[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
[tor-commits] [tor/master] Bug 7691 review fixes.
commit d05ff310a5547b15433314617d6f1b9e9ccfe5b8
Author: Mike Perry <mikeperry-git@xxxxxxxxxx>
Date: Tue Jan 8 18:07:34 2013 -0800
Bug 7691 review fixes.
Also add in the random nonce generation.
---
src/or/circuitbuild.c | 52 ++++++++++++++++++++++++++++++++++--------------
src/or/circuitbuild.h | 2 +-
src/or/or.h | 4 +-
3 files changed, 40 insertions(+), 18 deletions(-)
diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c
index 73bd3d4..b304aeb 100644
--- a/src/or/circuitbuild.c
+++ b/src/or/circuitbuild.c
@@ -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(ô->pathbias_probe_nonce, probe_nonce);
+ /* Generate a random address for the nonce */
+ crypto_rand((char*)ô->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, ô->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,
diff --git a/src/or/circuitbuild.h b/src/or/circuitbuild.h
index b1cedec..8d2b986 100644
--- a/src/or/circuitbuild.h
+++ b/src/or/circuitbuild.h
@@ -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
diff --git a/src/or/or.h b/src/or/or.h
index 4b4806c..eb0dc81 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -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
_______________________________________________
tor-commits mailing list
tor-commits@xxxxxxxxxxxxxxxxxxxx
https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-commits