From f3be05e6ea693b87a870820f06c88e7c4136e1b8 Mon Sep 17 00:00:00 2001
From: Aaron Klotz <aaron@tailscale.com>
Date: Fri, 24 Sep 2021 15:24:16 -0600
Subject: [PATCH] ipn, paths: unconditionally attempt to set state dir perms,
 but only if the state dir is ours

We unconditionally set appropriate perms on the statefile dir.

We look at the basename of the statefile dir, and if it is "tailscale", then
we set perms as appropriate.

Fixes #2925
Updates #2856

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
---
 ipn/store.go           |  8 +++++---
 paths/paths_unix.go    | 10 +++++-----
 paths/paths_windows.go |  5 +++++
 3 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/ipn/store.go b/ipn/store.go
index 826092a66..c95965619 100644
--- a/ipn/store.go
+++ b/ipn/store.go
@@ -98,6 +98,11 @@ func (s *FileStore) String() string { return fmt.Sprintf("FileStore(%q)", s.path
 
 // NewFileStore returns a new file store that persists to path.
 func NewFileStore(path string) (*FileStore, error) {
+	// We unconditionally call this to ensure that our perms are correct
+	if err := paths.MkStateDir(filepath.Dir(path)); err != nil {
+		return nil, fmt.Errorf("creating state directory: %w", err)
+	}
+
 	bs, err := ioutil.ReadFile(path)
 
 	// Treat an empty file as a missing file.
@@ -111,9 +116,6 @@ func NewFileStore(path string) (*FileStore, error) {
 		if os.IsNotExist(err) {
 			// Write out an initial file, to verify that we can write
 			// to the path.
-			if err := paths.MkStateDir(filepath.Dir(path)); err != nil {
-				return nil, fmt.Errorf("creating state directory: %w", err)
-			}
 			if err = atomicfile.WriteFile(path, []byte("{}"), 0600); err != nil {
 				return nil, err
 			}
diff --git a/paths/paths_unix.go b/paths/paths_unix.go
index 0bc413ad1..17662b0f8 100644
--- a/paths/paths_unix.go
+++ b/paths/paths_unix.go
@@ -63,9 +63,9 @@ func xdgDataHome() string {
 }
 
 func ensureStateDirPerms(dirPath string) error {
-	// Unfortunately there are currently numerous tests that set up state files
-	// right off of /tmp, on which Chmod will of course fail. We should fix our
-	// test harnesses to not do that, at which point we can return an error.
-	os.Chmod(dirPath, 0700)
-	return nil
+	if filepath.Base(dirPath) != "tailscale" {
+		return nil
+	}
+
+	return os.Chmod(dirPath, 0700)
 }
diff --git a/paths/paths_windows.go b/paths/paths_windows.go
index 75d49100a..e00a8062a 100644
--- a/paths/paths_windows.go
+++ b/paths/paths_windows.go
@@ -6,6 +6,8 @@ package paths
 
 import (
 	"os"
+	"path/filepath"
+	"strings"
 	"unsafe"
 
 	"golang.org/x/sys/windows"
@@ -86,6 +88,9 @@ func ensureStateDirPerms(dirPath string) error {
 	if !fi.IsDir() {
 		return os.ErrInvalid
 	}
+	if strings.ToLower(filepath.Base(dirPath)) != "tailscale" {
+		return nil
+	}
 
 	// We need the info for our current user as SIDs
 	sids, err := getCurrentUserSids()