Discard all cells on a marked connection

Fix for bug 4299

changes/bug4299

@@ -0,0 +1,5 @@
+  o Major bugfix:
+    - Do not process cells on a marked-for-close connection. We previously
+      avoided this by not calling read handlers on marked connections, but
+      that's not adequate for the case when cells are very small. Fixes
+      bug 4299; bugfix on 0.2.0.20-rc which first made small cells possible.

src/or/command.c

@@ -132,6 +132,9 @@ command_process_cell(cell_t *cell, or_connection_t *conn)
 #define PROCESS_CELL(tp, cl, cn) command_process_ ## tp ## _cell(cl, cn)
 #endif
 
+  if (conn->_base.marked_for_close)
+    return;
+
   /* Reject all but VERSIONS and NETINFO when handshaking. */
   if (handshaking && cell->command != CELL_VERSIONS &&
       cell->command != CELL_NETINFO)
@@ -205,6 +208,9 @@ command_process_var_cell(var_cell_t *cell, or_connection_t *conn)
   }
 #endif
 
+  if (conn->_base.marked_for_close)
+    return;
+
   /* reject all when not handshaking. */
   if (conn->_base.state != OR_CONN_STATE_OR_HANDSHAKING)
     return;