Fix name policy panic on empty or short domain

policy/engine_test.go

@@ -54,6 +54,20 @@ func TestNamePolicyEngine_matchDomainConstraint(t *testing.T) {
 			want:       false,
 			wantErr:    false,
 		},
+		{
+			name:       "fail/empty-domain",
+			domain:     "",
+			constraint: "host.example.com",
+			want:       false,
+			wantErr:    false,
+		},
+		{
+			name:       "fail/single-asterisk-domain",
+			domain:     "*",
+			constraint: "host.example.com",
+			want:       false,
+			wantErr:    false,
+		},
 		{
 			name:       "fail/period-domain",
 			domain:     ".host.example.com",

policy/validate.go

@@ -480,13 +480,18 @@ func (e *NamePolicyEngine) matchDomainConstraint(domain, constraint string) (boo
 		return false, nil
 	}
 
+	// An empty domain never matches a constraint.
+	if domain == "" {
+		return false, nil
+	}
+
 	// Block domains that start with just a period
 	if domain[0] == '.' {
 		return false, nil
 	}
 
 	// Block wildcard domains that don't start with exactly "*." (i.e. double wildcards and such)
-	if domain[0] == '*' && domain[1] != '.' {
+	if domain[0] == '*' && (len(domain) < 2 || domain[1] != '.') {
 		return false, nil
 	}