reverse: add symlink encryption and Readlink support

internal/fusefrontend_reverse/rfs.go

@@ -1,6 +1,7 @@
 package fusefrontend_reverse
 
 import (
+	"encoding/base64"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -275,3 +276,23 @@ func (rfs *reverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.
 func (rfs *reverseFS) StatFs(name string) *fuse.StatfsOut {
 	return rfs.loopbackfs.StatFs(name)
 }
+
+// Readlink - FUSE call
+func (rfs *reverseFS) Readlink(cipherPath string, context *fuse.Context) (string, fuse.Status) {
+	absPath, err := rfs.abs(rfs.decryptPath(cipherPath))
+	if err != nil {
+		return "", fuse.ToStatus(err)
+	}
+	plainTarget, err := os.Readlink(absPath)
+	if err != nil {
+		return "", fuse.ToStatus(err)
+	}
+	if rfs.args.PlaintextNames {
+		return plainTarget, fuse.OK
+	}
+	nonce := derivePathIV(cipherPath)
+	// Symlinks are encrypted like file contents and base64-encoded
+	cBinTarget := rfs.contentEnc.EncryptBlock([]byte(plainTarget), 0, nil, contentenc.ExternalNonce, nonce)
+	cTarget := base64.URLEncoding.EncodeToString(cBinTarget)
+	return cTarget, fuse.OK
+}

internal/fusefrontend_reverse/rpath.go

@@ -47,6 +47,12 @@ func (rfs *reverseFS) decryptPath(relPath string) (string, error) {
 				if _, ok := err.(base64.CorruptInputError); ok {
 					return "", syscall.ENOENT
 				}
+				// Stat attempts on the link target of encrypted symlinks.
+				// These are always valid base64 but the length is not a
+				// multiple of 16.
+				if err == syscall.EINVAL {
+					return "", syscall.ENOENT
+				}
 				return "", err
 			}
 		} else if nameType == nametransform.LongNameContent {

internal/nametransform/names.go

@@ -4,7 +4,6 @@ package nametransform
 import (
 	"crypto/aes"
 	"encoding/base64"
-	"fmt"
 	"syscall"
 
 	"github.com/rfjakob/eme"
@@ -38,7 +37,8 @@ func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error
 		return "", err
 	}
 	if len(bin)%aes.BlockSize != 0 {
-		return "", fmt.Errorf("Decoded length %d is not a multiple of the AES block size", len(bin))
+		tlog.Warn.Printf("DecryptName %q: decoded length %d is not a multiple of 16", cipherName, len(bin))
+		return "", syscall.EINVAL
 	}
 	bin = eme.Transform(n.cryptoCore.BlockCipher, iv, bin, eme.DirectionDecrypt)
 	bin, err = unPad16(bin)

tests/reverse/correctness_test.go

@@ -28,3 +28,24 @@ func TestLongnameStat(t *testing.T) {
 		test_helpers.VerifySize(t, path, 10)
 	*/
 }
+
+func TestSymlinks(t *testing.T) {
+	target := "/"
+	os.Symlink(target, dirA+"/symlink")
+	cSymlink := dirC + "/symlink"
+	_, err := os.Lstat(cSymlink)
+	if err != nil {
+		t.Errorf("Lstat: %v", err)
+	}
+	_, err = os.Stat(cSymlink)
+	if err != nil {
+		t.Errorf("Stat: %v", err)
+	}
+	actualTarget, err := os.Readlink(cSymlink)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if target != actualTarget {
+		t.Errorf("wrong symlink target: want=%q have=%q", target, actualTarget)
+	}
+}