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tor/src/or/hs_intropoint.c

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/* Copyright (c) 2016-2017, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file hs_intropoint.c
* \brief Implement next generation introductions point functionality
**/
#define HS_INTROPOINT_PRIVATE
#include "or.h"
#include "config.h"
#include "circuitlist.h"
#include "circuituse.h"
#include "relay.h"
#include "rendmid.h"
#include "rephist.h"
/* Trunnel */
#include "ed25519_cert.h"
#include "hs/cell_common.h"
#include "hs/cell_establish_intro.h"
#include "hs/cell_introduce1.h"
#include "hs_circuitmap.h"
#include "hs_descriptor.h"
#include "hs_intropoint.h"
#include "hs_common.h"
/** Extract the authentication key from an ESTABLISH_INTRO or INTRODUCE1 using
* the given <b>cell_type</b> from <b>cell</b> and place it in
* <b>auth_key_out</b>. */
STATIC void
get_auth_key_from_cell(ed25519_public_key_t *auth_key_out,
unsigned int cell_type, const void *cell)
{
size_t auth_key_len;
const uint8_t *key_array;
tor_assert(auth_key_out);
tor_assert(cell);
switch (cell_type) {
case RELAY_COMMAND_ESTABLISH_INTRO:
{
const trn_cell_establish_intro_t *c_cell = cell;
key_array = trn_cell_establish_intro_getconstarray_auth_key(c_cell);
auth_key_len = trn_cell_establish_intro_getlen_auth_key(c_cell);
break;
}
case RELAY_COMMAND_INTRODUCE1:
{
const trn_cell_introduce1_t *c_cell = cell;
key_array = trn_cell_introduce1_getconstarray_auth_key(cell);
auth_key_len = trn_cell_introduce1_getlen_auth_key(c_cell);
break;
}
default:
/* Getting here is really bad as it means we got a unknown cell type from
* this file where every call has an hardcoded value. */
tor_assert(0); /* LCOV_EXCL_LINE */
}
tor_assert(key_array);
tor_assert(auth_key_len == sizeof(auth_key_out->pubkey));
memcpy(auth_key_out->pubkey, key_array, auth_key_len);
}
/** We received an ESTABLISH_INTRO <b>cell</b>. Verify its signature and MAC,
* given <b>circuit_key_material</b>. Return 0 on success else -1 on error. */
STATIC int
verify_establish_intro_cell(const trn_cell_establish_intro_t *cell,
const uint8_t *circuit_key_material,
size_t circuit_key_material_len)
{
/* We only reach this function if the first byte of the cell is 0x02 which
* means that auth_key_type is of ed25519 type, hence this check should
* always pass. See hs_intro_received_establish_intro(). */
if (BUG(cell->auth_key_type != HS_INTRO_AUTH_KEY_TYPE_ED25519)) {
return -1;
}
/* Make sure the auth key length is of the right size for this type. For
* EXTRA safety, we check both the size of the array and the length which
* must be the same. Safety first!*/
if (trn_cell_establish_intro_getlen_auth_key(cell) != ED25519_PUBKEY_LEN ||
trn_cell_establish_intro_get_auth_key_len(cell) != ED25519_PUBKEY_LEN) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"ESTABLISH_INTRO auth key length is invalid");
return -1;
}
const uint8_t *msg = cell->start_cell;
/* Verify the sig */
{
ed25519_signature_t sig_struct;
const uint8_t *sig_array =
trn_cell_establish_intro_getconstarray_sig(cell);
/* Make sure the signature length is of the right size. For EXTRA safety,
* we check both the size of the array and the length which must be the
* same. Safety first!*/
if (trn_cell_establish_intro_getlen_sig(cell) != sizeof(sig_struct.sig) ||
trn_cell_establish_intro_get_sig_len(cell) != sizeof(sig_struct.sig)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"ESTABLISH_INTRO sig len is invalid");
return -1;
}
/* We are now sure that sig_len is of the right size. */
memcpy(sig_struct.sig, sig_array, cell->sig_len);
ed25519_public_key_t auth_key;
get_auth_key_from_cell(&auth_key, RELAY_COMMAND_ESTABLISH_INTRO, cell);
const size_t sig_msg_len = cell->end_sig_fields - msg;
int sig_mismatch = ed25519_checksig_prefixed(&sig_struct,
msg, sig_msg_len,
ESTABLISH_INTRO_SIG_PREFIX,
