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Diffstat (limited to 'src/core/or/sendme.c')
| -rw-r--r-- | src/core/or/sendme.c | 710 |
1 files changed, 710 insertions, 0 deletions
diff --git a/src/core/or/sendme.c b/src/core/or/sendme.c new file mode 100644 index 0000000000..788f56088c --- /dev/null +++ b/src/core/or/sendme.c @@ -0,0 +1,710 @@ +/* Copyright (c) 2019-2020, The Tor Project, Inc. */ +/* See LICENSE for licensing information */ + +/** + * \file sendme.c + * \brief Code that is related to SENDME cells both in terms of + * creating/parsing cells and handling the content. + */ + +#define SENDME_PRIVATE + +#include "core/or/or.h" + +#include "app/config/config.h" +#include "core/crypto/relay_crypto.h" +#include "core/mainloop/connection.h" +#include "core/or/cell_st.h" +#include "core/or/crypt_path.h" +#include "core/or/circuitlist.h" +#include "core/or/circuituse.h" +#include "core/or/or_circuit_st.h" +#include "core/or/relay.h" +#include "core/or/sendme.h" +#include "feature/nodelist/networkstatus.h" +#include "lib/ctime/di_ops.h" +#include "trunnel/sendme_cell.h" + +/* Return the minimum version given by the consensus (if any) that should be + * used when emitting a SENDME cell. */ +STATIC int +get_emit_min_version(void) +{ + return networkstatus_get_param(NULL, "sendme_emit_min_version", + SENDME_EMIT_MIN_VERSION_DEFAULT, + SENDME_EMIT_MIN_VERSION_MIN, + SENDME_EMIT_MIN_VERSION_MAX); +} + +/* Return the minimum version given by the consensus (if any) that should be + * accepted when receiving a SENDME cell. */ +STATIC int +get_accept_min_version(void) +{ + return networkstatus_get_param(NULL, "sendme_accept_min_version", + SENDME_ACCEPT_MIN_VERSION_DEFAULT, + SENDME_ACCEPT_MIN_VERSION_MIN, + SENDME_ACCEPT_MIN_VERSION_MAX); +} + +/* Pop the first cell digset on the given circuit from the SENDME last digests + * list. NULL is returned if the list is uninitialized or empty. + * + * The caller gets ownership of the returned digest thus is responsible for + * freeing the memory. */ +static uint8_t * +pop_first_cell_digest(const circuit_t *circ) +{ + uint8_t *circ_digest; + + tor_assert(circ); + + if (circ->sendme_last_digests == NULL || + smartlist_len(circ->sendme_last_digests) == 0) { + return NULL; + } + + /* More cell digest than the SENDME window is never suppose to happen. The + * cell should have been rejected before reaching this point due to its + * package_window down to 0 leading to a circuit close. Scream loudly but + * still pop the element so we don't memory leak. */ + tor_assert_nonfatal(smartlist_len(circ->sendme_last_digests) <= + CIRCWINDOW_START_MAX / CIRCWINDOW_INCREMENT); + + circ_digest = smartlist_get(circ->sendme_last_digests, 0); + smartlist_del_keeporder(circ->sendme_last_digests, 0); + return circ_digest; +} + +/* Return true iff the given cell digest matches the first digest in the + * circuit sendme list. */ +static bool +v1_digest_matches(const uint8_t *circ_digest, const uint8_t *cell_digest) +{ + tor_assert(circ_digest); + tor_assert(cell_digest); + + /* Compare the digest with the one in the SENDME. This cell is invalid + * without a perfect match. */ + if (tor_memneq(circ_digest, cell_digest, TRUNNEL_SENDME_V1_DIGEST_LEN)) { + log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, + "SENDME v1 cell digest do not match."); + return false; + } + + /* Digests matches! */ + return true; +} + +/* Return true iff the given decoded SENDME version 1 cell is valid and + * matches the expected digest on the circuit. + * + * Validation is done by comparing the digest in the cell from the previous + * cell we saw which tells us that the other side has in fact seen that cell. + * See proposal 289 for more details. */ +static bool +cell_v1_is_valid(const sendme_cell_t *cell, const uint8_t *circ_digest) +{ + tor_assert(cell); + tor_assert(circ_digest); + + const uint8_t *cell_digest = sendme_cell_getconstarray_data_v1_digest(cell); + return