teleport/lib/utils/fs.go

/*
 * Teleport
 * Copyright (C) 2023  Gravitational, Inc.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package utils

import (
	"context"
	"crypto/rand"
	"errors"
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"runtime"
	"strings"
	"syscall"
	"time"

	"github.com/gofrs/flock"
	"github.com/gravitational/trace"

	"github.com/gravitational/teleport"
)

// ErrUnsuccessfulLockTry designates an error when we temporarily couldn't acquire lock
// (most probably it was already locked by someone else), another try might succeed.
var ErrUnsuccessfulLockTry = errors.New("could not acquire lock on the file at this time")

const (
	// FSLockRetryDelay is a delay between attempts to acquire lock.
	FSLockRetryDelay = 10 * time.Millisecond
)

// OpenFileWithFlagsFunc defines a function used to open files providing options.
type OpenFileWithFlagsFunc func(name string, flag int, perm os.FileMode) (*os.File, error)

// EnsureLocalPath makes sure the path exists, or, if omitted results in the subpath in
// default gravity config directory, e.g.
//
// EnsureLocalPath("/custom/myconfig", ".gravity", "config") -> /custom/myconfig
// EnsureLocalPath("", ".gravity", "config") -> ${HOME}/.gravity/config
//
// It also makes sure that base dir exists
func EnsureLocalPath(customPath string, defaultLocalDir, defaultLocalPath string) (string, error) {
	if customPath == "" {
		homeDir, err := os.UserHomeDir()
		if err != nil || homeDir == "" {
			return "", trace.BadParameter("could not get user home dir: %v", err)
		}
		customPath = filepath.Join(homeDir, defaultLocalDir, defaultLocalPath)
	}
	baseDir := filepath.Dir(customPath)
	_, err := StatDir(baseDir)
	if err != nil {
		if trace.IsNotFound(err) {
			if err := os.MkdirAll(baseDir, teleport.PrivateDirMode); err != nil {
				return "", trace.ConvertSystemError(err)
			}
		} else {
			return "", trace.Wrap(err)
		}
	}
	return customPath, nil
}

// IsDir is a helper function to quickly check if a given path is a valid directory
func IsDir(path string) bool {
	fi, err := os.Stat(path)
	if err == nil {
		return fi.IsDir()
	}
	return false
}

// NormalizePath normalises path, evaluating symlinks and converting local
// paths to absolute
func NormalizePath(path string, evaluateSymlinks bool) (string, error) {
	s, err := filepath.Abs(path)
	if err != nil {
		return "", trace.ConvertSystemError(err)
	}
	if evaluateSymlinks {
		s, err = filepath.EvalSymlinks(s)
		if err != nil {
			return "", trace.ConvertSystemError(err)
		}
	}
	return s, nil
}

// OpenFileAllowingUnsafeLinks opens a file, if the path includes a symlink, the returned os.File will be resolved to
// the actual file.  This will return an error if the file is not found or is a directory.
func OpenFileAllowingUnsafeLinks(path string) (*os.File, error) {
	return openFile(path, true /* allowSymlink */, true /* allowMultipleHardlinks */)
}

// OpenFileNoUnsafeLinks opens a file, ensuring it's an actual file and not a directory or symlink.  Depending on
// the os, it may also prevent hardlinks.  This is important because MacOS allows hardlinks without validating write
// permissions (similar to a symlink in that regard).
func OpenFileNoUnsafeLinks(path string) (*os.File, error) {
	return openFile(path, false /* allowSymlink */, runtime.GOOS != "darwin" /* allowMultipleHardlinks */)
}

func openFile(path string, allowSymlink, allowMultipleHardlinks bool) (*os.File, error) {
	newPath, err := NormalizePath(path, allowSymlink)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	var fi os.FileInfo
	if allowSymlink {
		fi, err = os.Stat(newPath)
		if err != nil {
			return nil, trace.ConvertSystemError(err)
		}
	} else {
		components := strings.Split(newPath, string(os.PathSeparator))
		var subPath string
		for _, p := range components {
			subPath = filepath.Join(subPath, p)
			if subPath == "" {
				subPath = string(os.PathSeparator)
			}

			fi, err = os.Lstat(subPath)
			if err != nil {
				return nil, trace.ConvertSystemError(err)
			} else if fi.Mode().Type()&os.ModeSymlink != 0 {
				return nil, trace.BadParameter("opening file %s, symlink not allowed in path: %s", path, subPath)
			}
		}
	}
	if !allowMultipleHardlinks {
		// hardlinks can only exist at the end file, not for directories within the path
		if linkCount, ok := getHardLinkCount(fi); ok && linkCount > 1 {
			return nil, trace.BadParameter("file has hardlink count greater than 1: %s", path)
		}
	}
	if fi.IsDir() {
		return nil, trace.BadParameter("%s is not a file", path)
	}
	f, err := os.Open(newPath)
	if err != nil {
		return nil, trace.ConvertSystemError(err)
	}
	return f, nil
}

