We need to make sure that the worst thing that a weird consensus param
can do to us is to break our Tor (and only if the other Tors are
reliably broken in the same way) so that the majority of directory
authorities can't pull any attacks that are worse than the DoS that
they can trigger by simply shutting down.
One of these worse things was the cbtnummodes parameter, which could
lead to heap corruption on some systems if the value was sufficiently
large.
This commit fixes this particular issue and also introduces sanity
checking for all consensus parameters.
The reason the "streams problem" occurs is due to the complicated
interaction between Tor's congestion control and libevent. At some point
during the experiment, the circuit window is exhausted, which blocks all
edge streams. When a circuit level sendme is received at Exit, it
resumes edge reading by looping over linked list of edge streams, and
calling connection_start_reading() to inform libevent to resume reading.
When the streams are activated again, Tor gets the chance to service the
first three streams activated before the circuit window is exhausted
again, which causes all streams to be blocked again. As an experiment,
we reversed the order in which the streams are activated, and indeed the
first three streams, rather than the last three, got service, while the
others starved.
Our solution is to change the order in which streams are activated. We
choose a random edge connection from the linked list, and then we
activate streams starting from that chosen stream. When we reach the end
of the list, then we continue from the head of the list until our chosen
stream (treating the linked list as a circular linked list). It would
probably be better to actually remember which streams have received
service recently, but this way is simple and effective.
When the CellStatistics option is off, we don't store cell insertion
times. Doing so would also not be very smart, because there seem to
still be some performance issues with this type of statistics. Nothing
harmful happens when we don't have insertion times, so we don't need to
alarm the user.
Previously[*], the function would start with the first stream on the
circuit, and let it package as many cells as it wanted before
proceeding to the next stream in turn. If a circuit had many live
streams that all wanted to package data, the oldest would get
preference, and the newest would get ignored.
Now, we figure out how many cells we're willing to send per stream,
and try to allocate them fairly.
Roger diagnosed this in the comments for bug 1298.
[*] This bug has existed since before the first-ever public release
of Tor. It was added by r152 of Tor on 26 Jan 2003, which was
the first commit to implement streams (then called "topics").
This is not the oldest bug to be fixed in 0.2.2.x: that honor
goes to the windowing bug in r54, which got fixed in e50b7768 by
Roger with diagnosis by Karsten. This is, however, the most
long-lived bug to be fixed in 0.2.2.x: the r54 bug was fixed
2580 days after it was introduced, whereas I am writing this
commit message 2787 days after r152.
I'm going to use this to implement more fairness in
circuit_resume_edge_reading_helper in an attempt to fix bug 1298.
(Updated with fixes from arma and Sebastian)
We frequently add cells to stream-blocked queues for valid reasons
that don't mean we need to block streams. The most obvious reason
is if the cell arrives over a circuit rather than from an edge: we
don't block circuits, no matter how full queues get. The next most
obvious reason is that we allow CONNECTED cells from a newly created
stream to get delivered just fine.
This patch changes the behavior so that we only iterate over the
streams on a circuit when the cell in question came from a stream,
and we only block the stream that generated the cell, so that other
streams can still get their CONNECTEDs in.
When this happens, run through the streams on the circuit and make
sure they're all blocked. If some aren't, that's a bug: block them
all and log it! If they all are, where did the cell come from? Log
it!
(I suspect that this actually happens pretty frequently, so I'm making
these log messages appear at INFO.)
Do not start reading on exit streams when we get a SENDME unless we
have space in the appropriate circuit's cell queue.
Draft fix for bug 1653.
(commit message by nickm)
At best, this patch helps us avoid sending queued relayed cells that
would get ignored during the time between when a destroy cell is
sent and when the circuit is finally freed. At worst, it lets us
release some memory a little earlier than it would otherwise.
Fix for bug #1184. Bugfix on 0.2.0.1-alpha.
Everything that accepted the 'Circ' name handled it wrong, so even now
that we fixed the handling of the parameter, we wouldn't be able to
set it without making all the 0.2.2.7..0.2.2.10 relays act wonky.
This patch makes Tors accept the 'Circuit' name instead, so we can
turn on circuit priorities without confusing the versions that treated
the 'Circ' name as occasion to act weird.
When you mean (a=b(c,d)) >= 0, you had better not say (a=b(c,d)>=0).
We did the latter, and so whenever CircPriorityHalflife was in the
consensus, it was treated as having a value of 1 msec (that is,
boolean true).
