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Re: [tor-dev] Brainstorming ideas for controller features for improved testing; want feedback
On Fri, Mar 20, 2015 at 11:55 AM, Nick Mathewson <nickm@xxxxxxxxxxxxxx> wrote:
> Hi! I've got an end-of-month deliverable to flesh out as many good
> ideas here as I can, and I'd appreciate feedback on what kind of
> features it would be good to add to the controller protocol in order
> to better support testing.
>
> More ideas would be most welcome.
Thanks for the comments, all!
Here's the latest version, with more things folded in, and some syntax sketches.
All syntaxes below are examples meant to focus discussion around
what might appear in a spec, not final (ha!) formal specification.
IDEAS
=====
1. Step-by-step hidden service connections
Add the ability to create connections to hidden services step by
step, to best
What's necessary here is commands to:
* Establish a rendezvous point on a given circuit.
* Construct and send an introduce1 cell on a given circuit.
* Realize that a rendezvous circuit has been constructed.
ESTABLISH_REND {circuit_num} {rend_token}
SEND_INTRO1 {circuit_num} intro_key={key} authinfo={ nfo}
650 RECEIVED_REND_OK {circuit_num}
2. Send a single cell on a circuit
(TESTING ONLY)
For fuzzing and low-level testing purposes, it would be handy to be
able to send a single cell on a tor circuit.
This might be better to expose via a low-level modular API than via
the control port.
SEND_RAW_RELAY_CELL {circuit_num} LAYER={cpath layer} DATA={hex}
3. Intercept cell by cell on a circuit
(TESTING ONLY)
For fuzzing, testing, and debugging purposes, it might be handy for
a controller to be able to observe data cell by cell on a circuit of
interest.
This might be better to expose via a low-level modular API than via
the control port.
650 RELAY_CELL {circuit_num} LAYER={cpath layer} DATA={hex}
4. Send a single cell on a connection.
(TESTING ONLY)
As 2, but for connections. Note that we might even, for testing,
expose this at a sub-cell level.
SEND_RAW_CELL {conn id} DATA={hex}
5. Intercept all cells on a connection
(TESTING ONLY)
As 2, but for connections.
650 CONN_CELL {conn id} DATA={hex}
6. Plug-in to handle a relay or other command.
Right now, all Tor's features need to be baked into Tor; it's not
easy to write extensions. We could change that by having the
controller able to intersect particular relay or extension commands
and act accordingly. This could be used for prototyping new
features, etc.
HANDLE_EXTENSION {conn=id|circ=id|conn=*|circ=*} {command_num}
650 EXTENSION {conn=id|circ=id} {command_num} DATA
7. Force a given protocol on a given connection
We could add a feature to restrict what protocols can be negotiated
on a given connection we create. This could help us better test our
protocols for interoperatbility.
OPEN_CONN {addr=address...} {protos=1,2,3...} {KEYID1=...}
8. Examine fine-grained connection detail.
There are many data available for a given connection (such as
fine-grained TLS information) that are not currently exposed on the
GETINFO interface. We could make most of this available for testing,
pending security analysis.
GETINFO orconn/<id>/all
GETINFO orconn/<id>/item
9. Examine cache in detail
In the past we've seen crazy issues with our descriptor caching
code. It might be good to expose for testing information about
where exactly descriptors are stored, what attributes are set on
them, and so on. We could also expose events for cache compaction
and discarded expired descriptors.
This might also (TESTING ONLY) extend to events for access of cache
documents, information about HS Descs, etc, though that's a bit worrisome.
GETINFO cache/<itemtype>/keys
GETINFO cache/<itemtype>/by-key/<key>/ ...
raw
annotations
location
650 CACHE_COMPACTED (bytes_saved)
650 CACHE_DISCARDED (item)
10. Fetch literal documents
Currently there's no way for a controller to ask Tor to download a
given descriptor or microdescriptor or networkstatus. That could
change.
DOWNLOAD <itemtype> <keys> [{circ=circ_id} {anon=0|1} {cache=router_id}]
11. OOM stats
To resist out-of-memory attacks, we track our memory usage and kill
off circuits as needed when memory gets low. We could expose the
memory thresholds and current sizes via one or more controller
commands.
GETINFO mem-usage/all
GETINFO mem-usage/<type>
650 MEM_USAGE k=v k=v k=v
650 MEM_FREED k=v k=v k=v
12. Timeout values
Tor has a truly huge variety of internal timers to ensure that given
periodic events happen enough; we could expose those, and (TESTING
ONLY) allow controllers to adjust them or trigger their corresponding
events.
GETINFO timer/list
GETINFO timer/expires/<timer-name>
ADJTIMER <timer-name> <seconds>.<msec>
650 TIMER <timer-name> next=<seconds.msec>
13. Detailed connection debugging info
Current connection events expose only large-scale state changes in
connections; we could instead expose every state transition at the
cell-by-cell handshake level.
14. Detailed circuit debugging info
As 13 but for circuits.
