add support for add/remove CA Certificates via cloud-config (LP: #915232)

LP: #915232

2 files changed, 130 insertions, 5 deletions

diff --git a/cloudinit/CloudConfig/cc_ca_certs.py b/cloudinit/CloudConfig/cc_ca_certs.py
new file mode 100644
index 00000000..c18821f9
--- /dev/null
+++ b/cloudinit/CloudConfig/cc_ca_certs.py
@@ -0,0 +1,88 @@
+# vi: ts=4 expandtab
+#
+#    Author: Mike Milner <mike.milner@canonical.com>
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License version 3, as
+#    published by the Free Software Foundation.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+import os
+from subprocess import check_call
+from cloudinit.util import (write_file, get_cfg_option_list_or_str,
+                            delete_dir_contents)
+
+CA_CERT_PATH = "/usr/share/ca-certificates/"
+CA_CERT_FILENAME = "cloud-init-ca-certs.crt"
+CA_CERT_CONFIG = "/etc/ca-certificates.conf"
+CA_CERT_SYSTEM_PATH = "/etc/ssl/certs/"
+
+
+def update_ca_certs():
+    """
+    Updates the CA certificate cache on the current machine.
+    """
+    check_call(["update-ca-certificates"])
+
+
+def add_ca_certs(certs):
+    """
+    Adds certificates to the system. To actually apply the new certificates
+    you must also call L{update_ca_certs}.
+
+    @param certs: A list of certificate strings.
+    """
+    if certs:
+        cert_file_contents = "\n".join(certs)
+        cert_file_fullpath = os.path.join(CA_CERT_PATH, CA_CERT_FILENAME)
+        write_file(cert_file_fullpath, cert_file_contents, mode=0644)
+        # Append cert filename to CA_CERT_CONFIG file.
+        write_file(CA_CERT_CONFIG, "\n%s" % CA_CERT_FILENAME, omode="a")
+
+
+def remove_default_ca_certs():
+    """
+    Removes all default trusted CA certificates from the system. To actually
+    apply the change you must also call L{update_ca_certs}.
+    """
+    delete_dir_contents(CA_CERT_PATH)
+    delete_dir_contents(CA_CERT_SYSTEM_PATH)
+    write_file(CA_CERT_CONFIG, "", mode=0644)
+
+
+def handle(_name, cfg, _cloud, log, _args):
+    """
+    Call to handle ca-cert sections in cloud-config file.
+
+    @param name: The module name "ca-cert" from cloud.cfg
+    @param cfg: A nested dict containing the entire cloud config contents.
+    @param cloud: The L{CloudInit} object in use.
+    @param log: Pre-initialized Python logger object to use for logging.
+    @param args: Any module arguments from cloud.cfg
+    """
+    # If there isn't a ca-certs section in the configuration don't do anything
+    if "ca-certs" not in cfg:
+        return
+    ca_cert_cfg = cfg['ca-certs']
+
+    # If there is a remove-defaults option set to true, remove the system
+    # default trusted CA certs first.
+    if ca_cert_cfg.get("remove-defaults", False):
+        log.debug("removing default certificates")
+        remove_default_ca_certs()
+
+    # If we are given any new trusted CA certs to add, add them.
+    if "trusted" in ca_cert_cfg:
+        trusted_certs = get_cfg_option_list_or_str(ca_cert_cfg, "trusted")
+        if trusted_certs:
+            log.debug("adding %d certificates" % len(trusted_certs))
+            add_ca_certs(trusted_certs)
+
+    # Update the system with the new cert configuration.
+    update_ca_certs()
diff --git a/cloudinit/util.py b/cloudinit/util.py
index d8d735cc..e4337e3a 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -18,6 +18,7 @@
 import yaml
 import os
 import os.path
+import shutil
 import errno
 import subprocess
 from Cheetah.Template import Template
@@ -94,13 +95,24 @@ def get_cfg_option_str(yobj, key, default=None):
 
 
 def get_cfg_option_list_or_str(yobj, key, default=None):
-    if key not in yobj:
+    """
+    Gets the C{key} config option from C{yobj} as a list of strings. If the
+    key is present as a single string it will be returned as a list with one
+    string arg.
+
+    @param yobj: The configuration object.
+    @param key: The configuration key to get.
+    @param default: The default to return if key is not found.
+    @return: The configuration option as a list of strings or default if key
+        is not found.
+    """
+    if not key in yobj:
         return default
     if yobj[key] is None:
         return []
     if isinstance(yobj[key], list):
         return yobj[key]
-    return([yobj[key]])
+    return [yobj[key]]
 
 
 # get a cfg entry by its path array
@@ -114,9 +126,11 @@ def get_cfg_by_path(yobj, keyp, default=None):
     return(cur)
 
 
-# merge values from cand into source
-# if src has a key, cand will not override
 def mergedict(src, cand):
+    """
+    Merge values from C{cand} into C{src}. If C{src} has a key C{cand} will
+    not override. Nested dictionaries are merged recursively.
+    """
     if isinstance(src, dict) and isinstance(cand, dict):
         for k, v in cand.iteritems():
             if k not in src:
@@ -126,7 +140,30 @@ def mergedict(src, cand):
     return src
 
 
+def delete_dir_contents(dirname):
+    """
+    Deletes all contents of a directory without deleting the directory itself.
+
+    @param dirname: The directory whose contents should be deleted.
+    """
+    for node in os.listdir(dirname):
+        node_fullpath = os.path.join(dirname, node)
+        if os.path.isdir(node_fullpath):
+            shutil.rmtree(node_fullpath)
+        else:
+            os.unlink(node_fullpath)
+
+
 def write_file(filename, content, mode=0644, omode="wb"):
+    """
+    Writes a file with the given content and sets the file mode as specified.
+    Resotres the SELinux context if possible.
+
+    @param filename: The full path of the file to write.
+    @param content: The content to write to the file.
+    @param mode: The filesystem mode to set on the file.
+    @param omode: The open mode used when opening the file (r, rb, a, etc.)
+    """
     try:
         os.makedirs(os.path.dirname(filename))
     except OSError as e:
@@ -134,7 +171,7 @@ def write_file(filename, content, mode=0644, omode="wb"):
             raise e
 
     f = open(filename, omode)
-    if mode != None:
+    if mode is not None:
         os.chmod(filename, mode)
     f.write(content)
     f.close()