&auth_key);
if (sig_mismatch) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"ESTABLISH_INTRO signature not as expected");
return -1;
}
}
/* Verify the MAC */
{
const size_t auth_msg_len = cell->end_mac_fields - msg;
uint8_t mac[DIGEST256_LEN];
crypto_mac_sha3_256(mac, sizeof(mac),
circuit_key_material, circuit_key_material_len,
msg, auth_msg_len);
if (tor_memneq(mac, cell->handshake_mac, sizeof(mac))) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"ESTABLISH_INTRO handshake_auth not as expected");
return -1;
}
}
return 0;
}
/* Send an INTRO_ESTABLISHED cell to <b>circ</b>. */
MOCK_IMPL(int,
hs_intro_send_intro_established_cell,(or_circuit_t *circ))
{
int ret;
uint8_t *encoded_cell = NULL;
ssize_t encoded_len, result_len;
trn_cell_intro_established_t *cell;
trn_cell_extension_t *ext;
tor_assert(circ);
/* Build the cell payload. */
cell = trn_cell_intro_established_new();
ext = trn_cell_extension_new();
trn_cell_extension_set_num(ext, 0);
trn_cell_intro_established_set_extensions(cell, ext);
/* Encode the cell to binary format. */
encoded_len = trn_cell_intro_established_encoded_len(cell);
tor_assert(encoded_len > 0);
encoded_cell = tor_malloc_zero(encoded_len);
result_len = trn_cell_intro_established_encode(encoded_cell, encoded_len,
cell);
tor_assert(encoded_len == result_len);
ret = relay_send_command_from_edge(0, TO_CIRCUIT(circ),
RELAY_COMMAND_INTRO_ESTABLISHED,
(char *) encoded_cell, encoded_len,
NULL);
/* On failure, the above function will close the circuit. */
trn_cell_intro_established_free(cell);
tor_free(encoded_cell);
return ret;
}
/** We received an ESTABLISH_INTRO <b>parsed_cell</b> on <b>circ</b>. It's
* well-formed and passed our verifications. Perform appropriate actions to
* establish an intro point. */
static int
handle_verified_establish_intro_cell(or_circuit_t *circ,
const trn_cell_establish_intro_t *parsed_cell)
{
/* Get the auth key of this intro point */
ed25519_public_key_t auth_key;
get_auth_key_from_cell(&auth_key, RELAY_COMMAND_ESTABLISH_INTRO,
parsed_cell);
/* Then notify the hidden service that the intro point is established by
sending an INTRO_ESTABLISHED cell */
if (hs_intro_send_intro_established_cell(circ)) {
log_warn(LD_PROTOCOL, "Couldn't send INTRO_ESTABLISHED cell.");
return -1;
}
/* Associate intro point auth key with this circuit. */
hs_circuitmap_register_intro_circ_v3_relay_side(circ, &auth_key);
/* Repurpose this circuit into an intro circuit. */
circuit_change_purpose(TO_CIRCUIT(circ), CIRCUIT_PURPOSE_INTRO_POINT);
return 0;
}
/** We just received an ESTABLISH_INTRO cell in <b>circ</b> with payload in
* <b>request</b>. Handle it by making <b>circ</b> an intro circuit. Return 0
* if everything went well, or -1 if there were errors. */
static int
handle_establish_intro(or_circuit_t *circ, const uint8_t *request,
size_t request_len)
{
int cell_ok, retval = -1;
trn_cell_establish_intro_t *parsed_cell = NULL;
tor_assert(circ);
tor_assert(request);
log_info(LD_REND, "Received an ESTABLISH_INTRO request on circuit %" PRIu32,
circ->p_circ_id);
/* Check that the circuit is in shape to become an intro point */
if (!hs_intro_circuit_is_suitable_for_establish_intro(circ)) {
goto err;
}
/* Parse the cell */
ssize_t parsing_result = trn_cell_establish_intro_parse(&parsed_cell,
request, request_len);
if (parsing_result < 0) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Rejecting %s ESTABLISH_INTRO cell.",
parsing_result == -1 ? "invalid" : "truncated");
goto err;
}
cell_ok = verify_establish_intro_cell(parsed_cell,
(uint8_t *) circ->rend_circ_nonce,
sizeof(circ->rend_circ_nonce));
if (cell_ok < 0) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Failed to verify ESTABLISH_INTRO cell.");
goto err;
}
/* This cell is legit. Take the appropriate actions. */
cell_ok = handle_verified_establish_intro_cell(circ, parsed_cell);
if (cell_ok < 0) {