15. Halt main loop except for control layer.
(TESTING ONLY)
For inspection/debugging purposes, it might be clever to have Tor be
able to freeze itself, except for the control layer, and let the
controller inquire about information.
This presents implementation challenges, and is probably not a great
idea to do before a _big_ refactoring.
FREEZE {LOOP|CONN=id|CIRCUIT=id}
UNFREEZE {LOOP|CONN=id|CIRCUIT=id}
16. Service a single connection
(TESTING ONLY)
Currently controllers can disable circuit construction or stream
attachment, and do them manually. We might also do this for
connections, allowing a testing controller to trace what Tor does
cell by cell on a single connection.
STEP {LOOP|CONN=id|CIRCUIT=id}
17. All rephist data
There are many data about history and usage in rephist.c (which
stands for 'reputation and history!'). We could expose them, to let
us better test them. Some of this might be useful for Seth
(previously arm) users.
Spec: This would use GETINFO extensions, and probably some new
events.
18. All ratelim data
Sometimes our rate-limiting code can get wonky. It would be great
to expose it to Tor controllers in order to help ensure it's
behaving correctly. This would include send/receive windows and bw
stuff.
Spec: This would use GETINFO extensions, and probably some new
events.
19. All accounting data
As 17, but for hibernate.c, which performs bandwidth accounting.
20. All guard transitions
Our guard node state logic is very complicated, and much in need of
testing and refactoring. Exposing more state transitions and guard
selection transitions to the controller might help. (We have a
"GUARD" event now, but it is a bit out of sync with the main
implementation)
21. All key transitions
We could generate events every time we change keys, and (TESTING
ONLY) allow a controller to time-out a key early.
22. Examine mux settings
(TESTING ONLY)
The circuitmux code that we use to decide which cell to send next is
very complex; it would be good to expose its thinking and
decisionmaking to a testing controller for better observation.
23. Examine pathbias settings
Our pathbias code is also complex, and a bit flakier than the
circuitmux code. We could do for it as with 22 above.
24. Examine cpuworker queues
As of 0.2.6, we have a new cpuworker infrastructure that better
sends data to worker threads, but not much visibility into how well
it's working. Exposing some information about this to the
controller could help us tune better.
650 QUEUED_WORK TYPE=type ID=id RAW=hex NUM_QUEUED=n
650 FINISHED_WORK TYPE=type ID=id STATUS=status RAW=raw
GETINFO cpuworker/all/n_queued
GETINFO cpuworker/all/rate
GETINFO cpuworker/<num>/...
GETINFO cpuworker/<type>/...
25. All geoip data
As 17, but for any geoip information we aren't currently exporting.
26. Replay detection
For hidden service security (and maybe eventually for secure ntor Y
reuse) we have to keep replay caches to prevent us from being
tricked into handling the same value twice. We don't expose the
load on these caches to the controller, however. And we could, to
help us better tune them into using a good memory/error-rate
trade-off.
GETINFO replaycache/<type>/load
GETINFO replaycache/<type>/size
27. Hidden service intropoint changes, desc changes, uploads (+2)
Many hidden service transitions currently generate no events. We
could at minimum generate events for changed inroduction points,
changed hidden service descriptors, uploading our own HS descriptor.
650 HSSERV <id> <eventtype> k=v k=v k=v
28. Descriptor uploads.
We have an event for when our descriptor has changed, but not for a
successful upload for it. We could fix that.
650 UPLOADED <type> <authority> <status>
29. Path generation logic -- expose, allow.
Currently a controller's only visibility into path selection logic
is in its outputs, and in the opportunity to replace path selection
logic entirely. We could expose more details about the algorithm's
operation in order to help better test our path selection.
GEN_PATH <k=v> <k=v>
650 WANT_PATH id <k=v>
USE_PATH id node,node,node
30. All PT status information.
Pluggable transport feedback is, at present, very coarse-grained.
For testing we might expose more.
31. Crypto operation counts.
We ought to keep count of our various cryptographic operations, and
expose them to the controller. This would help us know where to
spend our optimization efforts.
GETINFO crypto/{<op>|all}/{<use>|all}/count
GETINFO crypto/{<op>|all}/{<use>|all}/speed
32. Forget cached information (+1)
To better test our download logic, it would be helpful to have a way
to drop items from our caches.
DROPCACHE {cachetype}
33. Expose number of bytes sent-received per circuit
(TESTING ONLY)
This could help us improve efficiency by investigating slow-circuit
issues.
650 CIRCBYTES sent={n} rcvd={n}
34. Modify state of existing connections and circuits
(TESTING ONLY)
This could help with fault injection to better validate error-handling
code.
IMPLEMENTATION NOTES:
=====================
Not lightly does one list 33 controller improvement areas. If we're
hoping to do these without too much programmer time and , we need to
take a much more principled approach to implementing controller
commands. For #8351 I worked on a branch called 'ticket8351' that has
some code we could use here.
COMPATIBILITY NOTES:
====================
Many of the features here are ones that we might not want to promise to
support indefinitely; we should gate them behind a USEFEATURE command,
and maybe place them in an annex of the control spec.
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