fusefronted: report plaintext size on symlink creation

gocryptfs 2.0 introduced the regression that the size
reported at symlink creation was the ciphertext size,
which is wrong.

Report the plaintext size.

Fixes https://github.com/rfjakob/gocryptfs/issues/574

internal/fusefrontend/node.go

@@ -354,6 +354,9 @@ func (n *Node) Symlink(ctx context.Context, target, name string, out *fuse.Entry
 		errno = fs.ToErrno(err)
 		return
 	}
+	// Report the plaintext size, not the encrypted blob size
+	st.Size = int64(len(target))
+
 	inode = n.newChild(ctx, st, out)
 	return inode, 0
 }

internal/fusefrontend/node_helpers.go

@@ -58,6 +58,8 @@ func (n *Node) readlink(dirfd int, cName string) (out []byte, errno syscall.Errn
 }
 
 // translateSize translates the ciphertext size in `out` into plaintext size.
+// Handles regular files & symlinks (and finds out what is what by looking at
+// `out.Mode`).
 func (n *Node) translateSize(dirfd int, cName string, out *fuse.Attr) {
 	if out.IsRegular() {
 		rn := n.rootNode()

tests/matrix/matrix_test.go

@@ -19,6 +19,7 @@ import (
 	"math/rand"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"runtime"
 	"sync"
 	"syscall"
@@ -882,3 +883,21 @@ func TestStatfs(t *testing.T) {
 		t.Errorf("statfs reports size zero: %#v", st)
 	}
 }
+
+// gocryptfs 2.0 reported the ciphertext size on symlink creation, causing
+// confusion: https://github.com/rfjakob/gocryptfs/issues/574
+func TestSymlinkSize(t *testing.T) {
+	p := filepath.Join(test_helpers.DefaultPlainDir, t.Name())
+	// SYMLINK reports the size to the kernel
+	if err := syscall.Symlink("foo", p); err != nil {
+		t.Fatal(err)
+	}
+	// Kernel serves us this value from the attr cache
+	var st syscall.Stat_t
+	if err := syscall.Lstat(p, &st); err != nil {
+		t.Fatal(err)
+	}
+	if st.Size != 3 {
+		t.Errorf("wrong size: have %d, want %d", st.Size, 3)
+	}
+}