goto err;
}
/* We are done! */
retval = 0;
goto done;
err:
/* When sending the intro establish ack, on error the circuit can be marked
* as closed so avoid a double close. */
if (!TO_CIRCUIT(circ)->marked_for_close) {
circuit_mark_for_close(TO_CIRCUIT(circ), END_CIRC_REASON_TORPROTOCOL);
}
done:
trn_cell_establish_intro_free(parsed_cell);
return retval;
}
/* Return True if circuit is suitable for being an intro circuit. */
static int
circuit_is_suitable_intro_point(const or_circuit_t *circ,
const char *log_cell_type_str)
{
tor_assert(circ);
tor_assert(log_cell_type_str);
/* Basic circuit state sanity checks. */
if (circ->base_.purpose != CIRCUIT_PURPOSE_OR) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Rejecting %s on non-OR circuit.", log_cell_type_str);
return 0;
}
if (circ->base_.n_chan) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Rejecting %s on non-edge circuit.", log_cell_type_str);
return 0;
}
/* Suitable. */
return 1;
}
/* Return True if circuit is suitable for being service-side intro circuit. */
int
hs_intro_circuit_is_suitable_for_establish_intro(const or_circuit_t *circ)
{
return circuit_is_suitable_intro_point(circ, "ESTABLISH_INTRO");
}
/* We just received an ESTABLISH_INTRO cell in <b>circ</b>. Figure out of it's
* a legacy or a next gen cell, and pass it to the appropriate handler. */
int
hs_intro_received_establish_intro(or_circuit_t *circ, const uint8_t *request,
size_t request_len)
{
tor_assert(circ);
tor_assert(request);
if (request_len == 0) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, "Empty ESTABLISH_INTRO cell.");
goto err;
}
/* Using the first byte of the cell, figure out the version of
* ESTABLISH_INTRO and pass it to the appropriate cell handler */
const uint8_t first_byte = request[0];
switch (first_byte) {
case HS_INTRO_AUTH_KEY_TYPE_LEGACY0:
case HS_INTRO_AUTH_KEY_TYPE_LEGACY1:
return rend_mid_establish_intro_legacy(circ, request, request_len);
case HS_INTRO_AUTH_KEY_TYPE_ED25519:
return handle_establish_intro(circ, request, request_len);
default:
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Unrecognized AUTH_KEY_TYPE %u.", first_byte);
goto err;
}
err:
circuit_mark_for_close(TO_CIRCUIT(circ), END_CIRC_REASON_TORPROTOCOL);
return -1;
}
/* Send an INTRODUCE_ACK cell onto the circuit <b>circ</b> with the status
* value in <b>status</b>. Depending on the status, it can be ACK or a NACK.
* Return 0 on success else a negative value on error which will close the
* circuit. */
static int
send_introduce_ack_cell(or_circuit_t *circ, hs_intro_ack_status_t status)
{
int ret = -1;
uint8_t *encoded_cell = NULL;
ssize_t encoded_len, result_len;
trn_cell_introduce_ack_t *cell;
trn_cell_extension_t *ext;
tor_assert(circ);
/* Setup the INTRODUCE_ACK cell. We have no extensions so the N_EXTENSIONS
* field is set to 0 by default with a new object. */
cell = trn_cell_introduce_ack_new();
ret = trn_cell_introduce_ack_set_status(cell, status);
/* We have no cell extensions in an INTRODUCE_ACK cell. */
ext = trn_cell_extension_new();
trn_cell_extension_set_num(ext, 0);
trn_cell_introduce_ack_set_extensions(cell, ext);
/* A wrong status is a very bad code flow error as this value is controlled
* by the code in this file and not an external input. This means we use a
* code that is not known by the trunnel ABI. */
tor_assert(ret == 0);
/* Encode the payload. We should never fail to get the encoded length. */
encoded_len = trn_cell_introduce_ack_encoded_len(cell);
tor_assert(encoded_len > 0);
encoded_cell = tor_malloc_zero(encoded_len);
result_len = trn_cell_introduce_ack_encode(encoded_cell, encoded_len, cell);
tor_assert(encoded_len == result_len);
ret = relay_send_command_from_edge(CONTROL_CELL_ID, TO_CIRCUIT(circ),
RELAY_COMMAND_INTRODUCE_ACK,
(char *) encoded_cell, encoded_len,
NULL);
/* On failure, the above function will close the circuit. */
