main: move masterkey logic into new helper getMasterKey

The new helper will also be used by fsck.

masterkey.go

@@ -7,8 +7,10 @@ import (
 
 	"golang.org/x/crypto/ssh/terminal"
 
+	"github.com/rfjakob/gocryptfs/internal/configfile"
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
 	"github.com/rfjakob/gocryptfs/internal/exitcodes"
+	"github.com/rfjakob/gocryptfs/internal/readpassword"
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
@@ -65,3 +67,46 @@ func parseMasterKey(masterkey string, fromStdin bool) []byte {
 	}
 	return key
 }
+
+// getMasterKey looks at "args" to determine where the master key should come
+// from (-masterkey=a-b-c-d or stdin or from the config file).
+// If it comes from the config file, the user is prompted for the password
+// and a ConfFile instance is returned.
+// Calls os.Exit on failure.
+func getMasterKey(args *argContainer) (masterkey []byte, confFile *configfile.ConfFile) {
+	masterkeyFromStdin := false
+	// "-masterkey=stdin"
+	if args.masterkey == "stdin" {
+		args.masterkey = string(readpassword.Once("", "Masterkey"))
+		masterkeyFromStdin = true
+	}
+	// "-masterkey=941a6029-3adc6a1c-..."
+	if args.masterkey != "" {
+		return parseMasterKey(args.masterkey, masterkeyFromStdin), nil
+	}
+	// "-zerokey"
+	if args.zerokey {
+		tlog.Info.Printf("Using all-zero dummy master key.")
+		tlog.Info.Printf(tlog.ColorYellow +
+			"ZEROKEY MODE PROVIDES NO SECURITY AT ALL AND SHOULD ONLY BE USED FOR TESTING." +
+			tlog.ColorReset)
+		return make([]byte, cryptocore.KeyLen), nil
+	}
+	var err error
+	// Load master key from config file (normal operation).
+	// Prompts the user for the password.
+	masterkey, confFile, err = loadConfig(args)
+	if err != nil {
+		if args._ctlsockFd != nil {
+			// Close the socket file (which also deletes it)
+			args._ctlsockFd.Close()
+		}
+		exitcodes.Exit(err)
+	}
+	readpassword.CheckTrailingGarbage()
+	if !args.fsck {
+		// We only want to print the masterkey message on a normal mount.
+		printMasterKey(masterkey)
+	}
+	return masterkey, confFile
+}

mount.go

@@ -29,7 +29,6 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/fusefrontend"
 	"github.com/rfjakob/gocryptfs/internal/fusefrontend_reverse"
 	"github.com/rfjakob/gocryptfs/internal/nametransform"
-	"github.com/rfjakob/gocryptfs/internal/readpassword"
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
@@ -96,37 +95,9 @@ func doMount(args *argContainer) {
 	var confFile *configfile.ConfFile
 	var srv *fuse.Server
 	{
-		// Get master key (may prompt for the password)
 		var masterkey []byte
-		masterkeyFromStdin := false
-		if args.masterkey == "stdin" {
-			args.masterkey = string(readpassword.Once("", "Masterkey"))
-			masterkeyFromStdin = true
-		}
-		if args.masterkey != "" {
-			// "-masterkey"
-			masterkey = parseMasterKey(args.masterkey, masterkeyFromStdin)
-		} else if args.zerokey {
-			// "-zerokey"
-			tlog.Info.Printf("Using all-zero dummy master key.")
-			tlog.Info.Printf(tlog.ColorYellow +
-				"ZEROKEY MODE PROVIDES NO SECURITY AT ALL AND SHOULD ONLY BE USED FOR TESTING." +
-				tlog.ColorReset)
-			masterkey = make([]byte, cryptocore.KeyLen)
-		} else {
-			// Load master key from config file
-			// Prompts the user for the password
-			masterkey, confFile, err = loadConfig(args)
-			if err != nil {
-				if args._ctlsockFd != nil {
-					// Close the socket file (which also deletes it)
-					args._ctlsockFd.Close()
-				}
-				exitcodes.Exit(err)
-			}
-			readpassword.CheckTrailingGarbage()
-			printMasterKey(masterkey)
-		}
+		// Get master key (may prompt for the password)
+		masterkey, confFile = getMasterKey(args)
 		// We cannot use JSON for pretty-printing as the fields are unexported
 		tlog.Debug.Printf("cli args: %#v", args)
 		// Initialize FUSE server