[tor-bugs] #10333 [BridgeDB]: Indexing list-like objects by 0L in Bridges.getConfigLine

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#10333: Indexing list-like objects by 0L in Bridges.getConfigLine
----------------------+----------------------
 Reporter:  isis      |          Owner:  isis
     Type:  defect    |         Status:  new
 Priority:  normal    |      Milestone:
Component:  BridgeDB  |        Version:
 Keywords:            |  Actual Points:
Parent ID:            |         Points:
----------------------+----------------------
 This bug occurs because, in the function
 `bridgedb.Bridges.getConfigLine()`, the following lines determine ― when a
 request comes in ― the client's position in the hashring:

 {{{
         if not request: request = 'default'
         digest = get_hmac_fn('Order-Or-Addresses')(request)
         pos = long(digest[:8], 16) # lower 8 bytes -> long
 }}}

 Later on, in the same function, `pos` modulo the number of addresses this
 `Bridge` has, is used to index the collected/filtered addresses.
 Similarly, `pos` modulo the number of ports in the portlist is used to
 index the portlist:

 {{{
         # default ip, orport should get a chance at being selected
         if isinstance(self.ip, addressClass):
             addresses.insert(0,(self.ip, addr.PortList(self.orport)))

         if addresses:
             address,portlist = addresses[pos % len(addresses)]
             if isinstance(address, ipaddr.IPv6Address): ip =
 "[%s]"%address
             else: ip = "%s"%address
             orport = portlist[pos % len(portlist)]
 }}}

 Meaning that the fewer number of addresses/ports there are, the higher the
 chance that the `pos` will be modulo some small number which is a factor.
 For example, if there is only one address, this would be something like:

 {{{
 >>>from bridgedb import Bridges
 >>> digest = Bridges.get_hmac_fn('Order-Or-Addresses')('default')
 >>> pos = long(digest[:8], 16)
 >>> pos
 3790090317L
 >>> pos % 1
 0L
 }}}

 Which causes the following bug. What is extra strange is that the
 ValueError from trying to index these list-like things with a `0L` doesn't
 seem to occur on the addresses, only on the `orport = portlist[…` line.
 Though, it's also worth noting that the `'default'` value used in the hmac
 generation is usually a client's IP address, truncated to the /24. This
 means that this indexing-by-0L bug will occur
 rather indeterminately.

 {{{
 (bridgedb)∃!isisⒶwintermute:(fix/9462-refactor-netstatus-parsers_r9462C
 *+$=)~/code/torproject/bridgedb ∴ bridgedb
 Unhandled Error
 Traceback (most recent call last):
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/twisted/protocols/basic.py", line 571, in dataReceived
     why = self.lineReceived(line)
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/twisted/web/http.py", line 1619, in lineReceived
     self.allContentReceived()
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/twisted/web/http.py", line 1694, in allContentReceived
     req.requestReceived(command, path, version)
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/twisted/web/http.py", line 790, in requestReceived
     self.process()
 --- <exception caught here> ---
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/twisted/web/server.py", line 189, in process
     self.render(resrc)
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/twisted/web/server.py", line 238, in render
     body = resrc.render(self)
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/bridgedb-0.0.1_274_g594a221_dirty-
 py2.7.egg/bridgedb/HTTPServer.py", line 140, in render
     return self.getBridgeRequestAnswer(request)
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/bridgedb-0.0.1_274_g594a221_dirty-
 py2.7.egg/bridgedb/HTTPServer.py", line 218, in getBridgeRequestAnswer
     ) for b in bridges)
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/bridgedb-0.0.1_274_g594a221_dirty-
 py2.7.egg/bridgedb/HTTPServer.py", line 218, in <genexpr>
     ) for b in bridges)
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/bridgedb-0.0.1_274_g594a221_dirty-py2.7.egg/bridgedb/Bridges.py",
 line 192, in getConfigLine
     orport = portlist[pos % len(portlist)]
   File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-
 packages/bridgedb-0.0.1_274_g594a221_dirty-
 py2.7.egg/bridgedb/parse/addr.py", line 372, in __getitem__
     return portlist[portlist.index(port)]
 exceptions.ValueError: 0L is not in list
 ^C
 }}}

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/10333>
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