1 // MsgSyncReq: copy files to the remote host
3 // Copyright (C) 2021 Simon Ruderich
5 // This program is free software: you can redistribute it and/or modify
6 // it under the terms of the GNU General Public License as published by
7 // the Free Software Foundation, either version 3 of the License, or
8 // (at your option) any later version.
10 // This program is distributed in the hope that it will be useful,
11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 // GNU General Public License for more details.
15 // You should have received a copy of the GNU General Public License
16 // along with this program. If not, see <http://www.gnu.org/licenses/>.
36 "github.com/ianbruene/go-difflib/difflib"
38 "ruderich.org/simon/safcm"
41 func (s *Sync) syncFiles() error {
42 // To create random file names for symlinks
43 rand.Seed(time.Now().UnixNano())
45 // Sort for deterministic order and so parent directories are present
46 // when files in them are created
47 var files []*safcm.File
48 for _, x := range s.req.Files {
49 files = append(files, x)
51 sort.Slice(files, func(i, j int) bool {
52 return files[i].Path < files[j].Path
55 for _, x := range files {
57 err := s.syncFile(x, &changed)
59 return fmt.Errorf("%q: %v", x.Path, err)
69 func (s *Sync) syncFile(file *safcm.File, changed *bool) error {
70 // The general strategy is "update by rename": If any property of a
71 // file changes it will be written to a temporary file and then
72 // renamed "over" the original file. This is simple and prevents race
73 // conditions where the file is partially readable while changes to
74 // permissions or owner/group are applied. However, this strategy does
75 // not work for directories which must be removed first (was
76 // directory), must remove the existing file (will be directory) or
77 // must be directly modified (changed permissions or owner). In the
78 // first two cases the old path is removed. In the last the directory
79 // is modified (carefully) in place.
81 // The implementation is careful not to follow any symlinks to prevent
82 // possible race conditions which can be exploited and are especially
83 // dangerous when running with elevated privileges (which will most
84 // likely be the case).
86 err := s.fileResolveIds(file)
91 change := safcm.FileChange{
93 New: safcm.FileChangeInfo{
102 debugf := func(format string, a ...interface{}) {
103 s.log.Debugf("files: %q (%s): %s",
104 file.Path, file.OrigGroup, fmt.Sprintf(format, a...))
106 verbosef := func(format string, a ...interface{}) {
107 s.log.Verbosef("files: %q (%s): %s",
108 file.Path, file.OrigGroup, fmt.Sprintf(format, a...))
111 var oldStat fs.FileInfo
113 oldFh, err := OpenFileNoFollow(file.Path)
115 err := err.(*fs.PathError)
116 if err.Err == syscall.ELOOP {
117 // Check if ELOOP was caused not by O_NOFOLLOW but by
118 // too many nested symlinks before the final path
120 x, err := os.Lstat(file.Path)
124 if x.Mode().Type() != fs.ModeSymlink {
125 debugf("type changed from symlink to %s, retry",
129 // ELOOP from symbolic link, this is fine
131 } else if os.IsNotExist(err) {
132 change.Created = true
133 debugf("will create")
140 x, err := oldFh.Stat()
148 var changeType, changePerm, changeUserOrGroup, changeData bool
150 // Compare permissions
151 change.Old.Mode = oldStat.Mode()
152 if change.Old.Mode != file.Mode {
153 if change.Old.Mode.Type() != file.Mode.Type() {
155 debugf("type differs %s -> %s",
156 change.Old.Mode.Type(),
159 // Be careful with .Perm() which does not
160 // contain the setuid/setgid/sticky bits!
162 debugf("permission differs %s -> %s",
163 change.Old.Mode, file.Mode)
167 // Compare user/group
168 x, ok := oldStat.Sys().(*syscall.Stat_t)
170 return fmt.Errorf("unsupported Stat().Sys()")
172 change.Old.Uid = int(x.Uid)
173 change.Old.Gid = int(x.Gid)
174 if change.Old.Uid != file.Uid || change.Old.Gid != file.Gid {
175 changeUserOrGroup = true
176 debugf("uid/gid differs %d/%d -> %d/%d",
177 change.Old.Uid, change.Old.Gid,
180 u, g, err := resolveIdsToNames(change.Old.Uid, change.Old.Gid)
181 // Errors are not relevant as this is only used to report the
182 // change. If the user/group no longer exits only the ids will
189 // Compare file content (if possible)
190 switch change.Old.Mode.Type() {
191 case 0: // regular file
192 x, err := io.ReadAll(oldFh)
194 return fmt.Errorf("reading old content: %v",
199 x, err := os.Readlink(file.Path)
201 return fmt.Errorf("reading old content: %v",
206 if !changeType && file.Mode.Type() != fs.ModeDir {
207 if !bytes.Equal(oldData, file.Data) {
209 debugf("content differs")
213 oldStat = nil // prevent accidental use
216 if !change.Created && !changeType &&
217 !changePerm && !changeUserOrGroup &&
224 // Don't show a diff with the full content for newly created files or
225 // on type changes. This is just noise for the user as the new file
226 // content is obvious. But we always want to see a diff when files are
227 // replaced because this destroys data.
228 if !change.Created &&
229 (change.Old.Mode.Type() == 0 ||
230 change.Old.Mode.Type() == fs.ModeSymlink) {
231 change.DataDiff, err = diffData(oldData, file.Data)
237 // Add change here so it is stored even when applying it fails. This
238 // way the user knows exactly what was attempted.
