Bug 7691 review fixes. (d05ff310) · Commits · Mike Perry / Tor

src/or/circuitbuild.c

+37 −15

Original line number	Diff line number	Diff line
		@@ -1505,7 +1505,19 @@ pathbias_count_build_success(origin_circuit_t *circ)
		}

		/**
		* Send a probe down a circuit that wasn't usable.
		* Send a probe down a circuit that the client attempted to use,
		* but for which the stream timed out/failed. The probe is a
		* RELAY_BEGIN cell with a 0.a.b.c destination address, which
		* the exit will reject and reply back, echoing that address.
		*
		* The reason for such probes is because it is possible to bias
		* a user's paths simply by causing timeouts, and these timeouts
		* are not possible to differentiate from unresponsive servers.
		*
		* The probe is sent at the end of the circuit lifetime for two
		* reasons: to prevent cyptographic taggers from being able to
		* drop cells to cause timeouts, and to prevent easy recognition
		* of probes before any real client traffic happens.
		*
		* Returns -1 if we couldn't probe, 0 otherwise.
		*/
		@@ -1517,8 +1529,7 @@ pathbias_send_usable_probe(circuit_t *circ)
		int payload_len;
		origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
		crypt_path_t *cpath_layer = NULL;
		// XXX: Generate a random 0.a.b.c adddress
		const char *probe_nonce = "0.1.2.3";
		char *probe_nonce = NULL;

		tor_assert(ocirc);

		@@ -1548,9 +1559,13 @@ pathbias_send_usable_probe(circuit_t *circ)
		/* Update timestamp for circuit_expire_building to kill us */
		tor_gettimeofday(&circ->timestamp_began);

		tor_snprintf(payload,RELAY_PAYLOAD_SIZE, "%s:25", probe_nonce);
		tor_addr_parse(&ocirc->pathbias_probe_nonce, probe_nonce);
		/* Generate a random address for the nonce */
		crypto_rand((char*)&ocirc->pathbias_probe_nonce,
		sizeof(ocirc->pathbias_probe_nonce));
		ocirc->pathbias_probe_nonce &= 0x00ffffff;
		probe_nonce = tor_dup_ip(ocirc->pathbias_probe_nonce);

		tor_snprintf(payload,RELAY_PAYLOAD_SIZE, "%s:25", probe_nonce);
		payload_len = (int)strlen(payload)+1;

		// XXX: need this? Can we assume ipv4 will always be supported?
		@@ -1567,12 +1582,14 @@ pathbias_send_usable_probe(circuit_t *circ)
		log_warn(LD_CIRC,
		"Ran out of stream IDs on circuit %u during "
		"pathbias probe attempt.", ocirc->global_identifier);
		tor_free(probe_nonce);
		return -1;
		}

		log_info(LD_CIRC,
		"Sending pathbias testing cell to %s:25 on stream %d for circ %d.",
		probe_nonce, ocirc->pathbias_probe_id, ocirc->global_identifier);
		tor_free(probe_nonce);

		/* Send a test relay cell */
		if (relay_send_command_from_edge(ocirc->pathbias_probe_id, circ,
		@@ -1591,18 +1608,19 @@ pathbias_send_usable_probe(circuit_t *circ)
		}

		/**
		* Check the response to a pathbias probe.
		* Check the response to a pathbias probe, to ensure the
		* cell is recognized and the nonce and other probe
		* characteristics are as expected.
		*
		* If the response is valid, return 0. Otherwise return < 0.
		*/
		int
		pathbias_check_probe_response(circuit_t circ, cell_t cell)
		pathbias_check_probe_response(circuit_t circ, const cell_t cell)
		{
		/* Based on connection_edge_process_relay_cell() */
		relay_header_t rh;
		int reason;
		uint32_t ipv4_host;
		tor_addr_t host;
		origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);

		tor_assert(cell);
		@@ -1620,24 +1638,28 @@ pathbias_check_probe_response(circuit_t circ, cell_t cell)

		/* Check length+extract host: It is in network order after the reason code.
		* See connection_edge_end(). */
		if (rh.length != 9) { /* reason+ipv4+dns_ttl */
		log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
		"Path bias probe response length field is insane (%d).",
		rh.length);
		if (rh.length < 9) { /* reason+ipv4+dns_ttl */
		log_notice(LD_PROTOCOL,
		"Short path bias probe response length field (%d).", rh.length);
		return - END_CIRC_REASON_TORPROTOCOL;
		}

		ipv4_host = get_uint32(cell->payload+RELAY_HEADER_SIZE+1);
		tor_addr_from_ipv4n(&host, ipv4_host);
		ipv4_host = ntohl(get_uint32(cell->payload+RELAY_HEADER_SIZE+1));

		/* Check nonce */
		if (memcmp(&host, &ocirc->pathbias_probe_nonce, sizeof(tor_addr_t)) == 0) {
		if (ipv4_host == ocirc->pathbias_probe_nonce) {
		ocirc->path_state = PATH_STATE_USE_SUCCEEDED;
		circuit_mark_for_close(circ, END_CIRC_REASON_FINISHED);
		log_info(LD_CIRC,
		"Got valid path bias probe back for circ %d, stream %d.",
		ocirc->global_identifier, ocirc->pathbias_probe_id);
		return 0;
		} else {
		log_notice(LD_CIRC,
		"Got strange probe value 0x%x vs 0x%x back for circ %d, "
		"stream %d.", ipv4_host, ocirc->pathbias_probe_nonce,
		ocirc->global_identifier, ocirc->pathbias_probe_id);
		return -1;
		}
		}
		log_info(LD_CIRC,

src/or/circuitbuild.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -61,7 +61,7 @@ double pathbias_get_extreme_rate(const or_options_t *options);
		int pathbias_get_dropguards(const or_options_t *options);
		void pathbias_count_timeout(origin_circuit_t *circ);
		int pathbias_check_close(origin_circuit_t *circ, int reason);
		int pathbias_check_probe_response(circuit_t circ, cell_t cell);
		int pathbias_check_probe_response(circuit_t circ, const cell_t cell);

		#endif

src/or/or.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -2894,8 +2894,8 @@ typedef struct origin_circuit_t {
		streamid_t pathbias_probe_id;

		/** For path probing. Store the temporary probe address nonce
		* for response comparison. */
		tor_addr_t pathbias_probe_nonce;
		* (in host byte order) for response comparison. */
		uint32_t pathbias_probe_nonce;

		/** Set iff this is a hidden-service circuit which has timed out
		* according to our current circuit-build timeout, but which has