Show undecryptable filenames if they match supplied glob

Resolves https://github.com/rfjakob/gocryptfs/issues/393

cli_args.go

@@ -32,8 +32,8 @@ type argContainer struct {
 	dev, nodev, suid, nosuid, exec, noexec, rw, ro bool
 	masterkey, mountpoint, cipherdir, cpuprofile,
 	memprofile, ko, passfile, ctlsock, fsname, force_owner, trace string
-	// -extpass can be passed multiple times
+	// -extpass and -badname can be passed multiple times
-	extpass multipleStrings
+	extpass, badname multipleStrings
 	// For reverse mode, several ways to specify exclusions. All can be specified multiple times.
 	exclude, excludeWildcard, excludeFrom multipleStrings
 	// Configuration file name override
@@ -199,6 +199,7 @@ func parseCliOpts() (args argContainer) {
 
 	// -extpass
 	flagSet.Var(&args.extpass, "extpass", "Use external program for the password prompt")
+	flagSet.Var(&args.badname, "badname", "Glob pattern invalid file names that should be shown")
 
 	flagSet.IntVar(&args.notifypid, "notifypid", 0, "Send USR1 to the specified process after "+
 		"successful mount - used internally for daemonization")

internal/nametransform/names.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"crypto/aes"
 	"encoding/base64"
+	"path/filepath"
 	"syscall"
 
 	"github.com/rfjakob/eme"
@@ -35,6 +36,8 @@ type NameTransform struct {
 	// B64 = either base64.URLEncoding or base64.RawURLEncoding, depending
 	// on the Raw64 feature flag
 	B64 *base64.Encoding
+	// Patterns to bypass decryption
+	BadnamePatterns []string
 }
 
 // New returns a new NameTransform instance.
@@ -50,9 +53,24 @@ func New(e *eme.EMECipher, longNames bool, raw64 bool) *NameTransform {
 	}
 }
 
-// DecryptName decrypts a base64-encoded encrypted filename "cipherName" using the
+// DecryptName calls decryptName to try and decrypt a base64-encoded encrypted
-// initialization vector "iv".
+// filename "cipherName", and failing that checks if it can be bypassed
 func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error) {
+	res, err := n.decryptName(cipherName, iv)
+	if err != nil {
+		for _, pattern := range n.BadnamePatterns {
+			match, err := filepath.Match(pattern, cipherName)
+			if err == nil && match { // Pattern should have been validated already
+				return "GOCRYPTFS_BAD_NAME " + cipherName, nil
+			}
+		}
+	}
+	return res, err
+}
+
+// decryptName decrypts a base64-encoded encrypted filename "cipherName" using the
+// initialization vector "iv".
+func (n *NameTransform) decryptName(cipherName string, iv []byte) (string, error) {
 	bin, err := n.B64.DecodeString(cipherName)
 	if err != nil {
 		return "", err

mount.go

@@ -286,6 +286,17 @@ func initFuseFrontend(args *argContainer) (pfs pathfs.FileSystem, wipeKeys func(
 	cCore := cryptocore.New(masterkey, cryptoBackend, contentenc.DefaultIVBits, args.hkdf, args.forcedecode)
 	cEnc := contentenc.New(cCore, contentenc.DefaultBS, args.forcedecode)
 	nameTransform := nametransform.New(cCore.EMECipher, frontendArgs.LongNames, args.raw64)
+	// Init badname patterns
+	nameTransform.BadnamePatterns = make([]string, 0)
+	for _, pattern := range args.badname {
+		_, err := filepath.Match(pattern, "") // Make sure pattern is valid
+		if err != nil {
+			tlog.Fatal.Printf("-badname: invalid pattern %q supplied", pattern)
+			os.Exit(exitcodes.Usage)
+		} else {
+			nameTransform.BadnamePatterns = append(nameTransform.BadnamePatterns, pattern)
+		}
+	}
 	// After the crypto backend is initialized,
 	// we can purge the master key from memory.
 	for i := range masterkey {

tests/cli/cli_test.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"os/exec"
 	"strconv"
+	"strings"
 	"syscall"
 	"testing"
 	"time"
@@ -644,3 +645,43 @@ func TestSymlinkedCipherdir(t *testing.T) {
 		t.Errorf("wrong Readdirnames result: %v", names)
 	}
 }
+
+func TestBypass(t *testing.T) {
+	dir := test_helpers.InitFS(t)
+	mnt := dir + ".mnt"
+
+	test_helpers.MountOrFatal(t, dir, mnt, "-badname=*", "-extpass=echo test")
+	defer test_helpers.UnmountPanic(mnt)
+
+	file := mnt + "/file"
+	err := ioutil.WriteFile(file, []byte("somecontent"), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	invalid_file_name := "invalid_file"
+	invalid_file := dir + "/" + invalid_file_name
+	err = ioutil.WriteFile(invalid_file, []byte("somecontent"), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	f, err := os.Open(mnt)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	names, err := f.Readdirnames(0)
+	found := false
+	for _, name := range names {
+		if strings.Contains(name, invalid_file_name) {
+			found = true
+			break
+		}
+	}
+
+	if !found {
+		t.Errorf("did not find invalid name %s in %v", invalid_file_name, names)
+	}
+}