os: add support for long path names on unix RemoveAll

On unix systems, long enough path names will fail when performing syscalls
like `Lstat`. The current RemoveAll uses several of these syscalls, and so
will fail for long paths. This can be risky, as it can let users "hide"
files from the system or otherwise make long enough paths for programs
to fail. By using `Unlinkat` and `Openat` syscalls instead, RemoveAll is
safer on unix systems. Initially implemented for linux, darwin, dragonfly,
netbsd and openbsd. Not yet implemented on freebsd due to fstatat 64-bit
inode compatibility issues.

Fixes #27029

Co-authored-by: Giuseppe Capizzi <gcapizzi@pivotal.io>
Co-authored-by: Julia Nedialkova <yulia.nedyalkova@sap.com>

Change-Id: I978a6a4986878fe076d3c7af86e7927675624a96
GitHub-Last-Rev: 9235489c81b90c228210144b7c25b28a46bb80b7
GitHub-Pull-Request: golang/go#28494
Reviewed-on: https://go-review.googlesource.com/c/146020
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 237 insertions, 0 deletions

diff --git a/src/os/removeall_test.go b/src/os/removeall_test.go
new file mode 100644
index 0000000000..a1006230da
--- /dev/null
+++ b/src/os/removeall_test.go
@@ -0,0 +1,237 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+	"fmt"
+	"io/ioutil"
+	. "os"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestRemoveAll(t *testing.T) {
+	tmpDir := TempDir()
+	// Work directory.
+	file := "file"
+	path := tmpDir + "/_TestRemoveAll_"
+	fpath := path + "/file"
+	dpath := path + "/dir"
+
+	// Make a regular file and remove
+	fd, err := Create(file)
+	if err != nil {
+		t.Fatalf("create %q: %s", file, err)
+	}
+	fd.Close()
+	if err = RemoveAll(file); err != nil {
+		t.Fatalf("RemoveAll %q (first): %s", file, err)
+	}
+	if _, err = Lstat(file); err == nil {
+		t.Fatalf("Lstat %q succeeded after RemoveAll (first)", file)
+	}
+
+	// Make directory with 1 file and remove.
+	if err := MkdirAll(path, 0777); err != nil {
+		t.Fatalf("MkdirAll %q: %s", path, err)
+	}
+	fd, err = Create(fpath)
+	if err != nil {
+		t.Fatalf("create %q: %s", fpath, err)
+	}
+	fd.Close()
+	if err = RemoveAll(path); err != nil {
+		t.Fatalf("RemoveAll %q (second): %s", path, err)
+	}
+	if _, err = Lstat(path); err == nil {
+		t.Fatalf("Lstat %q succeeded after RemoveAll (second)", path)
+	}
+
+	// Make directory with file and subdirectory and remove.
+	if err = MkdirAll(dpath, 0777); err != nil {
+		t.Fatalf("MkdirAll %q: %s", dpath, err)
+	}
+	fd, err = Create(fpath)
+	if err != nil {
+		t.Fatalf("create %q: %s", fpath, err)
+	}
+	fd.Close()
+	fd, err = Create(dpath + "/file")
+	if err != nil {
+		t.Fatalf("create %q: %s", fpath, err)
+	}
+	fd.Close()
+	if err = RemoveAll(path); err != nil {
+		t.Fatalf("RemoveAll %q (third): %s", path, err)
+	}
+	if _, err := Lstat(path); err == nil {
+		t.Fatalf("Lstat %q succeeded after RemoveAll (third)", path)
+	}
+
+	// Determine if we should run the following test.
+	testit := true
+	if runtime.GOOS == "windows" {
+		// Chmod is not supported under windows.
+		testit = false
+	} else {
+		// Test fails as root.
+		testit = Getuid() != 0
+	}
+	if testit {
+		// Make directory with file and subdirectory and trigger error.
+		if err = MkdirAll(dpath, 0777); err != nil {
+			t.Fatalf("MkdirAll %q: %s", dpath, err)
+		}
+
+		for _, s := range []string{fpath, dpath + "/file1", path + "/zzz"} {
+			fd, err = Create(s)
