fix(snapshots): Partly fix #544 by supporting setuid/setgid/sticky bits when snapshotting, restoring and fuse-mounting. (#2597)

Also modified an end-to-end test to also check that these extra mode flags work when snapshotting+restoring.
Manually tested fuse-mount.

Co-authored-by: Luca Citi <lciti@ieee.org>

fs/entry.go

@@ -9,6 +9,9 @@ import (
 	"github.com/pkg/errors"
 )
 
+// ModBits is a bitmask representing the mode flags supported.
+const ModBits = os.ModePerm | os.ModeSetgid | os.ModeSetuid | os.ModeSticky
+
 // ErrUnknown is returned by ErrorEntry.ErrorInfo() to indicate that type of an entry is unknown.
 var ErrUnknown = errors.Errorf("unknown or unsupported entry type")
 

internal/fusemount/fusefs.go

@@ -30,8 +30,26 @@ type fuseNode struct {
 	entry fs.Entry
 }
 
+func goModeToUnixMode(mode os.FileMode) uint32 {
+	unixmode := uint32(mode.Perm())
+
+	if mode&os.ModeSetuid != 0 {
+		unixmode |= 0o4000
+	}
+
+	if mode&os.ModeSetgid != 0 {
+		unixmode |= 0o2000
+	}
+
+	if mode&os.ModeSticky != 0 {
+		unixmode |= 0o1000
+	}
+
+	return unixmode
+}
+
 func populateAttributes(a *fuse.Attr, e fs.Entry) {
-	a.Mode = uint32(e.Mode()) & uint32(os.ModePerm)
+	a.Mode = goModeToUnixMode(e.Mode())
 	a.Size = uint64(e.Size())
 	a.Mtime = uint64(e.ModTime().Unix())
 	a.Ctime = a.Mtime

snapshot/restore/local_fs_output.go

@@ -21,7 +21,6 @@ import (
 )
 
 const (
-	modBits                           = os.ModePerm | os.ModeSetgid | os.ModeSetuid | os.ModeSticky
 	outputDirMode                     = 0o700 // default mode to create directories in before setting their ACLs
 	maxTimeDeltaToConsiderFileTheSame = 2 * time.Second
 )
@@ -273,7 +272,7 @@ func (o *FilesystemOutput) setAttributes(targetPath string, e fs.Entry, modclear
 
 	// Set file permissions from e
 	if o.shouldUpdatePermissions(le, e, modclear) {
-		if err = o.maybeIgnorePermissionError(osChmod(targetPath, (e.Mode()&modBits)&^modclear)); err != nil {
+		if err = o.maybeIgnorePermissionError(osChmod(targetPath, (e.Mode()&fs.ModBits)&^modclear)); err != nil {
 			return errors.Wrap(err, "could not change permissions on "+targetPath)
 		}
 	}
@@ -317,7 +316,7 @@ func (o *FilesystemOutput) shouldUpdatePermissions(local, remote fs.Entry, modcl
 		return false
 	}
 
-	return ((local.Mode() & modBits) &^ modclear) != (remote.Mode() & modBits)
+	return ((local.Mode() & fs.ModBits) &^ modclear) != (remote.Mode() & fs.ModBits)
 }
 
 func (o *FilesystemOutput) shouldUpdateTimes(local, remote fs.Entry) bool {

snapshot/snapshotfs/upload.go

@@ -454,7 +454,7 @@ func newDirEntry(md fs.Entry, fname string, oid object.ID) (*snapshot.DirEntry,
 	return &snapshot.DirEntry{
 		Name:        fname,
 		Type:        entryType,
-		Permissions: snapshot.Permissions(md.Mode() & os.ModePerm),
+		Permissions: snapshot.Permissions(md.Mode() & fs.ModBits),
 		FileSize:    md.Size(),
 		ModTime:     fs.UTCTimestampFromTime(md.ModTime()),
 		UserID:      md.Owner().UserID,

tests/end_to_end_test/restore_test.go

@@ -259,7 +259,7 @@ func TestSnapshotRestore(t *testing.T) {
 
 	// restoring single file
 	e.RunAndExpectSuccess(t, "snapshot", "restore", rootID+"/single-file", filepath.Join(restoreByOIDFile, "output-file"))
-	verifyFileMode(t, filepath.Join(restoreByOIDFile, "output-file"), os.FileMode(0o651))
+	verifyFileMode(t, filepath.Join(restoreByOIDFile, "output-file"), overriddenFilePermissions)
 
 	// Restore last snapshot using the snapshot ID
 	e.RunAndExpectSuccess(t, "snapshot", "restore", snapID, restoreDir)
@@ -461,22 +461,23 @@ func TestRestoreSnapshotOfSingleFile(t *testing.T) {
 	verifyFileMode(t, filepath.Join(restoreDir, "restored-2"), os.FileMode(0o653))
 
 	if runtime.GOOS != windowsOSName {
+		overriddenFilePermissions := 0o654 | os.ModeSetuid
+
 		// change source file permissions and create one more snapshot
 		// at this poing we will have multiple snapshot manifests with one root but different attributes.
-		os.Chmod(sourceFile, 0o654)
+		os.Chmod(sourceFile, overriddenFilePermissions)
 		e.RunAndExpectSuccess(t, "snapshot", "create", sourceFile)
 
 		// when restoring by root Kopia needs to pick which manifest to apply since they are conflicting
 		// We're passing --consistent-attributes which causes it to fail, since otherwise we'd restore arbitrary
 		// top-level object permissions.
 		e.RunAndExpectFailure(t, "snapshot", "restore", rootID, "--consistent-attributes", filepath.Join(restoreDir, "restored-3"))
+
+		// Without the flag kopia picks the attributes from the latest snapshot.
+		e.RunAndExpectSuccess(t, "snapshot", "restore", rootID, filepath.Join(restoreDir, "restored-3"))
+		verifyFileMode(t, filepath.Join(restoreDir, "restored-3"), overriddenFilePermissions)
 	}
 
-	// Without the flag kopia picks the attributes from the latest snapshot.
-	e.RunAndExpectSuccess(t, "snapshot", "restore", rootID, filepath.Join(restoreDir, "restored-3"))
-
-	verifyFileMode(t, filepath.Join(restoreDir, "restored-3"), os.FileMode(0o654))
-
 	// restoring using snapshot ID is unambiguous and always produces file with 0o653
 	e.RunAndExpectSuccess(t, "snapshot", "restore", snapID, filepath.Join(restoreDir, "restored-4"))
 	verifyFileMode(t, filepath.Join(restoreDir, "restored-4"), os.FileMode(0o653))