FW-449. Fixing overflow in DAGrank calculation

In the calculation of the tentativeDAGrank in neighbors_updateMyDAGrankAndNeighborPreference an overflow was possible. This results in occasional choosing a preferred parent with MAXDAGRANK.
qazer10 · Mar 10, 2016 · 499d915 · 499d915
1 parent f179a2d
commit 499d915
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/openstack/02b-MAChigh/neighbors.c b/openstack/02b-MAChigh/neighbors.c
@@ -543,7 +543,8 @@ void neighbors_updateMyDAGrankAndNeighborPreference() {
             rankIncrease = (uint16_t)(rankIncreaseIntermediary >> 10);
          }
 
-         tentativeDAGrank = neighbors_vars.neighbors[i].DAGrank+rankIncrease;
+         // cast the uint16_t summands to avoid an overflow if DAGrank == 0xFFFF (MAXDAGRANK)
+         tentativeDAGrank = (uint32_t)neighbors_vars.neighbors[i].DAGrank + (uint32_t)rankIncrease;
          if ( tentativeDAGrank<neighbors_vars.myDAGrank &&
               tentativeDAGrank<MAXDAGRANK) {
             // found better parent, lower my DAGrank