TUN-8630: Check checksum of downloaded binary to compare to current for auto-updating

In the rare case that the updater downloads the same binary (validated via checksum)
we want to make sure that the updater does not attempt to upgrade and restart the cloudflared
process. The binaries are equivalent and this would provide no value.

However, we are covering this case because there was an errant deployment of cloudflared
that reported itself as an older version and was then stuck in an infinite loop
attempting to upgrade to the latest version which didn't exist. By making sure that
the binary is different ensures that the upgrade will be attempted and cloudflared
will be restarted to run the new version.

This change only affects cloudflared tunnels running with default settings or
`--no-autoupdate=false` which allows cloudflared to auto-update itself in-place. Most
distributions that handle package management at the operating system level are
not affected by this change.

cmd/cloudflared/cliutil/build_info.go

@@ -1,7 +1,10 @@
 package cliutil
 
 import (
+	"crypto/sha256"
 	"fmt"
+	"io"
+	"os"
 	"runtime"
 
 	"github.com/rs/zerolog"
@@ -13,6 +16,7 @@ type BuildInfo struct {
 	GoArch             string `json:"go_arch"`
 	BuildType          string `json:"build_type"`
 	CloudflaredVersion string `json:"cloudflared_version"`
+	Checksum           string `json:"checksum"`
 }
 
 func GetBuildInfo(buildType, version string) *BuildInfo {
@@ -22,11 +26,12 @@ func GetBuildInfo(buildType, version string) *BuildInfo {
 		GoArch:             runtime.GOARCH,
 		BuildType:          buildType,
 		CloudflaredVersion: version,
+		Checksum:           currentBinaryChecksum(),
 	}
 }
 
 func (bi *BuildInfo) Log(log *zerolog.Logger) {
-	log.Info().Msgf("Version %s", bi.CloudflaredVersion)
+	log.Info().Msgf("Version %s (Checksum %s)", bi.CloudflaredVersion, bi.Checksum)
 	if bi.BuildType != "" {
 		log.Info().Msgf("Built%s", bi.GetBuildTypeMsg())
 	}
@@ -51,3 +56,28 @@ func (bi *BuildInfo) GetBuildTypeMsg() string {
 func (bi *BuildInfo) UserAgent() string {
 	return fmt.Sprintf("cloudflared/%s", bi.CloudflaredVersion)
 }
+
+// FileChecksum opens a file and returns the SHA256 checksum.
+func FileChecksum(filePath string) (string, error) {
+	f, err := os.Open(filePath)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	h := sha256.New()
+	if _, err := io.Copy(h, f); err != nil {
+		return "", err
+	}
+
+	return fmt.Sprintf("%x", h.Sum(nil)), nil
+}
+
+func currentBinaryChecksum() string {
+	currentPath, err := os.Executable()
+	if err != nil {
+		return ""
+	}
+	sum, _ := FileChecksum(currentPath)
+	return sum
+}

cmd/cloudflared/main.go

@@ -91,7 +91,7 @@ func main() {
 
 	tunnel.Init(bInfo, graceShutdownC) // we need this to support the tunnel sub command...
 	access.Init(graceShutdownC, Version)
-	updater.Init(Version)
+	updater.Init(bInfo)
 	tracing.Init(Version)
 	token.Init(Version)
 	tail.Init(bInfo)

cmd/cloudflared/updater/update.go

@@ -14,6 +14,7 @@ import (
 	"github.com/urfave/cli/v2"
 	"golang.org/x/term"
 
+	"github.com/cloudflare/cloudflared/cmd/cloudflared/cliutil"
 	"github.com/cloudflare/cloudflared/config"
 	"github.com/cloudflare/cloudflared/logger"
 )
@@ -31,7 +32,7 @@ const (
 )
 
 var (
-	version                string
+	buildInfo              *cliutil.BuildInfo
 	BuiltForPackageManager = ""
 )
 
@@ -81,8 +82,8 @@ func (uo *UpdateOutcome) noUpdate() bool {
 	return uo.Error == nil && uo.Updated == false
 }
 
-func Init(v string) {
-	version = v
+func Init(info *cliutil.BuildInfo) {
+	buildInfo = info
 }
 
 func CheckForUpdate(options updateOptions) (CheckResult, error) {
@@ -100,11 +101,12 @@ func CheckForUpdate(options updateOptions) (CheckResult, error) {
 		cfdPath = encodeWindowsPath(cfdPath)
 	}
 
