/* Copyright (c) 2017 The Tor Project, Inc. */ /* See LICENSE for licensing information */ /** * \file circuitpadding.c * \brief Circuit-level padding implementation * * \details * * This file implements Tor proposal 254 "Padding Negotiation" which is heavily * inspired by the paper "Toward an Efficient Website Fingerprinting Defense" * by M. Juarez, M. Imani, M. Perry, C. Diaz, M. Wright. * * In particular the code in this file describes mechanisms for clients to * negotiate various types of circuit-level padding from relays. * * Each padding type is described by a state machine (circpad_machine_spec_t), * which is also referred as a "padding machine" in this file. Currently, * these state machines are hardcoded in the source code (e.g. see * circpad_circ_client_machine_init()), but in the future we will be able to * serialize them in the torrc or the consensus. * * As specified by prop#254, clients can negotiate padding with relays by using * PADDING_NEGOTIATE cells. After successful padding negotiation, padding * machines are assigned to the circuit in their mutable form as a * circpad_machine_state_t. * * Each state of a padding state machine can be either: * - A histogram that specifies inter-arrival padding delays. * - Or a parametrized probability distribution that specifies inter-arrival * delays (see circpad_distribution_type_t). * * Padding machines start from the START state and finish with the END * state. They can transition between states using the events in * circpad_event_t. * * When a padding machine reaches the END state, it gets wiped from the circuit * so that other padding machines can take over if needed (see * circpad_machine_spec_transitioned_to_end()). **/ #define CIRCUITPADDING_PRIVATE #include #include "lib/math/fp.h" #include "lib/math/prob_distr.h" #include "core/or/or.h" #include "core/or/circuitpadding.h" #include "core/or/circuitlist.h" #include "core/or/circuituse.h" #include "core/or/relay.h" #include "feature/stats/rephist.h" #include "feature/nodelist/networkstatus.h" #include "core/or/channel.h" #include "lib/time/compat_time.h" #include "lib/defs/time.h" #include "lib/crypt_ops/crypto_rand.h" #include "core/or/crypt_path_st.h" #include "core/or/circuit_st.h" #include "core/or/origin_circuit_st.h" #include "feature/nodelist/routerstatus_st.h" #include "feature/nodelist/node_st.h" #include "core/or/cell_st.h" #include "core/or/extend_info_st.h" #include "core/crypto/relay_crypto.h" #include "feature/nodelist/nodelist.h" #include "app/config/config.h" static inline circpad_purpose_mask_t circpad_circ_purpose_to_mask(uint8_t circ_purpose); static inline circpad_circuit_state_t circpad_circuit_state( origin_circuit_t *circ); static void circpad_setup_machine_on_circ(circuit_t *on_circ, const circpad_machine_spec_t *machine); static double circpad_distribution_sample(circpad_distribution_t dist); /** Cached consensus params */ static uint8_t circpad_global_max_padding_percent; static uint16_t circpad_global_allowed_cells; /** Global cell counts, for rate limiting */ static uint64_t circpad_global_padding_sent; static uint64_t circpad_global_nonpadding_sent; /** This is the list of circpad_machine_spec_t's parsed from consensus and * torrc that have origin_side == 1 (ie: are for client side). * * The machines in this smartlist are considered immutable and they are used * as-is by circuits so they should not change or get deallocated in Tor's * runtime and as long as circuits are alive. */ STATIC smartlist_t *origin_padding_machines = NULL; /** This is the list of circpad_machine_spec_t's parsed from consensus and * torrc that have origin_side == 0 (ie: are for relay side). * * The machines in this smartlist are considered immutable and they are used * as-is by circuits so they should not change or get deallocated in Tor's * runtime and as long as circuits are alive. */ STATIC smartlist_t *relay_padding_machines = NULL; /** Loop over the current padding state machines using loop_var as the * loop variable. */ #define FOR_EACH_CIRCUIT_MACHINE_BEGIN(loop_var) \ STMT_BEGIN \ for (int loop_var = 0; loop_var < CIRCPAD_MAX_MACHINES; loop_var++) { #define FOR_EACH_CIRCUIT_MACHINE_END } STMT_END ; /** Loop over the current active padding state machines using loop_var * as the loop variable. If a machine is not active, skip it. */ #define FOR_EACH_ACTIVE_CIRCUIT_MACHINE_BEGIN(loop_var, circ) \ FOR_EACH_CIRCUIT_MACHINE_BEGIN(loop_var) \ if (!(circ)->padding_info[loop_var]) \ continue; #define FOR_EACH_ACTIVE_CIRCUIT_MACHINE_END } STMT_END ; /** * Return a human-readable description for a circuit padding state. */ static const char * circpad_state_to_string(circpad_statenum_t state) { const char *descr; switch (state) { case CIRCPAD_STATE_START: descr = "START"; break; case CIRCPAD_STATE_BURST: descr = "BURST"; break; case CIRCPAD_STATE_GAP: descr = "GAP"; break; case CIRCPAD_STATE_END: descr = "END"; break; default: descr = "CUSTOM"; // XXX: Just return # in static char buf? } return descr; } /** * Free the machineinfo at an index */ static void circpad_circuit_machineinfo_free_idx(circuit_t *circ, int idx) { if (circ->padding_info[idx]) { tor_free(circ->padding_info[idx]->histogram); timer_free(circ->padding_info[idx]->padding_timer); tor_free(circ->padding_info[idx]); } } /** Free all the machineinfos in circ that match machine_num. */ static void free_circ_machineinfos_with_machine_num(circuit_t *circ, int machine_num) { FOR_EACH_CIRCUIT_MACHINE_BEGIN(i) { if (circ->padding_machine[i] && circ->padding_machine[i]->machine_num == machine_num) { circpad_circuit_machineinfo_free_idx(circ, i); circ->padding_machine[i] = NULL; } } FOR_EACH_CIRCUIT_MACHINE_END; } /** * Free all padding machines and mutable info associated with circuit */ void circpad_circuit_free_all_machineinfos(circuit_t *circ) { FOR_EACH_CIRCUIT_MACHINE_BEGIN(i) { circpad_circuit_machineinfo_free_idx(circ, i); } FOR_EACH_CIRCUIT_MACHINE_END; } /** * Allocate a new mutable machineinfo structure. */ STATIC circpad_machine_state_t * circpad_circuit_machineinfo_new(circuit_t *on_circ, int machine_index) { circpad_machine_state_t *mi = tor_malloc_zero(sizeof(circpad_machine_state_t)); mi->machine_index = machine_index; mi->on_circ = on_circ; return mi; } /** * Return the circpad_state_t for the current state based on the * mutable info. * * This function returns NULL when the machine is in the end state or in an * invalid state. */ STATIC const circpad_state_t * circpad_machine_current_state(const circpad_machine_state_t *mi) { const circpad_machine_spec_t *machine = CIRCPAD_GET_MACHINE(mi); if (mi->current_state == CIRCPAD_STATE_END) { return NULL; } else if (BUG(mi->current_state >= machine->num_states)) { log_fn(LOG_WARN,LD_CIRC, "Invalid circuit padding state %d", mi->current_state); return NULL; } return &machine->states[mi->current_state]; } /** * Calculate the lower bound of a histogram bin. The upper bound * is obtained by calling this function with bin+1, and subtracting 1. * * The 0th bin has a special value -- it only represents start_usec. * This is so we can specify a probability on 0-delay values. * * After bin 0, bins are exponentially spaced, so that each subsequent * bin is twice as large as the previous. This is done so that higher * time resolution is given to lower time values. * * The infinity bin is a the last bin in the array (histogram_len-1). * It has a usec value of CIRCPAD_DELAY_INFINITE (UINT32_MAX). */ STATIC circpad_delay_t circpad_histogram_bin_to_usec(const circpad_machine_state_t *mi, circpad_hist_index_t bin) { const circpad_state_t *state = circpad_machine_current_state(mi); circpad_delay_t start_usec; /* Our state should have been checked to be non-null by the caller * (circpad_machine_remove_token()) */ if (BUG(state == NULL)) { return CIRCPAD_DELAY_INFINITE; } if (state->use_rtt_estimate) start_usec = mi->rtt_estimate_usec+state->start_usec; else start_usec = state->start_usec; if (bin >= CIRCPAD_INFINITY_BIN(state)) return CIRCPAD_DELAY_INFINITE; if (bin == 0) return start_usec; if (bin == 1) return start_usec+1; /* The bin widths double every index, so that we can have more resolution * for lower time values in the histogram. */ const circpad_time_t bin_width_exponent = 1 << (CIRCPAD_INFINITY_BIN(state) - bin); return (circpad_delay_t)MIN(start_usec + state->range_usec/bin_width_exponent, CIRCPAD_DELAY_INFINITE); } /** Return the midpoint of the histogram bin bin_index. */ static circpad_delay_t circpad_get_histogram_bin_midpoint(const circpad_machine_state_t *mi, int bin_index) { circpad_delay_t left_bound = circpad_histogram_bin_to_usec(mi, bin_index); circpad_delay_t right_bound = circpad_histogram_bin_to_usec(mi, bin_index+1)-1; return left_bound + (right_bound - left_bound)/2; } /** * Return the bin that contains the usec argument. * "Contains" is defined as us in [lower, upper). * * This function will never return the infinity bin (histogram_len-1), * in order to simplify the rest of the code. * * This means that technically the last bin (histogram_len-2) * has range [start_usec+range_usec, CIRCPAD_DELAY_INFINITE]. */ STATIC circpad_hist_index_t circpad_histogram_usec_to_bin(const circpad_machine_state_t *mi, circpad_delay_t usec) { const circpad_state_t *state = circpad_machine_current_state(mi); circpad_delay_t start_usec; int32_t bin; /* Larger than return type to properly clamp overflow */ /* Our state should have been checked to be non-null by the caller * (circpad_machine_remove_token()) */ if (BUG(state == NULL)) { return 0; } if (state->use_rtt_estimate) start_usec = mi->rtt_estimate_usec+state->start_usec; else