From 75ebb28a625bc16d145f5acd9e0cc1d305716afe Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Thu, 10 Nov 2016 00:27:08 +0100
Subject: ctlsock: add initial limited implementation

At the moment, in forward mode you can only encrypt paths
and in reverse mode you can only decrypt paths.
---
 cli_args.go                                        |   3 +-
 internal/ctlsock/ctlsock_serve.go                  | 137 +++++++++++++++++++++
 internal/fusefrontend/ctlsock_interface.go         |  19 +++
 internal/fusefrontend/write_lock.go                |   2 +-
 internal/fusefrontend_reverse/ctlsock_interface.go |  19 +++
 internal/fusefrontend_reverse/rfs.go               |   2 +-
 mount.go                                           |  16 ++-
 tests/defaults/main_test.go                        |  37 ++++++
 8 files changed, 228 insertions(+), 7 deletions(-)
 create mode 100644 internal/ctlsock/ctlsock_serve.go
 create mode 100644 internal/fusefrontend/ctlsock_interface.go
 create mode 100644 internal/fusefrontend_reverse/ctlsock_interface.go

diff --git a/cli_args.go b/cli_args.go
index 358a6a9..5751f81 100644
--- a/cli_args.go
+++ b/cli_args.go
@@ -18,7 +18,7 @@ type argContainer struct {
 	plaintextnames, quiet, nosyslog, wpanic,
 	longnames, allow_other, ro, reverse, aessiv, nonempty, raw64 bool
 	masterkey, mountpoint, cipherdir, cpuprofile, extpass,
-	memprofile, ko, passfile string
+	memprofile, ko, passfile, ctlsock string
 	// Configuration file name override
 	config             string
 	notifypid, scryptn int
@@ -112,6 +112,7 @@ func parseCliOpts() (args argContainer) {
 	flagSet.StringVar(&args.extpass, "extpass", "", "Use external program for the password prompt")
 	flagSet.StringVar(&args.passfile, "passfile", "", "Read password from file")
 	flagSet.StringVar(&args.ko, "ko", "", "Pass additional options directly to the kernel, comma-separated list")
+	flagSet.StringVar(&args.ctlsock, "ctlsock", "", "Create control socket at specified path")
 	flagSet.IntVar(&args.notifypid, "notifypid", 0, "Send USR1 to the specified process after "+
 		"successful mount - used internally for daemonization")
 	flagSet.IntVar(&args.scryptn, "scryptn", configfile.ScryptDefaultLogN, "scrypt cost parameter logN. "+
diff --git a/internal/ctlsock/ctlsock_serve.go b/internal/ctlsock/ctlsock_serve.go
new file mode 100644
index 0000000..571260d
--- /dev/null
+++ b/internal/ctlsock/ctlsock_serve.go
@@ -0,0 +1,137 @@
+// Package ctlsock implementes the control socket interface that can be
+// activated by passing "-ctlsock" on the command line.
+package ctlsock
+
+import (
+	"encoding/json"
+	"errors"
+	"io"
+	"net"
+	"os"
+	"syscall"
+
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+// Interface should be implemented by fusefrontend[_reverse]
+type Interface interface {
+	EncryptPath(string) (string, error)
+	DecryptPath(string) (string, error)
+}
+
+// RequestStruct is sent by a client
+type RequestStruct struct {
+	EncryptPath string
+	DecryptPath string
+}
+
+// ResponseStruct is sent by us as response to a request
+type ResponseStruct struct {
+	// Result is the resulting decrypted or encrypted path. Empty on error.
+	Result string
+	// ErrNo is the error number as defined in errno.h.
+	// 0 means success and -1 means that the error number is not known
+	// (look at ErrText in this case).
+	ErrNo int32
+	// ErrText is a detailed error message.
+	ErrText string
+}
+
+type ctlSockHandler struct {
+	fs     Interface
+	socket *net.UnixListener
+}
+
+// CreateAndServe creates an unix socket at "path" and serves incoming
+// connections in a new goroutine.
+func CreateAndServe(path string, fs Interface) error {
+	sock, err := net.Listen("unix", path)
+	if err != nil {
+		return err
+	}
+	handler := ctlSockHandler{
+		fs:     fs,
+		socket: sock.(*net.UnixListener),
+	}
+	go handler.acceptLoop()
+	return nil
+}
+
+func (ch *ctlSockHandler) acceptLoop() {
+	for {
+		conn, err := ch.socket.Accept()
+		if err != nil {
+			tlog.Warn.Printf("ctlsock: Accept error: %v", err)
+			break
+		}
+		go ch.handleConnection(conn.(*net.UnixConn))
+	}
+}
+
+func (ch *ctlSockHandler) handleConnection(conn *net.UnixConn) {
+	// 2*PATH_MAX is definitely big enough for requests to decrypt or
+	// encrypt paths.
+	buf := make([]byte, 2*syscall.PathMax)
+	for {
+		n, err := conn.Read(buf)
+		if err == io.EOF {
+			conn.Close()
+			return
+		} else if err != nil {
