From 2cf050d69e9cab45015619e48ea96993129bab44 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher <jakobunt@gmail.com>
Date: Sun, 18 Feb 2018 15:22:22 +0100
Subject: [PATCH] main: zero password once we are done with it

Overwrite the password we have got from the user
with zeros once we don't need it anymore, and make
sure the variable runs out of scope.
---
 gocryptfs-xray/xray_main.go |  3 +++
 init_dir.go                 |  5 +++--
 main.go                     | 15 ++++++++++++---
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/gocryptfs-xray/xray_main.go b/gocryptfs-xray/xray_main.go
index 85470ec..522878a 100644
--- a/gocryptfs-xray/xray_main.go
+++ b/gocryptfs-xray/xray_main.go
@@ -67,6 +67,9 @@ func dumpMasterKey(fn string) {
 		exitcodes.Exit(err)
 	}
 	fmt.Println(hex.EncodeToString(masterkey))
+	for i := range pw {
+		pw[i] = 0
+	}
 }
 
 func inspectCiphertext(fd *os.File) {
diff --git a/init_dir.go b/init_dir.go
index b13f741..ea902ec 100644
--- a/init_dir.go
+++ b/init_dir.go
@@ -45,8 +45,9 @@ func initDir(args *argContainer) {
 			tlog.Fatal.Println(err)
 			os.Exit(exitcodes.WriteConf)
 		}
-		// Note: cannot overwrite password because in Go, strings are
-		// read-only byte slices.
+		for i := range password {
+			password[i] = 0
+		}
 		// password runs out of scope here
 	}
 	// Forward mode with filename encryption enabled needs a gocryptfs.diriv
diff --git a/main.go b/main.go
index ed5784f..ddb4f4e 100644
--- a/main.go
+++ b/main.go
@@ -49,6 +49,9 @@ func loadConfig(args *argContainer) (masterkey []byte, confFile *configfile.Conf
 		pw := readpassword.Once(args.extpass)
 		tlog.Info.Println("Decrypting master key")
 		masterkey, confFile, err = configfile.LoadConfFile(args.config, pw)
+		for i := range pw {
+			pw[i] = 0
+		}
 	}
 	if err != nil {
 		tlog.Fatal.Println(err)
@@ -64,9 +67,15 @@ func changePassword(args *argContainer) {
 		exitcodes.Exit(err)
 	}
 	tlog.Info.Println("Please enter your new password.")
-	newPw := readpassword.Twice(args.extpass)
-	readpassword.CheckTrailingGarbage()
-	confFile.EncryptKey(masterkey, newPw, confFile.ScryptObject.LogN())
+	{
+		newPw := readpassword.Twice(args.extpass)
+		readpassword.CheckTrailingGarbage()
+		confFile.EncryptKey(masterkey, newPw, confFile.ScryptObject.LogN())
+		for i := range newPw {
+			newPw[i] = 0
+		}
+		// newPw runs out of scope here
+	}
 	// Are we resetting the password without knowing the old one using
 	// "-masterkey"?
 	if args.masterkey != "" {