start_usec = state->start_usec; /* The first bin (#0) has zero width and starts (and ends) at start_usec. */ if (usec <= start_usec) return 0; if (usec == start_usec+1) return 1; const circpad_time_t histogram_range_usec = state->range_usec; /* We need to find the bin corresponding to our position in the range. * Since bins are exponentially spaced in powers of two, we need to * take the log2 of our position in histogram_range_usec. However, * since tor_log2() returns the floor(log2(u64)), we have to adjust * it to behave like ceil(log2(u64)). This is verified in our tests * to properly invert the operation done in * circpad_histogram_bin_to_usec(). */ bin = CIRCPAD_INFINITY_BIN(state) - tor_log2(2*histogram_range_usec/(usec-start_usec+1)); /* Clamp the return value to account for timevals before the start * of bin 0, or after the last bin. Don't return the infinity bin * index. */ bin = MIN(MAX(bin, 1), CIRCPAD_INFINITY_BIN(state)-1); return bin; } /** * This function frees any token bins allocated from a previous state * * Called after a state transition, or if the bins are empty. */ STATIC void circpad_machine_setup_tokens(circpad_machine_state_t *mi) { const circpad_state_t *state = circpad_machine_current_state(mi); /* If this state doesn't exist, or doesn't have token removal, * free any previous state's histogram, and bail */ if (!state || state->token_removal == CIRCPAD_TOKEN_REMOVAL_NONE) { if (mi->histogram) { tor_free(mi->histogram); mi->histogram = NULL; mi->histogram_len = 0; } return; } /* Try to avoid re-mallocing if we don't really need to */ if (!mi->histogram || (mi->histogram && mi->histogram_len != state->histogram_len)) { tor_free(mi->histogram); // null ok mi->histogram = tor_malloc_zero(sizeof(circpad_hist_token_t) *state->histogram_len); } mi->histogram_len = state->histogram_len; memcpy(mi->histogram, state->histogram, sizeof(circpad_hist_token_t)*state->histogram_len); } /** * Choose a length for this state (in cells), if specified. */ static void circpad_choose_state_length(circpad_machine_state_t *mi) { const circpad_state_t *state = circpad_machine_current_state(mi); double length; if (!state || state->length_dist.type == CIRCPAD_DIST_NONE) { mi->state_length = CIRCPAD_STATE_LENGTH_INFINITE; return; } length = circpad_distribution_sample(state->length_dist); length = MAX(0, length); length += state->start_length; length = MIN(length, state->max_length); mi->state_length = clamp_double_to_int64(length); } /** * Sample a value from our iat_dist, and clamp it safely * to circpad_delay_t. */ static circpad_delay_t circpad_distribution_sample_iat_delay(const circpad_state_t *state, circpad_delay_t start_usec) { double val = circpad_distribution_sample(state->iat_dist); /* These comparisons are safe, because the output is in the range * [0, 2**32), and double has a precision of 53 bits. */ val = MAX(0, val); val = MIN(val, state->range_usec); /* This addition is exact: val is at most 2**32-1, start_usec * is at most 2**32-1, and doubles have a precision of 53 bits. */ val += start_usec; /* Clamp the distribution at infinite delay val */ return (circpad_delay_t)MIN(tor_llround(val), CIRCPAD_DELAY_INFINITE); } /** * Sample an expected time-until-next-packet delay from the histogram. * * The bin is chosen with probability proportional to the number * of tokens in each bin, and then a time value is chosen uniformly from * that bin's [start,end) time range. */ STATIC circpad_delay_t circpad_machine_sample_delay(circpad_machine_state_t *mi) { const circpad_state_t *state = circpad_machine_current_state(mi); const circpad_hist_token_t *histogram = NULL; circpad_hist_index_t curr_bin = 0; circpad_delay_t bin_start, bin_end; circpad_delay_t start_usec; /* These three must all be larger than circpad_hist_token_t, because * we sum several circpad_hist_token_t values across the histogram */ uint64_t curr_weight = 0; uint64_t histogram_total_tokens = 0; uint64_t bin_choice; tor_assert(state); if (state->use_rtt_estimate) start_usec = mi->rtt_estimate_usec+state->start_usec; else start_usec = state->start_usec; if (state->iat_dist.type != CIRCPAD_DIST_NONE) { /* Sample from a fixed IAT distribution and return */ return circpad_distribution_sample_iat_delay(state, start_usec); } else if (state->token_removal != CIRCPAD_TOKEN_REMOVAL_NONE) { /* We have a mutable histogram. Do basic sanity check and apply: */ if (BUG(!mi->histogram) || BUG(mi->histogram_len != state->histogram_len)) { return CIRCPAD_DELAY_INFINITE; } histogram = mi->histogram; for (circpad_hist_index_t b = 0; b < state->histogram_len; b++) histogram_total_tokens += histogram[b]; } else { /* We have a histogram, but it's immutable */ histogram = state->histogram; histogram_total_tokens = state->histogram_total_tokens; } bin_choice = crypto_rand_uint64(histogram_total_tokens); /* Skip all the initial zero bins */ while (!histogram[curr_bin]) { curr_bin++; } curr_weight = histogram[curr_bin]; // TODO: This is not constant-time. Pretty sure we don't // really need it to be, though. while (curr_weight < bin_choice) { curr_bin++; /* It should be impossible to run past the end of the histogram */ if (BUG(curr_bin >= state->histogram_len)) { return CIRCPAD_DELAY_INFINITE; } curr_weight += histogram[curr_bin]; } /* Do some basic checking of the current bin we are in */ if (BUG(curr_bin >= state->histogram_len) || BUG(histogram[curr_bin] == 0)) { return CIRCPAD_DELAY_INFINITE; } // Store this index to remove the token upon callback. if (state->token_removal != CIRCPAD_TOKEN_REMOVAL_NONE) { mi->chosen_bin = curr_bin; } if (curr_bin >= CIRCPAD_INFINITY_BIN(state)) { if (state->token_removal != CIRCPAD_TOKEN_REMOVAL_NONE && mi->histogram[curr_bin] > 0) { mi->histogram[curr_bin]--; } // Infinity: Don't send a padding packet. Wait for a real packet // and then see if our bins are empty or what else we should do. return CIRCPAD_DELAY_INFINITE; } tor_assert(curr_bin < CIRCPAD_INFINITY_BIN(state)); bin_start = circpad_histogram_bin_to_usec(mi, curr_bin); /* We don't need to reduct 1 from the upper bound because the random range * function below samples from [bin_start, bin_end) */ bin_end = circpad_histogram_bin_to_usec(mi, curr_bin+1); /* Truncate the high bin in case it's the infinity bin: * Don't actually schedule an "infinite"-1 delay */ bin_end = MIN(bin_end, start_usec+state->range_usec); // Sample uniformly between histogram[i] to histogram[i+1]-1, // but no need to sample if they are the same timeval (aka bin 0 or bin 1). if (bin_end <= bin_start+1) return bin_start; else return (circpad_delay_t)crypto_rand_uint64_range(bin_start, bin_end); } /** * Sample a value from the specified probability distribution. * * This performs inverse transform sampling * (https://en.wikipedia.org/wiki/Inverse_transform_sampling). * * XXX: These formulas were taken verbatim. Need a floating wizard * to check them for catastropic cancellation and other issues (teor?). * Also: is 32bits of double from [0.0,1.0) enough? */ static double circpad_distribution_sample(circpad_distribution_t dist) { log_fn(LOG_DEBUG,LD_CIRC, "Sampling delay with distribution %d", dist.type); switch (dist.type) { case CIRCPAD_DIST_NONE: { /* We should not get in here like this */ tor_assert_nonfatal_unreached(); return 0; } case CIRCPAD_DIST_UNIFORM: { // param2 is upper bound, param1 is lower const struct uniform my_uniform = { .base = UNIFORM(my_uniform), .a = dist.param1, .b = dist.param2, }; return dist_sample(&my_uniform.base); } case CIRCPAD_DIST_LOGISTIC: { /* param1 is Mu, param2 is sigma. */ const struct logistic my_logistic = { .base = LOGISTIC(my_logistic), .mu = dist.param1, .sigma = dist.param2, }; return dist_sample(&my_logistic.base); } case CIRCPAD_DIST_LOG_LOGISTIC: { /* param1 is Alpha, param2 is 1.0/Beta */ const struct log_logistic my_log_logistic = { .base = LOG_LOGISTIC(my_log_logistic), .alpha = dist.param1, .beta = dist.param2, }; return dist_sample(&my_log_logistic.base); } case CIRCPAD_DIST_GEOMETRIC: { /* param1 is 'p' (success probability) */ const struct geometric my_geometric = { .base = GEOMETRIC(my_geometric), .p = dist.param1, }; return dist_sample(&my_geometric.base); } case CIRCPAD_DIST_WEIBULL: { /* param1 is k, param2 is Lambda */ const struct weibull my_weibull = { .base = WEIBULL(my_weibull), .k = dist.param1, .lambda = dist.param2, }; return dist_sample(&my_weibull.base); } case CIRCPAD_DIST_PARETO: { /* param1 is sigma, param2 is xi, no more params for mu so we use 0 */ const struct genpareto my_genpareto = { .base = GENPARETO(my_genpareto), .mu = 0, .sigma = dist.param1, .xi = dist.param2, }; return dist_sample(&my_genpareto.base); } } tor_assert_nonfatal_unreached(); return 0; } /** * Find the index of the first bin whose upper bound is * greater than the target, and that has tokens remaining. */ static circpad_hist_index_t circpad_machine_first_higher_index(const circpad_machine_state_t *mi, circpad_delay_t target_bin_usec) { circpad_hist_index_t bin = circpad_histogram_usec_to_bin(mi, target_bin_usec); /* Don't remove from the infinity bin */ for (; bin < CIRCPAD_INFINITY_BIN(mi); bin++) { if (mi->histogram[bin] && circpad_histogram_bin_to_usec(mi, bin+1) > target_bin_usec) { return bin; } } return mi->histogram_len; } /** * Find the index of the first bin whose lower bound is lower or equal to * target_bin_usec, and that still has tokens remaining. */ static circpad_hist_index_t circpad_machine_first_lower_index(const circpad_machine_state_t *mi, circpad_delay_t target_bin_usec) { circpad_hist_index_t bin = circpad_histogram_usec_to_bin(mi, target_bin_usec); for (; bin >= 0; bin--) { if (mi->histogram[bin] && circpad_histogram_bin_to_usec(mi, bin) <= target_bin_usec) { return bin; } } return -1; } /** * Remove a token from the first non-empty bin whose upper bound is * greater than the target. */ STATIC void circpad_machine_remove_higher_token(circpad_machine_state_t *mi, circpad_delay_t target_bin_usec) { /* We need to remove the token from the first bin * whose upper bound is greater than the target, and that * has tokens remaining. */ circpad_hist_index_t bin = circpad_machine_first_higher_index(mi, target_bin_usec); if (bin >= 0 && bin < CIRCPAD_INFINITY_BIN(mi)) { if (!BUG(mi->histogram[bin] == 0)) { mi->histogram[bin]--; } } } /** * Remove a token from the first non-empty bin whose upper bound is * lower than the target. */ STATIC void circpad_machine_remove_lower_token(circpad_machine_state_t *mi, circpad_delay_t target_bin_usec) { circpad_hist_index_t bin = circpad_machine_first_lower_index(mi, target_bin_usec); if (bin >= 0 && bin < CIRCPAD_INFINITY_BIN(mi)) { if (!BUG(mi->histogram[bin] == 0)) { mi->histogram[bin]--; } } } /* Helper macro: Ensure that the bin has tokens available, and BUG out of the * function if it's not the case. */ #define ENSURE_BIN_CAPACITY(bin_index) \ if (BUG(mi->histogram[bin_index] == 0)) { \ return; \ } /** * Remove a token from the closest non-empty bin to the target. * * If use_usec is true, measure "closest" in terms of the next closest bin * midpoint. * * If it is false, use bin index distance only. */ STATIC void circpad_machine_remove_closest_token(circpad_machine_state_t *mi, circpad_delay_t target_bin_usec, bool use_usec) { circpad_hist_index_t lower, higher, current; circpad_hist_index_t bin_to_remove = -1; lower = circpad_machine_first_lower_index(mi, target_bin_usec); higher = circpad_machine_first_higher_index(mi, target_bin_usec); current = circpad_histogram_usec_to_bin(mi, target_bin_usec); /* Sanity check the results */ if (BUG(lower > current) || BUG(higher < current)) { return; } /* Take care of edge cases first */ if (higher == mi->histogram_len && lower == -1) { /* All bins are empty */ return; } else if (higher == mi->histogram_len) { /* All higher bins are empty */ ENSURE_BIN_CAPACITY(lower); mi->histogram[lower]--; return; } else if (lower == -1) { /* All lower bins are empty */ ENSURE_BIN_CAPACITY(higher); mi->histogram[higher]--; return; } /* Now handle the intermediate cases */ if (use_usec) { /* Find the closest bin midpoint to the target */ circpad_delay_t lower_usec = circpad_get_histogram_bin_midpoint(mi, lower); circpad_delay_t higher_usec = circpad_get_histogram_bin_midpoint(mi, higher); if (target_bin_usec < lower_usec) { // Lower bin is closer ENSURE_BIN_CAPACITY(lower); bin_to_remove = lower; } else if (target_bin_usec > higher_usec) { // Higher bin is closer ENSURE_BIN_CAPACITY(higher); bin_to_remove = higher; } else if (target_bin_usec-lower_usec > higher_usec-target_bin_usec) { // Higher bin is closer ENSURE_BIN_CAPACITY(higher); bin_to_remove = higher; } else { // Lower bin is closer ENSURE_BIN_CAPACITY(lower); bin_to_remove = lower; } mi->histogram[bin_to_remove]--; log_debug(LD_GENERAL, "Removing token from bin %d", bin_to_remove); return; } else { if (current - lower > higher - current) { // Higher bin is closer ENSURE_BIN_CAPACITY(higher); mi->histogram[higher]--; return; } else { // Lower bin is closer ENSURE_BIN_CAPACITY(lower); mi->histogram[lower]--; return; } } } #undef ENSURE_BIN_CAPACITY /** * Remove a token from the exact bin corresponding to the target. * * If it is empty, do nothing. */ static void circpad_machine_remove_exact(circpad_machine_state_t *mi, circpad_delay_t target_bin_usec) { circpad_hist_index_t bin = circpad_histogram_usec_to_bin(mi, target_bin_usec); if (mi->histogram[bin] > 0) mi->histogram[bin]--; } /** * Check our state's cell limit count and tokens. * * Returns 1 if either limits are hit and we decide to change states, * otherwise returns 0. */ static circpad_decision_t check_machine_token_supply(circpad_machine_state_t *mi) { uint32_t histogram_total_tokens = 0; /* Check if bins empty. This requires summing up the current mutable * machineinfo histogram token total and checking if it is zero. * Machineinfo does not keep a running token count. We're assuming the * extra space is not worth this short loop iteration. * * We also do not count infinity bin in histogram totals. */ if (mi->histogram_len && mi->histogram) { for (circpad_hist_index_t b = 0; b < CIRCPAD_INFINITY_BIN(mi); b++) histogram_total_tokens += mi->histogram[b]; /* If we change state, we're done */ if (histogram_total_tokens == 0) { if (circpad_internal_event_bins_empty(mi) == CIRCPAD_STATE_CHANGED) return CIRCPAD_STATE_CHANGED; } } if (mi->state_length == 0) { return circpad_internal_event_state_length_up(mi); } return CIRCPAD_STATE_UNCHANGED; } /** * Remove a token from the bin corresponding to the delta since * last packet. If that bin is empty, choose a token based on * the specified removal strategy in the state machine. * * This function also updates and checks rate limit and state * limit counters. * * Returns 1 if we transition states, 0 otherwise. */ STATIC circpad_decision_t circpad_machine_remove_token(circpad_machine_state_t *mi) { const circpad_state_t *state = NULL; circpad_time_t current_time; circpad_delay_t target_bin_usec; /* Update non-padding counts for rate limiting: We scale at UINT16_MAX * because we only use this for a percentile limit of 2 sig figs, and * space is scare in the machineinfo struct. */ mi->nonpadding_sent++; if (mi->nonpadding_sent == UINT16_MAX) { mi->padding_sent /= 2; mi->nonpadding_sent /= 2; } /* Dont remove any tokens if there was no padding scheduled */ if (!mi->padding_scheduled_at_usec) { return CIRCPAD_STATE_UNCHANGED; } state = circpad_machine_current_state(mi); current_time = monotime_absolute_usec(); /* If we have scheduled padding some time in the future, we want to see what bin we are in at the current time */ target_bin_usec = (circpad_delay_t) MIN((current_time - mi->padding_scheduled_at_usec), CIRCPAD_DELAY_INFINITE-1); /* We are treating this non-padding cell as a padding cell, so we cancel padding timer, if present. */ mi->padding_scheduled_at_usec = 0; if (mi->is_padding_timer_scheduled) { mi->is_padding_timer_scheduled = 0; timer_disable(mi->padding_timer); } /* If we are not in a padding state (like start or end), we're done */ if (!state) return CIRCPAD_STATE_UNCHANGED; /* If we're enforcing a state length on non-padding packets, * decrement it */ if (mi->state_length != CIRCPAD_STATE_LENGTH_INFINITE && state->length_includes_nonpadding && mi->state_length > 0) { mi->state_length--; } /* Perform the specified token removal strategy */ switch (state->token_removal) { case CIRCPAD_TOKEN_REMOVAL_NONE: break; case CIRCPAD_TOKEN_REMOVAL_CLOSEST_USEC: circpad_machine_remove_closest_token(mi, target_bin_usec, 1); break; case CIRCPAD_TOKEN_REMOVAL_CLOSEST: circpad_machine_remove_closest_token(mi, target_bin_usec, 0); break; case CIRCPAD_TOKEN_REMOVAL_LOWER: circpad_machine_remove_lower_token(mi, target_bin_usec); break; case CIRCPAD_TOKEN_REMOVAL_HIGHER: circpad_machine_remove_higher_token(mi, target_bin_usec); break; case CIRCPAD_TOKEN_REMOVAL_EXACT: circpad_machine_remove_exact(mi, target_bin_usec); break; } /* Check our token and state length limits */ return check_machine_token_supply(mi); } /** * Send a relay command with a relay cell payload on a circuit to * the particular hopnum. * * Hopnum starts at 1 (1=guard, 2=middle, 3=exit, etc). * * Payload may be null. * * Returns negative on error, 0 on success. */ MOCK_IMPL(STATIC signed_error_t, circpad_send_command_to_hop,(origin_circuit_t *circ, uint8_t hopnum, uint8_t relay_command, const uint8_t *payload, ssize_t payload_len)) { crypt_path_t *target_hop = circuit_get_cpath_hop(circ, hopnum); signed_error_t ret; /* Check that the cpath has the target hop */ if (!target_hop) { log_fn(LOG_WARN, LD_BUG, "Padding circuit %u has %d hops, not %d", circ->global_identifier, circuit_get_cpath_len(circ), hopnum); return -1; } /* Check that the target hop is opened */ if (target_hop->state != CPATH_STATE_OPEN) { log_fn(LOG_WARN,LD_CIRC, "Padding circuit %u has %d hops, not %d", circ->global_identifier, circuit_get_cpath_opened_len(circ), hopnum); return -1; } /* Send the drop command to the second hop */ ret = relay_send_command_from_edge(0, TO_CIRCUIT(circ), relay_command, (const char*)payload, payload_len, target_hop); return ret; } /** * Callback helper to send a padding cell. * * This helper is called after our histogram-sampled delay period passes * without another packet being sent first. If a packet is sent before this * callback happens, it is canceled. So when we're called here, send padding * right away. * * If sending this padding cell forced us to transition states return * CIRCPAD_STATE_CHANGED. Otherwise return CIRCPAD_STATE_UNCHANGED. */ circpad_decision_t circpad_send_padding_cell_for_callback(circpad_machine_state_t *mi) { circuit_t *circ = mi->on_circ; int machine_idx = mi->machine_index; mi->padding_scheduled_at_usec = 0; circpad_statenum_t state = mi->current_state; // Make sure circuit didn't close on us if (mi->on_circ->marked_for_close) { log_fn(LOG_INFO,LD_CIRC, "Padding callback on a circuit marked for close. Ignoring."); return CIRCPAD_STATE_CHANGED; } /* If it's a histogram, reduce the token count */ if (mi->histogram && mi->histogram_len) { /* Basic sanity check on the histogram before removing anything */ if (BUG(mi->chosen_bin >= mi->histogram_len) || BUG(mi->histogram[mi->chosen_bin] == 