+			tlog.Warn.Printf("ctlsock: Read error: %#v", err)
+			conn.Close()
+			return
+		}
+		buf = buf[:n]
+		var in RequestStruct
+		err = json.Unmarshal(buf, &in)
+		if err != nil {
+			tlog.Warn.Printf("ctlsock: Unmarshal error: %#v", err)
+			errorMsg := ResponseStruct{
+				ErrNo:   int32(syscall.EINVAL),
+				ErrText: err.Error(),
+			}
+			sendResponse(&errorMsg, conn)
+		}
+		ch.handleRequest(&in, conn)
+		// Restore original size.
+		buf = buf[:cap(buf)]
+	}
+}
+
+func (ch *ctlSockHandler) handleRequest(in *RequestStruct, conn *net.UnixConn) {
+	var err error
+	var out ResponseStruct
+	if in.DecryptPath != "" && in.EncryptPath != "" {
+		err = errors.New("Ambigous")
+	} else if in.DecryptPath == "" && in.EncryptPath == "" {
+		err = errors.New("No operation")
+	} else if in.DecryptPath != "" {
+		out.Result, err = ch.fs.DecryptPath(in.DecryptPath)
+	} else if in.EncryptPath != "" {
+		out.Result, err = ch.fs.EncryptPath(in.EncryptPath)
+	}
+	if err != nil {
+		out.ErrText = err.Error()
+		out.ErrNo = -1
+		// Try to extract the actual error number
+		if pe, ok := err.(*os.PathError); ok {
+			if se, ok := pe.Err.(syscall.Errno); ok {
+				out.ErrNo = int32(se)
+			}
+		}
+	}
+	sendResponse(&out, conn)
+}
+
+func sendResponse(msg *ResponseStruct, conn *net.UnixConn) {
+	jsonMsg, err := json.Marshal(msg)
+	if err != nil {
+		tlog.Warn.Printf("ctlsock: Marshal failed: %v", err)
+		return
+	}
+	_, err = conn.Write(jsonMsg)
+	if err != nil {
+		tlog.Warn.Printf("ctlsock: Write failed: %v", err)
+	}
+}
diff --git a/internal/fusefrontend/ctlsock_interface.go b/internal/fusefrontend/ctlsock_interface.go
new file mode 100644
index 0000000..c22dce6
--- /dev/null
+++ b/internal/fusefrontend/ctlsock_interface.go
@@ -0,0 +1,19 @@
+package fusefrontend
+
+import (
+	"errors"
+
+	"github.com/rfjakob/gocryptfs/internal/ctlsock"
+)
+
+var _ ctlsock.Interface = &FS{} // Verify that interface is implemented.
+
+// EncryptPath implements ctlsock.Backend
+func (fs *FS) EncryptPath(plainPath string) (string, error) {
+	return fs.encryptPath(plainPath)
+}
+
+// DecryptPath implements ctlsock.Backend
+func (fs *FS) DecryptPath(plainPath string) (string, error) {
+	return "", errors.New("Not implemented")
+}
diff --git a/internal/fusefrontend/write_lock.go b/internal/fusefrontend/write_lock.go
index 7394994..3addfd6 100644
--- a/internal/fusefrontend/write_lock.go
+++ b/internal/fusefrontend/write_lock.go
@@ -21,7 +21,7 @@ var wlock wlockMap
 // 2) lock ... unlock ...
 // 3) unregister
 type wlockMap struct {
-	// Counts lock() calls. As every operation that modifies a file should
+	// opCount counts lock() calls. As every operation that modifies a file should
 	// call it, this effectively serves as a write-operation counter.
 	// The variable is accessed without holding any locks so atomic operations
 	// must be used. It must be the first element of the struct to guarantee
diff --git a/internal/fusefrontend_reverse/ctlsock_interface.go b/internal/fusefrontend_reverse/ctlsock_interface.go
new file mode 100644
index 0000000..448663f
--- /dev/null
+++ b/internal/fusefrontend_reverse/ctlsock_interface.go
@@ -0,0 +1,19 @@
+package fusefrontend_reverse
+
+import (
+	"errors"
+
+	"github.com/rfjakob/gocryptfs/internal/ctlsock"
+)
+
+var _ ctlsock.Interface = &reverseFS{} // Verify that interface is implemented.
+
+// EncryptPath implements ctlsock.Backend
+func (rfs *reverseFS) EncryptPath(plainPath string) (string, error) {
+	return "", errors.New("Not implemented")
+}
+
+// DecryptPath implements ctlsock.Backend
+func (rfs *reverseFS) DecryptPath(plainPath string) (string, error) {
+	return rfs.decryptPath(plainPath)
+}
diff --git a/internal/fusefrontend_reverse/rfs.go b/internal/fusefrontend_reverse/rfs.go
index 87a2602..84348f7 100644
--- a/internal/fusefrontend_reverse/rfs.go
+++ b/internal/fusefrontend_reverse/rfs.go
@@ -49,7 +49,7 @@ var _ pathfs.FileSystem = &reverseFS{}
 // NewFS returns an encrypted FUSE overlay filesystem.
 // In this case (reverse mode) the backing directory is plain-text and
 // reverseFS provides an encrypted view.
-func NewFS(args fusefrontend.Args) pathfs.FileSystem {
+func NewFS(args fusefrontend.Args) *reverseFS {
 	if args.CryptoBackend != cryptocore.BackendAESSIV {
 		panic("reverse mode must use AES-SIV, everything else is insecure")
 	}
diff --git a/mount.go b/mount.go
index 1a00bb7..3bafd8c 100644
--- a/mount.go
+++ b/mount.go
@@ -18,6 +18,7 @@ import (
 
