3 files changed, 21 insertions, 14 deletions
diff --git a/internal/fusefrontend/node_xattr.go b/internal/fusefrontend/node_xattr.go
index 1470a2a..2ca5ff7 100644
--- a/internal/fusefrontend/node_xattr.go
+++ b/internal/fusefrontend/node_xattr.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/hanwen/go-fuse/v2/fuse"
 
+	"github.com/rfjakob/gocryptfs/v2/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/v2/internal/tlog"
 )
 
@@ -136,10 +137,22 @@ func (n *Node) Listxattr(ctx context.Context, dest []byte) (uint32, syscall.Errn
 	if rn.args.NoXattr {
 		return 0, 0
 	}
-	cNames, errno := n.listXAttr()
+	// cBuf is the buffer for the encrypted attr names. Double the size of what the user
+	// requested to allow for ciphertext expansion due to padding and base64 encoding.
+	// TODO: double-check max expansion factor
+	cBuf := make([]byte, 2*len(dest))
+	sz, errno := n.listXAttr(cBuf)
 	if errno != 0 {
 		return 0, errno
 	}
+	// A call with empty dest is a size probe as described in man 2 llistxattr.
+	// Should return the size of the full attr list and success.
+	// Because we don't know the size of the decrypted names yet, we return the
+	// size of the encrypted names. This is slightly higher and hence safe.
+	if len(dest) == 0 {
+		return uint32(sz), 0
+	}
+	cNames := syscallcompat.ParseListxattrBlob(cBuf[:sz])
 	var buf bytes.Buffer
 	for _, curName := range cNames {
 		// ACLs are passed through without encryption
diff --git a/internal/fusefrontend/node_xattr_darwin.go b/internal/fusefrontend/node_xattr_darwin.go
index f8f224f..ad0cd9e 100644
--- a/internal/fusefrontend/node_xattr_darwin.go
+++ b/internal/fusefrontend/node_xattr_darwin.go
@@ -88,7 +88,7 @@ func (n *Node) removeXAttr(cAttr string) (errno syscall.Errno) {
 	return fs.ToErrno(err)
 }
 
-func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
+func (n *Node) listXAttr(buf []byte) (sz int, errno syscall.Errno) {
 	dirfd, cName, errno := n.prepareAtSyscallMyself()
 	if errno != 0 {
 		return
@@ -98,13 +98,10 @@ func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
 	// O_NONBLOCK to not block on FIFOs.
 	fd, err := syscallcompat.Openat(dirfd, cName, 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)
 
-	cNames, err := syscallcompat.Flistxattr(fd)
-	if err != nil {
-		return nil, fs.ToErrno(err)
-	}
-	return cNames, 0
+	sz, err = unix.Flistxattr(fd, buf)
+	return sz, fs.ToErrno(err)
 }
diff --git a/internal/fusefrontend/node_xattr_linux.go b/internal/fusefrontend/node_xattr_linux.go
index 9964212..d1747e8 100644
--- a/internal/fusefrontend/node_xattr_linux.go
+++ b/internal/fusefrontend/node_xattr_linux.go
@@ -57,7 +57,7 @@ func (n *Node) removeXAttr(cAttr string) (errno syscall.Errno) {
 	return fs.ToErrno(unix.Lremovexattr(procPath, cAttr))
 }
 
-func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
+func (n *Node) listXAttr(buf []byte) (sz int, errno syscall.Errno) {
 	dirfd, cName, errno := n.prepareAtSyscallMyself()
 	if errno != 0 {
 		return
@@ -65,9 +65,6 @@ func (n *Node) listXAttr() (out []string, errno syscall.Errno) {
 	defer syscall.Close(dirfd)
 
 	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
-	cNames, err := syscallcompat.Llistxattr(procPath)
-	if err != nil {
-		return nil, fs.ToErrno(err)
-	}
-	return cNames, 0
+	sz, err := unix.Llistxattr(procPath, buf)
+	return sz, fs.ToErrno(err)
 }