add-build-sshkey: Remove only the master key

This implements a module to directly interact with the ssh-agent
so that the master key may be removed from the ssh-agent without
removing any per-project keys.

Change-Id: Ife91ad8afa9b41b0e779a832e298aca8d61ae98b

roles/add-build-sshkey/README.rst

@@ -3,9 +3,10 @@ Generate and install a build-local SSH key on all hosts
 This role is intended to be run on the Zuul Executor at the start of
 every job.  It generates an SSH keypair and installs the public key in
 the authorized_keys file of every host in the inventory.  It then
-removes all keys from this job's SSH agent so that the original key
-used to log into all of the hosts is no longer accessible, then adds
-the newly generated private key.
+removes the Zuul master key from this job's SSH agent so that the
+original key used to log into all of the hosts is no longer accessible
+(any per-project keys, if present, remain available), then adds the
+newly generated private key.
 
 **Role Variables**
 

roles/add-build-sshkey/library/sshagent_remove_keys.py

@@ -0,0 +1,126 @@
+# Copyright 2018 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import argparse
+import os
+import socket
+import struct
+import sys
+import re
+
+from ansible.module_utils.basic import AnsibleModule
+
+
+SSH_AGENT_FAILURE = 5
+SSH_AGENT_SUCCESS = 6
+SSH_AGENT_IDENTITIES_ANSWER = 12
+
+SSH_AGENTC_REQUEST_IDENTITIES = 11
+SSH_AGENTC_REMOVE_IDENTITY = 18
+
+
+def unpack_string(data):
+    (l,) = struct.unpack('!i', data[:4])
+    d = data[4:4 + l]
+    return (d, data[4 + l:])
+
+
+def pack_string(data):
+    ret = struct.pack('!i', len(data))
+    return ret + data
+
+
+class Agent(object):
+    def __init__(self):
+        path = os.environ['SSH_AUTH_SOCK']
+        self.sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        self.sock.connect(path)
+
+    def send(self, message_type, contents):
+        payload = struct.pack('!ib', len(contents) + 1, message_type)
+        payload += bytearray(contents)
+        self.sock.send(payload)
+
+    def recv(self):
+        buf = b''
+        while len(buf) < 5:
+            buf += self.sock.recv(1)
+        message_len, message_type = struct.unpack('!ib', buf[:5])
+        buf = buf[5:]
+        while len(buf) < message_len - 1:
+            buf += self.sock.recv(1)
+        return message_type, buf
+
+    def list(self):
+        self.send(SSH_AGENTC_REQUEST_IDENTITIES, b'')
+        mtype, data = self.recv()
+        if mtype != SSH_AGENT_IDENTITIES_ANSWER:
+            raise Exception("Invalid response to list")
+        (nkeys,) = struct.unpack('!i', data[:4])
+        data = data[4:]
+        keys = []
+        for i in range(nkeys):
+            blob, data = unpack_string(data)
+            comment, data = unpack_string(data)
+            keys.append((blob, comment))
+        return keys
+
+    def remove(self, blob):
+        self.send(SSH_AGENTC_REMOVE_IDENTITY, pack_string(blob))
+        mtype, data = self.recv()
+        if mtype != SSH_AGENT_SUCCESS:
+            raise Exception("Key was not removed")
+
+
+def run(remove):
+    a = Agent()
+    keys = a.list()
+    removed = []
+    to_remove = re.compile(remove)
+    for blob, comment in keys:
+        if not to_remove.match(comment.decode('utf8')):
+            continue
+        a.remove(blob)
+        removed.append(comment)
+    return removed
+
+
+def ansible_main():
+    module = AnsibleModule(
+        argument_spec=dict(
+            remove=dict(required=True, type='str')))
+
+    removed = run(module.params.get('remove'))
+
+    module.exit_json(changed=(removed != []),
+                     removed=removed)
+
+
+def cli_main():
+    parser = argparse.ArgumentParser(
+        description="Remove ssh keys from agent"
+    )
+    parser.add_argument('remove', nargs='+',
+                        help='regex matching comments of keys to remove')
+    args = parser.parse_args()
+
+    removed = run(args.remove)
+    print(removed)
+
+
+if __name__ == '__main__':
+    if sys.stdin.isatty():
+        cli_main()
+    else:
+        ansible_main()

