fix(watch): skip unreadable directories instead of failing the watch

Signed-off-by: Endika Iglesias <endika2@gmail.com>

Author: Endika

pkg/watch/watcher_naive.go

@@ -113,6 +113,12 @@ func (d *naiveNotify) watchRecursively(dir string) error {
 
 	return filepath.WalkDir(dir, func(path string, info fs.DirEntry, err error) error {
 		if err != nil {
+			// A directory we are not allowed to read is not a reason to abandon the
+			// whole watch: we simply cannot see inside it, so skip it and carry on.
+			if os.IsPermission(err) {
+				logrus.Debugf("Not watching %s: %v", path, err)
+				return filepath.SkipDir
+			}
 			return err
 		}
 
@@ -130,6 +136,10 @@ func (d *naiveNotify) watchRecursively(dir string) error {
 			if os.IsNotExist(err) {
 				return nil
 			}
+			if os.IsPermission(err) {
+				logrus.Debugf("Not watching %s: %v", path, err)
+				return filepath.SkipDir
+			}
 			return fmt.Errorf("watcher.Add(%q): %w", path, err)
 		}
 		return nil
@@ -180,6 +190,10 @@ func (d *naiveNotify) loop() { //nolint:gocyclo
 		// TODO(dbentley): if there's a delete should we call d.watcher.Remove to prevent leaking?
 		err := filepath.WalkDir(e.Name, func(path string, info fs.DirEntry, err error) error {
 			if err != nil {
+				if os.IsPermission(err) {
+					logrus.Debugf("Not watching %s: %v", path, err)
+					return filepath.SkipDir
+				}
 				return err
 			}
 

pkg/watch/watcher_naive_test.go

@@ -157,3 +157,39 @@ func TestDontRecurseWhenWatchingParentsOfNonExistentFiles(t *testing.T) {
 		t.Fatalf("watching more than 5 files: %d", n)
 	}
 }
+
+// A directory the current user cannot read costs us visibility into that
+// subtree, but it must not prevent the rest of the tree from being watched.
+func TestWatchRecursivelySkipsUnreadableDir(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("permission semantics differ on windows")
+	}
+	if os.Geteuid() == 0 {
+		t.Skip("root bypasses the permission bit this test relies on")
+	}
+
+	root := t.TempDir()
+	unreadable := filepath.Join(root, "unreadable")
+	if err := os.MkdirAll(filepath.Join(unreadable, "inner"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(root, "watched.txt"), []byte("x"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Chmod(unreadable, 0o000); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = os.Chmod(unreadable, 0o755) })
+
+	if _, err := os.ReadDir(unreadable); err == nil {
+		t.Skip("could not make the directory unreadable in this environment")
+	}
+
+	notify, err := NewWatcher([]string{root})
+	assert.NilError(t, err)
+	t.Cleanup(func() { _ = notify.Close() })
+
+	if err := notify.Start(); err != nil {
+		t.Fatalf("Start() must not fail because of an unreadable directory: %v", err)
+	}
+}