trn_cell_introduce_ack_free(cell);
tor_free(encoded_cell);
return ret;
}
/* Validate a parsed INTRODUCE1 <b>cell</b>. Return 0 if valid or else a
* negative value for an invalid cell that should be NACKed. */
STATIC int
validate_introduce1_parsed_cell(const trn_cell_introduce1_t *cell)
{
size_t legacy_key_id_len;
const uint8_t *legacy_key_id;
tor_assert(cell);
/* This code path SHOULD NEVER be reached if the cell is a legacy type so
* safety net here. The legacy ID must be zeroes in this case. */
legacy_key_id_len = trn_cell_introduce1_getlen_legacy_key_id(cell);
legacy_key_id = trn_cell_introduce1_getconstarray_legacy_key_id(cell);
if (BUG(!tor_mem_is_zero((char *) legacy_key_id, legacy_key_id_len))) {
goto invalid;
}
/* The auth key of an INTRODUCE1 should be of type ed25519 thus leading to a
* known fixed length as well. */
if (trn_cell_introduce1_get_auth_key_type(cell) !=
HS_INTRO_AUTH_KEY_TYPE_ED25519) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Rejecting invalid INTRODUCE1 cell auth key type. "
"Responding with NACK.");
goto invalid;
}
if (trn_cell_introduce1_get_auth_key_len(cell) != ED25519_PUBKEY_LEN ||
trn_cell_introduce1_getlen_auth_key(cell) != ED25519_PUBKEY_LEN) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Rejecting invalid INTRODUCE1 cell auth key length. "
"Responding with NACK.");
goto invalid;
}
if (trn_cell_introduce1_getlen_encrypted(cell) == 0) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Rejecting invalid INTRODUCE1 cell encrypted length. "
"Responding with NACK.");
goto invalid;
}
return 0;
invalid:
return -1;
}
/* We just received a non legacy INTRODUCE1 cell on <b>client_circ</b> with
* the payload in <b>request</b> of size <b>request_len</b>. Return 0 if
* everything went well, or -1 if an error occurred. This function is in charge
* of sending back an INTRODUCE_ACK cell and will close client_circ on error.
*/
STATIC int
handle_introduce1(or_circuit_t *client_circ, const uint8_t *request,
size_t request_len)
{
int ret = -1;
or_circuit_t *service_circ;
trn_cell_introduce1_t *parsed_cell;
hs_intro_ack_status_t status = HS_INTRO_ACK_STATUS_SUCCESS;
tor_assert(client_circ);
tor_assert(request);
/* Parse cell. Note that we can only parse the non encrypted section for
* which we'll use the authentication key to find the service introduction
* circuit and relay the cell on it. */
ssize_t cell_size = trn_cell_introduce1_parse(&parsed_cell, request,
request_len);
if (cell_size < 0) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Rejecting %s INTRODUCE1 cell. Responding with NACK.",
cell_size == -1 ? "invalid" : "truncated");
/* Inform client that the INTRODUCE1 has a bad format. */
status = HS_INTRO_ACK_STATUS_BAD_FORMAT;
goto send_ack;
}
/* Once parsed validate the cell format. */
if (validate_introduce1_parsed_cell(parsed_cell) < 0) {
/* Inform client that the INTRODUCE1 has bad format. */
status = HS_INTRO_ACK_STATUS_BAD_FORMAT;
goto send_ack;
}
/* Find introduction circuit through our circuit map. */
{
ed25519_public_key_t auth_key;
get_auth_key_from_cell(&auth_key, RELAY_COMMAND_INTRODUCE1, parsed_cell);
service_circ = hs_circuitmap_get_intro_circ_v3_relay_side(&auth_key);
if (service_circ == NULL) {
char b64_key[ED25519_BASE64_LEN + 1];
ed25519_public_to_base64(b64_key, &auth_key);
log_info(LD_REND, "No intro circuit found for INTRODUCE1 cell "
"with auth key %s from circuit %" PRIu32 ". "
"Responding with NACK.",
safe_str(b64_key), client_circ->p_circ_id);
/* Inform the client that we don't know the requested service ID. */
status = HS_INTRO_ACK_STATUS_UNKNOWN_ID;
goto send_ack;
}
}
/* Relay the cell to the service on its intro circuit with an INTRODUCE2
* cell which is the same exact payload. */
if (relay_send_command_from_edge(CONTROL_CELL_ID, TO_CIRCUIT(service_circ),
RELAY_COMMAND_INTRODUCE2,
(char *) request, request_len, NULL)) {