// StatFile stats path, returns error if it exists but a directory.
func StatFile(path string) (os.FileInfo, error) {
	newPath, err := NormalizePath(path, true)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	fi, err := os.Stat(newPath)
	if err != nil {
		return nil, trace.ConvertSystemError(err)
	}
	if fi.IsDir() {
		return nil, trace.BadParameter("%v is not a file", path)
	}
	return fi, nil
}

// StatDir stats directory, returns error if file exists, but not a directory
func StatDir(path string) (os.FileInfo, error) {
	fi, err := os.Stat(path)
	if err != nil {
		return nil, trace.ConvertSystemError(err)
	}
	if !fi.IsDir() {
		return nil, trace.BadParameter("%v is not a directory", path)
	}
	return fi, nil
}

// FSTryWriteLock tries to grab write lock, returns ErrUnsuccessfulLockTry
// if lock is already acquired by someone else
func FSTryWriteLock(filePath string) (unlock func() error, err error) {
	fileLock := flock.New(getPlatformLockFilePath(filePath))
	locked, err := fileLock.TryLock()
	if err != nil {
		return nil, trace.ConvertSystemError(err)
	}
	if !locked {
		return nil, trace.Retry(ErrUnsuccessfulLockTry, "")
	}

	return fileLock.Unlock, nil
}

// FSTryWriteLockTimeout tries to grab write lock, it's doing it until locks is acquired, or timeout is expired,
// or context is expired.
func FSTryWriteLockTimeout(ctx context.Context, filePath string, timeout time.Duration) (unlock func() error, err error) {
	fileLock := flock.New(getPlatformLockFilePath(filePath))
	timedCtx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()
	if _, err := fileLock.TryLockContext(timedCtx, FSLockRetryDelay); err != nil {
		return nil, trace.ConvertSystemError(err)
	}

	return fileLock.Unlock, nil
}

// FSTryReadLock tries to grab write lock, returns ErrUnsuccessfulLockTry
// if lock is already acquired by someone else
func FSTryReadLock(filePath string) (unlock func() error, err error) {
	fileLock := flock.New(getPlatformLockFilePath(filePath))
	locked, err := fileLock.TryRLock()
	if err != nil {
		return nil, trace.ConvertSystemError(err)
	}
	if !locked {
		return nil, trace.Retry(ErrUnsuccessfulLockTry, "")
	}

	return fileLock.Unlock, nil
}

// FSTryReadLockTimeout tries to grab read lock, it's doing it until locks is acquired, or timeout is expired,
// or context is expired.
func FSTryReadLockTimeout(ctx context.Context, filePath string, timeout time.Duration) (unlock func() error, err error) {
	fileLock := flock.New(getPlatformLockFilePath(filePath))
	timedCtx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()
	if _, err := fileLock.TryRLockContext(timedCtx, FSLockRetryDelay); err != nil {
		return nil, trace.ConvertSystemError(err)
	}

	return fileLock.Unlock, nil
}

// RemoveAllSecure is similar to [os.RemoveAll] but leverages [RemoveSecure] to delete files so that they are
// overwritten.  This helps guard against hardware attacks on magnetic disks.
func RemoveAllSecure(path string) error {
	if path == "" {
		// match behavior from os.RemoveAll
		return nil
	}
	// Match os.RemoveAll protections in not permitting removal of "." directories
	// This check comes directly from https://cs.opensource.google/go/go/+/refs/tags/go1.21.1:src/os/removeall_at.go;l=24
	if path == "." || (len(path) >= 2 && path[len(path)-1] == '.' && os.IsPathSeparator(path[len(path)-2])) {
		return &os.PathError{Op: "RemoveAllSecure", Path: path, Err: syscall.EINVAL} // error type matches os.RemoveAll
	}

	info, err := os.Lstat(path)
	switch {
	case err != nil && os.IsNotExist(err):
		return nil
	case err != nil:
		return trace.ConvertSystemError(err)
	case !info.IsDir():
		return removeSecure(path, info)
	}
	var removeErrors []error
	files, err := os.ReadDir(path)
	if err != nil {
		// Don't fail fast, allow removal at end to be attempted.
		removeErrors = append(removeErrors, err)
	}
	// It's possible for a partial file list to be returned even if an error above was returned.
	for _, f := range files {
		if err := RemoveAllSecure(filepath.Join(path, f.Name())); err != nil {
			removeErrors = append(removeErrors, err)
		}
	}
	if err := os.Remove(path); err != nil {
		removeErrors = append(removeErrors, err)
	}
	switch len(removeErrors) {
	case 1:
		return trace.ConvertSystemError(removeErrors[0])
	case 0:
		return nil
	default:
		return trace.NewAggregate(removeErrors...)
	}
}