0)) { return CIRCPAD_STATE_CHANGED; } mi->histogram[mi->chosen_bin]--; } /* If we have a valid state length bound, consider it */ if (mi->state_length != CIRCPAD_STATE_LENGTH_INFINITE && !BUG(mi->state_length <= 0)) { mi->state_length--; } /* * Update non-padding counts for rate limiting: We scale at UINT16_MAX * because we only use this for a percentile limit of 2 sig figs, and * space is scare in the machineinfo struct. */ mi->padding_sent++; if (mi->padding_sent == UINT16_MAX) { mi->padding_sent /= 2; mi->nonpadding_sent /= 2; } circpad_global_padding_sent++; if (CIRCUIT_IS_ORIGIN(mi->on_circ)) { circpad_send_command_to_hop(TO_ORIGIN_CIRCUIT(mi->on_circ), CIRCPAD_GET_MACHINE(mi)->target_hopnum, RELAY_COMMAND_DROP, NULL, 0); log_fn(LOG_INFO,LD_CIRC, "Callback: Sending padding to origin circuit %u.", TO_ORIGIN_CIRCUIT(mi->on_circ)->global_identifier); } else { // If we're a non-origin circ, we can just send from here as if we're the // edge. log_fn(LOG_INFO,LD_CIRC, "Callback: Sending padding to non-origin circuit."); relay_send_command_from_edge(0, mi->on_circ, RELAY_COMMAND_DROP, NULL, 0, NULL); } rep_hist_padding_count_write(PADDING_TYPE_DROP); /* This is a padding cell sent from the client or from the middle node, * (because it's invoked from circuitpadding.c) */ circpad_cell_event_padding_sent(circ); /* The circpad_cell_event_padding_sent() could cause us to transition. * Check that we still have a padding machineinfo, and then check our token * supply. */ if (circ->padding_info[machine_idx] != NULL) { if (state != circ->padding_info[machine_idx]->current_state) return CIRCPAD_STATE_CHANGED; else return check_machine_token_supply(circ->padding_info[machine_idx]); } else { return CIRCPAD_STATE_CHANGED; } } /** * Tor-timer compatible callback that tells us to send a padding cell. * * Timers are associated with circpad_machine_state_t's. When the machineinfo * is freed on a circuit, the timers are cancelled. Since the lifetime * of machineinfo is always longer than the timers, handles are not * needed. */ static void circpad_send_padding_callback(tor_timer_t *timer, void *args, const struct monotime_t *time) { circpad_machine_state_t *mi = ((circpad_machine_state_t*)args); (void)timer; (void)time; if (mi && mi->on_circ) { assert_circuit_ok(mi->on_circ); circpad_send_padding_cell_for_callback(mi); } else { // This shouldn't happen (represents a timer leak) log_fn(LOG_WARN,LD_CIRC, "Circuit closed while waiting for padding timer."); tor_fragile_assert(); } // TODO-MP-AP: Unify this counter with channelpadding for rephist stats //total_timers_pending--; } /** * Cache our consensus parameters upon consensus update. */ void circpad_new_consensus_params(const networkstatus_t *ns) { circpad_global_allowed_cells = networkstatus_get_param(ns, "circpad_global_allowed_cells", 0, 0, UINT16_MAX-1); circpad_global_max_padding_percent = networkstatus_get_param(ns, "circpad_global_max_padding_pct", 0, 0, 100); } /** * Check this machine against its padding limits, as well as global * consensus limits. * * We have two limits: a percent and a cell count. The cell count * limit must be reached before the percent is enforced (this is to * optionally allow very light padding of things like circuit setup * while there is no other traffic on the circuit). * * TODO: Don't apply limits to machines form torrc. * * Returns 1 if limits are set and we've hit them. Otherwise returns 0. */ STATIC bool circpad_machine_reached_padding_limit(circpad_machine_state_t *mi) { const circpad_machine_spec_t *machine = CIRCPAD_GET_MACHINE(mi); /* If machine_padding_pct is non-zero, and we've sent more * than the allowed count of padding cells, then check our * percent limits for this machine. */ if (machine->max_padding_percent && mi->padding_sent >= machine->allowed_padding_count) { uint32_t total_cells = mi->padding_sent + mi->nonpadding_sent; /* Check the percent */ if ((100*(uint32_t)mi->padding_sent) / total_cells > machine->max_padding_percent) { return 1; // limit is reached. Stop. } } /* If circpad_max_global_padding_pct is non-zero, and we've * sent more than the global padding cell limit, then check our * gloabl tor process percentage limit on padding. */ if (circpad_global_max_padding_percent && circpad_global_padding_sent >= circpad_global_allowed_cells) { uint64_t total_cells = circpad_global_padding_sent + circpad_global_nonpadding_sent; /* Check the percent */ if ((100*circpad_global_padding_sent) / total_cells > circpad_global_max_padding_percent) { return 1; // global limit reached. Stop. } } return 0; // All good! } /** * Schedule the next padding time according to the machineinfo on a * circuit. * * The histograms represent inter-packet-delay. Whenever you get an packet * event you should be scheduling your next timer (after cancelling any old * ones and updating tokens accordingly). * * Returns 1 if we decide to transition states (due to infinity bin), * 0 otherwise. */ MOCK_IMPL(circpad_decision_t, circpad_machine_schedule_padding,(circpad_machine_state_t *mi)) { circpad_delay_t in_usec = 0; struct timeval timeout; tor_assert(mi); // Don't pad in end (but also don't cancel any previously // scheduled padding either). if (mi->current_state == CIRCPAD_STATE_END) { log_fn(LOG_INFO, LD_CIRC, "Padding end state"); return CIRCPAD_STATE_UNCHANGED; } /* Check our padding limits */ if (circpad_machine_reached_padding_limit(mi)) { if (CIRCUIT_IS_ORIGIN(mi->on_circ)) { log_fn(LOG_INFO, LD_CIRC, "Padding machine has reached padding limit on circuit %u", TO_ORIGIN_CIRCUIT(mi->on_circ)->global_identifier); } else { log_fn(LOG_INFO, LD_CIRC, "Padding machine has reached padding limit on circuit %"PRIu64 ", %d", mi->on_circ->n_chan ? mi->on_circ->n_chan->global_identifier : 0, mi->on_circ->n_circ_id); } return CIRCPAD_STATE_UNCHANGED; } if (mi->is_padding_timer_scheduled) { /* Cancel current timer (if any) */ timer_disable(mi->padding_timer); mi->is_padding_timer_scheduled = 0; } /* in_usec = in microseconds */ in_usec = circpad_machine_sample_delay(mi); mi->padding_scheduled_at_usec = monotime_absolute_usec(); log_fn(LOG_INFO,LD_CIRC,"\tPadding in %u usec", in_usec); // Don't schedule if we have infinite delay. if (in_usec == CIRCPAD_DELAY_INFINITE) { return circpad_internal_event_infinity(mi); } if (mi->state_length == 0) { /* If we're at length 0, that means we hit 0 after sending * a cell earlier, and emitted an event for it, but * for whatever reason we did not decide to change states then. * So maybe the machine is waiting for bins empty, or for an * infinity event later? That would be a strange machine, * but there's no reason to make it impossible. */ return CIRCPAD_STATE_UNCHANGED; } if (in_usec <= 0) { return circpad_send_padding_cell_for_callback(mi); } timeout.tv_sec = in_usec/TOR_USEC_PER_SEC; timeout.tv_usec = (in_usec%TOR_USEC_PER_SEC); log_fn(LOG_INFO, LD_CIRC, "\tPadding in %u sec, %u usec", (unsigned)timeout.tv_sec, (unsigned)timeout.tv_usec); if (mi->padding_timer) { timer_set_cb(mi->padding_timer, circpad_send_padding_callback, mi); } else { mi->padding_timer = timer_new(circpad_send_padding_callback, mi); } timer_schedule(mi->padding_timer, &timeout); mi->is_padding_timer_scheduled = 1; // TODO-MP-AP: Unify with channelpadding counter //rep_hist_padding_count_timers(++total_timers_pending); return CIRCPAD_STATE_UNCHANGED; } /** * If the machine transitioned to the END state, we need * to check to see if it wants us to shut it down immediately. * If it does, then we need to send the appropate negotation commands * depending on which side it is. * * After this function is called, mi may point to freed memory. Do * not access it. */ static void circpad_machine_spec_transitioned_to_end(circpad_machine_state_t *mi) { const circpad_machine_spec_t *machine = CIRCPAD_GET_MACHINE(mi); /* * We allow machines to shut down and delete themselves as opposed * to just going back to START or waiting forever in END so that * we can handle the case where this machine started while it was * the only machine that matched conditions, but *since* then more * "higher ranking" machines now match the conditions, and would * be given a chance to take precidence over this one in * circpad_add_matching_machines(). * * Returning to START or waiting forever in END would not give those * other machines a chance to be launched, where as shutting down * here does. */ if (machine->should_negotiate_end) { circuit_t *on_circ = mi->on_circ; if (machine->is_origin_side) { /* We free the machine info here so that we can be replaced * by a different machine. But we must leave the padding_machine * in place to wait for the negotiated response */ circpad_circuit_machineinfo_free_idx(on_circ, machine->machine_index); circpad_negotiate_padding(TO_ORIGIN_CIRCUIT(on_circ), machine->machine_num, machine->target_hopnum, CIRCPAD_COMMAND_STOP); } else { circpad_circuit_machineinfo_free_idx(on_circ, machine->machine_index); circpad_padding_negotiated(on_circ, machine->machine_num, CIRCPAD_COMMAND_STOP, CIRCPAD_RESPONSE_OK); on_circ->padding_machine[machine->machine_index] = NULL; } } } /** * Generic state transition function for padding state machines. * * Given an event and our mutable machine info, decide if/how to * transition to a different state, and perform actions accordingly. * * Returns 1 if we transition states, 0 otherwise. */ MOCK_IMPL(circpad_decision_t, circpad_machine_spec_transition,(circpad_machine_state_t *mi, circpad_event_t event)) { const circpad_state_t *state = circpad_machine_current_state(mi); /* If state is null we are in the end state. */ if (!state) { /* If