Fall back to plain ZMQ if Curve is not available.

Use global flag for ZMQ_HAS_CURVE.
Closes #6646

8 files changed, 114 insertions, 44 deletions

diff --git a/changes/non-curve-zmq b/changes/non-curve-zmq
new file mode 100644
index 00000000..8c1097ee
--- /dev/null
+++ b/changes/non-curve-zmq
@@ -0,0 +1 @@
+- Gracefully fall back to plain ZMQ if CurveZMQ is not available (Feature #6646)
diff --git a/src/leap/bitmask/backend/backend.py b/src/leap/bitmask/backend/backend.py
index 75eff8a9..32f5c953 100644
--- a/src/leap/bitmask/backend/backend.py
+++ b/src/leap/bitmask/backend/backend.py
@@ -28,10 +28,14 @@ import psutil
 from twisted.internet import defer, reactor, threads
 
 import zmq
-from zmq.auth.thread import ThreadAuthenticator
+try:
+    from zmq.auth.thread import ThreadAuthenticator
+except ImportError:
+    pass
 
 from leap.bitmask.backend.api import API, PING_REQUEST
 from leap.bitmask.backend.utils import get_backend_certificates
+from leap.bitmask.config import flags
 from leap.bitmask.backend.signaler import Signaler
 
 import logging
@@ -73,18 +77,19 @@ class Backend(object):
         context = zmq.Context()
         socket = context.socket(zmq.REP)
 
-        # Start an authenticator for this context.
-        auth = ThreadAuthenticator(context)
-        auth.start()
-        # XXX do not hardcode this here.
-        auth.allow('127.0.0.1')
-
-        # Tell authenticator to use the certificate in a directory
-        auth.configure_curve(domain='*', location=zmq.auth.CURVE_ALLOW_ANY)
-        public, secret = get_backend_certificates()
-        socket.curve_publickey = public
-        socket.curve_secretkey = secret
-        socket.curve_server = True  # must come before bind
+        if flags.ZMQ_HAS_CURVE:
+            # Start an authenticator for this context.
+            auth = ThreadAuthenticator(context)
+            auth.start()
+            # XXX do not hardcode this here.
+            auth.allow('127.0.0.1')
+
+            # Tell authenticator to use the certificate in a directory
+            auth.configure_curve(domain='*', location=zmq.auth.CURVE_ALLOW_ANY)
+            public, secret = get_backend_certificates()
+            socket.curve_publickey = public
+            socket.curve_secretkey = secret
+            socket.curve_server = True  # must come before bind
 
         socket.bind(self.BIND_ADDR)
 
diff --git a/src/leap/bitmask/backend/backend_proxy.py b/src/leap/bitmask/backend/backend_proxy.py
index 3e79289f..06e6d840 100644
--- a/src/leap/bitmask/backend/backend_proxy.py
+++ b/src/leap/bitmask/backend/backend_proxy.py
@@ -30,6 +30,7 @@ import zmq
 from leap.bitmask.backend.api import API, STOP_REQUEST, PING_REQUEST
 from leap.bitmask.backend.utils import generate_zmq_certificates_if_needed
 from leap.bitmask.backend.utils import get_backend_certificates
+from leap.bitmask.config import flags
 
 import logging
 logger = logging.getLogger(__name__)
@@ -59,15 +60,16 @@ class BackendProxy(object):
         logger.debug("Connecting to server...")
         socket = context.socket(zmq.REQ)
 
-        # public, secret = zmq.curve_keypair()
-        client_keys = zmq.curve_keypair()
-        socket.curve_publickey = client_keys[0]
-        socket.curve_secretkey = client_keys[1]
+        if flags.ZMQ_HAS_CURVE:
+            # public, secret = zmq.curve_keypair()
+            client_keys = zmq.curve_keypair()
+            socket.curve_publickey = client_keys[0]
+            socket.curve_secretkey = client_keys[1]
 
