ctlsock: delete colliding orphaned socket file

Detect and delete an orphaned socket file that collides with
the ctlsock we want to create.

Fixes https://github.com/rfjakob/gocryptfs/issues/776

2 files changed, 72 insertions, 0 deletions

diff --git a/internal/ctlsocksrv/ctlsock_listen.go b/internal/ctlsocksrv/ctlsock_listen.go
index 1db9cbc..94ffca4 100644
--- a/internal/ctlsocksrv/ctlsock_listen.go
+++ b/internal/ctlsocksrv/ctlsock_listen.go
@@ -1,9 +1,44 @@
 package ctlsocksrv
 
 import (
+	"errors"
+	"io/fs"
 	"net"
+	"os"
+	"syscall"
+	"time"
+
+	"github.com/rfjakob/gocryptfs/v2/internal/tlog"
 )
 
+// cleanupOrphanedSocket deletes an orphaned socket file at `path`.
+// The file at `path` will only be deleted if:
+// 1) It is a socket file
+// 2) Connecting to it results in ECONNREFUSED
+func cleanupOrphanedSocket(path string) {
+	fi, err := os.Stat(path)
+	if err != nil {
+		return
+	}
+	if fi.Mode().Type() != fs.ModeSocket {
+		return
+	}
+	conn, err := net.DialTimeout("unix", path, time.Second)
+	if err == nil {
+		// This socket file is still active. Don't delete it.
+		conn.Close()
+		return
+	}
+	if errors.Is(err, syscall.ECONNREFUSED) {
+		tlog.Info.Printf("ctlsock: deleting orphaned socket file %q\n", path)
+		err = os.Remove(path)
+		if err != nil {
+			tlog.Warn.Printf("ctlsock: deleting socket file failed: %v", path)
+		}
+	}
+}
+
 func Listen(path string) (net.Listener, error) {
+	cleanupOrphanedSocket(path)
 	return net.Listen("unix", path)
 }
diff --git a/tests/cli/cli_test.go b/tests/cli/cli_test.go
index 686d14c..b2f9f40 100644
--- a/tests/cli/cli_test.go
+++ b/tests/cli/cli_test.go
@@ -4,6 +4,7 @@ package cli
 import (
 	"bytes"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -1033,3 +1034,39 @@ func TestMountCreat(t *testing.T) {
 		test_helpers.UnmountPanic(mnt)
 	}
 }
+
+// https://github.com/rfjakob/gocryptfs/issues/776
+func TestOrphanedSocket(t *testing.T) {
+	cDir := test_helpers.InitFS(t)
+	ctlSock := cDir + ".sock"
+	mnt := cDir + ".mnt"
+	test_helpers.MountOrFatal(t, cDir, mnt, "-extpass", "echo test", "-wpanic=false", "-ctlsock", ctlSock)
+
+	mnt2 := cDir + ".mnt2"
+	err := test_helpers.Mount(cDir, mnt2, false, "-extpass", "echo test", "-wpanic=false", "-ctlsock", ctlSock)
+	exitCode := test_helpers.ExtractCmdExitCode(err)
+	if exitCode != exitcodes.CtlSock {
+		t.Errorf("wrong exit code: want=%d, have=%d", exitcodes.CtlSock, exitCode)
+	}
+	test_helpers.UnmountPanic(mnt)
+
+	// Unmount returns before the gocryptfs process has terminated and before the
+	// socket file has been deleted. Wait out the deletion.
+	for i := 0; i < 100; i++ {
+		_, err := os.Stat(ctlSock)
+		if errors.Is(err, os.ErrNotExist) {
+			break
+		}
+		time.Sleep(time.Millisecond)
+	}
+
+	// Create orphaned socket file
+	err = syscall.Mknod(ctlSock, syscall.S_IFSOCK|0666, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Should delete the socket file automatically and the mount should work
+	test_helpers.MountOrFatal(t, cDir, mnt, "-extpass", "echo test", "-wpanic=false", "-ctlsock", ctlSock)
+	test_helpers.UnmountPanic(mnt)
+}