sendme: Always pop last SENDME digest from circuit

We must not accumulate digests on the circuit if the other end point is using
another SENDME version that is not using those digests like v0.

This commit makes it that we always pop the digest regardless of the version.

Part of #30428

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

2 files changed, 9 insertions, 0 deletions

diff --git a/src/test/test_relaycell.c b/src/test/test_relaycell.c
index d6372d3956..c65279fb25 100644
--- a/src/test/test_relaycell.c
+++ b/src/test/test_relaycell.c
@@ -17,6 +17,7 @@
 #include "core/or/circuitbuild.h"
 #include "core/or/circuitlist.h"
 #include "core/or/connection_edge.h"
+#include "core/or/sendme.h"
 #include "core/or/relay.h"
 #include "test/test.h"
 #include "test/log_test_helpers.h"
@@ -813,6 +814,10 @@ test_circbw_relay(void *arg)
 
   /* Sendme on circuit with non-full window: counted */
   PACK_CELL(0, RELAY_COMMAND_SENDME, "");
+  /* Recording a cell, the window is updated after decryption so off by one in
+   * order to record and then we process it with the proper window. */
+  circ->cpath->package_window = 901;
+  sendme_record_cell_digest_on_circ(TO_CIRCUIT(circ), circ->cpath);
   circ->cpath->package_window = 900;
   connection_edge_process_relay_cell(&cell, TO_CIRCUIT(circ), edgeconn,
                                      circ->cpath);
diff --git a/src/test/test_sendme.c b/src/test/test_sendme.c
index a36c904c28..fa5ae115ac 100644
--- a/src/test/test_sendme.c
+++ b/src/test/test_sendme.c
@@ -143,11 +143,13 @@ test_v1_build_cell(void *arg)
 
   or_circ = or_circuit_new(1, NULL);
   circ = TO_CIRCUIT(or_circ);
+  circ->sendme_last_digests = smartlist_new();
 
   cell_digest = crypto_digest_new();
   tt_assert(cell_digest);
   crypto_digest_add_bytes(cell_digest, "AAAAAAAAAAAAAAAAAAAA", 20);
   crypto_digest_get_digest(cell_digest, (char *) digest, sizeof(digest));
+  smartlist_add(circ->sendme_last_digests, tor_memdup(digest, sizeof(digest)));
 
   /* SENDME v1 payload is 3 bytes + 20 bytes digest. See spec. */
   ret = build_cell_payload_v1(digest, payload);
@@ -157,6 +159,8 @@ test_v1_build_cell(void *arg)
 
   /* An empty payload means SENDME version 0 thus valid. */
   tt_int_op(sendme_is_valid(circ, payload, 0), OP_EQ, true);
+  /* Current phoney digest should have been popped. */
+  tt_int_op(smartlist_len(circ->sendme_last_digests), OP_EQ, 0);
 
   /* An unparseable cell means invalid. */
   setup_full_capture_of_logs(LOG_INFO);