Experimental libhal RPC MUX based on PySerial and Tornado.

This is a work in progress, so far it only works with libhal.py
client, haven't adapted libhal C client code for this yet.

General idea is to let PySerial and Tornado handle all the pesky work
of dealing with Unix serial ports, PF_LOCAL connection management,
select() vs epoll() vs kqueue() vs ... I/O management, etcetera.

We could do this with just PySerial and the Python standard libraries,
but using Tornado allows us to do it in a single process, without
threading, and also leaves the door open for consolidating other HSM
management functions (eg, console access) into the same single daemon
process.

For the moment we're using SLIP framing over a SOCK_STREAM connection,
which is a bit silly but avoids the problem of OSX not supporting
SOCK_SEQPACKET.  In the long run we're going to want a real channel
security protocol here, so don't sweat this too much right now.

1 files changed, 180 insertions, 0 deletions

diff --git a/cryptech_rpcmuxd b/cryptech_rpcmuxd
new file mode 100644
index 0000000..d08d6df
--- /dev/null
+++ b/cryptech_rpcmuxd
@@ -0,0 +1,180 @@
+#!/usr/bin/env python
+#
+# Copyright (c) 2016, NORDUnet A/S All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+# - Redistributions of source code must retain the above copyright notice,
+#   this list of conditions and the following disclaimer.
+#
+# - Redistributions in binary form must reproduce the above copyright
+#   notice, this list of conditions and the following disclaimer in the
+#   documentation and/or other materials provided with the distribution.
+#
+# - Neither the name of the NORDUnet nor the names of its contributors may
+#   be used to endorse or promote products derived from this software
+#   without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+# IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+# TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+# TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+# LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+# NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""
+Implementation of Cryptech RPC protocol multiplexer in Python.
+
+Unlike the original C implementation, this uses SLIP encapsulation
+over a SOCK_STREAM channel, because support for SOCK_SEQPACKET is not
+what we might wish.  We outsource all the heavy lifting for serial and
+network I/O to the PySerial and Tornado libraries, respectively.
+"""
+
+import os
+import sys
+import time
+import struct
+import atexit
+import weakref
+import argparse
+
+import serial
+
+import tornado.tcpserver
+import tornado.iostream
+import tornado.netutil
+import tornado.ioloop
+import tornado.queues
+import tornado.locks
+import tornado.gen
+
+
+SLIP_END     = chr(0300)        # Indicates end of SLIP packet
+SLIP_ESC     = chr(0333)        # Indicates byte stuffing
+SLIP_ESC_END = chr(0334)        # ESC ESC_END means END data byte
+SLIP_ESC_ESC = chr(0335)        # ESC ESC_ESC means ESC data byte
+
+
+def slip_encode(buffer):
+    "Encode a buffer using SLIP encapsulation."
+    return SLIP_END + buffer.replace(SLIP_ESC, SLIP_ESC + SLIP_ESC_ESC).replace(SLIP_END, SLIP_ESC + SLIP_ESC_END) + SLIP_END
+
+def slip_decode(buffer):
+    "Decode a SLIP-encapsulated buffer."
+    return buffer.strip(SLIP_END).replace(SLIP_ESC + SLIP_ESC_END, SLIP_END).replace(SLIP_ESC + SLIP_ESC_ESC, SLIP_ESC)
+
+
+def client_handle_get(msg):
+    "Extract client_handle field from a Cryptech RPC message."
+    return struct.unpack(">L", msg[4:8])[0]
+
+def client_handle_set(msg, handle):
+    "Replace client_handle field in a Cryptech RPC message."
+    return msg[:4] + struct.pack(">L", handle) + msg[8:]
+
+
+class SerialIOStream(tornado.iostream.BaseIOStream):
+    """
+    Implementation of a Tornado IOStream over a PySerial device.