-        # The client must know the server's public key to make a CURVE
-        # connection.
-        public, _ = get_backend_certificates()
-        socket.curve_serverkey = public
+            # The client must know the server's public key to make a CURVE
+            # connection.
+            public, _ = get_backend_certificates()
+            socket.curve_serverkey = public
 
         socket.setsockopt(zmq.RCVTIMEO, 1000)
         socket.setsockopt(zmq.LINGER, 0)  # Terminate early
diff --git a/src/leap/bitmask/backend/signaler.py b/src/leap/bitmask/backend/signaler.py
index 43cba994..a8498d11 100644
--- a/src/leap/bitmask/backend/signaler.py
+++ b/src/leap/bitmask/backend/signaler.py
@@ -26,6 +26,7 @@ import zmq
 
 from leap.bitmask.backend.api import SIGNALS
 from leap.bitmask.backend.utils import get_frontend_certificates
+from leap.bitmask.config import flags
 
 import logging
 logger = logging.getLogger(__name__)
@@ -49,15 +50,16 @@ class Signaler(object):
         logger.debug("Connecting to signaling server...")
         socket = context.socket(zmq.REQ)
 
-        # public, secret = zmq.curve_keypair()
-        client_keys = zmq.curve_keypair()
-        socket.curve_publickey = client_keys[0]
-        socket.curve_secretkey = client_keys[1]
+        if flags.ZMQ_HAS_CURVE:
+            # public, secret = zmq.curve_keypair()
+            client_keys = zmq.curve_keypair()
+            socket.curve_publickey = client_keys[0]
+            socket.curve_secretkey = client_keys[1]
 
-        # The client must know the server's public key to make a CURVE
-        # connection.
-        public, _ = get_frontend_certificates()
-        socket.curve_serverkey = public
+            # The client must know the server's public key to make a CURVE
+            # connection.
+            public, _ = get_frontend_certificates()
+            socket.curve_serverkey = public
 
         socket.setsockopt(zmq.RCVTIMEO, 1000)
         socket.setsockopt(zmq.LINGER, 0)  # Terminate early
diff --git a/src/leap/bitmask/backend/signaler_qt.py b/src/leap/bitmask/backend/signaler_qt.py
index 433f18ed..94c24648 100644
--- a/src/leap/bitmask/backend/signaler_qt.py
+++ b/src/leap/bitmask/backend/signaler_qt.py
@@ -24,10 +24,14 @@ import time
 from PySide import QtCore
 
 import zmq
-from zmq.auth.thread import ThreadAuthenticator
+try:
+    from zmq.auth.thread import ThreadAuthenticator
+except ImportError:
+    pass
 
 from leap.bitmask.backend.api import SIGNALS
 from leap.bitmask.backend.utils import get_frontend_certificates
+from leap.bitmask.config import flags
 
 import logging
 logger = logging.getLogger(__name__)
@@ -67,17 +71,18 @@ class SignalerQt(QtCore.QObject):
         context = zmq.Context()
         socket = context.socket(zmq.REP)
 
-        # Start an authenticator for this context.
-        auth = ThreadAuthenticator(context)
-        auth.start()
-        auth.allow('127.0.0.1')
-
-        # Tell authenticator to use the certificate in a directory
-        auth.configure_curve(domain='*', location=zmq.auth.CURVE_ALLOW_ANY)
-        public, secret = get_frontend_certificates()
-        socket.curve_publickey = public
-        socket.curve_secretkey = secret
-        socket.curve_server = True  # must come before bind
+        if flags.ZMQ_HAS_CURVE:
+            # Start an authenticator for this context.
+            auth = ThreadAuthenticator(context)
+            auth.start()
+            auth.allow('127.0.0.1')
+
+            # Tell authenticator to use the certificate in a directory
+            auth.configure_curve(domain='*', location=zmq.auth.CURVE_ALLOW_ANY)
+            public, secret = get_frontend_certificates()
+            socket.curve_publickey = public
+            socket.curve_secretkey = secret
+            socket.curve_server = True  # must come before bind
 
         socket.bind(self.BIND_ADDR)
 
diff --git a/src/leap/bitmask/backend/utils.py b/src/leap/bitmask/backend/utils.py
index 18e70743..b2674330 100644
--- a/src/leap/bitmask/backend/utils.py
+++ b/src/leap/bitmask/backend/utils.py
@@ -22,20 +22,63 @@ import os
 import shutil
 import stat
 
-import zmq.auth
+import zmq
 
+try:
+    import zmq.auth
+except ImportError:
+    pass
+
+from leap.bitmask.config import flags
 from leap.bitmask.util import get_path_prefix
 from leap.common.files import mkdir_p
+from leap.common.check import leap_assert
 
 logger = logging.getLogger(__name__)
 
 KEYS_DIR = os.path.join(get_path_prefix(), 'leap', 'zmq_certificates')
 
