cli: add -longnamemax

Fixes https://github.com/rfjakob/gocryptfs/issues/499

8 files changed, 121 insertions, 10 deletions

diff --git a/Documentation/MANPAGE.md b/Documentation/MANPAGE.md
index 01e4b5a..b9c72dd 100644
--- a/Documentation/MANPAGE.md
+++ b/Documentation/MANPAGE.md
@@ -123,6 +123,28 @@ and https://github.com/rfjakob/gocryptfs/issues/596 for background info.
 Use HKDF to derive separate keys for content and name encryption from
 the master key. Default true.
 
+#### -longnamemax
+
+    integer value, allowed range 62...255
+
+Hash file names that (in encrypted form) exceed this length. The default
+is 255, which aligns with the usual name length limit on Linux and
+provides best performance.
+
+However, online storage may impose lower limits on file name and/or
+path length. In this case, setting -longnamemax to a lower value
+can be helpful.
+
+The lower the value, the more extra `.name` files
+must be created, which slows down directory listings.
+
+Values below 62 are not allowed as then the hashed name
+would be longer than the original name.
+
+Example:
+
+    -longnamemax 100
+
 #### -plaintextnames
 Do not encrypt file names and symlink targets.
 
diff --git a/README.md b/README.md
index 1a02857..35c2bda 100644
--- a/README.md
+++ b/README.md
@@ -196,6 +196,12 @@ RM:    2,367
 Changelog
 ---------
 
+#### vNEXT
+* Add **`-longnamemax`** flag to `-init` ([#499](https://github.com/rfjakob/gocryptfs/issues/499)).
+  Can be used to work around file or path length restrictions on online storage.
+  See the [man page](https://github.com/rfjakob/gocryptfs/blob/master/Documentation/MANPAGE.md#-longnamemax)
+  for details.
+
 #### v2.2.1, 2021-10-20
 * Fix `-force_owner` only taking effect after 2 seconds ([#609](https://github.com/rfjakob/gocryptfs/issues/609)).
   This was a regression introduced in v2.0.
diff --git a/cli_args.go b/cli_args.go
index b415b21..e925345 100644
--- a/cli_args.go
+++ b/cli_args.go
@@ -45,6 +45,8 @@ type argContainer struct {
 	notifypid, scryptn int
 	// Idle time before autounmount
 	idle time.Duration
+	// -longnamemax (hash encrypted names that are longer than this)
+	longnamemax uint8
 	// Helper variables that are NOT cli options all start with an underscore
 	// _configCustom is true when the user sets a custom config file name.
 	_configCustom bool
@@ -215,6 +217,8 @@ func parseCliOpts(osArgs []string) (args argContainer) {
 	flagSet.StringSliceVar(&args.badname, "badname", nil, "Glob pattern invalid file names that should be shown")
 	flagSet.StringSliceVar(&args.passfile, "passfile", nil, "Read password from file")
 
+	flagSet.Uint8Var(&args.longnamemax, "longnamemax", 255, "Hash encrypted names that are longer than this")
+
 	flagSet.IntVar(&args.notifypid, "notifypid", 0, "Send USR1 to the specified process after "+
 		"successful mount - used internally for daemonization")
 	const scryptn = "scryptn"
@@ -292,6 +296,10 @@ func parseCliOpts(osArgs []string) (args argContainer) {
 			os.Exit(exitcodes.Usage)
 		}
 	}
+	if args.longnamemax > 0 && args.longnamemax < 62 {
+		tlog.Fatal.Printf("-longnamemax: value %d is outside allowed range 62 ... 255", args.longnamemax)
+		os.Exit(exitcodes.Usage)
+	}
 
 	return args
 }
diff --git a/cli_args_test.go b/cli_args_test.go
index 6c923f4..74255f2 100644
--- a/cli_args_test.go
+++ b/cli_args_test.go
@@ -116,11 +116,12 @@ func TestConvertToDoubleDash(t *testing.T) {
 
 func TestParseCliOpts(t *testing.T) {
 	defaultArgs := argContainer{
-		longnames: true,
-		raw64:     true,
-		hkdf:      true,
-		openssl:   stupidgcm.PreferOpenSSLAES256GCM(), // depends on CPU and build flags
-		scryptn:   16,
+		longnames:   true,
+		longnamemax: 255,
+		raw64:       true,
+		hkdf:        true,
+		openssl:     stupidgcm.PreferOpenSSLAES256GCM(), // depends on CPU and build flags
+		scryptn:     16,
 	}
 
