Check for invalid utf-8 values in label values.

prometheus/prometheus#2822

Author: brian-brazil

expfmt/text_parse.go

@@ -315,6 +315,10 @@ func (p *TextParser) startLabelValue() stateFn {
 	if p.readTokenAsLabelValue(); p.err != nil {
 		return nil
 	}
+	if !model.LabelValue(p.currentToken.String()).IsValid() {
+		p.parseError(fmt.Sprintf("invalid label value %q", p.currentToken.String()))
+		return nil
+	}
 	p.currentLabelPair.Value = proto.String(p.currentToken.String())
 	// Special treatment of summaries:
 	// - Quantile labels are special, will result in dto.Quantile later.

expfmt/text_parse_test.go

@@ -559,6 +559,11 @@ metric_bucket{le="bla"} 3.14
 `,
 			err: "text format parsing error in line 3: expected float as value for 'le' label",
 		},
+		// 19: Invalid UTF-8 in label value.
+		{
+			in:  "metric{l=\"\xbd\"} 3.14\n",
+			err: "text format parsing error in line 1: invalid label value \"\\xbd\"",
+		},
 	}
 
 	for i, scenario := range scenarios {