 
+def _zmq_has_curve():
+    """
+    Return whether the current ZMQ has support for auth and CurveZMQ security.
+
+    :rtype: bool
+
+     Version notes:
+       `zmq.curve_keypair()` is new in version 14.0, new in version libzmq-4.0.
+            Requires libzmq (>= 4.0) to have been linked with libsodium.
+       `zmq.auth` module is new in version 14.1
+       `zmq.has()` is new in version 14.1, new in version libzmq-4.1.
+    """
+    zmq_version = zmq.zmq_version_info()
+    pyzmq_version = zmq.pyzmq_version_info()
+
+    if pyzmq_version >= (14, 1, 0) and zmq_version >= (4, 1):
+        return zmq.has('curve')
+
+    if pyzmq_version < (14, 1, 0):
+        return False
+
+    if zmq_version < (4, 0):
+        # security is new in libzmq 4.0
+        return False
+
+    try:
+        zmq.curve_keypair()
+    except zmq.error.ZMQError:
+        # security requires libzmq to be linked against libsodium
+        return False
+
+    return True
+
+
 def generate_zmq_certificates():
     """
     Generate client and server CURVE certificate files.
     """
+    leap_assert(flags.ZMQ_HAS_CURVE, "CurveZMQ not supported!")
+
     # Create directory for certificates, remove old content if necessary
     if os.path.exists(KEYS_DIR):
         shutil.rmtree(KEYS_DIR)
@@ -53,6 +96,8 @@ def get_frontend_certificates():
     """
     Return the frontend's public and secret certificates.
     """
+    leap_assert(flags.ZMQ_HAS_CURVE, "CurveZMQ not supported!")
+
     frontend_secret_file = os.path.join(KEYS_DIR, "frontend.key_secret")
     public, secret = zmq.auth.load_certificate(frontend_secret_file)
     return public, secret
@@ -62,6 +107,8 @@ def get_backend_certificates(base_dir='.'):
     """
     Return the backend's public and secret certificates.
     """
+    leap_assert(flags.ZMQ_HAS_CURVE, "CurveZMQ not supported!")
+
     backend_secret_file = os.path.join(KEYS_DIR, "backend.key_secret")
     public, secret = zmq.auth.load_certificate(backend_secret_file)
     return public, secret
@@ -84,5 +131,8 @@ def generate_zmq_certificates_if_needed():
     Generate the needed ZMQ certificates for backend/frontend communication if
     needed.
     """
-    if not _certificates_exist():
+    if flags.ZMQ_HAS_CURVE and not _certificates_exist():
         generate_zmq_certificates()
+
+
+flags.ZMQ_HAS_CURVE = _zmq_has_curve()
diff --git a/src/leap/bitmask/backend_app.py b/src/leap/bitmask/backend_app.py
index 286b04f7..3e88a95a 100644
--- a/src/leap/bitmask/backend_app.py
+++ b/src/leap/bitmask/backend_app.py
@@ -23,6 +23,7 @@ import signal
 
 from leap.bitmask.backend.leapbackend import LeapBackend
 from leap.bitmask.backend.utils import generate_zmq_certificates
+from leap.bitmask.config import flags
 from leap.bitmask.logs.utils import create_logger
 from leap.bitmask.util import dict_to_flags
 
@@ -57,7 +58,8 @@ def run_backend(bypass_checks=False, flags_dict=None, frontend_pid=None):
     """
     # The backend is the one who always creates the certificates. Either if it
     # is run separately or in a process in the same app as the frontend.
-    generate_zmq_certificates()
+    if flags.ZMQ_HAS_CURVE:
+        generate_zmq_certificates()
 
     # ignore SIGINT since app.py takes care of signaling SIGTERM to us.
     signal.signal(signal.SIGINT, signal.SIG_IGN)
diff --git a/src/leap/bitmask/config/flags.py b/src/leap/bitmask/config/flags.py
index 6b70659d..cdde1971 100644
--- a/src/leap/bitmask/config/flags.py
+++ b/src/leap/bitmask/config/flags.py
@@ -55,3 +55,6 @@ OPENVPN_VERBOSITY = 1
 
 # Skip the checks in the wizard, use for testing purposes only!
 SKIP_WIZARD_CHECKS = False
+
+# This flag tells us whether the current pyzmq supports using CurveZMQ or not.
+ZMQ_HAS_CURVE = None