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61 lines
2 KiB
C
61 lines
2 KiB
C
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/* Copyright (c) 2019, The Tor Project, Inc. */
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/* See LICENSE for licensing information */
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/**
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* \file hs_dos.c
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* \brief Implement denial of service mitigation for the onion service
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* subsystem.
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*
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* This module defenses:
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*
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* - Introduction Rate Limiting: If enabled by the consensus, an introduction
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* point will rate limit client introduction towards the service (INTRODUCE2
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* cells). It uses a token bucket model with a rate and burst per second.
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*
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* Proposal 305 will expand this module by allowing an operator to define
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* these values into the ESTABLISH_INTRO cell. Not yet implemented.
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**/
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#define HS_DOS_PRIVATE
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#include "core/or/circuitlist.h"
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#include "hs_dos.h"
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/*
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* Public API.
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*/
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/* Return true iff an INTRODUCE2 cell can be sent on the given service
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* introduction circuit. */
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bool
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hs_dos_can_send_intro2(or_circuit_t *s_intro_circ)
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{
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tor_assert(s_intro_circ);
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/* Should not happen but if so, scream loudly. */
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if (BUG(TO_CIRCUIT(s_intro_circ)->purpose != CIRCUIT_PURPOSE_INTRO_POINT)) {
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return false;
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}
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/* This is called just after we got a valid and parsed INTRODUCE1 cell. The
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* service has been found and we have its introduction circuit.
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*
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* First, the INTRODUCE2 bucket will be refilled (if any). Then, decremented
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* because we are about to send or not the cell we just got. Finally,
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* evaluate if we can send it based on our token bucket state. */
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/* Refill INTRODUCE2 bucket. */
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token_bucket_ctr_refill(&s_intro_circ->introduce2_bucket,
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(uint32_t) approx_time());
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/* Decrement the bucket for this valid INTRODUCE1 cell we just got. Don't
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* underflow else we end up with a too big of a bucket. */
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if (token_bucket_ctr_get(&s_intro_circ->introduce2_bucket) > 0) {
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token_bucket_ctr_dec(&s_intro_circ->introduce2_bucket, 1);
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}
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/* Finally, we can send a new INTRODUCE2 if there are still tokens. */
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return token_bucket_ctr_get(&s_intro_circ->introduce2_bucket) > 0;
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}
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