Use secure method to acquire IPA CA certificate

Major changes ipa-client-install:

* Use GSSAPI connection to LDAP server to download CA cert (now
  the default method)

* Add --ca-cert-file option to load the CA cert from a disk file.
  Validate the file. If this option is used the supplied CA cert
  is considered definitive.

* The insecure HTTP retrieval method is still supported but it must be
  explicitly forced and a warning will be emitted.

* Remain backward compatible with unattended case (except for aberrant
  condition when preexisting /etc/ipa/ca.crt differs from securely
  obtained CA cert, see below)

* If /etc/ipa/ca.crt CA cert preexists the validate it matches the
  securely acquired CA cert, if not:

  - If --unattended and not --force abort with error

  - If interactive query user to accept new CA cert, if not abort

  In either case warn user.

* If interactive and LDAP retrieval fails prompt user if they want to
  proceed with insecure HTTP method

* If not interactive and LDAP retrieval fails abort unless --force

* Backup preexisting /etc/ipa/ca.crt in FileStore prior to execution,
  if ipa-client-install fails it will be restored.

Other changes:

* Add new exception class CertificateInvalidError

* Add utility convert_ldap_error() to ipalib.ipautil

* Replace all hardcoded instances of /etc/ipa/ca.crt in
  ipa-client-install with CACERT constant (matches existing practice
  elsewhere).

* ipadiscovery no longer retrieves CA cert via HTTP.

* Handle LDAP minssf failures during discovery, treat failure to check
  ldap server as a warninbg in absebce of a provided CA certificate via
  --ca-cert-file or though existing /etc/ipa/ca.crt file.

Signed-off-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Rob Crittenden <rcritten@redhat.com>

ipa-client/ipaclient/ipadiscovery.py

@@ -30,11 +30,14 @@ from ipapython.ipautil import run, CalledProcessError, valid_ip, get_ipa_basedn,
                               realm_to_suffix, format_netloc
 from ipapython.dn import DN
 
+CACERT = '/etc/ipa/ca.crt'
+
 NOT_FQDN = -1
 NO_LDAP_SERVER = -2
 REALM_NOT_FOUND = -3
 NOT_IPA_SERVER = -4
 NO_ACCESS_TO_LDAP = -5
+NO_TLS_LDAP = -6
 BAD_HOST_CONFIG = -10
 UNKNOWN_ERROR = -15
 
@@ -45,6 +48,7 @@ error_names = {
     REALM_NOT_FOUND: 'REALM_NOT_FOUND',
     NOT_IPA_SERVER: 'NOT_IPA_SERVER',
     NO_ACCESS_TO_LDAP: 'NO_ACCESS_TO_LDAP',
+    NO_TLS_LDAP: 'NO_TLS_LDAP',
     BAD_HOST_CONFIG: 'BAD_HOST_CONFIG',
     UNKNOWN_ERROR: 'UNKNOWN_ERROR',
 }
@@ -135,7 +139,7 @@ class IPADiscovery(object):
                 domain = domain[p+1:]
         return (None, None)
 
-    def search(self, domain = "", server = "", hostname=None):
+    def search(self, domain = "", server = "", hostname=None, ca_cert_path=None):
         root_logger.debug("[IPA Discovery]")
         root_logger.debug(
             'Starting IPA discovery with domain=%s, server=%s, hostname=%s',
@@ -224,14 +228,14 @@ class IPADiscovery(object):
         ldapaccess = True
         if self.server:
             # check ldap now
-            ldapret = self.ipacheckldap(self.server, self.realm)
+            ldapret = self.ipacheckldap(self.server, self.realm, ca_cert_path=ca_cert_path)
 
             if ldapret[0] == 0:
                 self.server = ldapret[1]
                 self.realm = ldapret[2]
                 self.server_source = self.realm_source = (
                     'Discovered from LDAP DNS records in %s' % self.server)
-            elif ldapret[0] == NO_ACCESS_TO_LDAP:
+            elif ldapret[0] == NO_ACCESS_TO_LDAP or ldapret[0] == NO_TLS_LDAP:
                 ldapaccess = False
 
         # If one of LDAP servers checked rejects access (maybe anonymous
@@ -260,12 +264,10 @@ class IPADiscovery(object):
 
         return ldapret[0]
 
-    def ipacheckldap(self, thost, trealm):
+    def ipacheckldap(self, thost, trealm, ca_cert_path=None):
         """
         Given a host and kerberos realm verify that it is an IPA LDAP
-        server hosting the realm. The connection is an SSL connection
-        so the remote IPA CA cert must be available at
-        http://HOST/ipa/config/ca.crt
+        server hosting the realm.
 
         Returns a list [errno, host, realm] or an empty list on error.
         Errno is an error number:
@@ -279,31 +281,17 @@ class IPADiscovery(object):
 
         i = 0
 
-        # Get the CA certificate
-        try:
-            # Create TempDir
-            temp_ca_dir = tempfile.mkdtemp()
-        except OSError, e:
-            raise RuntimeError("Creating temporary directory failed: %s" % str(e))
-
-        try:
-            run(["/usr/bin/wget", "-O", "%s/ca.crt" % temp_ca_dir, "-T", "15", "-t", "2",
-                 "http://%s/ipa/config/ca.crt" % format_netloc(thost)])
-        except CalledProcessError, e:
-            root_logger.error('Retrieving CA from %s failed', thost)
-            root_logger.debug('Retrieving CA from %s failed: %s', thost, str(e))
-            return [NOT_IPA_SERVER]
-
         #now verify the server is really an IPA server
         try:
             ldap_url = "ldap://" + format_netloc(thost, 389)
             root_logger.debug("Init LDAP connection with: %s", ldap_url)
             lh = ldap.initialize(ldap_url)
-            ldap.set_option(ldap.OPT_X_TLS_REQUIRE_CERT, True)
-            ldap.set_option(ldap.OPT_X_TLS_CACERTFILE, "%s/ca.crt" % temp_ca_dir)
+            if ca_cert_path:
+                ldap.set_option(ldap.OPT_X_TLS_REQUIRE_CERT, True)
+                ldap.set_option(ldap.OPT_X_TLS_CACERTFILE, ca_cert_path)
+                lh.set_option(ldap.OPT_X_TLS_DEMAND, True)
+                lh.start_tls_s()
             lh.set_option(ldap.OPT_PROTOCOL_VERSION, 3)
-            lh.set_option(ldap.OPT_X_TLS_DEMAND, True)
-            lh.start_tls_s()
             lh.simple_bind_s("","")
 
             # get IPA base DN
@@ -358,14 +346,16 @@ class IPADiscovery(object):
                 root_logger.debug("LDAP Error: Anonymous acces not allowed")
                 return [NO_ACCESS_TO_LDAP]
 
+            # We should only get UNWILLING_TO_PERFORM if the remote LDAP server
+            # has minssf > 0 and we have attempted a non-TLS connection.
+            if ca_cert_path is None and isinstance(err, ldap.UNWILLING_TO_PERFORM):
+                root_logger.debug("LDAP server returned UNWILLING_TO_PERFORM. This likely means that minssf is enabled")
+                return [NO_TLS_LDAP]
+
             root_logger.error("LDAP Error: %s: %s" %
                (err.args[0]['desc'], err.args[0].get('info', '')))
             return [UNKNOWN_ERROR]
 
-        finally:
-            os.remove("%s/ca.crt" % temp_ca_dir)
-            os.rmdir(temp_ca_dir)
-
 
     def ipadns_search_srv(self, domain, srv_record_name, default_port,
                           break_on_first=True):