3 files changed, 225 insertions, 0 deletions
diff --git a/internal/ctlsocksrv/ctlsock_serve.go b/internal/ctlsocksrv/ctlsock_serve.go
new file mode 100644
index 0000000..b63759e
--- /dev/null
+++ b/internal/ctlsocksrv/ctlsock_serve.go
@@ -0,0 +1,163 @@
+// Package ctlsocksrv implements the control socket interface that can be
+// activated by passing "-ctlsock" on the command line.
+package ctlsocksrv
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"os"
+	"syscall"
+
+	"github.com/rfjakob/gocryptfs/ctlsock"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+// Interface should be implemented by fusefrontend[_reverse]
+type Interface interface {
+	EncryptPath(string) (string, error)
+	DecryptPath(string) (string, error)
+}
+
+type ctlSockHandler struct {
+	fs     Interface
+	socket *net.UnixListener
+}
+
+// Serve serves incoming connections on "sock". This call blocks so you
+// probably want to run it in a new goroutine.
+func Serve(sock net.Listener, fs Interface) {
+	handler := ctlSockHandler{
+		fs:     fs,
+		socket: sock.(*net.UnixListener),
+	}
+	handler.acceptLoop()
+}
+
+func (ch *ctlSockHandler) acceptLoop() {
+	for {
+		conn, err := ch.socket.Accept()
+		if err != nil {
+			// This can trigger on program exit with "use of closed network connection".
+			// Special-casing this is hard due to https://github.com/golang/go/issues/4373
+			// so just don't use tlog.Warn to not cause panics in the tests.
+			tlog.Info.Printf("ctlsock: Accept error: %v", err)
+			break
+		}
+		go ch.handleConnection(conn.(*net.UnixConn))
+	}
+}
+
+// ReadBufSize is the size of the request read buffer.
+// The longest possible path is 4096 bytes on Linux and 1024 on Mac OS X so
+// 5000 bytes should be enough to hold the whole JSON request. This
+// assumes that the path does not contain too many characters that had to be
+// be escaped in JSON (for example, a null byte blows up to "\u0000").
+// We abort the connection if the request is bigger than this.
+const ReadBufSize = 5000
+
+// handleConnection reads and parses JSON requests from "conn"
+func (ch *ctlSockHandler) handleConnection(conn *net.UnixConn) {
+	buf := make([]byte, ReadBufSize)
+	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
+		}
+		if n == ReadBufSize {
+			tlog.Warn.Printf("ctlsock: request too big (max = %d bytes)", ReadBufSize-1)
+			conn.Close()
+			return
+		}
+		data := buf[:n]
+		var in ctlsock.RequestStruct
+		err = json.Unmarshal(data, &in)
+		if err != nil {
+			tlog.Warn.Printf("ctlsock: JSON Unmarshal error: %#v", err)
+			err = errors.New("JSON Unmarshal error: " + err.Error())
+			sendResponse(conn, err, "", "")
+			continue
+		}
+		ch.handleRequest(&in, conn)
+	}
+}
+
+// handleRequest handles an already-unmarshaled JSON request
+func (ch *ctlSockHandler) handleRequest(in *ctlsock.RequestStruct, conn *net.UnixConn) {
+	var err error
+	var inPath, outPath, clean, warnText string
+	// You cannot perform both decryption and encryption in one request
+	if in.DecryptPath != "" && in.EncryptPath != "" {
+		err = errors.New("Ambiguous")
+		sendResponse(conn, err, "", "")
+		return
+	}
+	// Neither encryption nor encryption has been requested, makes no sense
+	if in.DecryptPath == "" && in.EncryptPath == "" {
+		err = errors.New("Empty input")
