.certificates_xml is not None:
+        ssh_keys = []
+        if goal_state.certificates_xml is not None and pubkey_info is not None:
             LOG.debug('Certificate XML found; parsing out public keys.')
-            public_keys = self.openssl_manager.parse_certificates(
+            keys_by_fingerprint = self.openssl_manager.parse_certificates(
                 goal_state.certificates_xml)
-        data = {
-            'public-keys': public_keys,
-        }
+            ssh_keys = self._filter_pubkeys(keys_by_fingerprint, pubkey_info)
         self._report_ready(goal_state, http_client)
-        return data
+        return {'public-keys': ssh_keys}
+
+    def _filter_pubkeys(self, keys_by_fingerprint, pubkey_info):
+        """cloud-init expects a straightforward array of keys to be dropped
+           into the user's authorized_keys file. Azure control plane exposes
+           multiple public keys to the VM via wireserver. Select just the
+           user's key(s) and return them, ignoring any other certs.
+        """
+        keys = []
+        for pubkey in pubkey_info:
+            if 'value' in pubkey and pubkey['value']:
+                keys.append(pubkey['value'])
+            elif 'fingerprint' in pubkey and pubkey['fingerprint']:
+                fingerprint = pubkey['fingerprint']
+                if fingerprint in keys_by_fingerprint:
+                    keys.append(keys_by_fingerprint[fingerprint])
+                else:
+                    LOG.warning("ovf-env.xml specified PublicKey fingerprint "
+                                "%s not found in goalstate XML", fingerprint)
+            else:
+                LOG.warning("ovf-env.xml specified PublicKey with neither "
+                            "value nor fingerprint: %s", pubkey)
+
+        return keys
 
     def _report_ready(self, goal_state, http_client):
         LOG.debug('Reporting ready to Azure fabric.')
@@ -373,11 +419,12 @@ class WALinuxAgentShim(object):
         LOG.info('Reported ready to Azure fabric.')
 
 
-def get_metadata_from_fabric(fallback_lease_file=None, dhcp_opts=None):
+def get_metadata_from_fabric(fallback_lease_file=None, dhcp_opts=None,
+                             pubkey_info=None):
     shim = WALinuxAgentShim(fallback_lease_file=fallback_lease_file,
                             dhcp_options=dhcp_opts)
     try:
-        return shim.register_with_azure_and_fetch_data()
+        return shim.register_with_azure_and_fetch_data(pubkey_info=pubkey_info)
     finally:
         shim.clean_up()