3 files changed, 19 insertions, 14 deletions
diff --git a/internal/fusefrontend_reverse/node_xattr.go b/internal/fusefrontend_reverse/node_xattr.go
index f22764a..9e99cfa 100644
--- a/internal/fusefrontend_reverse/node_xattr.go
+++ b/internal/fusefrontend_reverse/node_xattr.go
@@ -7,6 +7,7 @@ import (
 	"syscall"
 
 	"github.com/rfjakob/gocryptfs/v2/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/v2/internal/syscallcompat"
 )
 
 // We store encrypted xattrs under this prefix plus the base64-encoded
@@ -65,10 +66,18 @@ func (n *Node) Listxattr(ctx context.Context, dest []byte) (uint32, syscall.Errn
 	if rn.args.NoXattr {
 		return 0, 0
 	}
-	pNames, errno := n.listXAttr()
+	// Can use dest as a temporary buffer
+	sz, errno := n.listXAttr(dest)
 	if errno != 0 {
 		return 0, errno
 	}
+	// If dest empty, return the required size
+	if len(dest) == 0 {
+		// Asssume ciphertext expansion by a factor of 2
+		// TODO: double-check max expansion factor
+		return uint32(sz * 2), 0
+	}
+	pNames := syscallcompat.ParseListxattrBlob(dest[:sz])
 	var buf bytes.Buffer
 	for _, pName := range pNames {
 		// ACLs are passed through without encryption
diff --git a/internal/fusefrontend_reverse/node_xattr_darwin.go b/internal/fusefrontend_reverse/node_xattr_darwin.go
index 6816a18..1832f7f 100644
--- a/internal/fusefrontend_reverse/node_xattr_darwin.go
+++ b/internal/fusefrontend_reverse/node_xattr_darwin.go
@@ -4,6 +4,7 @@ import (
 	"syscall"
 
 	"github.com/hanwen/go-fuse/v2/fs"
+	"golang.org/x/sys/unix"
 
 	"github.com/rfjakob/gocryptfs/v2/internal/syscallcompat"
 )
@@ -33,7 +34,7 @@ func (n *Node) getXAttr(cAttr string) (out []byte, errno syscall.Errno) {
 	return cData, 0
 }
 
-func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
+func (n *Node) listXAttr(buf []byte) (sz int, errno syscall.Errno) {
 	d, errno := n.prepareAtSyscall("")
 	if errno != 0 {
 		return
@@ -43,13 +44,10 @@ func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
 	// O_NONBLOCK to not block on FIFOs.
 	fd, err := syscallcompat.Openat(d.dirfd, d.pName, syscall.O_RDONLY|syscall.O_NONBLOCK|syscall.O_NOFOLLOW, 0)
 	if err != nil {
-		return nil, fs.ToErrno(err)
+		return 0, fs.ToErrno(err)
 	}
 	defer syscall.Close(fd)
 
-	pNames, err := syscallcompat.Flistxattr(fd)
-	if err != nil {
-		return nil, fs.ToErrno(err)
-	}
-	return pNames, 0
+	sz, err = unix.Flistxattr(fd, buf)
+	return sz, fs.ToErrno(err)
 }
diff --git a/internal/fusefrontend_reverse/node_xattr_linux.go b/internal/fusefrontend_reverse/node_xattr_linux.go
index 3c574f5..226ace4 100644
--- a/internal/fusefrontend_reverse/node_xattr_linux.go
+++ b/internal/fusefrontend_reverse/node_xattr_linux.go
@@ -5,6 +5,7 @@ import (
 	"syscall"
 
 	"github.com/hanwen/go-fuse/v2/fs"
+	"golang.org/x/sys/unix"
 
 	"github.com/rfjakob/gocryptfs/v2/internal/syscallcompat"
 )
@@ -27,7 +28,7 @@ func (n *Node) getXAttr(cAttr string) (out []byte, errno syscall.Errno) {
 	return pData, 0
 }
 
-func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
+func (n *Node) listXAttr(buf []byte) (sz int, errno syscall.Errno) {
 	d, errno := n.prepareAtSyscall("")
 	if errno != 0 {
 		return
@@ -35,9 +36,6 @@ func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
 	defer syscall.Close(d.dirfd)
 
 	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", d.dirfd, d.pName)
-	pNames, err := syscallcompat.Llistxattr(procPath)
-	if err != nil {
-		return nil, fs.ToErrno(err)
-	}
-	return pNames, 0
+	sz, err := unix.Llistxattr(procPath, buf)
+	return sz, fs.ToErrno(err)
 }