roles/add-build-sshkey/library/test_sshagent_remove_keys.py

@@ -0,0 +1,85 @@
+# Copyright (C) 2018 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+#
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import absolute_import
+
+import os
+import testtools
+import fixtures
+import subprocess
+import paramiko
+import signal
+
+from .sshagent_remove_keys import Agent, run
+
+
+class AgentFixture(fixtures.Fixture):
+
+    def _setUp(self):
+        self.env = {}
+        with open('/dev/null', 'r+') as devnull:
+            ssh_agent = subprocess.Popen(['ssh-agent'], close_fds=True,
+                                         stdout=subprocess.PIPE,
+                                         stderr=devnull,
+                                         stdin=devnull)
+        (output, _) = ssh_agent.communicate()
+        output = output.decode('utf8')
+        for line in output.split("\n"):
+            if '=' in line:
+                line = line.split(";", 1)[0]
+                (key, value) = line.split('=')
+                self.env[key] = value
+                os.environ[key] = value
+        self.addCleanup(self.stop)
+
+    def stop(self):
+        if 'SSH_AGENT_PID' in self.env:
+            os.kill(int(self.env['SSH_AGENT_PID']), signal.SIGTERM)
+
+
+class TestAgent(testtools.TestCase):
+    def test_agent(self):
+        """Test the ssh agent library"""
+        self.useFixture(AgentFixture())
+        tmpdir = fixtures.TempDir()
+        self.useFixture(tmpdir)
+
+        k1_path = os.path.join(tmpdir.path, 'key1')
+        k1 = paramiko.RSAKey.generate(bits=1024)
+        k1.write_private_key_file(k1_path)
+        self.assertTrue(os.path.exists(k1_path))
+        subprocess.call(['ssh-add', k1_path])
+
+        k2_path = os.path.join(tmpdir.path, 'key2')
+        k2 = paramiko.RSAKey.generate(bits=1024)
+        k2.write_private_key_file(k2_path)
+        self.assertTrue(os.path.exists(k2_path))
+        with open(k2_path, 'r') as f:
+            k2_private = f.read()
+        proc = subprocess.Popen(['ssh-add', '-'],
+                                stdin=subprocess.PIPE,
+                                stderr=subprocess.PIPE)
+        proc.communicate(input=k2_private.encode('utf8'))
+
+        a = Agent()
+        l = a.list()
+        self.assertEqual(2, len(l))
+
+        run('^(?!\(stdin\)).*')
+
+        l = a.list()
+        self.assertEqual(1, len(l))
+        self.assertTrue(b'stdin' in l[0][1])

roles/add-build-sshkey/tasks/create-key-and-replace.yaml

@@ -29,8 +29,11 @@
     mode: 0644
     force: no
 
-- name: Remove all keys from local agent
-  command: ssh-add -D
+- name: Remove master key from local agent
+  # The master key has a filename, all others (e.g., per-project keys)
+  # have "(stdin)" as a comment.
+  sshagent_remove_keys:
+    remove: '^(?!\(stdin\)).*'
   delegate_to: localhost
   run_once: true
 

tox.ini

@@ -51,6 +51,6 @@ commands = {posargs}
 # These are ignored intentionally in openstack-infra projects;
 # please don't submit patches that solely correct them or enable them.
 # E402 - ansible modules put documentation before imports. Align to ansible.
-ignore = E125,E129,E402,H
+ignore = E125,E129,E402,E741,H
 show-source = True
 exclude = .venv,.tox,dist,doc,build,*.egg