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relay: Split link specifier checks from circuit_extend()

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Part of 33633.
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teor 2020-03-18 18:44:42 +10:00
parent 2563d74a5c
commit 5cb2bbea7d
1 changed files with 92 additions and 54 deletions
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146
src/feature/relay/circuitbuild_relay.c
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@ -67,6 +67,96 @@ circuit_extend_state_valid_helper(const struct circuit_t *circ)
return 0;
}
/* Make sure the extend cell <b>ec</b> has an ed25519 link specifier.
*
* First, check that the RSA node id is valid.
* If the node id is valid, add the ed25519 link specifier (if required),
* and return 0.
*
* Otherwise, if the node id is invalid, log a protocol warning,
* and return -1.(And do not modify the extend cell.)
*
* Must be called before circuit_extend_lspec_valid_helper().
*/
static int
circuit_extend_add_ed25519_helper(extend_cell_t *ec)
{
/* Check if they asked us for 0000..0000. We support using
* an empty fingerprint for the first hop (e.g. for a bridge relay),
* but we don't want to let clients send us extend cells for empty
* fingerprints -- a) because it opens the user up to a mitm attack,
* and b) because it lets an attacker force the relay to hold open a
* new TLS connection for each extend request. */
if (tor_digest_is_zero((const char*)ec->node_id)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend without specifying an id_digest.");
return -1;
}
/* Fill in ed_pubkey if it was not provided and we can infer it from
* our networkstatus */
if (ed25519_public_key_is_zero(&ec->ed_pubkey)) {
const node_t *node = node_get_by_id((const char*)ec->node_id);
const ed25519_public_key_t *node_ed_id = NULL;
if (node &&
node_supports_ed25519_link_authentication(node, 1) &&
(node_ed_id = node_get_ed25519_id(node))) {
ed25519_pubkey_copy(&ec->ed_pubkey, node_ed_id);
}
}
return 0;
}
/* Before replying to an extend cell, check the link specifiers in the extend
* cell <b>ec</b>, which was received on the circuit <b>circ</b>.
*
* If they are valid, return 0.
* Otherwise, if they are invalid, log a protocol warning, and return -1.
*
* Must be called after circuit_extend_add_ed25519_helper().
*/
static int
circuit_extend_lspec_valid_helper(const extend_cell_t *ec,
const struct circuit_t *circ)
{
if (!ec->orport_ipv4.port || tor_addr_is_null(&ec->orport_ipv4.addr)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend to zero destination port or addr.");
return -1;
}
if (tor_addr_is_internal(&ec->orport_ipv4.addr, 0) &&
!get_options()->ExtendAllowPrivateAddresses) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend to a private address");
return -1;
}
/* Next, check if we're being asked to connect to the hop that the
* extend cell came from. There isn't any reason for that, and it can
* assist circular-path attacks. */
if (tor_memeq(ec->node_id,
CONST_TO_OR_CIRCUIT(circ)->p_chan->identity_digest,
DIGEST_LEN)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend back to the previous hop.");
return -1;
}
/* Check the previous hop Ed25519 ID too */
if (! ed25519_public_key_is_zero(&ec->ed_pubkey) &&
ed25519_pubkey_eq(&ec->ed_pubkey,
&CONST_TO_OR_CIRCUIT(circ)->p_chan->ed25519_identity)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend back to the previous hop "
"(by Ed25519 ID).");
return -1;
}
return 0;
}
/** Take the 'extend' <b>cell</b>, pull out addr/port plus the onion
* skin and identity digest for the next hop. If we're already connected,
* pass the onion skin to the next hop using a create cell; otherwise
@ -97,63 +187,11 @@ circuit_extend(struct cell_t *cell, struct circuit_t *circ)
return -1;
}
if (!ec.orport_ipv4.port || tor_addr_is_null(&ec.orport_ipv4.addr)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend to zero destination port or addr.");
if (circuit_extend_add_ed25519_helper(&ec) < 0)
return -1;
}
if (tor_addr_is_internal(&ec.orport_ipv4.addr, 0) &&
!get_options()->ExtendAllowPrivateAddresses) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend to a private address");
if (circuit_extend_lspec_valid_helper(&ec, circ) < 0)
return -1;
}
/* Check if they asked us for 0000..0000. We support using
* an empty fingerprint for the first hop (e.g. for a bridge relay),
* but we don't want to let clients send us extend cells for empty
* fingerprints -- a) because it opens the user up to a mitm attack,
* and b) because it lets an attacker force the relay to hold open a
* new TLS connection for each extend request. */
if (tor_digest_is_zero((const char*)ec.node_id)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend without specifying an id_digest.");
return -1;
}
/* Fill in ed_pubkey if it was not provided and we can infer it from
* our networkstatus */
if (ed25519_public_key_is_zero(&ec.ed_pubkey)) {
const node_t *node = node_get_by_id((const char*)ec.node_id);
const ed25519_public_key_t *node_ed_id = NULL;
if (node &&
node_supports_ed25519_link_authentication(node, 1) &&
(node_ed_id = node_get_ed25519_id(node))) {
ed25519_pubkey_copy(&ec.ed_pubkey, node_ed_id);
}
}
/* Next, check if we're being asked to connect to the hop that the
* extend cell came from. There isn't any reason for that, and it can
* assist circular-path attacks. */
if (tor_memeq(ec.node_id,
TO_OR_CIRCUIT(circ)->p_chan->identity_digest,
DIGEST_LEN)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend back to the previous hop.");
return -1;
}
/* Check the previous hop Ed25519 ID too */
if (! ed25519_public_key_is_zero(&ec.ed_pubkey) &&
ed25519_pubkey_eq(&ec.ed_pubkey,
&TO_OR_CIRCUIT(circ)->p_chan->ed25519_identity)) {
log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
"Client asked me to extend back to the previous hop "
"(by Ed25519 ID).");
return -1;
}
n_chan = channel_get_for_extend((const char*)ec.node_id,
&ec.ed_pubkey,