prop289: Remember the last cell digest for v1 SENDMEs

In order to do so, depending on where the cell is going, we'll keep the last
cell digest that is either received inbound or sent outbound.

Then it can be used for validation.

Part of #26288

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

1 files changed, 19 insertions, 9 deletions

diff --git a/src/core/or/sendme.c b/src/core/or/sendme.c
index afade43f74..76f551a929 100644
--- a/src/core/or/sendme.c
+++ b/src/core/or/sendme.c
@@ -14,6 +14,7 @@
 #include "core/or/cell_st.h"
 #include "core/or/circuitlist.h"
 #include "core/or/circuituse.h"
+#include "core/or/or_circuit_st.h"
 #include "core/or/relay.h"
 #include "core/or/sendme.h"
 #include "feature/nodelist/networkstatus.h"
@@ -342,18 +343,20 @@ sendme_connection_edge_consider_sending(edge_connection_t *conn)
  * more.
  */
 void
-sendme_circuit_consider_sending(circuit_t *circ, crypt_path_t *layer_hint,
-                                crypto_digest_t *digest)
+sendme_circuit_consider_sending(circuit_t *circ, crypt_path_t *layer_hint)
 {
-  tor_assert(digest);
+  crypto_digest_t *digest;
 
   while ((layer_hint ? layer_hint->deliver_window : circ->deliver_window) <=
           CIRCWINDOW_START - CIRCWINDOW_INCREMENT) {
     log_debug(LD_CIRC,"Queuing circuit sendme.");
-    if (layer_hint)
+    if (layer_hint) {
       layer_hint->deliver_window += CIRCWINDOW_INCREMENT;
-    else
+      digest = layer_hint->crypto.sendme_digest;
+    } else {
       circ->deliver_window += CIRCWINDOW_INCREMENT;
+      digest = TO_OR_CIRCUIT(circ)->crypto.sendme_digest;
+    }
     if (send_circuit_level_sendme(circ, layer_hint, digest) < 0) {
       return; /* The circuit's closed, don't continue */
     }
@@ -557,9 +560,16 @@ sendme_note_cell_digest(circuit_t *circ)
     return;
   }
 
-  digest = tor_malloc_zero(4);
-  if (circ->sendme_last_digests == NULL) {
-    circ->sendme_last_digests = smartlist_new();
+  /* Only note the digest if we actually have the digest of the previous cell
+   * recorded. It should never happen in theory as we always record the last
+   * digest for the v1 SENDME. */
+  if (TO_OR_CIRCUIT(circ)->crypto.sendme_digest) {
+    digest = tor_malloc_zero(4);
+    crypto_digest_get_digest(TO_OR_CIRCUIT(circ)->crypto.sendme_digest,
+                             (char *) digest, 4);
+    if (circ->sendme_last_digests == NULL) {
+      circ->sendme_last_digests = smartlist_new();
+    }
+    smartlist_add(circ->sendme_last_digests, digest);
   }
-  smartlist_add(circ->sendme_last_digests, digest);
 }