mirror of
https://github.com/torproject/torspec.git
synced 2024-12-12 04:35:37 +00:00
6bd09d5076
Tor doesn't use SVN anymore, making $Revision$, $Id$ and $Date$ meaningless. Remove them without replacement.
58 lines
2.4 KiB
Plaintext
58 lines
2.4 KiB
Plaintext
Filename: 148-uniform-client-end-reason.txt
|
|
Title: Stream end reasons from the client side should be uniform
|
|
Author: Roger Dingledine
|
|
Created: 2-Jul-2008
|
|
Status: Closed
|
|
Implemented-In: 0.2.1.9-alpha
|
|
|
|
Overview
|
|
|
|
When a stream closes before it's finished, the end relay cell that's
|
|
sent includes an "end stream reason" to tell the other end why it
|
|
closed. It's useful for the exit relay to send a reason to the client,
|
|
so the client can choose a different circuit, inform the user, etc. But
|
|
there's no reason to include it from the client to the exit relay,
|
|
and in some cases it can even harm anonymity.
|
|
|
|
We should pick a single reason for the client-to-exit-relay direction
|
|
and always just send that.
|
|
|
|
Motivation
|
|
|
|
Back when I first deployed the Tor network, it was useful to have
|
|
the Tor relays learn why a stream closed, so I could debug both ends
|
|
of the stream at once. Now that streams have worked for many years,
|
|
there's no need to continue telling the exit relay whether the client
|
|
gave up on a stream because of "timeout" or "misc" or what.
|
|
|
|
Then in Tor 0.2.0.28-rc, I fixed this bug:
|
|
- Fix a bug where, when we were choosing the 'end stream reason' to
|
|
put in our relay end cell that we send to the exit relay, Tor
|
|
clients on Windows were sometimes sending the wrong 'reason'. The
|
|
anonymity problem is that exit relays may be able to guess whether
|
|
the client is running Windows, thus helping partition the anonymity
|
|
set. Down the road we should stop sending reasons to exit relays,
|
|
or otherwise prevent future versions of this bug.
|
|
|
|
It turned out that non-Windows clients were choosing their reason
|
|
correctly, whereas Windows clients were potentially looking at errno
|
|
wrong and so always choosing 'misc'.
|
|
|
|
I fixed that particular bug, but I think we should prevent future
|
|
versions of the bug too.
|
|
|
|
(We already fixed it so *circuit* end reasons don't get sent from
|
|
the client to the exit relay. But we appear to be have skipped over
|
|
stream end reasons thus far.)
|
|
|
|
Design:
|
|
|
|
One option would be to no longer include any 'reason' field in end
|
|
relay cells. But that would introduce a partitioning attack ("users
|
|
running the old version" vs "users running the new version").
|
|
|
|
Instead I suggest that clients all switch to sending the "misc" reason,
|
|
like most of the Windows clients currently do and like the non-Windows
|
|
clients already do sometimes.
|
|
|