les/utils: fix panic in weighted select

les/utils/weighted_select.go

@@ -83,13 +83,13 @@ func (w *WeightedRandomSelect) Choose() WrsItem {
 		if w.root.sumWeight == 0 {
 			return nil
 		}
-		val := uint64(rand.Int63n(int64(w.root.sumWeight)))
+		val := rand.Uint64() % w.root.sumWeight
 		choice, lastWeight := w.root.choose(val)
 		weight := w.wfn(choice)
 		if weight != lastWeight {
 			w.setWeight(choice, weight)
 		}
-		if weight >= lastWeight || uint64(rand.Int63n(int64(lastWeight))) < weight {
+		if weight >= lastWeight || rand.Uint64()%lastWeight < weight {
 			return choice
 		}
 	}

les/utils/weighted_select_test.go

@@ -66,3 +66,17 @@ func TestWeightedRandomSelect(t *testing.T) {
 	testFn(100000)
 	testFn(1000000)
 }
+
+// TestOOB tests values which doesn't fit in int64
+func TestOOB(t *testing.T) {
+	s := NewWeightedRandomSelect(func(i interface{}) uint64 {
+		// Dummy weight function to return a very large weight
+		return uint64(0xffffffffffffffff)
+	})
+	s.Update(testWrsItem{idx: 0, widx: nil})
+	// int64 conversion should make the sumweight negative
+	if int64(s.root.sumWeight) >= 0 {
+		t.Fatalf("test is dysfunctional, sumweight not negative: %d", int64(s.root.sumWeight))
+	}
+	s.Choose()
+}