log_warn(LD_PROTOCOL, "Unable to send INTRODUCE2 cell to the service.");
/* Inform the client that we can't relay the cell. */
status = HS_INTRO_ACK_STATUS_CANT_RELAY;
goto send_ack;
}
/* Success! Send an INTRODUCE_ACK success status onto the client circuit. */
status = HS_INTRO_ACK_STATUS_SUCCESS;
ret = 0;
send_ack:
/* Send INTRODUCE_ACK or INTRODUCE_NACK to client */
if (send_introduce_ack_cell(client_circ, status) < 0) {
log_warn(LD_PROTOCOL, "Unable to send an INTRODUCE ACK status %d "
"to client.", status);
/* Circuit has been closed on failure of transmission. */
goto done;
}
if (status != HS_INTRO_ACK_STATUS_SUCCESS) {
/* We just sent a NACK that is a non success status code so close the
* circuit because it's not useful to keep it open. Remember, a client can
* only send one INTRODUCE1 cell on a circuit. */
circuit_mark_for_close(TO_CIRCUIT(client_circ), END_CIRC_REASON_INTERNAL);
}
done:
trn_cell_introduce1_free(parsed_cell);
return ret;
}
/* Identify if the encoded cell we just received is a legacy one or not. The
* <b>request</b> should be at least DIGEST_LEN bytes long. */
STATIC int
introduce1_cell_is_legacy(const uint8_t *request)
{
tor_assert(request);
/* If the first 20 bytes of the cell (DIGEST_LEN) are NOT zeroes, it
* indicates a legacy cell (v2). */
if (!tor_mem_is_zero((const char *) request, DIGEST_LEN)) {
/* Legacy cell. */
return 1;
}
/* Not a legacy cell. */
return 0;
}
/* Return true iff the circuit <b>circ</b> is suitable for receiving an
* INTRODUCE1 cell. */
STATIC int
circuit_is_suitable_for_introduce1(const or_circuit_t *circ)
{
tor_assert(circ);
/* Is this circuit an intro point circuit? */
if (!circuit_is_suitable_intro_point(circ, "INTRODUCE1")) {
return 0;
}
if (circ->already_received_introduce1) {
log_fn(LOG_PROTOCOL_WARN, LD_REND,
"Blocking multiple introductions on the same circuit. "
"Someone might be trying to attack a hidden service through "
"this relay.");
return 0;
}
return 1;
}
/* We just received an INTRODUCE1 cell on <b>circ</b>. Figure out which type
* it is and pass it to the appropriate handler. Return 0 on success else a
* negative value and the circuit is closed. */
int
hs_intro_received_introduce1(or_circuit_t *circ, const uint8_t *request,
size_t request_len)
{
int ret;
tor_assert(circ);
tor_assert(request);
/* A cell that can't hold a DIGEST_LEN is invalid as we need to check if
* it's a legacy cell or not using the first DIGEST_LEN bytes. */
if (request_len < DIGEST_LEN) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, "Invalid INTRODUCE1 cell length.");
goto err;
}
/* Make sure we have a circuit that can have an INTRODUCE1 cell on it. */
if (!circuit_is_suitable_for_introduce1(circ)) {
/* We do not send a NACK because the circuit is not suitable for any kind
* of response or transmission as it's a violation of the protocol. */
goto err;
}
/* Mark the circuit that we got this cell. None are allowed after this as a
* DoS mitigation since one circuit with one client can hammer a service. */
circ->already_received_introduce1 = 1;
/* We are sure here to have at least DIGEST_LEN bytes. */
if (introduce1_cell_is_legacy(request)) {
/* Handle a legacy cell. */
ret = rend_mid_introduce_legacy(circ, request, request_len);
} else {
/* Handle a non legacy cell. */
ret = handle_introduce1(circ, request, request_len);
}
return ret;
err:
circuit_mark_for_close(TO_CIRCUIT(circ), END_CIRC_REASON_TORPROTOCOL);
return -1;
}
/* Clear memory allocated by the given intropoint object ip (but don't free the
* object itself). */
void
hs_intropoint_clear(hs_intropoint_t *ip)
{
if (ip == NULL) {
return;
}
tor_cert_free(ip->auth_key_cert);
SMARTLIST_FOREACH(ip->link_specifiers, hs_desc_link_specifier_t *, ls,
hs_desc_link_specifier_free(ls));
smartlist_free(ip->link_specifiers);
memset(ip, 0, sizeof(hs_intropoint_t));
}
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