we in end state we don't pad no matter what. */ return CIRCPAD_STATE_UNCHANGED; } /* Check if this event is ignored or causes a cancel */ if (state->next_state[event] == CIRCPAD_STATE_IGNORE) { return CIRCPAD_STATE_UNCHANGED; } else if (state->next_state[event] == CIRCPAD_STATE_CANCEL) { /* Check cancel events and cancel any pending padding */ mi->padding_scheduled_at_usec = 0; if (mi->is_padding_timer_scheduled) { mi->is_padding_timer_scheduled = 0; /* Cancel current timer (if any) */ timer_disable(mi->padding_timer); } return CIRCPAD_STATE_UNCHANGED; } else { circpad_statenum_t s = state->next_state[event]; /* See if we need to transition to any other states based on this event. * Whenever a transition happens, even to our own state, we schedule * padding. * * So if a state only wants to schedule padding for an event, it specifies * a transition to itself. All non-specified events are ignored. */ log_fn(LOG_INFO, LD_CIRC, "Circpad machine %d transitioning from %s to %s", mi->machine_index, circpad_state_to_string(mi->current_state), circpad_state_to_string(s)); /* If this is not the same state, switch and init tokens, * otherwise just reschedule padding. */ if (mi->current_state != s) { mi->current_state = s; circpad_machine_setup_tokens(mi); circpad_choose_state_length(mi); /* If we transition to the end state, check to see * if this machine wants to be shut down at end */ if (s == CIRCPAD_STATE_END) { circpad_machine_spec_transitioned_to_end(mi); /* We transitioned but we don't pad in end. Also, mi * may be freed. Returning STATE_CHANGED prevents us * from accessing it in any callers of this function. */ return CIRCPAD_STATE_CHANGED; } /* We transitioned to a new state, schedule padding */ circpad_machine_schedule_padding(mi); return CIRCPAD_STATE_CHANGED; } /* We transitioned back to the same state. Schedule padding, * and inform if that causes a state transition. */ return circpad_machine_schedule_padding(mi); } return CIRCPAD_STATE_UNCHANGED; } /** * Estimate the circuit RTT from the current middle hop out to the * end of the circuit. * * We estimate RTT by calculating the time between "receive" and * "send" at a middle hop. This is because we "receive" a cell * from the origin, and then relay it towards the exit before a * response comes back. It is that response time from the exit side * that we want to measure, so that we can make use of it for synthetic * response delays. */ static void circpad_estimate_circ_rtt_on_received(circuit_t *circ, circpad_machine_state_t *mi) { /* Origin circuits don't estimate RTT. They could do it easily enough, * but they have no reason to use it in any delay calculations. */ if (CIRCUIT_IS_ORIGIN(circ) || mi->stop_rtt_update) return; /* If we already have a last receieved packet time, that means we * did not get a response before this packet. The RTT estimate * only makes sense if we do not have multiple packets on the * wire, so stop estimating if this is the second packet * back to back. However, for the first set of back-to-back * packets, we can wait until the very first response comes back * to us, to measure that RTT (for the response to optimistic * data, for example). Hence stop_rtt_update is only checked * in this received side function, and not in send side below. */ if (mi->last_received_time_usec) { /* We also allow multiple back-to-back packets if the circuit is not * opened, to handle var cells. * XXX: Will this work with out var cell plans? Maybe not, * since we're opened at the middle hop as soon as we process * one var extend2 :/ */ if (circ->state == CIRCUIT_STATE_OPEN) { log_fn(LOG_INFO, LD_CIRC, "Stopping padding RTT estimation on circuit (%"PRIu64 ", %d) after two back to back packets. Current RTT: %d", circ->n_chan ? circ->n_chan->global_identifier : 0, circ->n_circ_id, mi->rtt_estimate_usec); mi->stop_rtt_update = 1; } } else { mi->last_received_time_usec = monotime_absolute_usec(); } } /** * Handles the "send" side of RTT calculation at middle nodes. * * This function calculates the RTT from the middle to the end * of the circuit by subtracting the last received cell timestamp * from the current time. It allows back-to-back cells until * the circuit is opened, to allow for var cell handshakes. * XXX: Check our var cell plans to make sure this will work. */ static void circpad_estimate_circ_rtt_on_send(circuit_t *circ, circpad_machine_state_t *mi) { /* Origin circuits don't estimate RTT. They could do it easily enough, * but they have no reason to use it in any delay calculations. */ if (CIRCUIT_IS_ORIGIN(circ)) return; /* If last_received_time_usec is non-zero, we are waiting for a response * from the exit side. Calculate the time delta and use it as RTT. */ if (mi->last_received_time_usec) { circpad_time_t rtt_time = monotime_absolute_usec() - mi->last_received_time_usec; /* Reset the last RTT packet time, so we can tell if two cells * arrive back to back */ mi->last_received_time_usec = 0; /* Use INT32_MAX to ensure the addition doesn't overflow */ if (rtt_time >= INT32_MAX) { log_fn(LOG_WARN,LD_CIRC, "Circuit padding RTT estimate overflowed: %"PRIu64 " vs %"PRIu64, monotime_absolute_usec(), mi->last_received_time_usec); return; } /* If the old RTT estimate is lower than this one, use this one, because * the circuit is getting longer. If this estimate is somehow * faster than the previous, then maybe that was network jitter. * In that case, average them. */ if (mi->rtt_estimate_usec < (circpad_delay_t)rtt_time) { mi->rtt_estimate_usec = (circpad_delay_t)rtt_time; } else { mi->rtt_estimate_usec += (circpad_delay_t)rtt_time; mi->rtt_estimate_usec /= 2; } } else if (circ->state == CIRCUIT_STATE_OPEN) { /* If last_received_time_usec is zero, then we have gotten two cells back * to back. Stop estimating RTT in this case. Note that we only * stop RTT update if the circuit is opened, to allow for RTT estimates * of var cells during circ setup. */ mi->stop_rtt_update = 1; if (!mi->rtt_estimate_usec) { log_fn(LOG_NOTICE, LD_CIRC, "Got two cells back to back on a circuit before estimating RTT."); } } } /** * A "non-padding" cell has been sent from this endpoint. React * according to any padding state machines on the circuit. * * For origin circuits, this means we sent a cell into the network. * For middle relay circuits, this means we sent a cell towards the * origin. */ void circpad_cell_event_nonpadding_sent(circuit_t *on_circ) { /* Update global cell count */ circpad_global_nonpadding_sent++; /* If there are no machines then this loop should not iterate */ FOR_EACH_ACTIVE_CIRCUIT_MACHINE_BEGIN(i, on_circ) { /* First, update any RTT estimate */ circpad_estimate_circ_rtt_on_send(on_circ, on_circ->padding_info[i]); /* Remove a token: this is the idea of adaptive padding, since we have an * ideal distribution that we want our distribution to look like. */ if (!circpad_machine_remove_token(on_circ->padding_info[i])) { /* If removing a token did not cause a transition, check if * non-padding sent event should */ circpad_machine_spec_transition(on_circ->padding_info[i], CIRCPAD_EVENT_NONPADDING_SENT); } } FOR_EACH_ACTIVE_CIRCUIT_MACHINE_END; } /** * A "non-padding" cell has been received by this endpoint. React * according to any padding state machines on the circuit. * * For origin circuits, this means we read a cell from the network. * For middle relay circuits, this means we received a cell from the * origin. */ void circpad_cell_event_nonpadding_received(circuit_t *on_circ) { FOR_EACH_ACTIVE_CIRCUIT_MACHINE_BEGIN(i, on_circ) { /* First, update any RTT estimate */ circpad_estimate_circ_rtt_on_received(on_circ, on_circ->padding_info[i]); circpad_machine_spec_transition(on_circ->padding_info[i], CIRCPAD_EVENT_NONPADDING_RECV); } FOR_EACH_ACTIVE_CIRCUIT_MACHINE_END; } /** * A padding cell has been sent from this endpoint. React * according to any padding state machines on the circuit. * * For origin circuits, this means we sent a cell into the network. * For middle relay circuits, this means we sent a cell towards the * origin. */ void circpad_cell_event_padding_sent(circuit_t *on_circ) { FOR_EACH_ACTIVE_CIRCUIT_MACHINE_BEGIN(i, on_circ) { circpad_machine_spec_transition(on_circ->padding_info[i], CIRCPAD_EVENT_PADDING_SENT); } FOR_EACH_ACTIVE_CIRCUIT_MACHINE_END; } /** * A padding cell has been received by this endpoint. React * according to any padding state machines on the circuit. * * For origin circuits, this means we read a cell from the network. * For middle relay circuits, this means we received a cell from the * origin. */ void circpad_cell_event_padding_received(circuit_t *on_circ) { /* identical to padding sent */ FOR_EACH_ACTIVE_CIRCUIT_MACHINE_BEGIN(i, on_circ) { circpad_machine_spec_transition(on_circ->padding_info[i], CIRCPAD_EVENT_PADDING_RECV); } FOR_EACH_ACTIVE_CIRCUIT_MACHINE_END; } /** * An "infinite" delay has ben chosen from one of our histograms. * * "Infinite" delays mean don't send padding -- but they can also * mean transition to another state depending on the state machine * definitions. Check the rules and react accordingly. * * Return 1 if we decide to transition, 0 otherwise. */ circpad_decision_t circpad_internal_event_infinity(circpad_machine_state_t *mi) { return circpad_machine_spec_transition(mi, CIRCPAD_EVENT_INFINITY); } /** * All of the bins of our current state's histogram's are empty. * * Check to see if this means transition to another state, and if * not, refill the tokens. * * Return 1 if we decide to transition, 0 otherwise. */ circpad_decision_t circpad_internal_event_bins_empty(circpad_machine_state_t *mi) { if (circpad_machine_spec_transition(mi, CIRCPAD_EVENT_BINS_EMPTY) == CIRCPAD_STATE_CHANGED) { return CIRCPAD_STATE_CHANGED; } else { /* If we dont transition, then we refill the tokens */ circpad_machine_setup_tokens(mi); return CIRCPAD_STATE_UNCHANGED; } } /** * This state has used up its cell count. Emit the event and * see if we transition. * * Return 1 if we decide to transition, 0 otherwise. */ circpad_decision_t circpad_internal_event_state_length_up(circpad_machine_state_t *mi) { return circpad_machine_spec_transition(mi, CIRCPAD_EVENT_LENGTH_COUNT); } /** * Returns true if the circuit matches the conditions. */ static inline bool circpad_machine_conditions_met(origin_circuit_t *circ, const circpad_machine_spec_t *machine) { if (!