[tor-commits] [stem/master] Only validate RELAY cells when unencrypted

[atagar at torproject.org]

commit 0d0a018d721db77015453d284bb348e7db72cb84
Author: Damian Johnson <atagar at torproject.org>
Date:   Wed Feb 7 10:35:59 2018 -0800

    Only validate RELAY cells when unencrypted
    
    When the cell is encrypted these fields are obviously essentially noise. In
    practice this seems to be causing inconsistent failures roughly 1/10 of the
    time...
    
      Traceback (most recent call last):
        File "client-or-stream-raw.py", line 30, in <module>
          reply = circ.send('RELAY_BEGIN_DIR', stream_id = 1)
        File "/home/atagar/Desktop/tor/endosome/stem/client/__init__.py", line 246, in send
          reply = next(stem.client.cell.Cell.unpack(self.relay._orport.recv(), self.relay.link_protocol))
        File "/home/atagar/Desktop/tor/endosome/stem/client/cell.py", line 135, in unpack
          cell, content = Cell.pop(content, link_protocol)
        File "/home/atagar/Desktop/tor/endosome/stem/client/cell.py", line 166, in pop
          return cls._unpack(payload, circ_id, link_protocol), content
        File "/home/atagar/Desktop/tor/endosome/stem/client/cell.py", line 349, in _unpack
          return RelayCell(circ_id, command, data, digest, stream_id, recognized)
        File "/home/atagar/Desktop/tor/endosome/stem/client/cell.py", line 327, in __init__
          raise ValueError('%s relay cells concern the circuit itself and cannot have a stream id' % self.command)
      ValueError: RELAY_TRUNCATE relay cells concern the circuit itself and cannot have a stream id
---
 stem/client/__init__.py | 4 +---
 stem/client/cell.py     | 9 +++++----
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/stem/client/__init__.py b/stem/client/__init__.py
index f4fc718b..2b853baa 100644
--- a/stem/client/__init__.py
+++ b/stem/client/__init__.py
@@ -218,7 +218,7 @@ class Circuit(object):
     self.forward_key = Cipher(algorithms.AES(kdf.forward_key), ctr, default_backend()).encryptor()
     self.backward_key = Cipher(algorithms.AES(kdf.backward_key), ctr, default_backend()).decryptor()
 
-  def send(self, command, data, stream_id = 0):
+  def send(self, command, data = '', stream_id = 0):
     """
     Sends a message over the circuit.
 
@@ -227,8 +227,6 @@ class Circuit(object):
     :param int stream_id: specific stream this concerns
     """
 
-    # TODO: move RelayCommand to this base module?
-
     with self.relay._orport_lock:
       orig_digest = self.forward_digest.copy()
       orig_key = copy.copy(self.forward_key)
diff --git a/stem/client/cell.py b/stem/client/cell.py
index 13f14f3c..c5f8f20b 100644
--- a/stem/client/cell.py
+++ b/stem/client/cell.py
@@ -321,10 +321,11 @@ class RelayCell(CircuitCell):
     self.digest = digest
     self.stream_id = stream_id
 
-    if not stream_id and self.command in STREAM_ID_REQUIRED:
-      raise ValueError('%s relay cells require a stream id' % self.command)
-    elif stream_id and self.command in STREAM_ID_DISALLOWED:
-      raise ValueError('%s relay cells concern the circuit itself and cannot have a stream id' % self.command)
+    if digest == 0:
+      if not stream_id and self.command in STREAM_ID_REQUIRED:
+        raise ValueError('%s relay cells require a stream id' % self.command)
+      elif stream_id and self.command in STREAM_ID_DISALLOWED:
+        raise ValueError('%s relay cells concern the circuit itself and cannot have a stream id' % self.command)
 
   def pack(self, link_protocol):
     payload = io.BytesIO()