Allow the backdoor to serve from a local unix domain socket

Local files can be made accessible to certain users vs random
ports which can be accessible to anyone on a machine so allow
using unix files as a way to start the eventlet backdoor (so that
user and group permissions common on unix are not lost).

To use this new type of files `socat` is needed (or other way
to interact with telnet over a unix domain socket).

For example (with the path at /tmp/my_special_socket):

  socat - UNIX-CONNECT:/tmp/my_special_socket

Depends-On: Ia2385879e09991102f8f305ec41dbb651a4374de

Change-Id: I7f25913168ebe5854f360db3d6310b72a56b2b4d

oslo_service/_options.py

@@ -24,7 +24,14 @@ help_for_backdoor_port = (
     "chosen port is displayed in the service's log file.")
 eventlet_backdoor_opts = [
     cfg.StrOpt('backdoor_port',
-               help="Enable eventlet backdoor.  %s" % help_for_backdoor_port)
+               help="Enable eventlet backdoor.  %s" % help_for_backdoor_port),
+    cfg.StrOpt('backdoor_socket',
+               help="Enable eventlet backdoor, using the provided path"
+                    " as a unix socket that can receive connections. This"
+                    " option is mutually exclusive with 'backdoor_port' in"
+                    " that only one should be be provided. If both are"
+                    " provided then the existence of this option overrides"
+                    " the usage of that option.")
 ]
 
 periodic_opts = [

oslo_service/eventlet_backdoor.py

@@ -133,6 +133,27 @@ def _listen(host, start_port, end_port, listen_func):
             try_port += 1
 
 
+def _try_open_unix_domain_socket(socket_path):
+    try:
+        return eventlet.listen(socket_path, socket.AF_UNIX)
+    except socket.error as e:
+        if e.errno != errno.EADDRINUSE:
+            # NOTE(harlowja): Some other non-address in use error
+            # occurred, since we aren't handling those, re-raise
+            # and give up...
+            raise
+        else:
+            # Attempt to remove the file before opening it again.
+            try:
+                os.unlink(socket_path)
+            except OSError as e:
+                if e.errno != errno.ENOENT:
+                    # NOTE(harlowja): File existed, but we couldn't
+                    # delete it, give up...
+                    raise
+            return eventlet.listen(socket_path, socket.AF_UNIX)
+
+
 def _initialize_if_enabled(conf):
     conf.register_opts(_options.eventlet_backdoor_opts)
     backdoor_locals = {
@@ -143,10 +164,18 @@ def _initialize_if_enabled(conf):
         'pnt': _print_nativethreads,
     }
 
-    if conf.backdoor_port is None:
+    if conf.backdoor_port is None and conf.backdoor_socket is None:
         return None
 
-    start_port, end_port = _parse_port_range(str(conf.backdoor_port))
+    if conf.backdoor_socket is None:
+        start_port, end_port = _parse_port_range(str(conf.backdoor_port))
+        sock = _listen('localhost', start_port, end_port, eventlet.listen)
+        # In the case of backdoor port being zero, a port number is assigned by
+        # listen().  In any case, pull the port number out here.
+        where_running = sock.getsockname()[1]
+    else:
+        sock = _try_open_unix_domain_socket(conf.backdoor_socket)
+        where_running = conf.backdoor_socket
 
     # NOTE(johannes): The standard sys.displayhook will print the value of
     # the last expression and set it to __builtin__._, which overwrites
@@ -158,27 +187,23 @@ def _initialize_if_enabled(conf):
             pprint.pprint(val)
     sys.displayhook = displayhook
 
-    sock = _listen('localhost', start_port, end_port, eventlet.listen)
-
-    # In the case of backdoor port being zero, a port number is assigned by
-    # listen().  In any case, pull the port number out here.
-    port = sock.getsockname()[1]
     LOG.info(
-        _LI('Eventlet backdoor listening on %(port)s for process %(pid)d'),
-        {'port': port, 'pid': os.getpid()}
+        _LI('Eventlet backdoor listening on %(where_running)s for'
+            ' process %(pid)d'),
+        {'where_running': where_running, 'pid': os.getpid()}
     )
     thread = eventlet.spawn(eventlet.backdoor.backdoor_server, sock,
                             locals=backdoor_locals)
-    return (port, thread)
+    return (where_running, thread)
 
 
 def initialize_if_enabled(conf):
-    port_thread = _initialize_if_enabled(conf)
-    if not port_thread:
+    where_running_thread = _initialize_if_enabled(conf)
+    if not where_running_thread:
         return None
     else:
-        port, _thread = port_thread
-        return port
+        where_running, _thread = where_running_thread
+        return where_running
 
 
 def _main():
@@ -193,11 +218,11 @@ def _main():
     conf.register_cli_opts(_options.eventlet_backdoor_opts)
     conf(sys.argv[1:])
 