v1_digest_matches(circ_digest, cell_digest); +} + +/* Return true iff the given cell version can be handled or if the minimum + * accepted version from the consensus is known to us. */ +STATIC bool +cell_version_can_be_handled(uint8_t cell_version) +{ + int accept_version = get_accept_min_version(); + + /* We will first check if the consensus minimum accepted version can be + * handled by us and if not, regardless of the cell version we got, we can't + * continue. */ + if (accept_version > SENDME_MAX_SUPPORTED_VERSION) { + log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, + "Unable to accept SENDME version %u (from consensus). " + "We only support <= %u. Probably your tor is too old?", + accept_version, SENDME_MAX_SUPPORTED_VERSION); + goto invalid; + } + + /* Then, is this version below the accepted version from the consensus? If + * yes, we must not handle it. */ + if (cell_version < accept_version) { + log_info(LD_PROTOCOL, "Unacceptable SENDME version %u. Only " + "accepting %u (from consensus). Closing circuit.", + cell_version, accept_version); + goto invalid; + } + + /* Is this cell version supported by us? */ + if (cell_version > SENDME_MAX_SUPPORTED_VERSION) { + log_info(LD_PROTOCOL, "SENDME cell version %u is not supported by us. " + "We only support <= %u", + cell_version, SENDME_MAX_SUPPORTED_VERSION); + goto invalid; + } + + return true; + invalid: + return false; +} + +/* Return true iff the encoded SENDME cell in cell_payload of length + * cell_payload_len is valid. For each version: + * + * 0: No validation + * 1: Authenticated with last cell digest. + * + * This is the main critical function to make sure we can continue to + * send/recv cells on a circuit. If the SENDME is invalid, the circuit should + * be marked for close by the caller. */ +STATIC bool +sendme_is_valid(const circuit_t *circ, const uint8_t *cell_payload, + size_t cell_payload_len) +{ + uint8_t cell_version; + uint8_t *circ_digest = NULL; + sendme_cell_t *cell = NULL; + + tor_assert(circ); + tor_assert(cell_payload); + + /* An empty payload means version 0 so skip trunnel parsing. We won't be + * able to parse a 0 length buffer into a valid SENDME cell. */ + if (cell_payload_len == 0) { + cell_version = 0; + } else { + /* First we'll decode the cell so we can get the version. */ + if (sendme_cell_parse(&cell, cell_payload, cell_payload_len) < 0) { + log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, + "Unparseable SENDME cell received. Closing circuit."); + goto invalid; + } + cell_version = sendme_cell_get_version(cell); + } + + /* Validate that we can handle this cell version. */ + if (!cell_version_can_be_handled(cell_version)) { + goto invalid; + } + + /* Pop the first element that was added (FIFO). We do that regardless of the + * version so we don't accumulate on the circuit if v0 is used by the other + * end point. */ + circ_digest = pop_first_cell_digest(circ); + if (circ_digest == NULL) { + /* We shouldn't have received a SENDME if we have no digests. Log at + * protocol warning because it can be tricked by sending many SENDMEs + * without prior data cell. */ + log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, + "We received a SENDME but we have no cell digests to match. " + "Closing circuit."); + goto invalid; + } + + /* Validate depending on the version now. */ + switch (cell_version) { + case 0x01: + if (!cell_v1_is_valid(cell, circ_digest)) { + goto invalid; + } + break; + case 0x00: + /* Version 0, there is no work to be done on the payload so it is + * necessarily valid if we pass the version validation. */ + break; + default: + log_warn(LD_PROTOCOL, "Unknown SENDME cell version %d received.", + cell_version); + tor_assert_nonfatal_unreached(); + break; + } + + /* Valid cell. */ + sendme_cell_free(cell); + tor_free(circ_digest); + return true; + invalid: + sendme_cell_free(cell); + tor_free(circ_digest); + return false; +} + +/* Build and encode a version 1 SENDME cell into