#32040: HS intro padding machine reactivates after receiving INTRODUCE_ACK
-----------------------------+------------------------------------
Reporter: asn | Owner: (none)
Type: defect | Status: new
Priority: Medium | Milestone: Tor: 0.4.3.x-final
Component: Core Tor/Tor | Version:
Severity: Normal | Resolution:
Keywords: wtf-pad padding | Actual Points:
Parent ID: | Points: 1
Reviewer: | Sponsor: Sponsor2
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Description changed by asn:
Old description:
> While reseaching wtf-pad I noticed that the intro machines don't work
> together and they display a weird shutdown/reactivation pattern.
>
> In particular, what happens is that after INTRODUCE1 is sent, the machine
> starts up and sends all its padding, and then shuts down. Then when
> INTRODUCE_ACK arrives, it reactivates (probably because INTRODUCE_ACK is
> part of the accepted purposes and the machine is shutdown/freed at that
> time) and sends again padding, then again shuts down...
>
> This does not work as intended and causes extra cells to fly in with a
> pattern that probably does not help them blend in.
>
> Here are some Tor logs (with padanalysis incoming/outgoing cells logs):
> {{{
> Oct 11 13:25:54.000 [warn] outgoing-cell: EXTEND2 0
> Oct 11 13:25:54.000 [warn] incoming-cell: EXTENDED2 0 66
> Oct 11 13:25:54.000 [warn] outgoing-cell: EXTEND2 0
> Oct 11 13:25:54.000 [warn] incoming-cell: EXTENDED2 0 66
> Oct 11 13:25:57.000 [warn] outgoing-cell: EXTEND 0
> Oct 11 13:25:58.000 [warn] incoming-cell: EXTENDED 0 148
> Oct 11 13:25:58.000 [warn] outgoing-cell: INTRODUCE1 4
> Oct 11 13:25:57.000 [info] circpad_negotiate_padding(): Negotiating
> padding on circuit 8 (10), command 2
> Oct 11 13:25:58.000 [warn] outgoing-cell: PADDING_NEGOTIATE 4
> Oct 11 13:25:57.000 [info] circpad_machine_spec_transition(): Circuit 8
> circpad machine 0 transitioning from 0 to 1
> Oct 11 13:25:58.000 [warn] incoming-cell: PADDING_NEGOTIATED 4 4
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: PADDING_NEGOTIATED 4 4
> Oct 11 13:25:58.000 [info] circpad_handle_padding_negotiated(): Received
> STOP command on PADDING_NEGOTIATED for circuit 5
> Oct 11 13:25:58.000 [info] circpad_circuit_machineinfo_free_idx():
> Freeing padding info idx 0 on circuit 5 (7)
> Oct 11 13:25:58.000 [warn] incoming-cell: INTRODUCE_ACK 4 0
> Oct 11 13:25:58.000 [info] rend_client_introduction_acked(): Received
> ack. Telling rend circ...
> Oct 11 13:25:58.000 [info] circpad_setup_machine_on_circ(): Registering
> machine client_ip_circ to origin circ 5 (8)
> Oct 11 13:25:58.000 [info] circpad_node_supports_padding(): Checking
> padding: supported
> Oct 11 13:25:58.000 [info] circpad_negotiate_padding(): Negotiating
> padding on circuit 5 (8), command 2
> Oct 11 13:25:58.000 [warn] outgoing-cell: 8 PADDING_NEGOTIATE 4
> Oct 11 13:25:58.000 [info] circpad_machine_spec_transition(): Circuit 5
> circpad machine 0 transitioning from 0 to 1
> Oct 11 13:25:58.000 [info] circpad_marked_circuit_for_padding(): Circuit
> 5 is not marked for close because of a pending padding machine in index
> 0.
> Oct 11 13:25:58.000 [warn] incoming-cell: PADDING_NEGOTIATED 4 4
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
> Oct 11 13:25:58.000 [warn] incoming-cell: PADDING_NEGOTIATED 4 4
> Oct 11 13:25:58.000 [info] circpad_handle_padding_negotiated(): Received
> STOP command on PADDING_NEGOTIATED for circuit 5
> Oct 11 13:25:58.000 [info] circpad_circuit_machineinfo_free_idx():
> Freeing padding info idx 0 on circuit 5 (15)
> ...