// RemoveSecure attempts to securely delete the file by first overwriting the file with random data three times
// followed by calling os.Remove(filePath).
func RemoveSecure(filePath string) error {
	info, err := os.Lstat(filePath)
	if err != nil && os.IsNotExist(err) {
		return err
	}
	// Don't fast return on other errors, still allow removeSecure to attempt removal.
	return removeSecure(filePath, info)
}

func removeSecure(filePath string, fi os.FileInfo) error {
	if fi.Mode().Type()&os.ModeSymlink != 0 {
		return os.Remove(filePath)
	}
	f, openErr := os.OpenFile(filePath, os.O_WRONLY, 0)
	switch {
	case os.IsNotExist(openErr):
		return trace.ConvertSystemError(openErr)
	case openErr != nil:
		// Attempt delete anyway.
		return trace.ConvertSystemError(os.Remove(filePath))
	}
	defer f.Close()

	if runtime.GOOS == "windows" {
		// Windows can't unlink the file before overwriting.
		if f != nil {
			for i := 0; i < 3; i++ {
				if err := overwriteFile(f, fi); err != nil {
					break
				}
			}
		}
		// The file should be closed before removing it on Windows.
		closeErr := trace.ConvertSystemError(f.Close())
		removeErr := trace.ConvertSystemError(os.Remove(filePath))
		return trace.NewAggregate(closeErr, removeErr)
	} else {
		removeErr := os.Remove(filePath)
		if f != nil {
			for i := 0; i < 3; i++ {
				if err := overwriteFile(f, fi); err != nil {
					break
				}
			}
		}
		return trace.ConvertSystemError(removeErr)
	}
}

func overwriteFile(f *os.File, fi os.FileInfo) error {
	// Rounding up to 4k to hide the original file size. 4k was chosen because it's a common block size.
	const block = 4096
	size := fi.Size() / block * block
	if fi.Size()%block != 0 {
		size += block
	}

	_, copyErr := io.CopyN(f, rand.Reader, size)

	// Attempt sync regardless of above error
	syncErr := f.Sync() // sync to ensure commit to hardware
	if copyErr != nil {
		return trace.Wrap(copyErr)
	} else if syncErr != nil {
		return trace.Wrap(syncErr)
	}
	return nil
}

// RemoveFileIfExist removes file if exits.
func RemoveFileIfExist(filePath string) error {
	if !FileExists(filePath) {
		return nil
	}
	if err := os.Remove(filePath); err != nil {
		return trace.ConvertSystemError(err)
	}
	return nil
}

func RecursiveChown(dir string, uid, gid int) error {
	// First, walk the directory to gather a list of files and directories to update before we open up to modifications
	var pathsToUpdate []string
	err := filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return trace.Wrap(err)
		}
		pathsToUpdate = append(pathsToUpdate, path)
		return nil
	})
	if err != nil {
		return trace.Wrap(err)
	}

	// filepath.WalkDir is documented to walk the paths in lexical order, iterating
	// in the reverse order ensures that files are always Lchowned before their parent directory
	for i := len(pathsToUpdate) - 1; i >= 0; i-- {
		path := pathsToUpdate[i]
		if err := os.Lchown(path, uid, gid); err != nil {
			if errors.Is(err, os.ErrNotExist) {
				// Unexpected condition where file was removed after discovery.
				continue
			}
			return trace.Wrap(err)
		}
	}
	return nil
}

func CopyFile(src, dest string, perm os.FileMode) error {
	srcFile, err := os.Open(src)
	if err != nil {
		return trace.ConvertSystemError(err)
	}
	destFile, err := os.OpenFile(dest, os.O_RDWR|os.O_CREATE|os.O_TRUNC, perm)
	if err != nil {
		return trace.ConvertSystemError(err)
	}
	_, err = destFile.ReadFrom(srcFile)
	if err != nil {
		return trace.ConvertSystemError(err)
	}
	return nil
}

// RecursivelyCopy will copy a directory from src to dest, if the
// directory exists, files will be overwritten. The skip paramater, if
// provided, will be passed the source and destination paths, and will
// skip files upon returning true
func RecursiveCopy(src, dest string, skip func(src, dest string) (bool, error)) error {
	return trace.Wrap(fs.WalkDir(os.DirFS(src), ".", func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return trace.Wrap(err)
		}

		absSrcPath := filepath.Join(src, path)
		destPath := filepath.Join(dest, path)
		info, err := d.Info()
		if err != nil {
			return trace.Wrap(err)
		}
		originalPerm := info.Mode().Perm()

		if skip != nil {
			doSkip, err := skip(absSrcPath, destPath)
			if err != nil {
				return trace.Wrap(err)
			}
			if doSkip {
				return nil
			}
		}

		if d.IsDir() {
			err := os.Mkdir(destPath, originalPerm)
			if os.IsExist(err) {
				return nil
			}
			return trace.ConvertSystemError(err)
		}

		if d.Type().IsRegular() {
			if err := CopyFile(absSrcPath, destPath, originalPerm); err != nil {
				return trace.Wrap(err)
			}
			return nil
		}

		if info.Mode().Type()&os.ModeSymlink != 0 {
			linkDest, err := os.Readlink(absSrcPath)
			if err != nil {
				return trace.ConvertSystemError(err)
			}
			if err := os.Symlink(linkDest, destPath); err != nil {
				return trace.ConvertSystemError(err)
			}
			return nil
		}

		return nil
	}))
}