Fix kubelet to not accept negative eviction (hard, soft) thresholds

and add unit tests

pkg/kubelet/eviction/helpers.go

@@ -157,6 +157,10 @@ func parseThresholdStatement(statement string) (Threshold, error) {
 	if err != nil {
 		return Threshold{}, err
 	}
+	if quantity.Sign() < 0 {
+		return Threshold{}, fmt.Errorf("eviction threshold %v cannot be negative: %s", signal, &quantity)
+	}
+
 	return Threshold{
 		Signal:   signal,
 		Operator: operator,

pkg/kubelet/eviction/helpers_test.go

@@ -83,6 +83,22 @@ func TestParseThresholdConfig(t *testing.T) {
 			expectErr:               true,
 			expectThresholds:        []Threshold{},
 		},
+		"hard-signal-negative": {
+			evictionHard:            "memory.available<-150Mi",
+			evictionSoft:            "",
+			evictionSoftGracePeriod: "",
+			evictionMinReclaim:      "",
+			expectErr:               true,
+			expectThresholds:        []Threshold{},
+		},
+		"soft-signal-negative": {
+			evictionHard:            "",
+			evictionSoft:            "memory.available<-150Mi",
+			evictionSoftGracePeriod: "",
+			evictionMinReclaim:      "",
+			expectErr:               true,
+			expectThresholds:        []Threshold{},
+		},
 		"duplicate-signal": {
 			evictionHard:            "memory.available<150Mi,memory.available<100Mi",
 			evictionSoft:            "",