payload, which must be at + * least of RELAY_PAYLOAD_SIZE bytes, using the digest for the cell data. + * + * Return the size in bytes of the encoded cell in payload. A negative value + * is returned on encoding failure. */ +STATIC ssize_t +build_cell_payload_v1(const uint8_t *cell_digest, uint8_t *payload) +{ + ssize_t len = -1; + sendme_cell_t *cell = NULL; + + tor_assert(cell_digest); + tor_assert(payload); + + cell = sendme_cell_new(); + + /* Building a payload for version 1. */ + sendme_cell_set_version(cell, 0x01); + /* Set the data length field for v1. */ + sendme_cell_set_data_len(cell, TRUNNEL_SENDME_V1_DIGEST_LEN); + + /* Copy the digest into the data payload. */ + memcpy(sendme_cell_getarray_data_v1_digest(cell), cell_digest, + sendme_cell_get_data_len(cell)); + + /* Finally, encode the cell into the payload. */ + len = sendme_cell_encode(payload, RELAY_PAYLOAD_SIZE, cell); + + sendme_cell_free(cell); + return len; +} + +/* Send a circuit-level SENDME on the given circuit using the layer_hint if + * not NULL. The digest is only used for version 1. + * + * Return 0 on success else a negative value and the circuit will be closed + * because we failed to send the cell on it. */ +static int +send_circuit_level_sendme(circuit_t *circ, crypt_path_t *layer_hint, + const uint8_t *cell_digest) +{ + uint8_t emit_version; + uint8_t payload[RELAY_PAYLOAD_SIZE]; + ssize_t payload_len; + + tor_assert(circ); + tor_assert(cell_digest); + + emit_version = get_emit_min_version(); + switch (emit_version) { + case 0x01: + payload_len = build_cell_payload_v1(cell_digest, payload); + if (BUG(payload_len < 0)) { + /* Unable to encode the cell, abort. We can recover from this by closing + * the circuit but in theory it should never happen. */ + return -1; + } + log_debug(LD_PROTOCOL, "Emitting SENDME version 1 cell."); + break; + case 0x00: + FALLTHROUGH; + default: + /* Unknown version, fallback to version 0 meaning no payload. */ + payload_len = 0; + log_debug(LD_PROTOCOL, "Emitting SENDME version 0 cell. " + "Consensus emit version is %d", emit_version); + break; + } + + if (relay_send_command_from_edge(0, circ, RELAY_COMMAND_SENDME, + (char *) payload, payload_len, + layer_hint) < 0) { + log_warn(LD_CIRC, + "SENDME relay_send_command_from_edge failed. Circuit's closed."); + return -1; /* the circuit's closed, don't continue */ + } + return 0; +} + +/* Record the cell digest only if the next cell is expected to be a SENDME. */ +static void +record_cell_digest_on_circ(circuit_t *circ, const uint8_t *sendme_digest) +{ + tor_assert(circ); + tor_assert(sendme_digest); + + /* Add the digest to the last seen list in the circuit. */ + if (circ->sendme_last_digests == NULL) { + circ->sendme_last_digests = smartlist_new(); + } + smartlist_add(circ->sendme_last_digests, + tor_memdup(sendme_digest, DIGEST_LEN)); +} + +/* + * Public API + */ + +/** Return true iff the next cell for the given cell window is expected to be + * a SENDME. + * + * We are able to know that because the package or deliver window value minus + * one cell (the possible SENDME cell) should be a multiple of the increment + * window value. */ +static bool +circuit_sendme_cell_is_next(int window) +{ + /* At the start of the window, no SENDME will be expected. */ + if (window == CIRCWINDOW_START) { + return false; + } + + /* Are we at the limit of the increment and if not, we don't expect next + * cell is a SENDME. + * + * We test against the window minus 1 because when we are looking if the + * next cell is a SENDME, the window (either package or deliver) hasn't been + * decremented just yet so when this is called, we are currently processing + * the "window - 1" cell. + * + * This function is used when recording a cell digest and this is done quite + * low in the stack when decrypting or encrypting a cell. The window is only + * updated once the cell is actually put in the outbuf. */ + if (((window - 1) % CIRCWINDOW_INCREMENT) != 0) { + return