os: permit RemoveAll with paths that end in ".."

Prohibiting RemoveAll with paths that end in ".." was added with
CL 137442 in this release cycle, but it worked before and it should
continue to work.

Also run TestRemoveAllDot on all systems; the test is not specific to
the use of unlinkat and friends.

Change-Id: I277784c8915cd748fec318d2936062440d5d1fde
Reviewed-on: https://go-review.googlesource.com/c/150497Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

src/os/removeall_at.go

@@ -19,7 +19,8 @@ func RemoveAll(path string) error {
 		return nil
 	}
 
-	// Not allowed in unix
+	// The rmdir system call does not permit removing ".",
+	// so we don't permit it either.
 	if endsWithDot(path) {
 		return syscall.EINVAL
 	}
@@ -130,16 +131,13 @@ func openFdAt(fd int, path string) (*File, error) {
 	return NewFile(uintptr(fd), path), nil
 }
 
+// endsWithDot returns whether the final component of path is ".".
 func endsWithDot(path string) bool {
-	if path == "." || path == ".." {
+	if path == "." {
 		return true
 	}
-	if len(path) >= 2 && path[len(path)-2:] == "/." {
+	if len(path) >= 2 && path[len(path)-1] == '.' && IsPathSeparator(path[len(path)-2]) {
 		return true
 	}
-	if len(path) >= 3 && path[len(path)-3:] == "/.." {
-		return true
-	}
-
 	return false
 }

src/os/removeall_test.go

@@ -215,13 +215,6 @@ func TestRemoveAllLongPath(t *testing.T) {
 }
 
 func TestRemoveAllDot(t *testing.T) {
-	switch runtime.GOOS {
-	case "aix", "darwin", "dragonfly", "freebsd", "linux", "netbsd", "openbsd", "solaris":
-		break
-	default:
-		t.Skip("skipping for not implemented platforms")
-	}
-
 	prevDir, err := Getwd()
 	if err != nil {
 		t.Fatalf("Could not get wd: %s", err)
@@ -242,13 +235,32 @@ func TestRemoveAllDot(t *testing.T) {
 		t.Errorf("RemoveAll succeed to remove .")
 	}
 
-	err = RemoveAll("..")
-	if err == nil {
-		t.Errorf("RemoveAll succeed to remove ..")
-	}
-
 	err = Chdir(prevDir)
 	if err != nil {
 		t.Fatalf("Could not chdir %s: %s", prevDir, err)
 	}
 }
+
+func TestRemoveAllDotDot(t *testing.T) {
+	t.Parallel()
+
+	tempDir, err := ioutil.TempDir("", "TestRemoveAllDotDot-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer RemoveAll(tempDir)
+
+	subdir := filepath.Join(tempDir, "x")
+	subsubdir := filepath.Join(subdir, "y")
+	if err := MkdirAll(subsubdir, 0777); err != nil {
+		t.Fatal(err)
+	}
+	if err := RemoveAll(filepath.Join(subsubdir, "..")); err != nil {
+		t.Error(err)
+	}
+	for _, dir := range []string{subsubdir, subdir} {
+		if _, err := Stat(dir); err == nil {
+			t.Errorf("%s: exists after RemoveAll", dir)
+		}
+	}
+}