 	"github.com/rfjakob/gocryptfs/internal/configfile"
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+	"github.com/rfjakob/gocryptfs/internal/ctlsock"
 	"github.com/rfjakob/gocryptfs/internal/fusefrontend"
 	"github.com/rfjakob/gocryptfs/internal/fusefrontend_reverse"
 	"github.com/rfjakob/gocryptfs/internal/tlog"
@@ -165,10 +166,18 @@ func initFuseFrontend(key []byte, args *argContainer, confFile *configfile.ConfF
 	jsonBytes, _ := json.MarshalIndent(frontendArgs, "", "\t")
 	tlog.Debug.Printf("frontendArgs: %s", string(jsonBytes))
 	var finalFs pathfs.FileSystem
+	var ctlSockBackend ctlsock.Interface
 	if args.reverse {
-		finalFs = fusefrontend_reverse.NewFS(frontendArgs)
+		fs := fusefrontend_reverse.NewFS(frontendArgs)
+		finalFs = fs
+		ctlSockBackend = fs
 	} else {
-		finalFs = fusefrontend.NewFS(frontendArgs)
+		fs := fusefrontend.NewFS(frontendArgs)
+		finalFs = fs
+		ctlSockBackend = fs
+	}
+	if args.ctlsock != "" {
+		ctlsock.CreateAndServe(args.ctlsock, ctlSockBackend)
 	}
 	pathFsOpts := &pathfs.PathNodeFsOptions{ClientInodes: true}
 	pathFs := pathfs.NewPathNodeFs(finalFs, pathFsOpts)
@@ -200,9 +209,8 @@ func initFuseFrontend(key []byte, args *argContainer, confFile *configfile.ConfF
 	if args.reverse {
 		mOpts.Name += "-reverse"
 	}
-
 	// The kernel enforces read-only operation, we just have to pass "ro".
-	// Reverse mounts are always read-only
+	// Reverse mounts are always read-only.
 	if args.ro || args.reverse {
 		mOpts.Options = append(mOpts.Options, "ro")
 	}
diff --git a/tests/defaults/main_test.go b/tests/defaults/main_test.go
index 849aa69..8733c8b 100644
--- a/tests/defaults/main_test.go
+++ b/tests/defaults/main_test.go
@@ -2,10 +2,16 @@
 package defaults
 
 import (
+	"encoding/json"
+	"fmt"
+	"net"
 	"os"
 	"os/exec"
+	"syscall"
 	"testing"
+	"time"
 
+	"github.com/rfjakob/gocryptfs/internal/ctlsock"
 	"github.com/rfjakob/gocryptfs/tests/test_helpers"
 )
 
@@ -35,3 +41,34 @@ func Test1980Tar(t *testing.T) {
 		t.Errorf("Wrong mtime: %d", m)
 	}
 }
+
+func TestCtlSock(t *testing.T) {
+	cDir := test_helpers.InitFS(t)
+	pDir := cDir + ".mnt"
+	sock := cDir + ".sock"
+	test_helpers.MountOrFatal(t, cDir, pDir, "-ctlsock="+sock, "-extpass", "echo test")
+	defer test_helpers.UnmountPanic(pDir)
+	conn, err := net.DialTimeout("unix", sock, 1*time.Second)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer conn.Close()
+	conn.SetDeadline(time.Now().Add(time.Second))
+	msg := []byte(`{"EncryptPath": "foobar"}`)
+	_, err = conn.Write(msg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	buf := make([]byte, 2*syscall.PathMax)
+	n, err := conn.Read(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	buf = buf[:n]
+	var response ctlsock.ResponseStruct
+	json.Unmarshal(buf, &response)
+	if response.Result == "" || response.ErrNo != 0 {
+		fmt.Printf("%s\n", string(buf))
+		t.Errorf("got an error reply")
+	}
+}
-- 
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