+			if err != nil {
+				t.Fatalf("create %q: %s", s, err)
+			}
+			fd.Close()
+		}
+		if err = Chmod(dpath, 0); err != nil {
+			t.Fatalf("Chmod %q 0: %s", dpath, err)
+		}
+
+		// No error checking here: either RemoveAll
+		// will or won't be able to remove dpath;
+		// either way we want to see if it removes fpath
+		// and path/zzz. Reasons why RemoveAll might
+		// succeed in removing dpath as well include:
+		//	* running as root
+		//	* running on a file system without permissions (FAT)
+		RemoveAll(path)
+		Chmod(dpath, 0777)
+
+		for _, s := range []string{fpath, path + "/zzz"} {
+			if _, err = Lstat(s); err == nil {
+				t.Fatalf("Lstat %q succeeded after partial RemoveAll", s)
+			}
+		}
+	}
+	if err = RemoveAll(path); err != nil {
+		t.Fatalf("RemoveAll %q after partial RemoveAll: %s", path, err)
+	}
+	if _, err = Lstat(path); err == nil {
+		t.Fatalf("Lstat %q succeeded after RemoveAll (final)", path)
+	}
+}
+
+// Test RemoveAll on a large directory.
+func TestRemoveAllLarge(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+
+	tmpDir := TempDir()
+	// Work directory.
+	path := tmpDir + "/_TestRemoveAllLarge_"
+
+	// Make directory with 1000 files and remove.
+	if err := MkdirAll(path, 0777); err != nil {
+		t.Fatalf("MkdirAll %q: %s", path, err)
+	}
+	for i := 0; i < 1000; i++ {
+		fpath := fmt.Sprintf("%s/file%d", path, i)
+		fd, err := Create(fpath)
+		if err != nil {
+			t.Fatalf("create %q: %s", fpath, err)
+		}
+		fd.Close()
+	}
+	if err := RemoveAll(path); err != nil {
+		t.Fatalf("RemoveAll %q: %s", path, err)
+	}
+	if _, err := Lstat(path); err == nil {
+		t.Fatalf("Lstat %q succeeded after RemoveAll", path)
+	}
+}
+
+func TestRemoveAllLongPath(t *testing.T) {
+	switch runtime.GOOS {
+	case "linux", "darwin", "openbsd", "netbsd", "dragonfly":
+		break
+	default:
+		t.Skip("skipping for not implemented platforms")
+	}
+
+	prevDir, err := Getwd()
+	if err != nil {
+		t.Fatalf("Could not get wd: %s", err)
+	}
+
+	startPath, err := ioutil.TempDir("", "TestRemoveAllLongPath-")
+	if err != nil {
+		t.Fatalf("Could not create TempDir: %s", err)
+	}
+	err = Chdir(startPath)
+	if err != nil {
+		t.Fatalf("Could not chdir %s: %s", startPath, err)
+	}
+
+	// Removing paths with over 4096 chars commonly fails
+	for i := 0; i < 41; i++ {
+		name := strings.Repeat("a", 100)
+
+		err = Mkdir(name, 0755)
+		if err != nil {
+			t.Fatalf("Could not mkdir %s: %s", name, err)
+		}
+
+		err = Chdir(name)
+		if err != nil {
+			t.Fatalf("Could not chdir %s: %s", name, err)
+		}
+	}
+
+	err = Chdir(prevDir)
+	if err != nil {
+		t.Fatalf("Could not chdir %s: %s", prevDir, err)
+	}
+
+	err = RemoveAll(startPath)
+	if err != nil {
+		t.Errorf("RemoveAll could not remove long file path %s: %s", startPath, err)
+	}
+}
+
+func TestRemoveAllDot(t *testing.T) {
+	switch runtime.GOOS {
+	case "linux", "darwin", "openbsd", "netbsd", "dragonfly":
+		break
+	default:
+		t.Skip("skipping for not implemented platforms")
+	}
+
+	prevDir, err := Getwd()
+	if err != nil {
+		t.Fatalf("Could not get wd: %s", err)
+	}
+	tempDir, err := ioutil.TempDir("", "TestRemoveAllDot-")
+	if err != nil {
+		t.Fatalf("Could not create TempDir: %s", err)
+	}
+	err = Chdir(tempDir)
+	if err != nil {
+		t.Fatalf("Could not chdir to tempdir: %s", err)
+	}
+
+	err = RemoveAll(".")
+	if err == nil {
+		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)
+	}
+}