false; + } + + /* Next cell is expected to be a SENDME. */ + return true; +} + +/** Called when we've just received a relay data cell, when we've just + * finished flushing all bytes to stream <b>conn</b>, or when we've flushed + * *some* bytes to the stream <b>conn</b>. + * + * If conn->outbuf is not too full, and our deliver window is low, send back a + * suitable number of stream-level sendme cells. + */ +void +sendme_connection_edge_consider_sending(edge_connection_t *conn) +{ + tor_assert(conn); + + int log_domain = TO_CONN(conn)->type == CONN_TYPE_AP ? LD_APP : LD_EXIT; + + /* Don't send it if we still have data to deliver. */ + if (connection_outbuf_too_full(TO_CONN(conn))) { + goto end; + } + + if (circuit_get_by_edge_conn(conn) == NULL) { + /* This can legitimately happen if the destroy has already arrived and + * torn down the circuit. */ + log_info(log_domain, "No circuit associated with edge connection. " + "Skipping sending SENDME."); + goto end; + } + + while (conn->deliver_window <= + (STREAMWINDOW_START - STREAMWINDOW_INCREMENT)) { + log_debug(log_domain, "Outbuf %" TOR_PRIuSZ ", queuing stream SENDME.", + TO_CONN(conn)->outbuf_flushlen); + conn->deliver_window += STREAMWINDOW_INCREMENT; + if (connection_edge_send_command(conn, RELAY_COMMAND_SENDME, + NULL, 0) < 0) { + log_warn(LD_BUG, "connection_edge_send_command failed while sending " + "a SENDME. Circuit probably closed, skipping."); + goto end; /* The circuit's closed, don't continue */ + } + } + + end: + return; +} + +/** Check if the deliver_window for circuit <b>circ</b> (at hop + * <b>layer_hint</b> if it's defined) is low enough that we should + * send a circuit-level sendme back down the circuit. If so, send + * enough sendmes that the window would be overfull if we sent any + * more. + */ +void +sendme_circuit_consider_sending(circuit_t *circ, crypt_path_t *layer_hint) +{ + bool sent_one_sendme = false; + const uint8_t *digest; + + while ((layer_hint ? layer_hint->deliver_window : circ->deliver_window) <= + CIRCWINDOW_START - CIRCWINDOW_INCREMENT) { + log_debug(LD_CIRC,"Queuing circuit sendme."); + if (layer_hint) { + layer_hint->deliver_window += CIRCWINDOW_INCREMENT; + digest = cpath_get_sendme_digest(layer_hint); + } else { + circ->deliver_window += CIRCWINDOW_INCREMENT; + digest = relay_crypto_get_sendme_digest(&TO_OR_CIRCUIT(circ)->crypto); + } + if (send_circuit_level_sendme(circ, layer_hint, digest) < 0) { + return; /* The circuit's closed, don't continue */ + } + /* Current implementation is not suppose to send multiple SENDME at once + * because this means we would use the same relay crypto digest for each + * SENDME leading to a mismatch on the other side and the circuit to + * collapse. Scream loudly if it ever happens so we can address it. */ + tor_assert_nonfatal(!sent_one_sendme); + sent_one_sendme = true; + } +} + +/* Process a circuit-level SENDME cell that we just received. The layer_hint, + * if not NULL, is the Exit hop of the connection which means that we are a + * client. In that case, circ must be an origin circuit. The cell_body_len is + * the length of the SENDME cell payload (excluding the header). The + * cell_payload is the payload. + * + * Return 0 on success (the SENDME is valid and the package window has + * been updated properly). + * + * On error, a negative value is returned, which indicates that the + * circuit must be closed using the value as the reason for it. */ +int +sendme_process_circuit_level(crypt_path_t *layer_hint, + circuit_t *circ, const uint8_t *cell_payload, + uint16_t cell_payload_len) +{ + tor_assert(circ); + tor_assert(cell_payload); + + /* Validate the SENDME cell. Depending on the version, different validation + * can be done. An invalid SENDME requires us to close the circuit. */ + if (!sendme_is_valid(circ, cell_payload, cell_payload_len)) { + return -END_CIRC_REASON_TORPROTOCOL; + } + + /* If we are the origin of the circuit, we are the Client so