-	s := NewWorkersService(version, url, cfdPath, Options{IsBeta: options.isBeta,
+	s := NewWorkersService(buildInfo.CloudflaredVersion, url, cfdPath, Options{IsBeta: options.isBeta,
 		IsForced: options.isForced, RequestedVersion: options.intendedVersion})
 
 	return s.Check()
 }
+
 func encodeWindowsPath(path string) string {
 	// We do this because Windows allows spaces in directories such as
 	// Program Files but does not allow these directories to be spaced in batch files.
@@ -237,7 +239,7 @@ func (a *AutoUpdater) Run(ctx context.Context) error {
 	for {
 		updateOutcome := loggedUpdate(a.log, updateOptions{updateDisabled: !a.configurable.enabled})
 		if updateOutcome.Updated {
-			Init(updateOutcome.Version)
+			buildInfo.CloudflaredVersion = updateOutcome.Version
 			if IsSysV() {
 				// SysV doesn't have a mechanism to keep service alive, we have to restart the process
 				a.log.Info().Msg("Restarting service managed by SysV...")

cmd/cloudflared/updater/update_test.go

@@ -9,8 +9,14 @@ import (
 	"github.com/rs/zerolog"
 	"github.com/stretchr/testify/assert"
 	"github.com/urfave/cli/v2"
+
+	"github.com/cloudflare/cloudflared/cmd/cloudflared/cliutil"
 )
 
+func init() {
+	Init(cliutil.GetBuildInfo("TEST", "TEST"))
+}
+
 func TestDisabledAutoUpdater(t *testing.T) {
 	listeners := &gracenet.Net{}
 	log := zerolog.Nop()

cmd/cloudflared/updater/workers_service.go

@@ -3,6 +3,7 @@ package updater
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
 	"net/http"
 	"runtime"
 )
@@ -79,6 +80,10 @@ func (s *WorkersService) Check() (CheckResult, error) {
 	}
 	defer resp.Body.Close()
 
+	if resp.StatusCode != 200 {
+		return nil, fmt.Errorf("unable to check for update: %d", resp.StatusCode)
+	}
+
 	var v VersionResponse
 	if err := json.NewDecoder(resp.Body).Decode(&v); err != nil {
 		return nil, err

cmd/cloudflared/updater/workers_update.go

@@ -3,7 +3,6 @@ package updater
 import (
 	"archive/tar"
 	"compress/gzip"
-	"crypto/sha256"
 	"errors"
 	"fmt"
 	"io"
@@ -16,6 +15,10 @@ import (
 	"strings"
 	"text/template"
 	"time"
+
+	"github.com/getsentry/sentry-go"
+
+	"github.com/cloudflare/cloudflared/cmd/cloudflared/cliutil"
 )
 
 const (
@@ -86,8 +89,25 @@ func (v *WorkersVersion) Apply() error {
 		return err
 	}
 
-	// check that the file is what is expected
-	if err := isValidChecksum(v.checksum, newFilePath); err != nil {
+	downloadSum, err := cliutil.FileChecksum(newFilePath)
+	if err != nil {
+		return err
+	}
+
+	// Check that the file downloaded matches what is expected.
+	if v.checksum != downloadSum {
+		return errors.New("checksum validation failed")
+	}
+
+	// Check if the currently running version has the same checksum
+	if downloadSum == buildInfo.Checksum {
+		// Currently running binary matches the downloaded binary so we have no reason to update. This is
+		// typically unexpected, as such we emit a sentry event.
+		localHub := sentry.CurrentHub().Clone()
+		err := errors.New("checksum validation matches currently running process")
+		localHub.CaptureException(err)
+		// Make sure to cleanup the new downloaded file since we aren't upgrading versions.
+		os.Remove(newFilePath)
 		return err
 	}
 
@@ -189,27 +209,6 @@ func isCompressedFile(urlstring string) bool {
 	return strings.HasSuffix(u.Path, ".tgz")
 }
 
-// checks if the checksum in the json response matches the checksum of the file download
-func isValidChecksum(checksum, filePath string) error {
-	f, err := os.Open(filePath)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	h := sha256.New()
-	if _, err := io.Copy(h, f); err != nil {
-		return err
-	}
-
-	hash := fmt.Sprintf("%x", h.Sum(nil))
-
-	if checksum != hash {
-		return errors.New("checksum validation failed")
-	}
-	return nil
-}
-
 // writeBatchFile writes a batch file out to disk
 // see the dicussion on why it has to be done this way
 func writeBatchFile(targetPath string, newPath string, oldPath string) error {