(circpad_circ_purpose_to_mask(TO_CIRCUIT(circ)->purpose) & machine->conditions.purpose_mask)) return 0; if (machine->conditions.requires_vanguards) { const or_options_t *options = get_options(); /* Pinned middles are effectively vanguards */ if (!(options->HSLayer2Nodes || options->HSLayer3Nodes)) return 0; } /* We check for any bits set in the circuit state mask so that machines * can say any of the following through their state bitmask: * "I want to apply to circuits with either streams or no streams"; OR * "I only want to apply to circuits with streams"; OR * "I only want to apply to circuits without streams". */ if (!(circpad_circuit_state(circ) & machine->conditions.state_mask)) return 0; if (circuit_get_cpath_opened_len(circ) < machine->conditions.min_hops) return 0; return 1; } /** * Returns a minimized representation of the circuit state. * * The padding code only cares if the circuit is building, * opened, used for streams, and/or still has relay early cells. * This returns a bitmask of all state properities that apply to * this circuit. */ static inline circpad_circuit_state_t circpad_circuit_state(origin_circuit_t *circ) { circpad_circuit_state_t retmask = 0; if (circ->p_streams) retmask |= CIRCPAD_CIRC_STREAMS; else retmask |= CIRCPAD_CIRC_NO_STREAMS; /* We use has_opened to prevent cannibialized circs from flapping. */ if (circ->has_opened) retmask |= CIRCPAD_CIRC_OPENED; else retmask |= CIRCPAD_CIRC_BUILDING; if (circ->remaining_relay_early_cells > 0) retmask |= CIRCPAD_CIRC_HAS_RELAY_EARLY; else retmask |= CIRCPAD_CIRC_HAS_NO_RELAY_EARLY; return retmask; } /** * Convert a normal circuit purpose into a bitmask that we can * use for determining matching circuits. */ static inline circpad_purpose_mask_t circpad_circ_purpose_to_mask(uint8_t circ_purpose) { /* Treat OR circ purposes as ignored. They should not be passed here*/ if (BUG(circ_purpose <= CIRCUIT_PURPOSE_OR_MAX_)) { return 0; } /* Treat new client circuit purposes as "OMG ITS EVERYTHING". * This also should not happen */ if (BUG(circ_purpose - CIRCUIT_PURPOSE_OR_MAX_ - 1 > 32)) { return CIRCPAD_PURPOSE_ALL; } /* Convert the purpose to a bit position */ return 1 << (circ_purpose - CIRCUIT_PURPOSE_OR_MAX_ - 1); } /** * Shut down any machines whose conditions no longer match * the current circuit. */ static void circpad_shutdown_old_machines(origin_circuit_t *on_circ) { circuit_t *circ = TO_CIRCUIT(on_circ); FOR_EACH_ACTIVE_CIRCUIT_MACHINE_BEGIN(i, circ) { if (!circpad_machine_conditions_met(on_circ, circ->padding_machine[i])) { // Clear machineinfo (frees timers) circpad_circuit_machineinfo_free_idx(circ, i); // Send padding negotiate stop circpad_negotiate_padding(on_circ, circ->padding_machine[i]->machine_num, circ->padding_machine[i]->target_hopnum, CIRCPAD_COMMAND_STOP); } } FOR_EACH_ACTIVE_CIRCUIT_MACHINE_END; } /** * Negotiate new machines that would apply to this circuit. * * This function checks to see if we have any free machine indexes, * and for each free machine index, it initializes the most recently * added origin-side padding machine that matches the target machine * index and circuit conditions, and negotiates it with the appropriate * middle relay. */ static void circpad_add_matching_machines(origin_circuit_t *on_circ) { circuit_t *circ = TO_CIRCUIT(on_circ); #ifdef TOR_UNIT_TESTS /* Tests don't have to init our padding machines */ if (!origin_padding_machines) return; #endif /* If padding negotiation failed before, do not try again */ if (on_circ->padding_negotiation_failed) return; FOR_EACH_CIRCUIT_MACHINE_BEGIN(i) { /* If there is a padding machine info, this index is occupied. * No need to check conditions for this index. */ if (circ->padding_info[i]) continue; /* We have a free machine index. Check the origin padding * machines in reverse order, so that more recently added * machines take priority over older ones. */ SMARTLIST_FOREACH_REVERSE_BEGIN(origin_padding_machines, circpad_machine_spec_t *, machine) { /* Machine definitions have a specific target machine index. * This is so event ordering is deterministic with respect * to which machine gets events first when there are two * machines installed on a circuit. Make sure we only * add this machine if its target machine index is free. */ if (machine->machine_index == i && circpad_machine_conditions_met(on_circ, machine)) { // We can only replace this machine if the target hopnum // is the same, otherwise we'll get invalid data if (circ->padding_machine[i]) { if (circ->padding_machine[i]->target_hopnum != machine->target_hopnum) continue; /* Replace it. (Don't free - is global). */ circ->padding_machine[i] = NULL; } /* Set up the machine immediately so that the slot is occupied. * We will tear it down on error return, or if there is an error * response from the relay. */ circpad_setup_machine_on_circ(circ, machine); if (circpad_negotiate_padding(on_circ, machine->machine_num, machine->target_hopnum, CIRCPAD_COMMAND_START) < 0) { circpad_circuit_machineinfo_free_idx(circ, i); circ->padding_machine[i] = NULL; on_circ->padding_negotiation_failed = 1; } else { /* Success. Don't try any more machines */ return; } } } SMARTLIST_FOREACH_END(machine); } FOR_EACH_CIRCUIT_MACHINE_END; } /** * Event that tells us we added a hop to an origin circuit. * * This event is used to decide if we should create a padding machine * on a circuit. */ void circpad_machine_event_circ_added_hop(origin_circuit_t *on_circ) { /* Since our padding conditions do not specify a max_hops, * all we can do is add machines here */ circpad_add_matching_machines(on_circ); } /** * Event that tells us that an origin circuit is now built. * * Shut down any machines that only applied to un-built circuits. * Activate any new ones. */ void circpad_machine_event_circ_built(origin_circuit_t *circ) { circpad_shutdown_old_machines(circ); circpad_add_matching_machines(circ); } /** * Circpad purpose changed event. * * Shut down any machines that don't apply to our circ purpose. * Activate any new ones that do. */ void circpad_machine_event_circ_purpose_changed(origin_circuit_t *circ) { circpad_shutdown_old_machines(circ); circpad_add_matching_machines(circ); } /** * Event that tells us that an origin circuit is out of RELAY_EARLY * cells. * * Shut down any machines that only applied to RELAY_EARLY circuits. * Activate any new ones. */ void circpad_machine_event_circ_has_no_relay_early(origin_circuit_t *circ) { circpad_shutdown_old_machines(circ); circpad_add_matching_machines(circ); } /** * Streams attached event. * * Called from link_apconn_to_circ() and handle_hs_exit_conn() * * Shut down any machines that only applied to machines without * streams. Activate any new ones. */ void circpad_machine_event_circ_has_streams(origin_circuit_t *circ) { circpad_shutdown_old_machines(circ); circpad_add_matching_machines(circ); } /** * Streams detached event. * * Called from circuit_detach_stream() * * Shut down any machines that only applied to machines without * streams. Activate any new ones. */ void circpad_machine_event_circ_has_no_streams(origin_circuit_t *circ) { circpad_shutdown_old_machines(circ); circpad_add_matching_machines(circ); } /** * Verify that padding is coming from the expected hop. * * Returns true if from_hop matches the target hop from * one of our padding machines. * * Returns false if we're not an origin circuit, or if from_hop * does not match one of the padding machines. */ bool circpad_padding_is_from_expected_hop(circuit_t *circ, crypt_path_t *from_hop) { crypt_path_t *target_hop = NULL; if (!CIRCUIT_IS_ORIGIN(circ)) return 0; FOR_EACH_CIRCUIT_MACHINE_BEGIN(i) { /* We have to check padding_machine and not padding_info/active * machines here because padding may arrive after we shut down a * machine. The info is gone, but the padding_machine waits * for the padding_negotiated response to come back. */ if (!circ->padding_machine[i]) continue; target_hop = circuit_get_cpath_hop(TO_ORIGIN_CIRCUIT(circ), circ->padding_machine[i]->target_hopnum); if (target_hop == from_hop) return 1; } FOR_EACH_CIRCUIT_MACHINE_END; return 0; } /** * Deliver circpad events for an "unrecognized cell". * * Unrecognized cells are sent to relays and are forwarded * onto the next hop of their circuits. Unrecognized cells * are by definition not padding. We need to tell relay-side * state machines that a non-padding cell was sent or received, * depending on the direction, so they can update their histograms * and decide to pad or not. */ void circpad_deliver_unrecognized_cell_events(circuit_t *circ, cell_direction_t dir) { // We should never see unrecognized cells at origin. // Our caller emits a warn when this happens. if (CIRCUIT_IS_ORIGIN(circ)) { return; } if (dir == CELL_DIRECTION_OUT) { /* When direction is out (away from origin), then we received non-padding cell coming from the origin to us. */ circpad_cell_event_nonpadding_received(circ); } else