239 s.resp.FileChanges = append(s.resp.FileChanges, change)
248 debugf("dry-run, skipping changes")
252 // We cannot rename over directories and vice versa
253 if changeType && (change.Old.Mode.IsDir() || file.Mode.IsDir()) {
254 debugf("removing (due to type change)")
255 err := os.RemoveAll(file.Path)
261 // Directory: create new directory (also type change to directory)
262 if file.Mode.IsDir() && (change.Created || changeType) {
263 debugf("creating directory")
264 err := os.Mkdir(file.Path, 0700)
268 // We must be careful not to chmod arbitrary files. If the
269 // target directory is writable then it might have changed to
270 // a symlink at this point. There's no lchmod so open the
272 debugf("chmodding %s", file.Mode)
273 dh, err := OpenFileNoFollow(file.Path)
277 err = dh.Chmod(file.Mode)
282 // Less restrictive access is not relevant here because there
283 // are no files present yet.
284 debugf("chowning %d/%d", file.Uid, file.Gid)
285 err = dh.Chown(file.Uid, file.Gid)
293 // Directory: changed permission or user/group
294 if file.Mode.IsDir() {
295 // We don't know if the new permission or if the new
296 // user/group is more restrictive (e.g. root:root 0750 ->
297 // user:group 0700; applying group first gives group
298 // unexpected access). To prevent a short window where the
299 // access might be too lax we temporarily deny all access.
300 if changePerm && changeUserOrGroup {
301 // Only drop group and other permission because user
302 // has access anyway (either before or after the
303 // change). This also prevents temporary errors during
304 // the error when the user tries to access this
305 // directory (access for the group will fail though).
306 mode := change.Old.Mode & fs.ModePerm & 0700
307 debugf("chmodding %#o (temporary)", mode)
308 err := oldFh.Chmod(mode)
313 if changeUserOrGroup {
314 debugf("chowning %d/%d", file.Uid, file.Gid)
315 err := oldFh.Chown(file.Uid, file.Gid)
321 debugf("chmodding %s", file.Mode)
322 err := oldFh.Chmod(file.Mode)
330 dir := filepath.Dir(file.Path)
331 // Create hidden file which should be ignored by most other tools and
332 // thus not affect anything during creation
333 base := "." + filepath.Base(file.Path)
336 switch file.Mode.Type() {
337 case 0: // regular file
338 debugf("creating temporary file %q",
339 filepath.Join(dir, base+"*"))
340 newFh, err := os.CreateTemp(dir, base)
344 tmpPath = newFh.Name()
346 _, err = newFh.Write(file.Data)
352 // CreateTemp() creates the file with 0600
353 err = newFh.Chown(file.Uid, file.Gid)
359 err = newFh.Chmod(file.Mode)
381 // Similar to os.CreateTemp() but for symlinks which we cannot
383 tmpPath = filepath.Join(dir,
384 base+strconv.Itoa(rand.Int()))
385 debugf("creating temporary symlink %q", tmpPath)
386 err := os.Symlink(string(file.Data), tmpPath)
388 if os.IsExist(err) && i < 10000 {
394 err = os.Lchown(tmpPath, file.Uid, file.Gid)
399 // Permissions are irrelevant for symlinks
402 panic(fmt.Sprintf("invalid file type %s", file.Mode))
405 debugf("renaming %q", tmpPath)
406 err = os.Rename(tmpPath, file.Path)
419 func (s *Sync) fileResolveIds(file *safcm.File) error {
420 if file.User != "" && file.Uid != -1 {
421 return fmt.Errorf("cannot set both User (%q) and Uid (%d)",
424 if file.Group != "" && file.Gid != -1 {
425 return fmt.Errorf("cannot set both Group (%q) and Gid (%d)",
426 file.Group, file.Gid)
429 if file.User == "" && file.Uid == -1 {
430 file.User = s.defaultUser
433 x, err := user.Lookup(file.User)
437 id, err := strconv.Atoi(x.Uid)
444 if file.Group == "" && file.Gid == -1 {
445 file.Group = s.defaultGroup
447 if file.Group != "" {
448 x, err := user.LookupGroup(file.Group)
452 id, err := strconv.Atoi(x.Gid)
462 func resolveIdsToNames(uid, gid int) (string, string, error) {
463 u, err := user.LookupId(strconv.Itoa(uid))
467 g, err := user.LookupGroupId(strconv.Itoa(gid))
471 return u.Username, g.Name, nil
474 func diffData(oldData []byte, newData []byte) (string, error) {
475 oldBin := !strings.HasPrefix(http.DetectContentType(oldData), "text/")
476 newBin := !strings.HasPrefix(http.DetectContentType(newData), "text/")
477 if oldBin && newBin {
478 return "Binary files differ, cannot show diff", nil
481 oldData = []byte("<binary content>\n")
484 newData = []byte("<binary content>\n")
487 // TODO: difflib shows empty context lines at the end of the file
488 // which should not be there
489 // TODO: difflib has issues with missing newlines in either side
490 result, err := difflib.GetUnifiedDiffString(difflib.LineDiffParams{
491 A: difflib.SplitLines(string(oldData)),
492 B: difflib.SplitLines(string(newData)),
501 func OpenFileNoFollow(path string) (*os.File, error) {
502 return os.OpenFile(path,
503 // O_NOFOLLOW prevents symlink attacks
504 // O_NONBLOCK is necessary to prevent blocking on FIFOs
505 os.O_RDONLY|syscall.O_NOFOLLOW|syscall.O_NONBLOCK, 0)
508 // syncPath syncs path, which should be a directory. To guarantee durability
509 // it must be called on a parent directory after adding, renaming or removing
512 // Calling sync on the files itself is not enough according to POSIX; man 2
513 // fsync: "Calling fsync() does not necessarily ensure that the entry in the
514 // directory containing the file has also reached disk. For that an explicit
515 // fsync() on a file descriptor for the directory is also needed."
516 func syncPath(path string) error {
517 x, err := os.Open(path)
522 closeErr := x.Close()