[tor-commits] [tor/master] Circuit padding implementation.
nickm at torproject.org
nickm at torproject.org
Mon Jan 14 19:50:35 UTC 2019
commit 9aaf72ea58bd52d0af694411d16194ea15d612d1
Author: Mike Perry <mikeperry-git at torproject.org>
Date: Tue Oct 23 19:49:26 2018 +0000
Circuit padding implementation.
This implements all of the event handling, state machines, and padding
decisions for circuit padding.
I recommend reviewing this after you look at the call-in points into it from
the rest of Tor.
Co-authored-by: George Kadianakis <desnacked at riseup.net>
---
src/core/include.am | 2 +
src/core/or/circuitpadding.c | 2467 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 2469 insertions(+)
diff --git a/src/core/include.am b/src/core/include.am
index 5e69cb9ad..ae47c75e0 100644
--- a/src/core/include.am
+++ b/src/core/include.am
@@ -32,6 +32,7 @@ LIBTOR_APP_A_SOURCES = \
src/core/or/circuitlist.c \
src/core/or/circuitmux.c \
src/core/or/circuitmux_ewma.c \
+ src/core/or/circuitpadding.c \
src/core/or/circuitstats.c \
src/core/or/circuituse.c \
src/core/or/command.c \
@@ -227,6 +228,7 @@ noinst_HEADERS += \
src/core/or/circuitmux.h \
src/core/or/circuitmux_ewma.h \
src/core/or/circuitstats.h \
+ src/core/or/circuitpadding.h \
src/core/or/circuituse.h \
src/core/or/command.h \
src/core/or/connection_edge.h \
diff --git a/src/core/or/circuitpadding.c b/src/core/or/circuitpadding.c
new file mode 100644
index 000000000..9d65e2cf2
--- /dev/null
+++ b/src/core/or/circuitpadding.c
@@ -0,0 +1,2467 @@
+/* Copyright (c) 2017 The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#include <math.h>
+#include "lib/math/fp.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/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"
+
+/* XXX: This is a dup of the constant in ./src/lib/time/tvdiff.c.
+ * Should/Do we have a header for time constants like this? */
+#define TOR_USEC_PER_SEC (1000000)
+
+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_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_t's parsed from consensus and torrc
+ * that have origin_side == 1 (ie: are for client side) */
+STATIC smartlist_t *origin_padding_machines = NULL;
+
+/** This is the list of circpad_machine_t's parsed from consensus and torrc
+ * that have origin_side == 0 (ie: are for relay side) */
+STATIC smartlist_t *relay_padding_machines = NULL;
+
+/** Loop over the current padding state machines using <b>loop_var</b> 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 <b>loop_var</b>
+ * 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 <b>circ</b> that match <b>machine_num</b>. */
+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_machineinfo_t *
+circpad_circuit_machineinfo_new(circuit_t *on_circ, int machine_index)
+{
+ circpad_machineinfo_t *mi = tor_malloc_zero(sizeof(circpad_machineinfo_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(circpad_machineinfo_t *mi)
+{
+ const circpad_machine_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(circpad_machineinfo_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 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_machineinfo_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;
+
+ 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_machineinfo_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_machineinfo_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_machineinfo_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);
+ 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)
+{
+ double p = 0;
+
+ switch (dist.type) {
+ case CIRCPAD_DIST_NONE:
+ return 0;
+ case CIRCPAD_DIST_UNIFORM:
+ p = crypto_rand_double();
+ // param2 is upper bound, param1 is lower
+ /* The subtraction is exact as long as param2 and param1 are less than
+ * 2**53. The multiplication is accurate as long as (param2 - param1)
+ * is less than 2**52. (And when they are large, the low bits aren't
+ * important.) The result covers the full range of outputs, as long as
+ * p has a resolution of 1/2**32 or greater. */
+ p *= (dist.param2 - dist.param1);
+ p += dist.param1;
+ return p;
+ case CIRCPAD_DIST_LOGISTIC:
+ p = crypto_rand_double();
+ /* https://en.wikipedia.org/wiki/Logistic_distribution#Quantile_function
+ * param1 is Mu, param2 is s. */
+ if (p <= 0.0) // Avoid log(0)
+ return 0;
+ return dist.param1 + dist.param2*tor_mathlog(p/(1.0-p));
+ case CIRCPAD_DIST_LOG_LOGISTIC:
+ p = crypto_rand_double();
+ /* https://en.wikipedia.org/wiki/Log-logistic_distribution#Quantiles
+ * param1 is Alpha, param2 is Beta */
+ return dist.param1 * pow(p/(1.0-p), 1.0/dist.param2);
+ case CIRCPAD_DIST_GEOMETRIC:
+ p = crypto_rand_double();
+ /* https://github.com/distributions-io/geometric-quantile/