we use the + * layer hint (the Exit hop) for the package window tracking. */ + if (CIRCUIT_IS_ORIGIN(circ)) { + /* If we are the origin of the circuit, it is impossible to not have a + * cpath. Just in case, bug on it and close the circuit. */ + if (BUG(layer_hint == NULL)) { + return -END_CIRC_REASON_TORPROTOCOL; + } + if ((layer_hint->package_window + CIRCWINDOW_INCREMENT) > + CIRCWINDOW_START_MAX) { + static struct ratelim_t exit_warn_ratelim = RATELIM_INIT(600); + log_fn_ratelim(&exit_warn_ratelim, LOG_WARN, LD_PROTOCOL, + "Unexpected sendme cell from exit relay. " + "Closing circ."); + return -END_CIRC_REASON_TORPROTOCOL; + } + layer_hint->package_window += CIRCWINDOW_INCREMENT; + log_debug(LD_APP, "circ-level sendme at origin, packagewindow %d.", + layer_hint->package_window); + + /* We count circuit-level sendme's as valid delivered data because they + * are rate limited. */ + circuit_read_valid_data(TO_ORIGIN_CIRCUIT(circ), cell_payload_len); + } else { + /* We aren't the origin of this circuit so we are the Exit and thus we + * track the package window with the circuit object. */ + if ((circ->package_window + CIRCWINDOW_INCREMENT) > + CIRCWINDOW_START_MAX) { + static struct ratelim_t client_warn_ratelim = RATELIM_INIT(600); + log_fn_ratelim(&client_warn_ratelim, LOG_PROTOCOL_WARN, LD_PROTOCOL, + "Unexpected sendme cell from client. " + "Closing circ (window %d).", circ->package_window); + return -END_CIRC_REASON_TORPROTOCOL; + } + circ->package_window += CIRCWINDOW_INCREMENT; + log_debug(LD_EXIT, "circ-level sendme at non-origin, packagewindow %d.", + circ->package_window); + } + + return 0; +} + +/* Process a stream-level SENDME cell that we just received. The conn is the + * edge connection (stream) that the circuit circ is associated with. The + * cell_body_len is the length of the payload (excluding the header). + * + * Return 0 on success (the SENDME is valid and the package window has + * been updated properly). + * + * On error, a negative value is returned, which indicates that the + * circuit must be closed using the value as the reason for it. */ +int +sendme_process_stream_level(edge_connection_t *conn, circuit_t *circ, + uint16_t cell_body_len) +{ + tor_assert(conn); + tor_assert(circ); + + /* Don't allow the other endpoint to request more than our maximum (i.e. + * initial) stream SENDME window worth of data. Well-behaved stock clients + * will not request more than this max (as per the check in the while loop + * of sendme_connection_edge_consider_sending()). */ + if ((conn->package_window + STREAMWINDOW_INCREMENT) > + STREAMWINDOW_START_MAX) { + static struct ratelim_t stream_warn_ratelim = RATELIM_INIT(600); + log_fn_ratelim(&stream_warn_ratelim, LOG_PROTOCOL_WARN, LD_PROTOCOL, + "Unexpected stream sendme cell. Closing circ (window %d).", + conn->package_window); + return -END_CIRC_REASON_TORPROTOCOL; + } + /* At this point, the stream sendme is valid */ + conn->package_window += STREAMWINDOW_INCREMENT; + + /* We count circuit-level sendme's as valid delivered data because they are + * rate limited. */ + if (CIRCUIT_IS_ORIGIN(circ)) { + circuit_read_valid_data(TO_ORIGIN_CIRCUIT(circ), cell_body_len); + } + + log_debug(CIRCUIT_IS_ORIGIN(circ) ? LD_APP : LD_EXIT, + "stream-level sendme, package_window now %d.", + conn->package_window); + return 0; +} + +/* Called when a relay DATA cell is received on the given circuit. If + * layer_hint is NULL, this means we are the Exit end point else we are the + * Client. Update the deliver window and return its new value. */ +int +sendme_circuit_data_received(circuit_t *circ, crypt_path_t *layer_hint) +{ + int deliver_window, domain; + + if (CIRCUIT_IS_ORIGIN(circ)) { + tor_assert(layer_hint); + --layer_hint->deliver_window; + deliver_window = layer_hint->deliver_window; + domain = LD_APP; + } else { + tor_assert(!layer_hint); + --circ->deliver_window; + deliver_window = circ->deliver_window; + domain = LD_EXIT; + } + + log_debug(domain, "Circuit