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Diffstat (limited to 'src/or/channelpadding.c')
| -rw-r--r-- | src/or/channelpadding.c | 574 |
1 files changed, 574 insertions, 0 deletions
diff --git a/src/or/channelpadding.c b/src/or/channelpadding.c new file mode 100644 index 0000000000..3976424faf --- /dev/null +++ b/src/or/channelpadding.c @@ -0,0 +1,574 @@ +/* Copyright (c) 2001 Matej Pfajfar. + * Copyright (c) 2001-2004, Roger Dingledine. + * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson. + * Copyright (c) 2007-2015, The Tor Project, Inc. */ +/* See LICENSE for licensing information */ + +/* TOR_CHANNEL_INTERNAL_ define needed for an O(1) implementation of + * channelpadding_channel_to_channelinfo() */ +#define TOR_CHANNEL_INTERNAL_ + +#include "or.h" +#include "channel.h" +#include "channelpadding.h" +#include "channeltls.h" +#include "config.h" +#include "networkstatus.h" +#include "connection.h" +#include "connection_or.h" +#include "main.h" +#include "rephist.h" +#include "router.h" +#include "compat_time.h" +#include <event.h> + +STATIC int channelpadding_get_netflow_inactive_timeout_ms(const channel_t *); +STATIC int channelpadding_send_disable_command(channel_t *); +STATIC int64_t channelpadding_compute_time_until_pad_for_netflow(channel_t *); + +/** The total number of pending channelpadding timers */ +static uint64_t total_timers_pending; + +/** + * Get a random netflow inactive timeout keepalive period in milliseconds, + * the range for which is determined by consensus parameters, negotiation, + * configuration, or default values. The consensus parameters enforce the + * minimum possible value, to avoid excessively frequent padding. + * + * The ranges for this value were chosen to be low enough to ensure that + * routers do not emit a new netflow record for a connection due to it + * being idle. + * + * Specific timeout values for major routers are listed in Proposal 251. + * No major router appeared capable of setting an inactive timeout below 10 + * seconds, so we set the defaults below that value, since we can always + * scale back if it ends up being too much padding. + * + * Returns the next timeout period (in milliseconds) after which we should + * send a padding packet, or 0 if padding is disabled. + */ +#define DFLT_NETFLOW_INACTIVE_KEEPALIVE_LOW 1500 +#define DFLT_NETFLOW_INACTIVE_KEEPALIVE_HIGH 9500 +#define DFLT_NETFLOW_INACTIVE_KEEPALIVE_MIN 0 +#define DFLT_NETFLOW_INACTIVE_KEEPALIVE_MAX 60000 +STATIC int +channelpadding_get_netflow_inactive_timeout_ms(const channel_t *chan) +{ + int low_timeout = networkstatus_get_param(NULL, "nf_ito_low", + DFLT_NETFLOW_INACTIVE_KEEPALIVE_LOW, + DFLT_NETFLOW_INACTIVE_KEEPALIVE_MIN, + DFLT_NETFLOW_INACTIVE_KEEPALIVE_MAX); + int high_timeout = networkstatus_get_param(NULL, "nf_ito_high", + DFLT_NETFLOW_INACTIVE_KEEPALIVE_HIGH, + low_timeout, + DFLT_NETFLOW_INACTIVE_KEEPALIVE_MAX); + int X1, X2; + + if (low_timeout == 0 && low_timeout == high_timeout) + return 0; // No padding + + /* If we have negotiated different timeout values, use those, but + * don't allow them to be lower than the consensus ones */ + if (chan->padding_timeout_low_ms && chan->padding_timeout_high_ms) { + low_timeout = MAX(low_timeout, chan->padding_timeout_low_ms); + high_timeout = MAX(high_timeout, chan->padding_timeout_high_ms); + } + + if (low_timeout == high_timeout) + return low_timeout; // No randomization + + /* + * This MAX() hack is here because we apply the timeout on both the client + * and the server. This creates the situation where the total time before + * sending a packet in either direction is actually + * min(client_timeout,server_timeout). + * + * If X is a random variable uniform from 0..R-1 (where R=high-low), + * then Y=max(X,X) has Prob(Y == i) = (2.0*i + 1)/(R*R). + * + * If we create a third random variable Z=min(Y,Y), then it turns out that + * Exp[Z] ~= Exp[X]. Here's a table: + * + * R Exp[X] Exp[Z] Exp[min(X,X)] Exp[max(X,X)] + * 