PORT Consolidated Security Fixes for 1.2.6 to 1.3.0

plugins/net_plugin/net_plugin.cpp

@@ -1344,19 +1344,16 @@ namespace eosio {
             }
 
             //scan the list of peers looking for another able to provide sync blocks.
-            while (cptr != cend) {
+            auto cstart_it = cptr;
+            do {
                //select the first one which is current and break out.
-               if ((*cptr)->current()) {
+               if((*cptr)->current()) {
                   source = *cptr;
                   break;
                }
-               else {
-                  // advance the iterator in a round robin fashion.
-                  if (++cptr == my_impl->connections.end()) {
+               if(++cptr == my_impl->connections.end())
                      cptr = my_impl->connections.begin();
-                  }
-               }
-            }
+            } while(cptr != cstart_it);
             // no need to check the result, either source advanced or the whole list was checked and the old source is reused.
          }
       }