+		sendResponse(conn, err, "", "")
+		return
+	}
+	// Canonicalize input path
+	if in.EncryptPath != "" {
+		inPath = in.EncryptPath
+	} else {
+		inPath = in.DecryptPath
+	}
+	clean = SanitizePath(inPath)
+	// Warn if a non-canonical path was passed
+	if inPath != clean {
+		warnText = fmt.Sprintf("Non-canonical input path '%s' has been interpreted as '%s'.", inPath, clean)
+	}
+	// Error out if the canonical path is now empty
+	if clean == "" {
+		err = errors.New("Empty input after canonicalization")
+		sendResponse(conn, err, "", warnText)
+		return
+	}
+	// Actual encrypt or decrypt operation
+	if in.EncryptPath != "" {
+		outPath, err = ch.fs.EncryptPath(clean)
+	} else {
+		outPath, err = ch.fs.DecryptPath(clean)
+	}
+	sendResponse(conn, err, outPath, warnText)
+}
+
+// sendResponse sends a JSON response message
+func sendResponse(conn *net.UnixConn, err error, result string, warnText string) {
+	msg := ctlsock.ResponseStruct{
+		Result:   result,
+		WarnText: warnText,
+	}
+	if err != nil {
+		msg.ErrText = err.Error()
+		msg.ErrNo = -1
+		// Try to extract the actual error number
+		if pe, ok := err.(*os.PathError); ok {
+			if se, ok := pe.Err.(syscall.Errno); ok {
+				msg.ErrNo = int32(se)
+			}
+		} else if err == syscall.ENOENT {
+			msg.ErrNo = int32(syscall.ENOENT)
+		}
+	}
+	jsonMsg, err := json.Marshal(msg)
+	if err != nil {
+		tlog.Warn.Printf("ctlsock: Marshal failed: %v", err)
+		return
+	}
+	// For convenience for the user, add a newline at the end.
+	jsonMsg = append(jsonMsg, '\n')
+	_, err = conn.Write(jsonMsg)
+	if err != nil {
+		tlog.Warn.Printf("ctlsock: Write failed: %v", err)
+	}
+}
diff --git a/internal/ctlsocksrv/sanitize.go b/internal/ctlsocksrv/sanitize.go
new file mode 100644
index 0000000..4333872
--- /dev/null
+++ b/internal/ctlsocksrv/sanitize.go
@@ -0,0 +1,32 @@
+package ctlsocksrv
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// SanitizePath adapts filepath.Clean for FUSE paths.
+// 1) Leading slash(es) are dropped
+// 2) It returns "" instead of "."
+// 3) If the cleaned path points above CWD (start with ".."), an empty string
+//    is returned
+// See the TestSanitizePath testcases for examples.
+func SanitizePath(path string) string {
+	// (1)
+	for len(path) > 0 && path[0] == '/' {
+		path = path[1:]
+	}
+	if len(path) == 0 {
+		return ""
+	}
+	clean := filepath.Clean(path)
+	// (2)
+	if clean == "." {
+		return ""
+	}
+	// (3)
+	if clean == ".." || strings.HasPrefix(clean, "../") {
+		return ""
+	}
+	return clean
+}
diff --git a/internal/ctlsocksrv/sanitize_test.go b/internal/ctlsocksrv/sanitize_test.go
new file mode 100644
index 0000000..2462d5d
--- /dev/null
+++ b/internal/ctlsocksrv/sanitize_test.go
@@ -0,0 +1,30 @@
+package ctlsocksrv
+
+import (
+	"testing"
+)
+
+func TestSanitizePath(t *testing.T) {
+	testCases := [][]string{
+		{"", ""},
+		{".", ""},
+		{"/", ""},
+		{"foo", "foo"},
+		{"/foo", "foo"},
+		{"foo/", "foo"},
+		{"/foo/", "foo"},
+		{"/foo/./foo", "foo/foo"},
+		{"./", ""},
+		{"..", ""},
+		{"foo/../..", ""},
+		{"foo/../../aaaaaa", ""},
+		{"/foo/../../aaaaaa", ""},
+		{"/////", ""},
+	}
+	for _, tc := range testCases {
+		res := SanitizePath(tc[0])
+		if res != tc[1] {
+			t.Errorf("%q: got %q, want %q", tc[0], res, tc[1])
+		}
+	}
+}