fusefrontend: mark symlink-safe FUSE calls

Document which FUSE calls are already symlink-safe in
the function comment.

3 files changed, 32 insertions, 20 deletions

diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
index d2f4867..8e443b7 100644
--- a/internal/fusefrontend/fs.go
+++ b/internal/fusefrontend/fs.go
@@ -120,7 +120,9 @@ func (fs *FS) mangleOpenFlags(flags uint32) (newFlags int) {
 	return newFlags
 }
 
-// Open implements pathfs.Filesystem.
+// Open - FUSE call. Open already-existing file.
+//
+// Symlink-safe through Openat().
 func (fs *FS) Open(path string, flags uint32, context *fuse.Context) (fuseFile nodefs.File, status fuse.Status) {
 	if fs.isFiltered(path) {
 		return nil, fuse.EPERM
@@ -201,7 +203,9 @@ func (fs *FS) openWriteOnlyFile(dirfd int, cName string, newFlags int) (fuseFile
 	return NewFile(f, fs)
 }
 
-// Create implements pathfs.Filesystem.
+// Create - FUSE call. Creates a new file.
+//
+// Symlink-safe through the use of Openat().
 func (fs *FS) Create(path string, flags uint32, mode uint32, context *fuse.Context) (nodefs.File, fuse.Status) {
 	if fs.isFiltered(path) {
 		return nil, fuse.EPERM
@@ -245,7 +249,9 @@ func (fs *FS) Create(path string, flags uint32, mode uint32, context *fuse.Conte
 	return NewFile(f, fs)
 }
 
-// Chmod implements pathfs.Filesystem.
+// Chmod - FUSE call. Change permissons on "path".
+//
+// Symlink-safe through use of Fchmodat().
 func (fs *FS) Chmod(path string, mode uint32, context *fuse.Context) (code fuse.Status) {
 	if fs.isFiltered(path) {
 		return fuse.EPERM
@@ -261,7 +267,9 @@ func (fs *FS) Chmod(path string, mode uint32, context *fuse.Context) (code fuse.
 	return fuse.ToStatus(err)
 }
 
-// Chown implements pathfs.Filesystem.
+// Chown - FUSE call. Change the owner of "path".
+//
+// Symlink-safe through use of Fchownat().
 func (fs *FS) Chown(path string, uid uint32, gid uint32, context *fuse.Context) (code fuse.Status) {
 	if fs.isFiltered(path) {
 		return fuse.EPERM
@@ -286,7 +294,9 @@ func (fs *FS) Chown(path string, uid uint32, gid uint32, context *fuse.Context)
 	return fuse.OK
 }
 
-// Mknod implements pathfs.Filesystem.
+// Mknod - FUSE call. Create a device file.
+//
+// Symlink-safe through use of Mknodat().
 func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context) (code fuse.Status) {
 	if fs.isFiltered(path) {
 		return fuse.EPERM
@@ -339,7 +349,7 @@ func (fs *FS) Truncate(path string, offset uint64, context *fuse.Context) (code
 	return code
 }
 
-// Utimens implements pathfs.Filesystem.
+// Utimens - FUSE call. Set the timestamps on file "path".
 func (fs *FS) Utimens(path string, a *time.Time, m *time.Time, context *fuse.Context) (code fuse.Status) {
 	if fs.isFiltered(path) {
 		return fuse.EPERM
@@ -351,16 +361,11 @@ func (fs *FS) Utimens(path string, a *time.Time, m *time.Time, context *fuse.Con
 	return fs.FileSystem.Utimens(cPath, a, m, context)
 }
 
-// StatFs implements pathfs.Filesystem.
+// StatFs - FUSE call. Returns information about the filesystem.
+//
+// Symlink-safe because the passed path is ignored.
 func (fs *FS) StatFs(path string) *fuse.StatfsOut {
-	if fs.isFiltered(path) {
-		return nil
-	}
-	cPath, err := fs.encryptPath(path)
-	if err != nil {
-		return nil
-	}
-	return fs.FileSystem.StatFs(cPath)
+	return fs.FileSystem.StatFs("")
 }
 
 // decryptSymlinkTarget: "cData64" is base64-decoded and decrypted
@@ -548,7 +553,10 @@ func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (cod
 	return fuse.OK
 }
 
-// Link implements pathfs.Filesystem.
+// Link - FUSE call. Creates a hard link at "newPath" pointing to file
+// "oldPath".
+//
+// Symlink-safe through use of Linkat().
 func (fs *FS) Link(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
 	if fs.isFiltered(newPath) {
 		return fuse.EPERM
diff --git a/internal/fusefrontend/fs_dir.go b/internal/fusefrontend/fs_dir.go
index 76dff8e..8d27791 100644
--- a/internal/fusefrontend/fs_dir.go
+++ b/internal/fusefrontend/fs_dir.go
@@ -49,7 +49,9 @@ func (fs *FS) mkdirWithIv(dirfd int, cName string, mode uint32) error {
 	return err
 }
 
-// Mkdir implements pathfs.FileSystem
+// Mkdir - FUSE call. Create a directory at "newPath" with permissions "mode".
+//
+// Symlink-safe through use of Mkdirat().
 func (fs *FS) Mkdir(newPath string, mode uint32, context *fuse.Context) (code fuse.Status) {
 	if fs.isFiltered(newPath) {
 		return fuse.EPERM
diff --git a/internal/fusefrontend/xattr.go b/internal/fusefrontend/xattr.go
index 30f417e..2fd51a3 100644
--- a/internal/fusefrontend/xattr.go
+++ b/internal/fusefrontend/xattr.go
@@ -23,8 +23,8 @@ var xattrNameIV = []byte("xattr_name_iv_xx")
 // encrypted original name.
 var xattrStorePrefix = "user.gocryptfs."
 
-// GetXAttr reads the value of extended attribute "attr".
-// Implements pathfs.Filesystem.
+// GetXAttr - FUSE call. Reads the value of extended attribute "attr".
+// TODO: Make symlink-safe. Blocker: package xattr does not provide fgetxattr(2).
 func (fs *FS) GetXAttr(path string, attr string, context *fuse.Context) ([]byte, fuse.Status) {
 	if fs.isFiltered(path) {
 		return nil, fuse.EPERM
@@ -85,7 +85,9 @@ func (fs *FS) RemoveXAttr(path string, attr string, context *fuse.Context) fuse.
 	return unpackXattrErr(xattr.LRemove(cPath, cAttr))
 }
 
-// ListXAttr implements pathfs.Filesystem.
+// ListXAttr - FUSE call. Lists extended attributes on the file at "path".
+// TODO: Make symlink-safe. Blocker: package xattr does not provide
+// flistxattr(2).
 func (fs *FS) ListXAttr(path string, context *fuse.Context) ([]string, fuse.Status) {
 	if fs.isFiltered(path) {
 		return nil, fuse.EPERM