+ * param1 is 'p' (success probability) */
+ return ceil(tor_mathlog(1.0-p)/tor_mathlog(1.0-dist.param1));
+ case CIRCPAD_DIST_WEIBULL:
+ p = crypto_rand_double();
+ /* https://en.wikipedia.org/wiki/Weibull_distribution \
+ * #Cumulative_distribution_function
+ * param1 is k, param2 is Lambda */
+ return dist.param2*pow(-tor_mathlog(1.0-p), 1.0/dist.param1);
+ case CIRCPAD_DIST_PARETO:
+ p = 1.0-crypto_rand_double(); // Pareto quantile needs (0,1]
+
+ /* https://en.wikipedia.org/wiki/Generalized_Pareto_distribution \
+ * #Generating_generalized_Pareto_random_variables
+ * param1 is Sigma, param2 is Xi
+ * Since it's piecewise, we must define it for 0 (or close to 0) */
+ if (fabs(dist.param2) <= 1e-22)
+ return -dist.param1*tor_mathlog(p);
+ else
+ return dist.param1*(pow(p, -dist.param2) - 1.0)/dist.param2;
+ }
+ 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(circpad_machineinfo_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
+ * <b>target_bin_usec</b>, and that still has tokens remaining.
+ */
+static circpad_hist_index_t
+circpad_machine_first_lower_index(circpad_machineinfo_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_machineinfo_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_machineinfo_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 bin start usec.
+ * If it is false, use bin index distance only.
+ */
+STATIC void
+circpad_machine_remove_closest_token(circpad_machineinfo_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;
+ }
+
+ if (higher == mi->histogram_len && lower == -1) {
+ // 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;
+ }
+
+ 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;
+ }
+ } 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_machineinfo_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_machineinfo_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.
+ */
+circpad_decision_t
+circpad_machine_remove_token(circpad_machineinfo_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.
+ */
+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_machineinfo_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_machineinfo_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_machineinfo_t *mi = ((circpad_machineinfo_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_machineinfo_t *mi)
+{
+ const circpad_machine_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.
+ */
+circpad_decision_t
+circpad_machine_schedule_padding(circpad_machineinfo_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_transitioned_to_end(circpad_machineinfo_t *mi)
+{
+ const circpad_machine_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.
+ */
+circpad_decision_t
+circpad_machine_transition(circpad_machineinfo_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_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_machineinfo_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_machineinfo_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_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_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_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_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_machineinfo_t *mi)
+{
+ return circpad_machine_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_machineinfo_t *mi)
+{
+ if (circpad_machine_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_machineinfo_t *mi)
+{
+ return circpad_machine_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_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_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_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_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;
+}
+
+static void
+circpad_circ_client_machine_init(void)
+{
+ circpad_machine_t *circ_client_machine
+ = tor_malloc_zero(sizeof(circpad_machine_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_t *circ_responder_machine
+ = tor_malloc_zero(sizeof(circpad_machine_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);
+}
+
+/**
+ * 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
+
+ circpad_circ_client_machine_init();
+ circpad_circ_responder_machine_init();
+}
+
+/**
+ * Free our padding machines
+ */
+void
+circpad_machines_free(void)
+{
+ if (origin_padding_machines) {
+ SMARTLIST_FOREACH(origin_padding_machines,
+ circpad_machine_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_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_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_to_string(const circpad_machine_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_t *
+circpad_string_to_machine(const char *str)
+{
+ (void)str;
+ return NULL;
+}
+
+#endif
More information about the tor-commits
mailing list