gVisor metric library: Verify path-style metric names.

The `unimplemented_syscalls` metric did not conform (whoops), so fix that one.

PiperOrigin-RevId: 539767799

pkg/metric/metric.go

@@ -19,6 +19,7 @@ import (
 	"errors"
 	"fmt"
 	"math"
+	re "regexp"
 	"sort"
 	"strings"
 	"time"
@@ -486,6 +487,20 @@ func nameToPrometheusName(name string) string {
 	return strings.ReplaceAll(strings.TrimPrefix(name, "/"), "/", "_")
 }
 
+var validMetricNameRegexp = re.MustCompile("^(?:/[_\\w]+)+$")
+
+// verifyName verifies that the given metric name is a valid path-style metric
+// name.
+func verifyName(name string) error {
+	if !strings.HasPrefix(name, "/") {
+		return fmt.Errorf("metric name must start with a '/': %q", name)
+	}
+	if !validMetricNameRegexp.MatchString(name) {
+		return fmt.Errorf("invalid metric name: %q", name)
+	}
+	return nil
+}
+
 // RegisterCustomUint64Metric registers a metric with the given name.
 //
 // Register must only be called at init and will return and error if called
@@ -555,6 +570,9 @@ func MustRegisterCustomUint64Metric(name string, cumulative, sync bool, descript
 //
 // Metrics must be statically defined (i.e., at init).
 func NewUint64Metric(name string, sync bool, units pb.MetricMetadata_Units, description string, fields ...Field) (*Uint64Metric, error) {
+	if err := verifyName(name); err != nil {
+		return nil, err
+	}
 	f, err := newFieldMapper(fields...)
 	if err != nil {
 		return nil, err
@@ -832,6 +850,9 @@ type DistributionMetric struct {
 
 // NewDistributionMetric creates and registers a new distribution metric.
 func NewDistributionMetric(name string, sync bool, bucketer Bucketer, unit pb.MetricMetadata_Units, description string, fields ...Field) (*DistributionMetric, error) {
+	if err := verifyName(name); err != nil {
+		return nil, err
+	}
 	if initialized.Load() {
 		return nil, ErrInitializationDone
 	}

pkg/metric/metric_test.go

@@ -66,6 +66,32 @@ func verifyPrometheusParsing(t *testing.T) {
 	}
 }
 
+func TestVerifyName(t *testing.T) {
+	for name, wantErr := range map[string]bool{
+		"":              true,
+		"/":             true,
+		"/foo":          false,
+		"/foo/bar":      false,
+		"/foo/bar/baz":  false,
+		"/foo/bar/bar":  false,
+		"/foo//bar/baz": true,
+		"//foo/bar":     true,
+		"//":            true,
+		"foo":           true,
+		"foo/bar":       true,
+		"/foo-bar":      true,
+		"/foo bar":      true,
+		"/foo_bar":      false,
+	} {
+		t.Run(name, func(t *testing.T) {
+			err := verifyName(name)
+			if gotErr := (err != nil); gotErr != wantErr {
+				t.Errorf("verifyName(%q) got err=%v wantErr=%v", name, err, wantErr)
+			}
+		})
+	}
+}
+
 func TestInitialize(t *testing.T) {
 	defer resetTest()
 

pkg/sentry/kernel/syscalls.go

@@ -402,7 +402,7 @@ func RegisterSyscallTable(s *SyscallTable) {
 			unimplementedSyscallNumbers[i] = []*metric.FieldValue{s}
 		}
 		allowedValues[len(allowedValues)-1] = outOfRangeSyscallNumber[0]
-		unimplementedSyscallCounter = metric.MustCreateNewUint64Metric("unimplemented_syscalls", true, "Number of times the application tried to call an unimplemented syscall, broken down by syscall number", metric.NewField("sysno", allowedValues...))
+		unimplementedSyscallCounter = metric.MustCreateNewUint64Metric("/unimplemented_syscalls", true, "Number of times the application tried to call an unimplemented syscall, broken down by syscall number", metric.NewField("sysno", allowedValues...))
 	})
 	s.Init()
 }