From 8dda62cc24692b17e9bec0156160d8e54046d762 Mon Sep 17 00:00:00 2001
From: kari-ts <135075563+kari-ts@users.noreply.github.com>
Date: Fri, 17 Apr 2026 10:28:35 -0700
Subject: [PATCH] feature/clientupdate: windows update should use tailscale.exe
 update (#19438)

Currently, clientupdate.NewUpdater().Update() is called directly inside tailscaled, which fatals. There is also a failure that doesn't return, causing a panic.

This fix allows us to use the same approach as startAutoUpdate, which is to find tailscale.exe and run tailscale.exe --update, though since it's calling the updater library directly, we get progress messages.

Fixes tailscale/corp#40430s

Signed-off-by: kari-ts <kari@tailscale.com>
---
 clientupdate/clientupdate_windows.go | 32 ++++++++++++++++++++++------
 feature/clientupdate/clientupdate.go |  1 +
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/clientupdate/clientupdate_windows.go b/clientupdate/clientupdate_windows.go
index 70a3c5091..50b77c38b 100644
--- a/clientupdate/clientupdate_windows.go
+++ b/clientupdate/clientupdate_windows.go
@@ -38,12 +38,12 @@ const (
 	updaterPrefix = "tailscale-updater"
 )
 
-func makeSelfCopy() (origPathExe, tmpPathExe string, err error) {
-	selfExe, err := os.Executable()
+func makeCmdTailscaleCopy() (origPathExe, tmpPathExe string, err error) {
+	srcExe, err := findCmdTailscale()
 	if err != nil {
 		return "", "", err
 	}
-	f, err := os.Open(selfExe)
+	f, err := os.Open(srcExe)
 	if err != nil {
 		return "", "", err
 	}
@@ -59,7 +59,25 @@ func makeSelfCopy() (origPathExe, tmpPathExe string, err error) {
 		f2.Close()
 		return "", "", err
 	}
-	return selfExe, f2.Name(), f2.Close()
+	return srcExe, f2.Name(), f2.Close()
+}
+
+// findCmdTailscale returns the path to the binary that should be copied for the update
+// re-execution. The copy is re-executed with "update" as a subcommand, so it must be
+// a binary that handles "update" (ie tailscale.exe, not tailscaled.exe)
+func findCmdTailscale() (string, error) {
+	selfExe, err := os.Executable()
+	if err != nil {
+		return "", err
+	}
+	if strings.EqualFold(filepath.Base(selfExe), "tailscale.exe") {
+		return selfExe, nil
+	}
+	ts := filepath.Join(filepath.Dir(selfExe), "tailscale.exe")
+	if _, err := os.Stat(ts); err != nil {
+		return "", fmt.Errorf("cannot find tailscale.exe alongside %s: %w", selfExe, err)
+	}
+	return ts, nil
 }
 
 func markTempFileWindows(name string) error {
@@ -159,14 +177,14 @@ you can run the command prompt as Administrator one of these ways:
 
 	up.Logf("making tailscale.exe copy to switch to...")
 	up.cleanupOldDownloads(filepath.Join(os.TempDir(), updaterPrefix+"-*.exe"))
-	_, selfCopy, err := makeSelfCopy()
+	_, cmdTailscaleCopy, err := makeCmdTailscaleCopy()
 	if err != nil {
 		return err
 	}
-	defer os.Remove(selfCopy)
+	defer os.Remove(cmdTailscaleCopy)
 	up.Logf("running tailscale.exe copy for final install...")
 
-	cmd := exec.Command(selfCopy, "update")
+	cmd := exec.Command(cmdTailscaleCopy, "update")
 	cmd.Env = append(os.Environ(), winMSIEnv+"="+msiTarget, winVersionEnv+"="+ver)
 	cmd.Stdout = up.Stderr
 	cmd.Stderr = up.Stderr
diff --git a/feature/clientupdate/clientupdate.go b/feature/clientupdate/clientupdate.go
index d47d04815..999dd7920 100644
--- a/feature/clientupdate/clientupdate.go
+++ b/feature/clientupdate/clientupdate.go
@@ -163,6 +163,7 @@ func (e *extension) DoSelfUpdate() {
 	})
 	if err != nil {
 		e.pushSelfUpdateProgress(ipnstate.NewUpdateProgress(ipnstate.UpdateFailed, err.Error()))
+		return
 	}
 	err = up.Update()
 	if err != nil {