+    """
+
+    def __init__(self, device, baudrate = 921600, debug = False, *pargs, **kwargs):
+        self.serial = serial.Serial(device, baudrate, timeout = 0, write_timeout = 0)
+        self.queues = weakref.WeakValueDictionary()
+        self.debug = debug
+        self.hsm_write_lock = tornado.locks.Lock()
+        super(SerialIOStream, self).__init__(*pargs, **kwargs)
+
+    # The next four methods are required: BaseIOStream is an abstract
+    # class, we provide a driver by overriding them.
+
+    def fileno(self):
+        return self.serial.fileno()
+
+    def close_fd(self):
+        self.serial.close()
+
+    def write_to_fd(self, data):
+        return self.serial.write(data)
+
+    def read_from_fd(self):
+        return self.serial.read(self.read_chunk_size) or None
+
+    @tornado.gen.coroutine
+    def hsm_write(self, query, handle, queue):
+        "Send a query to the HSM."
+        if self.debug:
+            sys.stdout.write("+send: {}\n".format(":".join("{:02x}".format(ord(c)) for c in query)))
+        self.queues[handle] = queue
+        with (yield self.hsm_write_lock.acquire()):
+            yield self.write(query)
+
+    @tornado.gen.coroutine
+    def hsm_read_loop(self):
+        "Handle reply stream HSM -> network."
+        while True:
+            reply = yield self.read_until(SLIP_END)
+            if self.debug:
+                sys.stdout.write("+recv: {}\n".format(":".join("{:02x}".format(ord(c)) for c in reply)))
+            if len(reply) < 9:
+                continue
+            handle = client_handle_get(slip_decode(reply))
+            self.queues[handle].put_nowait(reply)
+
+
+class UnixServer(tornado.tcpserver.TCPServer):
+    """
+    Variant on tornado.tcpserver.TCPServer, listening on a PF_UNIX
+    (aka PF_LOCAL) socket instead of a TCP socket.
+    """
+
+    def listen(self, filename, mode = 0600):
+        self.add_socket(tornado.netutil.bind_unix_socket(filename, mode))
+
+    def set_serial(self, serial_stream):
+        self.serial = serial_stream
+
+    @tornado.gen.coroutine
+    def handle_stream(self, stream, address):
+        "Handle one network connection."
+        handle = stream.socket.fileno()
+        queue  = tornado.queues.Queue()
+        closed = False
+        while not closed:
+            try:
+                query = yield stream.read_until(SLIP_END)
+                if len(query) < 9:
+                    continue
+                query = slip_encode(client_handle_set(slip_decode(query), handle))
+                yield self.serial.hsm_write(query, handle, queue)
+                reply = yield queue.get()
+                yield stream.write(SLIP_END + reply)
+            except tornado.iostream.StreamClosedError:
+                closed = True
+
+
+parser = argparse.ArgumentParser(formatter_class = argparse.ArgumentDefaultsHelpFormatter)
+parser.add_argument("-v", "--verbose",  action = "store_true",  help = "produce human-readable output")
+parser.add_argument("-d", "--debug",    action = "store_true",  help = "blather about what we're doing")
+parser.add_argument("device",           nargs = "?",            help = "serial device name",
+                    default = os.getenv("CRYPTECH_RPC_CLIENT_SERIAL_DEVICE", "/dev/ttyUSB0"))
+parser.add_argument("socket",           nargs = "?",            help = "PF_UNIX socket name",
+                    default = os.getenv("CRYPTECH_RPC_CLIENT_SOCKET_NAME", "/tmp/.cryptech_rpcmuxd"))
+args = parser.parse_args()
+
+serial_stream = SerialIOStream(device = args.device, debug = args.debug)
+
+unix_server = UnixServer()
+unix_server.set_serial(serial_stream)
+unix_server.listen(args.socket)
+
+atexit.register(os.unlink, args.socket)
+
+tornado.ioloop.IOLoop.current().run_sync(serial_stream.hsm_read_loop)