8559e20237
Instead, trust (and test) that the temp file has appropriate permissions from the start. The only place where this changes our behavior is for ignores which go from 0644 to 0600. I'm OK with that. GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3756
108 lines
2.7 KiB
Go
108 lines
2.7 KiB
Go
// Copyright (C) 2015 The Syncthing Authors.
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this file,
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// You can obtain one at http://mozilla.org/MPL/2.0/.
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package osutil
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import (
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"errors"
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"io/ioutil"
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"os"
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"path/filepath"
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"runtime"
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)
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var (
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ErrClosed = errors.New("write to closed writer")
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TempPrefix = ".syncthing.tmp."
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)
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// An AtomicWriter is an *os.File that writes to a temporary file in the same
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// directory as the final path. On successful Close the file is renamed to
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// it's final path. Any error on Write or during Close is accumulated and
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// returned on Close, so a lazy user can ignore errors until Close.
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type AtomicWriter struct {
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path string
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next *os.File
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err error
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}
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// CreateAtomic is like os.Create, except a temporary file name is used
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// instead of the given name. The file is created with secure (0600)
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// permissions.
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func CreateAtomic(path string) (*AtomicWriter, error) {
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// The security of this depends on the tempfile having secure
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// permissions, 0600, from the beginning. This is what ioutil.TempFile
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// does. We have a test that verifies that that is the case, should this
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// ever change in the standard library in the future.
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fd, err := ioutil.TempFile(filepath.Dir(path), TempPrefix)
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if err != nil {
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return nil, err
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}
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w := &AtomicWriter{
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path: path,
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next: fd,
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}
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return w, nil
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}
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// Write is like io.Writer, but is a no-op on an already failed AtomicWriter.
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func (w *AtomicWriter) Write(bs []byte) (int, error) {
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if w.err != nil {
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return 0, w.err
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}
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n, err := w.next.Write(bs)
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if err != nil {
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w.err = err
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w.next.Close()
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}
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return n, err
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}
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// Close closes the temporary file and renames it to the final path. It is
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// invalid to call Write() or Close() after Close().
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func (w *AtomicWriter) Close() error {
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if w.err != nil {
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return w.err
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}
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// Try to not leave temp file around, but ignore error.
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defer os.Remove(w.next.Name())
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if err := w.next.Sync(); err != nil {
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w.err = err
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return err
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}
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if err := w.next.Close(); err != nil {
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w.err = err
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return err
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}
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// Remove the destination file, on Windows only. If it fails, and not due
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// to the file not existing, we won't be able to complete the rename
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// either. Return this error because it may be more informative. On non-
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// Windows we want the atomic rename behavior so we don't attempt remove.
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if runtime.GOOS == "windows" {
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if err := os.Remove(w.path); err != nil && !os.IsNotExist(err) {
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return err
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}
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}
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if err := os.Rename(w.next.Name(), w.path); err != nil {
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w.err = err
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return err
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}
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SyncDir(filepath.Dir(w.next.Name()))
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// Set w.err to return appropriately for any future operations.
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w.err = ErrClosed
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return nil
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}
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