Add "HiddenServiceMaxStreams" as a per-HS tunable.

When set, this limits the maximum number of simultaneous streams per
rendezvous circuit on the server side of a HS, with further RELAY_BEGIN
cells being silently ignored.

This can be modified via "HiddenServiceMaxStreamsCloseCircuit", which
if set will cause offending rendezvous circuits to be torn down instead.

Addresses part of #16052.

1 files changed, 19 insertions, 8 deletions

diff --git a/src/or/circuituse.c b/src/or/circuituse.c
index b54a4d2a7f..a429a7d053 100644
--- a/src/or/circuituse.c
+++ b/src/or/circuituse.c
@@ -1189,17 +1189,28 @@ circuit_detach_stream(circuit_t *circ, edge_connection_t *conn)
 
   if (CIRCUIT_IS_ORIGIN(circ)) {
     origin_circuit_t *origin_circ = TO_ORIGIN_CIRCUIT(circ);
+    int removed = 0;
     if (conn == origin_circ->p_streams) {
       origin_circ->p_streams = conn->next_stream;
-      return;
+      removed = 1;
+    } else {
+      for (prevconn = origin_circ->p_streams;
+           prevconn && prevconn->next_stream && prevconn->next_stream != conn;
+           prevconn = prevconn->next_stream)
+        ;
+      if (prevconn && prevconn->next_stream) {
+        prevconn->next_stream = conn->next_stream;
+        removed = 1;
+      }
     }
-
-    for (prevconn = origin_circ->p_streams;
-         prevconn && prevconn->next_stream && prevconn->next_stream != conn;
-         prevconn = prevconn->next_stream)
-      ;
-    if (prevconn && prevconn->next_stream) {
-      prevconn->next_stream = conn->next_stream;
+    if (removed) {
+      /* If the stream was removed, and it was a rend stream, decrement the
+       * number of streams on the circuit associated with the rend service.
+       */
+      if (circ->purpose == CIRCUIT_PURPOSE_S_REND_JOINED) {
+        tor_assert(origin_circ->rend_data);
+        origin_circ->rend_data->nr_streams--;
+      }
       return;
     }
   } else {