> Oct 11 13:36:11.000 [info] circuit_mark_for_close_(): Circuit 4130340667
> (id: 5) marked for close at src/core/or/circuituse.c:1509 (orig reason:
> 9, new reason: 0)
> }}}
>
> I'm not sure what the fix should be here. It might be that we need to
> remove INTRODUCE_ACK from the list of accepted purposes, but if we do
> that then if INTRODUCE_ACK arrives earlier we will stop padding after.
> Hmm.
New description:
While reseaching wtf-pad I noticed that the intro machines display a weird
shutdown/reactivation pattern.
In particular, what happens is that after INTRODUCE1 is sent, the machine
starts up and sends all its padding, and then shuts down. Then when
INTRODUCE_ACK arrives, it reactivates (probably because INTRODUCE_ACK is
part of the accepted purposes and the machine is shutdown/freed at that
time) and sends again padding, then again shuts down...
This does not work as intended and causes extra cells to fly in with a
pattern that probably does not help them blend in.
Here are some Tor logs (with padanalysis incoming/outgoing cells logs):
{{{
Oct 11 13:25:54.000 [warn] outgoing-cell: EXTEND2 0
Oct 11 13:25:54.000 [warn] incoming-cell: EXTENDED2 0 66
Oct 11 13:25:54.000 [warn] outgoing-cell: EXTEND2 0
Oct 11 13:25:54.000 [warn] incoming-cell: EXTENDED2 0 66
Oct 11 13:25:57.000 [warn] outgoing-cell: EXTEND 0
Oct 11 13:25:58.000 [warn] incoming-cell: EXTENDED 0 148
Oct 11 13:25:58.000 [warn] outgoing-cell: INTRODUCE1 4
Oct 11 13:25:58.000 [warn] outgoing-cell: PADDING_NEGOTIATE 4
Oct 11 13:25:58.000 [warn] incoming-cell: PADDING_NEGOTIATED 4 4
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: PADDING_NEGOTIATED 4 4
Oct 11 13:25:58.000 [info] circpad_handle_padding_negotiated(): Received
STOP command on PADDING_NEGOTIATED for circuit 5
Oct 11 13:25:58.000 [info] circpad_circuit_machineinfo_free_idx(): Freeing
padding info idx 0 on circuit 5 (7)
Oct 11 13:25:58.000 [warn] incoming-cell: INTRODUCE_ACK 4 0
Oct 11 13:25:58.000 [info] rend_client_introduction_acked(): Received ack.
Telling rend circ...
Oct 11 13:25:58.000 [info] circpad_setup_machine_on_circ(): Registering
machine client_ip_circ to origin circ 5 (8)
Oct 11 13:25:58.000 [info] circpad_node_supports_padding(): Checking
padding: supported
Oct 11 13:25:58.000 [info] circpad_negotiate_padding(): Negotiating
padding on circuit 5 (8), command 2
Oct 11 13:25:58.000 [warn] outgoing-cell: 8 PADDING_NEGOTIATE 4
Oct 11 13:25:58.000 [info] circpad_machine_spec_transition(): Circuit 5
circpad machine 0 transitioning from 0 to 1
Oct 11 13:25:58.000 [info] circpad_marked_circuit_for_padding(): Circuit 5
is not marked for close because of a pending padding machine in index 0.
Oct 11 13:25:58.000 [warn] incoming-cell: PADDING_NEGOTIATED 4 4
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: DROP 4 0
Oct 11 13:25:58.000 [warn] incoming-cell: PADDING_NEGOTIATED 4 4
Oct 11 13:25:58.000 [info] circpad_handle_padding_negotiated(): Received
STOP command on PADDING_NEGOTIATED for circuit 5
Oct 11 13:25:58.000 [info] circpad_circuit_machineinfo_free_idx(): Freeing
padding info idx 0 on circuit 5 (15)
...
Oct 11 13:36:11.000 [info] circuit_mark_for_close_(): Circuit 4130340667
(id: 5) marked for close at src/core/or/circuituse.c:1509 (orig reason: 9,
new reason: 0)
}}}
I'm not sure what the fix should be here. It might be that we need to
remove INTRODUCE_ACK from the list of accepted purposes, but if we do that
then if INTRODUCE_ACK arrives earlier we will stop padding after. Hmm.
--
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32040#comment:1>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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