deliver_window now %d.", deliver_window); + return deliver_window; +} + +/* Called when a relay DATA cell is received for the given edge connection + * conn. Update the deliver window and return its new value. */ +int +sendme_stream_data_received(edge_connection_t *conn) +{ + tor_assert(conn); + return --conn->deliver_window; +} + +/* Called when a relay DATA cell is packaged on the given circuit. If + * layer_hint is NULL, this means we are the Exit end point else we are the + * Client. Update the package window and return its new value. */ +int +sendme_note_circuit_data_packaged(circuit_t *circ, crypt_path_t *layer_hint) +{ + int package_window, domain; + + tor_assert(circ); + + if (CIRCUIT_IS_ORIGIN(circ)) { + /* Client side. */ + tor_assert(layer_hint); + --layer_hint->package_window; + package_window = layer_hint->package_window; + domain = LD_APP; + } else { + /* Exit side. */ + tor_assert(!layer_hint); + --circ->package_window; + package_window = circ->package_window; + domain = LD_EXIT; + } + + log_debug(domain, "Circuit package_window now %d.", package_window); + return package_window; +} + +/* Called when a relay DATA cell is packaged for the given edge connection + * conn. Update the package window and return its new value. */ +int +sendme_note_stream_data_packaged(edge_connection_t *conn) +{ + tor_assert(conn); + + --conn->package_window; + log_debug(LD_APP, "Stream package_window now %d.", conn->package_window); + return conn->package_window; +} + +/* Record the cell digest into the circuit sendme digest list depending on + * which edge we are. The digest is recorded only if we expect the next cell + * that we will receive is a SENDME so we can match the digest. */ +void +sendme_record_cell_digest_on_circ(circuit_t *circ, crypt_path_t *cpath) +{ + int package_window; + uint8_t *sendme_digest; + + tor_assert(circ); + + package_window = circ->package_window; + if (cpath) { + package_window = cpath->package_window; + } + + /* Is this the last cell before a SENDME? The idea is that if the + * package_window reaches a multiple of the increment, after this cell, we + * should expect a SENDME. */ + if (!circuit_sendme_cell_is_next(package_window)) { + return; + } + + /* Getting the digest is expensive so we only do it once we are certain to + * record it on the circuit. */ + if (cpath) { + sendme_digest = cpath_get_sendme_digest(cpath); + } else { + sendme_digest = + relay_crypto_get_sendme_digest(&TO_OR_CIRCUIT(circ)->crypto); + } + + record_cell_digest_on_circ(circ, sendme_digest); +} + +/* Called once we decrypted a cell and recognized it. Record the cell digest + * as the next sendme digest only if the next cell we'll send on the circuit + * is expected to be a SENDME. */ +void +sendme_record_received_cell_digest(circuit_t *circ, crypt_path_t *cpath) +{ + tor_assert(circ); + + /* Only record if the next cell is expected to be a SENDME. */ + if (!circuit_sendme_cell_is_next(cpath ? cpath->deliver_window : + circ->deliver_window)) { + return; + } + + if (cpath) { + /* Record incoming digest. */ + cpath_sendme_record_cell_digest(cpath, false); + } else { + /* Record foward digest. */ + relay_crypto_record_sendme_digest(&TO_OR_CIRCUIT(circ)->crypto, true); + } +} + +/* Called once we encrypted a cell. Record the cell digest as the next sendme + * digest only if the next cell we expect to receive is a SENDME so we can + * match the digests. */ +void +sendme_record_sending_cell_digest(circuit_t *circ, crypt_path_t *cpath) +{ + tor_assert(circ); + + /* Only record if the next cell is expected to be a SENDME. */ + if (!circuit_sendme_cell_is_next(cpath ? cpath->package_window : + circ->package_window)) { + goto end; + } + + if (cpath) { + /* Record the forward digest. */ + cpath_sendme_record_cell_digest(cpath, true); + } else { + /* Record the incoming digest. */ + relay_crypto_record_sendme_digest(&TO_OR_CIRCUIT(circ)->crypto, false); + } + + end: + return; +} |