fusefrontend: Allow to set/remove xattr on directory without read permission.

Setting/removing extended attributes on directories was partially fixed with
commit eff35e60b63331e3e10f921792baa10b236a721d. However, on most file systems
it is also possible to do these operations without read access (see tests).

Since we cannot open a write-access fd to a directory, we have to use the
/proc/self/fd trick (already used for ListXAttr) for the other operations aswell.
For simplicity, let's separate the Linux and Darwin code again (basically revert
commit f320b76fd189a363a34bffe981aa67ab97df3362), and always use the
/proc/self/fd trick on Linux. On Darwin we use the best-effort approach with
openBackingFile() as a fallback.

More discussion about the available options is available in
https://github.com/rfjakob/gocryptfs/issues/308.

1 files changed, 62 insertions, 0 deletions

diff --git a/internal/fusefrontend/xattr_linux.go b/internal/fusefrontend/xattr_linux.go
index fd3b7e5..3a64412 100644
--- a/internal/fusefrontend/xattr_linux.go
+++ b/internal/fusefrontend/xattr_linux.go
@@ -4,7 +4,15 @@
 package fusefrontend
 
 import (
+	"fmt"
 	"strings"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 )
 
 // Only allow the "user" namespace, block "trusted" and "security", as
@@ -19,3 +27,57 @@ func disallowedXAttrName(attr string) bool {
 func filterXattrSetFlags(flags int) int {
 	return flags
 }
+
+func (fs *FS) getXAttr(relPath string, cAttr string, context *fuse.Context) ([]byte, fuse.Status) {
+	dirfd, cName, err := fs.openBackingDir(relPath)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+
+	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
+	cData, err := syscallcompat.Lgetxattr(procPath, cAttr)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	return cData, fuse.OK
+}
+
+func (fs *FS) setXAttr(relPath string, cAttr string, cData []byte, flags int, context *fuse.Context) fuse.Status {
+	dirfd, cName, err := fs.openBackingDir(relPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+
+	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
+	err = unix.Lsetxattr(procPath, cAttr, cData, flags)
+	return fuse.ToStatus(err)
+}
+
+func (fs *FS) removeXAttr(relPath string, cAttr string, context *fuse.Context) fuse.Status {
+	dirfd, cName, err := fs.openBackingDir(relPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+
+	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
+	err = unix.Lremovexattr(procPath, cAttr)
+	return fuse.ToStatus(err)
+}
+
+func (fs *FS) listXAttr(relPath string, context *fuse.Context) ([]string, fuse.Status) {
+	dirfd, cName, err := fs.openBackingDir(relPath)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+
+	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
+	cNames, err := syscallcompat.Llistxattr(procPath)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	return cNames, fuse.OK
+}