-    port_thread = _initialize_if_enabled(conf)
-    if not port_thread:
-        raise RuntimeError("Did not create backdoor at requested port")
+    where_running_thread = _initialize_if_enabled(conf)
+    if not where_running_thread:
+        raise RuntimeError("Did not create backdoor at requested location")
     else:
-        _port, thread = port_thread
+        _where_running, thread = where_running_thread
         thread.wait()
 
 

oslo_service/tests/test_eventlet_backdoor.py

@@ -18,6 +18,7 @@
 Unit Tests for eventlet backdoor
 """
 import errno
+import os
 import socket
 
 import eventlet
@@ -27,6 +28,63 @@ from oslo_service import eventlet_backdoor
 from oslo_service.tests import base
 
 
+class BackdoorSocketPathTest(base.ServiceBaseTestCase):
+
+    @mock.patch.object(eventlet, 'spawn')
+    @mock.patch.object(eventlet, 'listen')
+    def test_backdoor_path(self, listen_mock, spawn_mock):
+        self.config(backdoor_socket="/tmp/my_special_socket")
+        listen_mock.side_effect = mock.MagicMock()
+        path = eventlet_backdoor.initialize_if_enabled(self.conf)
+        self.assertEqual(path, "/tmp/my_special_socket")
+
+    @mock.patch.object(os, 'unlink')
+    @mock.patch.object(eventlet, 'spawn')
+    @mock.patch.object(eventlet, 'listen')
+    def test_backdoor_path_already_exists(self, listen_mock,
+                                          spawn_mock, unlink_mock):
+        self.config(backdoor_socket="/tmp/my_special_socket")
+        sock = mock.MagicMock()
+        listen_mock.side_effect = [socket.error(errno.EADDRINUSE, ''), sock]
+        path = eventlet_backdoor.initialize_if_enabled(self.conf)
+        self.assertEqual(path, "/tmp/my_special_socket")
+        unlink_mock.assert_called_with("/tmp/my_special_socket")
+
+    @mock.patch.object(os, 'unlink')
+    @mock.patch.object(eventlet, 'spawn')
+    @mock.patch.object(eventlet, 'listen')
+    def test_backdoor_path_already_exists_and_gone(self, listen_mock,
+                                                   spawn_mock, unlink_mock):
+        self.config(backdoor_socket="/tmp/my_special_socket")
+        sock = mock.MagicMock()
+        listen_mock.side_effect = [socket.error(errno.EADDRINUSE, ''), sock]
+        unlink_mock.side_effect = OSError(errno.ENOENT, '')
+        path = eventlet_backdoor.initialize_if_enabled(self.conf)
+        self.assertEqual(path, "/tmp/my_special_socket")
+        unlink_mock.assert_called_with("/tmp/my_special_socket")
+
+    @mock.patch.object(os, 'unlink')
+    @mock.patch.object(eventlet, 'spawn')
+    @mock.patch.object(eventlet, 'listen')
+    def test_backdoor_path_already_exists_and_not_gone(self, listen_mock,
+                                                       spawn_mock,
+                                                       unlink_mock):
+        self.config(backdoor_socket="/tmp/my_special_socket")
+        listen_mock.side_effect = socket.error(errno.EADDRINUSE, '')
+        unlink_mock.side_effect = OSError(errno.EPERM, '')
+        self.assertRaises(OSError, eventlet_backdoor.initialize_if_enabled,
+                          self.conf)
+
+    @mock.patch.object(eventlet, 'spawn')
+    @mock.patch.object(eventlet, 'listen')
+    def test_backdoor_path_no_perms(self, listen_mock, spawn_mock):
+        self.config(backdoor_socket="/tmp/my_special_socket")
+        listen_mock.side_effect = socket.error(errno.EPERM, '')
+        self.assertRaises(socket.error,
+                          eventlet_backdoor.initialize_if_enabled,
+                          self.conf)
+
+
 class BackdoorPortTest(base.ServiceBaseTestCase):
 
     @mock.patch.object(eventlet, 'spawn')