 	type testcaseContainer struct {
diff --git a/init_dir.go b/init_dir.go
index ab4c3df..9658bab 100644
--- a/init_dir.go
+++ b/init_dir.go
@@ -102,7 +102,9 @@ func initDir(args *argContainer) {
 			Fido2CredentialID:  fido2CredentialID,
 			Fido2HmacSalt:      fido2HmacSalt,
 			DeterministicNames: args.deterministic_names,
-			XChaCha20Poly1305:  args.xchacha})
+			XChaCha20Poly1305:  args.xchacha,
+			LongNameMax:        args.longnamemax,
+		})
 		if err != nil {
 			tlog.Fatal.Println(err)
 			os.Exit(exitcodes.WriteConf)
diff --git a/internal/configfile/validate.go b/internal/configfile/validate.go
index 1611ab0..ab8917d 100644
--- a/internal/configfile/validate.go
+++ b/internal/configfile/validate.go
@@ -47,10 +47,10 @@ func (cf *ConfFile) Validate() error {
 	}
 	// Filename encryption
 	{
-		if cf.IsFeatureFlagSet(FlagPlaintextNames) && cf.IsFeatureFlagSet(FlagEMENames) {
-			return fmt.Errorf("Can't have both PlaintextNames and EMENames feature flags")
-		}
 		if cf.IsFeatureFlagSet(FlagPlaintextNames) {
+			if cf.IsFeatureFlagSet(FlagEMENames) {
+				return fmt.Errorf("PlaintextNames conflicts with EMENames feature flag")
+			}
 			if cf.IsFeatureFlagSet(FlagDirIV) {
 				return fmt.Errorf("PlaintextNames conflicts with DirIV feature flag")
 			}
@@ -60,10 +60,19 @@ func (cf *ConfFile) Validate() error {
 			if cf.IsFeatureFlagSet(FlagRaw64) {
 				return fmt.Errorf("PlaintextNames conflicts with Raw64 feature flag")
 			}
+			if cf.IsFeatureFlagSet(FlagLongNameMax) {
+				return fmt.Errorf("PlaintextNames conflicts with LongNameMax feature flag")
+			}
 		}
 		if cf.IsFeatureFlagSet(FlagEMENames) {
 			// All combinations of DirIV, LongNames, Raw64 allowed
 		}
+		if cf.LongNameMax != 0 && !cf.IsFeatureFlagSet(FlagLongNameMax) {
+			return fmt.Errorf("LongNameMax=%d but the LongNameMax feature flag is NOT set", cf.LongNameMax)
+		}
+		if cf.LongNameMax == 0 && cf.IsFeatureFlagSet(FlagLongNameMax) {
+			return fmt.Errorf("LongNameMax=0 but the LongNameMax feature flag IS set")
+		}
 	}
 	return nil
 }
diff --git a/mount.go b/mount.go
index 004c646..434edad 100644
--- a/mount.go
+++ b/mount.go
@@ -292,6 +292,8 @@ func initFuseFrontend(args *argContainer) (rootNode fs.InodeEmbedder, wipeKeys f
 		// Settings from the config file override command line args
 		frontendArgs.PlaintextNames = confFile.IsFeatureFlagSet(configfile.FlagPlaintextNames)
 		frontendArgs.DeterministicNames = !confFile.IsFeatureFlagSet(configfile.FlagDirIV)
+		// Things that don't have to be in frontendArgs are only in args
+		args.longnamemax = confFile.LongNameMax
 		args.raw64 = confFile.IsFeatureFlagSet(configfile.FlagRaw64)
 		args.hkdf = confFile.IsFeatureFlagSet(configfile.FlagHKDF)
 		// Note: this will always return the non-openssl variant
@@ -324,7 +326,7 @@ func initFuseFrontend(args *argContainer) (rootNode fs.InodeEmbedder, wipeKeys f
 	// Init crypto backend
 	cCore := cryptocore.New(masterkey, cryptoBackend, IVBits, args.hkdf)
 	cEnc := contentenc.New(cCore, contentenc.DefaultBS)
-	nameTransform := nametransform.New(cCore.EMECipher, frontendArgs.LongNames, 0,
+	nameTransform := nametransform.New(cCore.EMECipher, frontendArgs.LongNames, args.longnamemax,
 		args.raw64, []string(args.badname), frontendArgs.DeterministicNames)
 	// After the crypto backend is initialized,
 	// we can purge the master key from memory.
diff --git a/tests/cli/longnamemax_test.go b/tests/cli/longnamemax_test.go
new file mode 100644
index 0000000..fc429f6
--- /dev/null
+++ b/tests/cli/longnamemax_test.go
@@ -0,0 +1,61 @@
+package cli
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"testing"
+
+	"github.com/rfjakob/gocryptfs/v2/internal/configfile"
+
+	"github.com/rfjakob/gocryptfs/v2/tests/test_helpers"
+)
+
+// Create & test fs with -longnamemax=100
+func TestLongnamemax100(t *testing.T) {
+	cDir := test_helpers.InitFS(nil, "-longnamemax", "100")
+	pDir := cDir + ".mnt"
+
+	// Check config file sanity
+	_, c, err := configfile.LoadAndDecrypt(cDir+"/"+configfile.ConfDefaultName, testPw)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+	if !c.IsFeatureFlagSet(configfile.FlagLongNameMax) {
+		t.Error("FlagLongNameMax should be on")
+	}
+	if c.LongNameMax != 100 {
+		t.Errorf("LongNameMax=%d, want 100", c.LongNameMax)
+	}
+
+	// Check that it takes effect
+	test_helpers.MountOrExit(cDir, pDir, "-extpass", "echo test")
+	defer test_helpers.UnmountPanic(pDir)
+
+	for l := 1; l <= 255; l++ {
+		path := pDir + "/" + strings.Repeat("x", l)
+		if err := ioutil.WriteFile(path, nil, 0600); err != nil {
+			t.Fatal(err)
+		}
+		matches, err := filepath.Glob(cDir + "/gocryptfs.longname.*")
+		if err != nil {
+			t.Fatal(err)
+		}
+		err = syscall.Unlink(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		// As determined experimentally, a name of length >= 64 causes a longname
+		// to be created.
+		if l <= 63 && len(matches) != 0 {
+			t.Errorf("l=%d: should not see a longname yet", l)
+		}
+		if l >= 64 && len(matches) != 2 {
+			t.Errorf("l=%d: should see a longname now", l)
+		}
+	}
+}