[tor-commits] [tor/main] circpad: Be smarter on when to send back STOP cells.

[nickm@xxxxxxxxxxxxxx]

commit 72aa23a9fd1772de214ea8a22e1371c2d026dc7c
Author: George Kadianakis <desnacked@xxxxxxxxxx>
Date:   Thu Jul 22 15:02:13 2021 +0300

    circpad: Be smarter on when to send back STOP cells.
---
 changes/bug40435               |  4 ++++
 src/core/or/circuitpadding.c   | 19 +++++++++++++++----
 src/test/test_circuitpadding.c |  6 ++----
 3 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/changes/bug40435 b/changes/bug40435
new file mode 100644
index 0000000000..76d0a687eb
--- /dev/null
+++ b/changes/bug40435
@@ -0,0 +1,4 @@
+  o Minor bugfixes (circuit padding):
+    - Don't send STOP circuit padding cells when the other side has already
+      shut down the corresponding padding machine. Fixes bug 40435; bugfix on
+      0.4.0.1-alpha.
\ No newline at end of file
diff --git a/src/core/or/circuitpadding.c b/src/core/or/circuitpadding.c
index 6dfe94de01..99dc5f9d83 100644
--- a/src/core/or/circuitpadding.c
+++ b/src/core/or/circuitpadding.c
@@ -2967,6 +2967,8 @@ signed_error_t
 circpad_handle_padding_negotiate(circuit_t *circ, cell_t *cell)
 {
   int retval = 0;
+  /* Should we send back a STOP cell? */
+  bool respond_with_stop = true;
   circpad_negotiate_t *negotiate;
 
   if (CIRCUIT_IS_ORIGIN(circ)) {
@@ -2992,6 +2994,12 @@ circpad_handle_padding_negotiate(circuit_t *circ, cell_t *cell)
                negotiate->machine_type, negotiate->machine_ctr);
       goto done;
     }
+
+    /* If we reached this point we received a STOP command from an old or
+       unknown machine. Don't reply with our own STOP since there is no one to
+       handle it on the other end */
+    respond_with_stop = false;
+
     if (negotiate->machine_ctr <= circ->padding_machine_ctr) {
       log_info(LD_CIRC, "Received STOP command for old machine %u, ctr %u",
                negotiate->machine_type, negotiate->machine_ctr);
@@ -3023,10 +3031,13 @@ circpad_handle_padding_negotiate(circuit_t *circ, cell_t *cell)
     retval = -1;
 
   done:
-    circpad_padding_negotiated(circ, negotiate->machine_type,
-                   negotiate->command,
-                   (retval == 0) ? CIRCPAD_RESPONSE_OK : CIRCPAD_RESPONSE_ERR,
-                   negotiate->machine_ctr);
+    if (respond_with_stop) {
+      circpad_padding_negotiated(circ, negotiate->machine_type,
+                    negotiate->command,
+                    (retval == 0) ? CIRCPAD_RESPONSE_OK : CIRCPAD_RESPONSE_ERR,
+                    negotiate->machine_ctr);
+    }
+
     circpad_negotiate_free(negotiate);
 
     return retval;
diff --git a/src/test/test_circuitpadding.c b/src/test/test_circuitpadding.c
index 86baf54f40..6ced3f4111 100644
--- a/src/test/test_circuitpadding.c
+++ b/src/test/test_circuitpadding.c
@@ -1367,7 +1367,7 @@ test_circuitpadding_wronghop(void *arg)
   tt_ptr_op(client_side->padding_info[0], OP_NE, NULL);
   tt_ptr_op(relay_side->padding_machine[0], OP_NE, NULL);
   tt_ptr_op(relay_side->padding_info[0], OP_NE, NULL);
-  tt_int_op(n_relay_cells, OP_EQ, 3);
+  tt_int_op(n_relay_cells, OP_EQ, 2);
   tt_int_op(n_client_cells, OP_EQ, 2);
 
   /* 6. Sending negotiated command to relay does nothing */
@@ -1396,11 +1396,9 @@ test_circuitpadding_wronghop(void *arg)
   /* verify no padding was negotiated */
   tt_ptr_op(relay_side->padding_machine[0], OP_EQ, NULL);
   tt_ptr_op(client_side->padding_machine[0], OP_EQ, NULL);
-  tt_int_op(n_relay_cells, OP_EQ, 3);
-  tt_int_op(n_client_cells, OP_EQ, 2);
 
   /* verify no echo was sent */
-  tt_int_op(n_relay_cells, OP_EQ, 3);
+  tt_int_op(n_relay_cells, OP_EQ, 2);
   tt_int_op(n_client_cells, OP_EQ, 2);
 
   /* Finish circuit */



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