2000 999.5 1066 666.2 1332.8 + * 3000 1499.5 1599.5 999.5 1999.5 + * 5000 2499.5 2666 1666.2 3332.8 + * 6000 2999.5 3199.5 1999.5 3999.5 + * 7000 3499.5 3732.8 2332.8 4666.2 + * 8000 3999.5 4266.2 2666.2 5332.8 + * 10000 4999.5 5328 3332.8 6666.2 + * 15000 7499.5 7995 4999.5 9999.5 + * 20000 9900.5 10661 6666.2 13332.8 + * + * In other words, this hack makes it so that when both the client and + * the guard are sending this padding, then the averages work out closer + * to the midpoint of the range, making the overhead easier to tune. + * If only one endpoint is padding (for example: if the relay does not + * support padding, but the client has set ConnectionPadding 1; or + * if the relay does support padding, but the client has set + * ReducedConnectionPadding 1), then the defense will still prevent + * record splitting, but with less overhead than the midpoint + * (as seen by the Exp[max(X,X)] column). + * + * To calculate average padding packet frequency (and thus overhead), + * index into the table by picking a row based on R = high-low. Then, + * use the appropriate column (Exp[Z] for two-sided padding, and + * Exp[max(X,X)] for one-sided padding). Finally, take this value + * and add it to the low timeout value. This value is the average + * frequency which padding packets will be sent. + */ + + X1 = crypto_rand_int(high_timeout - low_timeout); + X2 = crypto_rand_int(high_timeout - low_timeout); + return low_timeout + MAX(X1, X2); +} + +/** + * Update this channel's padding settings based on the PADDING_NEGOTIATE + * contents. + * + * Returns -1 on error; 1 on success. + */ +int +channelpadding_update_padding_for_channel(channel_t *chan, + const channelpadding_negotiate_t *pad_vars) +{ + if (pad_vars->version != 0) { + static ratelim_t version_limit = RATELIM_INIT(600); + + log_fn_ratelim(&version_limit,LOG_PROTOCOL_WARN,LD_PROTOCOL, + "Got a PADDING_NEGOTIATE cell with an unknown version. Ignoring."); + return -1; + } + + // We should not allow malicious relays to disable or reduce padding for + // us as clients. In fact, we should only accept this cell at all if we're + // operating as a relay. Brides should not accept it from relays, either + // (only from their clients). + if ((get_options()->BridgeRelay && + connection_or_digest_is_known_relay(chan->identity_digest)) || + !get_options()->ORPort_set) { + static ratelim_t relay_limit = RATELIM_INIT(600); + + log_fn_ratelim(&relay_limit,LOG_PROTOCOL_WARN,LD_PROTOCOL, + "Got a PADDING_NEGOTIATE from relay at %s (%s). " + "This should not happen.", + chan->get_remote_descr(chan, 0), + hex_str(chan->identity_digest, DIGEST_LEN)); + return -1; + } + + chan->padding_enabled = (pad_vars->command == CHANNELPADDING_COMMAND_START); + + /* Min must not be lower than the current consensus parameter + nf_ito_low. */ + chan->padding_timeout_low_ms = MAX(networkstatus_get_param(NULL, + "nf_ito_low", + DFLT_NETFLOW_INACTIVE_KEEPALIVE_LOW, + DFLT_NETFLOW_INACTIVE_KEEPALIVE_MIN, + DFLT_NETFLOW_INACTIVE_KEEPALIVE_MAX), + pad_vars->ito_low_ms); + + /* Max must not be lower than ito_low_ms */ + chan->padding_timeout_high_ms = MAX(chan->padding_timeout_low_ms, + pad_vars->ito_high_ms); + + log_fn(LOG_INFO,LD_OR, + "Negotiated padding=%d, lo=%d, hi=%d on "U64_FORMAT, + chan->padding_enabled, chan->padding_timeout_low_ms, + chan->padding_timeout_high_ms, + U64_PRINTF_ARG(chan->global_identifier)); + + return 1; +} + +/** + * Sends a CELL_PADDING_NEGOTIATE on the channel to tell the other side not + * to send padding. + * + * Returns -1 on error, 0 on success. + */ +STATIC int +channelpadding_send_disable_command(channel_t *chan) +{ + channelpadding_negotiate_t disable; + cell_t cell; + + tor_assert(BASE_CHAN_TO_TLS(chan)->conn->link_proto >= + MIN_LINK_PROTO_FOR_CHANNEL_PADDING); + + memset(&cell, 0, sizeof(cell_t)); + memset(&disable, 0, sizeof(channelpadding_negotiate_t)); + cell.command = CELL_PADDING_NEGOTIATE; + + channelpadding_negotiate_set_command(&disable, CHANNELPADDING_COMMAND_STOP); + + if (channelpadding_negotiate_encode(cell.payload, CELL_PAYLOAD_SIZE, + &disable) < 0) + return -1; + + if (chan->write_cell(chan, &cell) == 1) + return 0; + else + return -1; +} + +/** + * Sends a CELL_PADDING_NEGOTIATE on the channel to tell the other side to + * resume sending padding at some rate. + * + * Returns -1 on error, 0 on success. + */ +int +channelpadding_send_enable_command(channel_t *chan, uint16_t low_timeout, + uint16_t high_timeout) +{ + channelpadding_negotiate_t enable; + cell_t cell; + + tor_assert(BASE_CHAN_TO_TLS(chan)->conn->link_proto >= + MIN_LINK_PROTO_FOR_CHANNEL_PADDING); + + memset(&cell, 0, sizeof(cell_t)); + memset(&enable, 0, sizeof(channelpadding_negotiate_t)); + cell.command = CELL_PADDING_NEGOTIATE; + + channelpadding_negotiate_set_command(&enable, CHANNELPADDING_COMMAND_START); + channelpadding_negotiate_set_ito_low_ms(&enable, low_timeout); + channelpadding_negotiate_set_ito_high_ms(&enable, high_timeout); + + if (channelpadding_negotiate_encode(cell.payload, CELL_PAYLOAD_SIZE, + &enable) < 0) + return -1; + + if (chan->write_cell(chan, &cell) == 1) + return 0; + else + return -1; +} + +/** + * Sends a CELL_PADDING cell on a channel if it has been idle since + * our callback was scheduled. + * + * This function also clears the pending padding timer and the callback + * flags. + */ +static void +channelpadding_send_padding_cell_for_callback(channel_t *chan) +{ + cell_t cell; + + /* Check that the channel is still valid and open */ + if (!chan || chan->state != CHANNEL_STATE_OPEN) { + if (chan) chan->pending_padding_callback = 0; + log_fn(LOG_INFO,LD_OR, + "Scheduled a netflow padding cell, but connection already closed."); + return; + } + + /* We should have a pending callback flag set. */ + if (BUG(chan->pending_padding_callback == 0)) + return; + + chan->pending_padding_callback = 0; + + if (!chan->next_padding_time_ms || + chan->has_queued_writes(chan)) { + /* We must have been active before the timer fired */ + chan->next_padding_time_ms = 0; + return; + } + + { + uint64_t now = monotime_coarse_absolute_msec(); + + log_fn(LOG_INFO,LD_OR, + "Sending netflow keepalive on "U64_FORMAT" to %s (%s) after " + I64_FORMAT" ms. Delta "I64_FORMAT"ms", + U64_PRINTF_ARG(chan->global_identifier), + safe_str_client(chan->get_remote_descr(chan, 0)), + safe_str_client(hex_str(chan->identity_digest, DIGEST_LEN)), + U64_PRINTF_ARG(now - chan->timestamp_xfer_ms), + U64_PRINTF_ARG(now - chan->next_padding_time_ms)); + } + + /* Clear the timer */ + chan->next_padding_time_ms = 0; + + /* Send the padding cell. This will cause the channel to get a + * fresh timestamp_active */ + memset(&cell, 0, sizeof(cell)); + cell.command = CELL_PADDING; + chan->write_cell(chan, &cell); +} + +/** + * tor_timer callback function for us to send padding on an idle channel. + * + * This function just obtains the channel from the callback handle, ensures + * it is still valid, and then hands it off to + * channelpadding_send_padding_cell_for_callback(), which checks if + * the channel is still idle before sending padding. + */ +static void +channelpadding_send_padding_callback(tor_timer_t *timer, void *args, + const struct monotime_t *time) +{ + channel_t *chan = channel_handle_get((struct channel_handle_t*)args); + (void)timer; (void)time; + + if (chan && CHANNEL_CAN_HANDLE_CELLS(chan)) { + /* Hrmm.. It might be nice to have an equivalent to assert_connection_ok + * for channels. Then we could get rid of the channeltls dependency */ + tor_assert(BASE_CHAN_TO_TLS(chan)->conn->base_.magic == + OR_CONNECTION_MAGIC); + assert_connection_ok(&BASE_CHAN_TO_TLS(chan)->conn->base_, approx_time()); + + channelpadding_send_padding_cell_for_callback(chan); + } else { + log_fn(LOG_INFO,LD_OR, + "Channel closed while waiting for timer."); + } + + total_timers_pending--; +} + +/** + * Schedules a callback to send padding on a channel in_ms milliseconds from + * now. + * + * Returns CHANNELPADDING_WONTPAD on error, CHANNELPADDING_PADDING_SENT if we + * sent the packet immediately without a timer, and + * CHANNELPADDING_PADDING_SCHEDULED if we decided to schedule a timer. + */ +static channelpadding_decision_t +channelpadding_schedule_padding(channel_t *chan, int in_ms) +{ + struct timeval timeout; + tor_assert(!chan->pending_padding_callback); + + if (in_ms <= 0) { + chan->pending_padding_callback = 1; + channelpadding_send_padding_cell_for_callback(chan); + return CHANNELPADDING_PADDING_SENT; + } + + timeout.tv_sec = in_ms/1000; + timeout.tv_usec = (in_ms%1000)*1000; + + if (!chan->timer_handle) { + chan->timer_handle = channel_handle_new(chan); + } + + if (chan->padding_timer) { + timer_set_cb(chan->padding_timer, + channelpadding_send_padding_callback, + chan->timer_handle); + } else { + chan->padding_timer = timer_new(channelpadding_send_padding_callback, + chan->timer_handle); + } + timer_schedule(chan->padding_timer, &timeout); + + rep_hist_padding_count_timers(++total_timers_pending); + + chan->pending_padding_callback = 1; + return CHANNELPADDING_PADDING_SCHEDULED; +} + +/** + * Calculates the number of milliseconds from now to schedule a padding cell. + * + * Returns the number of milliseconds from now (relative) to schedule the + * padding callback. If the padding timer is more than 1.1 seconds in the + * future, we return -1, to avoid scheduling excessive callbacks. If padding + * is disabled in the consensus, we return -2. + * + * Side-effects: Updates chan->next_padding_time_ms, storing an (absolute, not + * relative) millisecond representation of when we should send padding, unless + * other activity happens first. This side-effect allows us to avoid + * scheduling a libevent callback until we're within 1.1 seconds of the padding + * time. + */ +#define CHANNELPADDING_TIME_LATER -1 +#define CHANNELPADDING_TIME_DISABLED -2 +STATIC int64_t +channelpadding_compute_time_until_pad_for_netflow(channel_t *chan) +{ + uint64_t long_now = monotime_coarse_absolute_msec(); + + if (!chan->next_padding_time_ms) { + int64_t padding_timeout = + channelpadding_get_netflow_inactive_timeout_ms(chan); + + if (!padding_timeout) + return CHANNELPADDING_TIME_DISABLED; + + chan->next_padding_time_ms = padding_timeout + + chan->timestamp_xfer_ms; + } + + /* If the next padding time is beyond the maximum possible consensus value, + * then this indicates a clock jump, so just send padding now. This is + * better than using monotonic time because we want to avoid the situation + * where we wait around forever for monotonic time to move forward after + * a clock jump far into the past. + */ + if (chan->next_padding_time_ms > long_now + + DFLT_NETFLOW_INACTIVE_KEEPALIVE_MAX) { + tor_fragile_assert(); + log_warn(LD_BUG, + "Channel padding timeout scheduled "I64_FORMAT"ms in the future. " + "Did the monotonic clock just jump?", + I64_PRINTF_ARG(chan->next_padding_time_ms - long_now)); + return 0; /* Clock jumped: Send padding now */ + } + + /* If the timeout will expire before the next time we're called (1000ms + from now, plus some slack), then calcualte the number of milliseconds + from now which we should send padding, so we can schedule a callback + then. + */ + if (long_now + 1100 >= chan->next_padding_time_ms) { + int64_t ms_until_pad_for_netflow = chan->next_padding_time_ms - + long_now; + if (ms_until_pad_for_netflow < 0) { + log_warn(LD_BUG, + "Channel padding timeout scheduled "I64_FORMAT"ms in the past. " + "Did the monotonic clock just jump?", + I64_PRINTF_ARG(-ms_until_pad_for_netflow)); + return 0; /* Clock jumped: Send padding now */ + } + + return ms_until_pad_for_netflow; + } + return CHANNELPADDING_TIME_LATER; +} + +/** + * Calling this function on a channel causes it to tell the other side + * not to send padding, and disables sending padding from this side as well. + */ +void +channelpadding_disable_padding_on_channel(channel_t *chan) +{ + chan->padding_enabled = 0; + + // Send cell to disable padding on the other end + channelpadding_send_disable_command(chan); +} + +/** + * Calling this function on a channel causes it to tell the other side + * not to send padding, and reduces the rate that padding is sent from + * this side. + */ +void +channelpadding_reduce_padding_on_channel(channel_t *chan) +{ + /* Padding can be forced and reduced by clients, regardless of if + * the channel supports it. So we check for support here before + * sending any commands. */ + if (chan->padding_enabled) { + channelpadding_send_disable_command(chan); + } + +#define DFLT_NETFLOW_REDUCED_KEEPALIVE_LOW 9000 +#define DFLT_NETFLOW_REDUCED_KEEPALIVE_HIGH 14000 +#define DFLT_NETFLOW_REDUCED_KEEPALIVE_MIN 0 +#define DFLT_NETFLOW_REDUCED_KEEPALIVE_MAX 60000 + chan->padding_timeout_low_ms = + networkstatus_get_param(NULL, "nf_ito_low_reduced", + DFLT_NETFLOW_REDUCED_KEEPALIVE_LOW, + DFLT_NETFLOW_REDUCED_KEEPALIVE_MIN, + DFLT_NETFLOW_REDUCED_KEEPALIVE_MAX); + + chan->padding_timeout_high_ms = + networkstatus_get_param(NULL, "nf_ito_high_reduced", + DFLT_NETFLOW_REDUCED_KEEPALIVE_HIGH, + chan->padding_timeout_low_ms, + DFLT_NETFLOW_REDUCED_KEEPALIVE_MAX); + + log_fn(LOG_INFO,LD_OR, + "Reduced padding on channel "U64_FORMAT": lo=%d, hi=%d", + U64_PRINTF_ARG(chan->global_identifier), + chan->padding_timeout_low_ms, chan->padding_timeout_high_ms); +} + +/** + * This function is called once per second by run_connection_housekeeping(), + * but only if the channel is still open, valid, and non-wedged. + * + * It decides if and when we should send a padding cell, and if needed, + * schedules a callback to send that cell at the appropriate time. + * + * Returns an enum that represents the current padding decision state. + * Return value is currently used only by unit tests. + */ +channelpadding_decision_t +channelpadding_decide_to_pad_channel(channel_t *chan) +{ + const or_options_t *options = get_options(); + + /* Only pad open channels */ + if (chan->state != CHANNEL_STATE_OPEN) + return CHANNELPADDING_WONTPAD; + + if (chan->channel_usage == CHANNEL_USED_FOR_FULL_CIRCS) { + if (!networkstatus_get_param(NULL, "nf_pad_before_usage", 1, 0, 1)) + return CHANNELPADDING_WONTPAD; + } else if (chan->channel_usage != CHANNEL_USED_FOR_USER_TRAFFIC) { + return CHANNELPADDING_WONTPAD; + } + + if (chan->pending_padding_callback) + return CHANNELPADDING_PADDING_ALREADY_SCHEDULED; + + /* Don't pad the channel if we didn't negotiate it, but still + * allow clients to force padding if options->ChannelPadding is + * explicitly set to 1. + */ + if (!chan->padding_enabled && options->ConnectionPadding != 1) { + return CHANNELPADDING_WONTPAD; + } + + if (!chan->has_queued_writes(chan)) { + int is_client_channel = 0; + + if (!public_server_mode(options) || chan->is_client || + !connection_or_digest_is_known_relay(chan->identity_digest)) { + is_client_channel = 1; + } + + /* If nf_pad_relays=1 is set in the consensus, we pad + * on *all* idle connections, relay-relay or relay-client. + * Otherwise pad only for client+bridge cons */ + if (is_client_channel || + networkstatus_get_param(NULL, "nf_pad_relays", 0, 0, 1)) { + int64_t pad_time_ms = + channelpadding_compute_time_until_pad_for_netflow(chan); + + if (pad_time_ms == CHANNELPADDING_TIME_DISABLED) { + return CHANNELPADDING_WONTPAD; + } else if (pad_time_ms == CHANNELPADDING_TIME_LATER) { + chan->currently_padding = 1; + return CHANNELPADDING_PADLATER; + } else { + /* We have to schedule a callback because we're called exactly once per + * second, but we don't want padding packets to go out exactly on an + * integer multiple of seconds. This callback will only be scheduled + * if we're within 1.1 seconds of the padding time. + */ + chan->currently_padding = 1; + return channelpadding_schedule_padding(chan, pad_time_ms); + } + } else { + chan->currently_padding = 0; + return CHANNELPADDING_WONTPAD; + } + } else { + return CHANNELPADDING_PADLATER; + } +} + |