relay: Split link specifier checks from circuit_extend()

Part of 33633.

1 files changed, 87 insertions, 49 deletions

diff --git a/src/feature/relay/circuitbuild_relay.c b/src/feature/relay/circuitbuild_relay.c
index 469fd44b82..2781d14005 100644
--- a/src/feature/relay/circuitbuild_relay.c
+++ b/src/feature/relay/circuitbuild_relay.c
@@ -67,56 +67,27 @@ circuit_extend_state_valid_helper(const struct circuit_t *circ)
   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
- * launch a new OR connection, and <b>circ</b> will notice when the
- * connection succeeds or fails.
+/* Make sure the extend cell <b>ec</b> has an ed25519 link specifier.
  *
- * Return -1 if we want to warn and tear down the circuit, else return 0.
+ * 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().
  */
-int
-circuit_extend(struct cell_t *cell, struct circuit_t *circ)
+static int
+circuit_extend_add_ed25519_helper(extend_cell_t *ec)
 {
-  channel_t *n_chan;
-  relay_header_t rh;
-  extend_cell_t ec;
-  const char *msg = NULL;
-  int should_launch = 0;
-
-  if (circuit_extend_state_valid_helper(circ) < 0)
-    return -1;
-
-  relay_header_unpack(&rh, cell->payload);
-
-  if (extend_cell_parse(&ec, rh.command,
-                        cell->payload+RELAY_HEADER_SIZE,
-                        rh.length) < 0) {
-    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-           "Can't parse extend cell. Closing circuit.");
-    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.");
-    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;
-  }
-
   /* 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)) {
+  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;
@@ -124,21 +95,49 @@ circuit_extend(struct cell_t *cell, struct circuit_t *circ)
 
   /* 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);
+  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);
+      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,
-                TO_OR_CIRCUIT(circ)->p_chan->identity_digest,
+  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.");
@@ -146,15 +145,54 @@ circuit_extend(struct cell_t *cell, struct circuit_t *circ)
   }
 
   /* 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)) {
+  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
+ * launch a new OR connection, and <b>circ</b> will notice when the
+ * connection succeeds or fails.
+ *
+ * Return -1 if we want to warn and tear down the circuit, else return 0.
+ */
+int
+circuit_extend(struct cell_t *cell, struct circuit_t *circ)
+{
+  channel_t *n_chan;
+  relay_header_t rh;
+  extend_cell_t ec;
+  const char *msg = NULL;
+  int should_launch = 0;
+
+  if (circuit_extend_state_valid_helper(circ) < 0)
+    return -1;
+
+  relay_header_unpack(&rh, cell->payload);
+
+  if (extend_cell_parse(&ec, rh.command,
+                        cell->payload+RELAY_HEADER_SIZE,
+                        rh.length) < 0) {
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+           "Can't parse extend cell. Closing circuit.");
+    return -1;
+  }
+
+  if (circuit_extend_add_ed25519_helper(&ec) < 0)
+    return -1;
+
+  if (circuit_extend_lspec_valid_helper(&ec, circ) < 0)
+    return -1;
+
   n_chan = channel_get_for_extend((const char*)ec.node_id,
                                   &ec.ed_pubkey,
                                   &ec.orport_ipv4.addr,