if (dir == CELL_DIRECTION_IN) { /* It's in and not origin, so the cell is going away from us. * So we are relaying a non-padding cell towards the origin. */ circpad_cell_event_nonpadding_sent(circ); } } /** * Deliver circpad events for "recognized" relay cells. * * Recognized cells are destined for this hop, either client or middle. * Check if this is a padding cell or not, and send the appropiate * received event. */ void circpad_deliver_recognized_relay_cell_events(circuit_t *circ, uint8_t relay_command, crypt_path_t *layer_hint) { /* Padding negotiate cells are ignored by the state machines * for simplicity. */ if (relay_command == RELAY_COMMAND_PADDING_NEGOTIATE || relay_command == RELAY_COMMAND_PADDING_NEGOTIATED) { return; } if (relay_command == RELAY_COMMAND_DROP) { rep_hist_padding_count_read(PADDING_TYPE_DROP); if (CIRCUIT_IS_ORIGIN(circ)) { if (circpad_padding_is_from_expected_hop(circ, layer_hint)) { circuit_read_valid_data(TO_ORIGIN_CIRCUIT(circ), 0); } else { /* This is unexpected padding. Ignore it for now. */ return; } } /* The cell should be recognized by now, which means that we are on the destination, which means that we received a padding cell. We might be the client or the Middle node, still, because leaky-pipe. */ circpad_cell_event_padding_received(circ); log_fn(LOG_INFO, LD_CIRC, "Got padding cell on %s circuit %u.", CIRCUIT_IS_ORIGIN(circ) ? "origin" : "non-origin", CIRCUIT_IS_ORIGIN(circ) ? TO_ORIGIN_CIRCUIT(circ)->global_identifier : 0); } else { /* We received a non-padding cell on the edge */ circpad_cell_event_nonpadding_received(circ); } } /** * Deliver circpad events for relay cells sent from us. * * If this is a padding cell, update our padding stats * and deliver the event. Otherwise just deliver the event. */ void circpad_deliver_sent_relay_cell_events(circuit_t *circ, uint8_t relay_command) { /* Padding negotiate cells are ignored by the state machines * for simplicity. */ if (relay_command == RELAY_COMMAND_PADDING_NEGOTIATE || relay_command == RELAY_COMMAND_PADDING_NEGOTIATED) { return; } /* RELAY_COMMAND_DROP is the multi-hop (aka circuit-level) padding cell in * tor. (CELL_PADDING is a channel-level padding cell, which is not relayed * or processed here) */ if (relay_command == RELAY_COMMAND_DROP) { /* Optimization: The event for RELAY_COMMAND_DROP is sent directly * from circpad_send_padding_cell_for_callback(). This is to avoid * putting a cell_t and a relay_header_t on the stack repeatedly * if we decide to send a long train of padidng cells back-to-back * with 0 delay. So we do nothing here. */ return; } else { /* This is a non-padding cell sent from the client or from * this node. */ circpad_cell_event_nonpadding_sent(circ); } } /** * Initialize the states array for a circpad machine. */ void circpad_machine_states_init(circpad_machine_spec_t *machine, circpad_statenum_t num_states) { if (BUG(num_states > CIRCPAD_MAX_MACHINE_STATES)) { num_states = CIRCPAD_MAX_MACHINE_STATES; } machine->num_states = num_states; machine->states = tor_malloc_zero(sizeof(circpad_state_t)*num_states); /* Initialize the default next state for all events to * "ignore" -- if events aren't specified, they are ignored. */ for (circpad_statenum_t s = 0; s < num_states; s++) { for (int e = 0; e < CIRCPAD_NUM_EVENTS; e++) { machine->states[s].next_state[e] = CIRCPAD_STATE_IGNORE; } } } static void circpad_setup_machine_on_circ(circuit_t *on_circ, const circpad_machine_spec_t *machine) { if (CIRCUIT_IS_ORIGIN(on_circ) && !machine->is_origin_side) { log_fn(LOG_WARN, LD_BUG, "Can't set up non-origin machine on origin circuit!"); return; } if (!CIRCUIT_IS_ORIGIN(on_circ) && machine->is_origin_side) { log_fn(LOG_WARN, LD_BUG, "Can't set up origin machine on non-origin circuit!"); return; } tor_assert_nonfatal(on_circ->padding_machine[machine->machine_index] == NULL); tor_assert_nonfatal(on_circ->padding_info[machine->machine_index] == NULL); on_circ->padding_info[machine->machine_index] = circpad_circuit_machineinfo_new(on_circ, machine->machine_index); on_circ->padding_machine[machine->machine_index] = machine; } /* These padding machines are only used for tests pending #28634. */ #ifdef TOR_UNIT_TESTS static void circpad_circ_client_machine_init(void) { circpad_machine_spec_t *circ_client_machine = tor_malloc_zero(sizeof(circpad_machine_spec_t)); // XXX: Better conditions for merge.. Or disable this machine in // merge? circ_client_machine->conditions.min_hops = 2; circ_client_machine->conditions.state_mask = CIRCPAD_CIRC_BUILDING|CIRCPAD_CIRC_OPENED|CIRCPAD_CIRC_HAS_RELAY_EARLY; circ_client_machine->conditions.purpose_mask = CIRCPAD_PURPOSE_ALL; circ_client_machine->target_hopnum = 2; circ_client_machine->is_origin_side = 1; /* Start, gap, burst */ circpad_machine_states_init(circ_client_machine, 3); circ_client_machine->states[CIRCPAD_STATE_START]. next_state[CIRCPAD_EVENT_NONPADDING_RECV] = CIRCPAD_STATE_BURST; circ_client_machine->states[CIRCPAD_STATE_BURST]. next_state[CIRCPAD_EVENT_NONPADDING_RECV] = CIRCPAD_STATE_BURST; circ_client_machine->states[CIRCPAD_STATE_BURST]. next_state[CIRCPAD_EVENT_PADDING_RECV] = CIRCPAD_STATE_BURST; /* If we are in burst state, and we send a non-padding cell, then we cancel the timer for the next padding cell: We dont want to send fake extends when actual extends are going on */ circ_client_machine->states[CIRCPAD_STATE_BURST]. next_state[CIRCPAD_EVENT_NONPADDING_SENT] = CIRCPAD_STATE_CANCEL; circ_client_machine->states[CIRCPAD_STATE_BURST]. next_state[CIRCPAD_EVENT_BINS_EMPTY] = CIRCPAD_STATE_END; circ_client_machine->states[CIRCPAD_STATE_BURST].token_removal = CIRCPAD_TOKEN_REMOVAL_CLOSEST; // FIXME: Tune this histogram circ_client_machine->states[CIRCPAD_STATE_BURST].histogram_len = 2; circ_client_machine->states[CIRCPAD_STATE_BURST].start_usec = 500; circ_client_machine->states[CIRCPAD_STATE_BURST].range_usec = 1000000; /* We have 5 tokens in the histogram, which means that all circuits will look * like they have 7 hops (since we start this machine after the second hop, * and tokens are decremented for any valid hops, and fake extends are * used after that -- 2+5==7). */ circ_client_machine->states[CIRCPAD_STATE_BURST].histogram[0] = 5; circ_client_machine->states[CIRCPAD_STATE_BURST].histogram_total_tokens = 5; circ_client_machine->machine_num = smartlist_len(origin_padding_machines); smartlist_add(origin_padding_machines, circ_client_machine); } static void circpad_circ_responder_machine_init(void) { circpad_machine_spec_t *circ_responder_machine = tor_malloc_zero(sizeof(circpad_machine_spec_t)); /* Shut down the machine after we've sent enough packets */ circ_responder_machine->should_negotiate_end = 1; /* The relay-side doesn't care what hopnum it is, but for consistency, * let's match the client */ circ_responder_machine->target_hopnum = 2; circ_responder_machine->is_origin_side = 0; /* Start, gap, burst */ circpad_machine_states_init(circ_responder_machine, 3); /* This is the settings of the state machine. In the future we are gonna serialize this into the consensus or the torrc */ /* We transition to the burst state on padding receive and on non-padding * recieve */ circ_responder_machine->states[CIRCPAD_STATE_START]. next_state[CIRCPAD_EVENT_PADDING_RECV] = CIRCPAD_STATE_BURST; circ_responder_machine->states[CIRCPAD_STATE_START]. next_state[CIRCPAD_EVENT_NONPADDING_RECV] = CIRCPAD_STATE_BURST; /* Inside the burst state we _stay_ in the burst state when a non-padding * is sent */ circ_responder_machine->states[CIRCPAD_STATE_BURST]. next_state[CIRCPAD_EVENT_NONPADDING_SENT] = CIRCPAD_STATE_BURST; /* Inside the burst state we transition to the gap state when we receive a * padding cell */ circ_responder_machine->states[CIRCPAD_STATE_BURST]. next_state[CIRCPAD_EVENT_PADDING_RECV] = CIRCPAD_STATE_GAP; /* These describe the padding charasteristics when in burst state */ /* use_rtt_estimate tries to estimate how long padding cells take to go from C->M, and uses that as what as the base of the histogram */ circ_responder_machine->states[CIRCPAD_STATE_BURST].use_rtt_estimate = 1; /* The histogram is 2 bins: an empty one, and infinity */ circ_responder_machine->states[CIRCPAD_STATE_BURST].histogram_len = 2; circ_responder_machine->states[CIRCPAD_STATE_BURST].start_usec = 5000; circ_responder_machine->states[CIRCPAD_STATE_BURST].range_usec = 1000000; /* During burst state we wait forever for padding to arrive. We are waiting for a padding cell from the client to come in, so that we respond, and we immitate how extend looks like */ circ_responder_machine->states[CIRCPAD_STATE_BURST].histogram[0] = 0; // Only infinity bin: circ_responder_machine->states[CIRCPAD_STATE_BURST].histogram[1] = 1; circ_responder_machine->states[CIRCPAD_STATE_BURST]. histogram_total_tokens = 1; /* From the gap state, we _stay_ in the gap state, when we receive padding * or non padding */ circ_responder_machine->states[CIRCPAD_STATE_GAP]. next_state[CIRCPAD_EVENT_PADDING_RECV] = CIRCPAD_STATE_GAP; circ_responder_machine->states[CIRCPAD_STATE_GAP]. next_state[CIRCPAD_EVENT_NONPADDING_RECV] = CIRCPAD_STATE_GAP; /* And from the gap state, we go to the end, when the bins are empty or a * non-padding cell is sent */ circ_responder_machine->states[CIRCPAD_STATE_GAP]. next_state[CIRCPAD_EVENT_BINS_EMPTY] = CIRCPAD_STATE_END; circ_responder_machine->states[CIRCPAD_STATE_GAP]. next_state[CIRCPAD_EVENT_NONPADDING_SENT] = CIRCPAD_STATE_END; // FIXME: Tune this histogram /* The gap state is the delay you wait after you receive a padding cell before you send a padding response */ circ_responder_machine->states[CIRCPAD_STATE_GAP].use_rtt_estimate = 1; circ_responder_machine->states[CIRCPAD_STATE_GAP].histogram_len = 6; circ_responder_machine->states[CIRCPAD_STATE_GAP].start_usec = 5000; circ_responder_machine->states[CIRCPAD_STATE_GAP].range_usec = 1000000; circ_responder_machine->states[CIRCPAD_STATE_GAP].histogram[0] = 0; circ_responder_machine->states[CIRCPAD_STATE_GAP].histogram[1] = 1; circ_responder_machine->states[CIRCPAD_STATE_GAP].histogram[2] = 2; circ_responder_machine->states[CIRCPAD_STATE_GAP].histogram[3] = 2; circ_responder_machine->states[CIRCPAD_STATE_GAP].histogram[4] = 1; /* Total number of tokens */ circ_responder_machine->states[CIRCPAD_STATE_GAP].histogram_total_tokens = 6; circ_responder_machine->states[CIRCPAD_STATE_GAP].token_removal = CIRCPAD_TOKEN_REMOVAL_CLOSEST_USEC; circ_responder_machine->machine_num = smartlist_len(relay_padding_machines); smartlist_add(relay_padding_machines, circ_responder_machine); } #endif /** * Initialize all of our padding machines. * * This is called at startup. It sets up some global machines, and then * loads some from torrc, and from the tor consensus. */ void circpad_machines_init(void) { tor_assert_nonfatal(origin_padding_machines == NULL); tor_assert_nonfatal(relay_padding_machines == NULL); origin_padding_machines = smartlist_new(); relay_padding_machines = smartlist_new(); // TODO: Parse machines from consensus and torrc #ifdef TOR_UNIT_TESTS circpad_circ_client_machine_init(); circpad_circ_responder_machine_init(); #endif } /** * Free our padding machines */ void circpad_machines_free(void) { if (origin_padding_machines) { SMARTLIST_FOREACH(origin_padding_machines, circpad_machine_spec_t *, m, tor_free(m->states); tor_free(m)); smartlist_free(origin_padding_machines); } if (relay_padding_machines) { SMARTLIST_FOREACH(relay_padding_machines, circpad_machine_spec_t *, m, tor_free(m->states); tor_free(m)); smartlist_free(relay_padding_machines); } } /** * Check the Protover info to see if a node supports padding. */ static bool circpad_node_supports_padding(const node_t *node) { if (node->rs) { log_fn(LOG_INFO, LD_CIRC, "Checking padding: %s", node->rs->pv.supports_padding ? "supported" : "unsupported"); return node->rs->pv.supports_padding; } log_fn(LOG_INFO, LD_CIRC, "Empty routerstatus in padding check"); return 0; } /** * Get a node_t for the nth hop in our circuit, starting from 1. * * Returns node_t from the consensus for that hop, if it is opened. * Otherwise returns NULL. */ static const node_t * circuit_get_nth_node(origin_circuit_t *circ, int hop) { crypt_path_t *iter = circuit_get_cpath_hop(circ, hop); if (!iter || iter->state != CPATH_STATE_OPEN) return NULL; return node_get_by_id(iter->extend_info->identity_digest); } /** * Return true if a particular circuit supports padding * at the desired hop. */ static bool circpad_circuit_supports_padding(origin_circuit_t *circ, int target_hopnum) { const node_t *hop; if (!(hop = circuit_get_nth_node(circ, target_hopnum))) { return 0; } return circpad_node_supports_padding(hop); } /** * Try to negotiate padding. * * Returns -1 on error, 0 on success. */ signed_error_t circpad_negotiate_padding(origin_circuit_t *circ, circpad_machine_num_t machine, uint8_t target_hopnum, uint8_t command) { circpad_negotiate_t type; cell_t cell; ssize_t len; /* Check that the target hop lists support for padding in * its ProtoVer fields */ if (!circpad_circuit_supports_padding(circ, target_hopnum)) { return -1; } memset(&cell, 0, sizeof(cell_t)); memset(&type, 0, sizeof(circpad_negotiate_t)); // This gets reset to RELAY_EARLY appropriately by // relay_send_command_from_edge_. At least, it looks that way. // QQQ-MP-AP: Verify that. cell.command = CELL_RELAY; circpad_negotiate_set_command(&type, command); circpad_negotiate_set_version(&type, 0); circpad_negotiate_set_machine_type(&type, machine); if ((len = circpad_negotiate_encode(cell.payload, CELL_PAYLOAD_SIZE, &type)) < 0) return -1; log_fn(LOG_INFO,LD_CIRC, "Negotiating padding on circuit %u", circ->global_identifier); return circpad_send_command_to_hop(circ, target_hopnum, RELAY_COMMAND_PADDING_NEGOTIATE, cell.payload, len); } /** * Try to negotiate padding. * * Returns 1 if successful (or already set up), 0 otherwise. */ bool circpad_padding_negotiated(circuit_t *circ, circpad_machine_num_t machine, uint8_t command, uint8_t response) { circpad_negotiated_t type; cell_t cell; ssize_t len; memset(&cell, 0, sizeof(cell_t)); memset(&type, 0, sizeof(circpad_negotiated_t)); // This gets reset to RELAY_EARLY appropriately by // relay_send_command_from_edge_. At least, it looks that way. // QQQ-MP-AP: Verify that. cell.command = CELL_RELAY; circpad_negotiated_set_command(&type, command); circpad_negotiated_set_response(&type, response); circpad_negotiated_set_version(&type, 0); circpad_negotiated_set_machine_type(&type, machine); if ((len = circpad_negotiated_encode(cell.payload, CELL_PAYLOAD_SIZE, &type)) < 0) return 0; /* Use relay_send because we're from the middle to the origin. We don't * need to specify a target hop or layer_hint. */ return relay_send_command_from_edge(0, circ, RELAY_COMMAND_PADDING_NEGOTIATED, (void*)cell.payload, (size_t)len, NULL) == 0; } /** * Parse and react to a padding_negotiate cell. * * This is called at the middle node upon receipt of the client's choice of * state machine, so that it can use the requested state machine index, if * it is available. * * Returns -1 on error, 0 on success. */ signed_error_t circpad_handle_padding_negotiate(circuit_t *circ, cell_t *cell) { int retval = 0; circpad_negotiate_t *negotiate; if (CIRCUIT_IS_ORIGIN(circ)) { log_fn(LOG_WARN, LD_PROTOCOL, "Padding negotiate cell unsupported at origin."); return -1; } if (circpad_negotiate_parse(&negotiate, cell->payload+RELAY_HEADER_SIZE, CELL_PAYLOAD_SIZE-RELAY_HEADER_SIZE) < 0) { log_fn(LOG_WARN, LD_CIRC, "Received malformed PADDING_NEGOTIATE cell; dropping."); return -1; } if (negotiate->command == CIRCPAD_COMMAND_STOP) { /* Free the machine corresponding to this machine type */ free_circ_machineinfos_with_machine_num(circ, negotiate->machine_type); log_fn(LOG_WARN, LD_CIRC, "Received circuit padding stop command for unknown machine."); goto err; } else if (negotiate->command == CIRCPAD_COMMAND_START) { SMARTLIST_FOREACH_BEGIN(relay_padding_machines, const circpad_machine_spec_t *, m) { if (m->machine_num == negotiate->machine_type) { circpad_setup_machine_on_circ(circ, m); goto done; } } SMARTLIST_FOREACH_END(m); } err: retval = -1; done: circpad_padding_negotiated(circ, negotiate->machine_type, negotiate->command, (retval == 0) ? CIRCPAD_RESPONSE_OK : CIRCPAD_RESPONSE_ERR); circpad_negotiate_free(negotiate); return retval; } /** * Parse and react to a padding_negotiated cell. * * This is called at the origin upon receipt of the middle's response * to our choice of state machine. * * Returns -1 on error, 0 on success. */ signed_error_t circpad_handle_padding_negotiated(circuit_t *circ, cell_t *cell, crypt_path_t *layer_hint) { circpad_negotiated_t *negotiated; if (!CIRCUIT_IS_ORIGIN(circ)) { log_fn(LOG_WARN, LD_PROTOCOL, "Padding negotiated cell unsupported at non-origin."); return -1; } /* Verify this came from the expected hop */ if (!circpad_padding_is_from_expected_hop(circ, layer_hint)) { log_fn(LOG_WARN, LD_PROTOCOL, "Padding negotiated cell from wrong hop!"); return -1; } if (circpad_negotiated_parse(&negotiated, cell->payload+RELAY_HEADER_SIZE, CELL_PAYLOAD_SIZE-RELAY_HEADER_SIZE) < 0) { log_fn(LOG_WARN, LD_CIRC, "Received malformed PADDING_NEGOTIATED cell; " "dropping."); return -1; } if (negotiated->command == CIRCPAD_COMMAND_STOP) { /* There may not be a padding_info here if we shut down the * machine in circpad_shutdown_old_machines(). Or, if * circpad_add_matching_matchines() added a new machine, * there may be a padding_machine for a different machine num * than this response. */ free_circ_machineinfos_with_machine_num(circ, negotiated->machine_type); } else if (negotiated->command == CIRCPAD_COMMAND_START && negotiated->response == CIRCPAD_RESPONSE_ERR) { // This can happen due to consensus drift.. free the machines // and be sad free_circ_machineinfos_with_machine_num(circ, negotiated->machine_type); TO_ORIGIN_CIRCUIT(circ)->padding_negotiation_failed = 1; log_fn(LOG_INFO, LD_CIRC, "Middle node did not accept our padding request."); } circpad_negotiated_free(negotiated); return 0; } /* Serialization */ // TODO: Should we use keyword=value here? Are there helpers for that? #if 0 static void circpad_state_serialize(const circpad_state_t *state, smartlist_t *chunks) { smartlist_add_asprintf(chunks, " %u", state->histogram[0]); for (int i = 1; i < state->histogram_len; i++) { smartlist_add_asprintf(chunks, ",%u", state->histogram[i]); } smartlist_add_asprintf(chunks, " 0x%x", state->transition_cancel_events); for (int i = 0; i < CIRCPAD_NUM_STATES; i++) { smartlist_add_asprintf(chunks, ",0x%x", state->transition_events[i]); } smartlist_add_asprintf(chunks, " %u %u", state->use_rtt_estimate, state->token_removal); } char * circpad_machine_spec_to_string(const circpad_machine_spec_t *machine) { smartlist_t *chunks = smartlist_new(); char *out; (void)machine; circpad_state_serialize(&machine->start, chunks); circpad_state_serialize(&machine->gap, chunks); circpad_state_serialize(&machine->burst, chunks); out = smartlist_join_strings(chunks, "", 0, NULL); SMARTLIST_FOREACH(chunks, char *, cp, tor_free(cp)); smartlist_free(chunks); return out; } // XXX: Writeme const circpad_machine_spec_t * circpad_string_to_machine(const char *str) { (void)str; return NULL; } #endif