main: add "-nonempty" option

Documentation/MANPAGE.md

@@ -79,6 +79,10 @@ anybody on the machine who can execute "ps -auxwww".
 :	Write memory profile to specified file. This is useful when debugging
 memory usage of gocryptfs.
 
+**-nonempty**
+:	Allow mounting over non-empty directories. FUSE by default disallows
+this because to prevent accidential shadowing of files.
+
 **-nosyslog**
 :	Diagnostic messages are normally redirected to syslog once gocryptfs
 daemonizes. This option disables the redirection and messages will

cli_args.go

@@ -14,7 +14,7 @@ import (
 type argContainer struct {
 	debug, init, zerokey, fusedebug, openssl, passwd, foreground, version,
 	plaintextnames, quiet, nosyslog, wpanic,
-	longnames, allow_other, ro, reverse, aessiv bool
+	longnames, allow_other, ro, reverse, aessiv, nonempty bool
 	masterkey, mountpoint, cipherdir, cpuprofile, extpass,
 	memprofile, o string
 	// Configuration file name override
@@ -52,6 +52,7 @@ func parseCliOpts() (args argContainer) {
 	flagSet.BoolVar(&args.ro, "ro", false, "Mount the filesystem read-only")
 	flagSet.BoolVar(&args.reverse, "reverse", false, "Reverse mode")
 	flagSet.BoolVar(&args.aessiv, "aessiv", false, "AES-SIV encryption")
+	flagSet.BoolVar(&args.nonempty, "nonempty", false, "Allow mounting over non-empty directories")
 	flagSet.StringVar(&args.masterkey, "masterkey", "", "Mount with explicit master key")
 	flagSet.StringVar(&args.cpuprofile, "cpuprofile", "", "Write cpu profile to specified file")
 	flagSet.StringVar(&args.memprofile, "memprofile", "", "Write memory profile to specified file")

main.go

@@ -236,7 +236,11 @@ func main() {
 		tlog.Fatal.Printf("Invalid mountpoint: %v", err)
 		os.Exit(ErrExitMountPoint)
 	}
-	err = checkDirEmpty(args.mountpoint)
+	if args.nonempty {
+		err = checkDir(args.mountpoint)
+	} else {
+		err = checkDirEmpty(args.mountpoint)
+	}
 	if err != nil {
 		tlog.Fatal.Printf("Invalid mountpoint: %v", err)
 		os.Exit(ErrExitMountPoint)
@@ -348,6 +352,9 @@ func initFuseFrontend(key []byte, args argContainer, confFile *configfile.ConfFi
 		// Make the kernel check the file permissions for us
 		mOpts.Options = append(mOpts.Options, "default_permissions")
 	}
+	if args.nonempty {
+		mOpts.Options = append(mOpts.Options, "nonempty")
+	}
 	// Set values shown in "df -T" and friends
 	// First column, "Filesystem"
 	mOpts.Options = append(mOpts.Options, "fsname="+args.cipherdir)

tests/normal/cli_test.go

@@ -3,6 +3,7 @@ package normal
 // Test CLI operations like "-init", "-password" etc
 
 import (
+	"io/ioutil"
 	"os"
 	"os/exec"
 	"testing"
@@ -146,3 +147,24 @@ func TestRo(t *testing.T) {
 		t.Errorf("Create should have failed")
 	}
 }
+
+// Test "-nonempty"
+func TestNonempty(t *testing.T) {
+	dir := test_helpers.InitFS(t)
+	mnt := dir + ".mnt"
+	err := os.Mkdir(mnt, 0700)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = ioutil.WriteFile(mnt+"/somefile", []byte("xyz"), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = test_helpers.Mount(dir, mnt, false, "-extpass=echo test")
+	if err == nil {
+		t.Errorf("Mounting over a file should fail per default")
+	}
+	// Should work with "-nonempty"
+	test_helpers.MountOrFatal(t, dir, mnt, "-nonempty", "-extpass=echo test")
+	test_helpers.UnmountPanic(mnt)
+}