channel: Refactor NETINFO process function

In order to process a NETINFO cell, the OR connection needs to go through a
series of validation else we don't process the cell.

Move those into its own function in and improve documentation.

This is an attempt at reducing technical debt of the rather large and
complicated channel_tls_process_netinfo_cell() function.

Related to #40022

Signed-off-by: David Goulet <dgoulet@torproject.org>

1 files changed, 39 insertions, 12 deletions

diff --git a/src/core/or/channeltls.c b/src/core/or/channeltls.c
index a51fbf1dd6..9b2ac7d167 100644
--- a/src/core/or/channeltls.c
+++ b/src/core/or/channeltls.c
@@ -1688,6 +1688,41 @@ time_abs(time_t val)
   return (val < 0) ? -val : val;
 }
 
+/** Return true iff the channel can process a NETINFO cell. For this to return
+ * true, these channel conditions apply:
+ *
+ *    1. Link protocol is version 2 or higher (tor-spec.txt, NETINFO cells
+ *       section).
+ *
+ *    2. Underlying OR connection of the channel is either in v2 or v3
+ *       handshaking state.
+ */
+static bool
+can_process_netinfo_cell(const channel_tls_t *chan)
+{
+  /* NETINFO cells can only be negotiated on link protocol 2 or higher. */
+  if (chan->conn->link_proto < 2) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Received a NETINFO cell on %s connection; dropping.",
+           chan->conn->link_proto == 0 ? "non-versioned" : "a v1");
+    return false;
+  }
+
+  /* Can't process a NETINFO cell if the connection is not handshaking. */
+  if (chan->conn->base_.state != OR_CONN_STATE_OR_HANDSHAKING_V2 &&
+      chan->conn->base_.state != OR_CONN_STATE_OR_HANDSHAKING_V3) {
+    log_fn(LOG_PROTOCOL_WARN, LD_OR,
+           "Received a NETINFO cell on non-handshaking connection; dropping.");
+    return false;
+  }
+
+  /* Make sure we do have handshake state. */
+  tor_assert(chan->conn->handshake_state);
+  tor_assert(chan->conn->handshake_state->received_versions);
+
+  return true;
+}
+
 /**
  * Process a 'netinfo' cell
  *
@@ -1713,20 +1748,12 @@ channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan)
   tor_assert(chan);
   tor_assert(chan->conn);
 
-  if (chan->conn->link_proto < 2) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Received a NETINFO cell on %s connection; dropping.",
-           chan->conn->link_proto == 0 ? "non-versioned" : "a v1");
+  /* Make sure we can process a NETINFO cell. Link protocol and state
+   * validation is done to make sure of it. */
+  if (!can_process_netinfo_cell(chan)) {
     return;
   }
-  if (chan->conn->base_.state != OR_CONN_STATE_OR_HANDSHAKING_V2 &&
-      chan->conn->base_.state != OR_CONN_STATE_OR_HANDSHAKING_V3) {
-    log_fn(LOG_PROTOCOL_WARN, LD_OR,
-           "Received a NETINFO cell on non-handshaking connection; dropping.");
-    return;
-  }
-  tor_assert(chan->conn->handshake_state &&
-             chan->conn->handshake_state->received_versions);
+
   started_here = connection_or_nonopen_was_started_here(chan->conn);
   identity_digest = chan->conn->identity_digest;