Fix file mode check in fsgofer Attach

PiperOrigin-RevId: 263189654

runsc/fsgofer/fsgofer.go

@@ -125,7 +125,7 @@ func (a *attachPoint) Attach() (p9.File, error) {
 		return nil, fmt.Errorf("stat file %q, err: %v", a.prefix, err)
 	}
 	mode := syscall.O_RDWR
-	if a.conf.ROMount || stat.Mode&syscall.S_IFDIR != 0 {
+	if a.conf.ROMount || (stat.Mode&syscall.S_IFMT) == syscall.S_IFDIR {
 		mode = syscall.O_RDONLY
 	}
 
@@ -141,9 +141,13 @@ func (a *attachPoint) Attach() (p9.File, error) {
 		f.Close()
 		return nil, fmt.Errorf("attach point already attached, prefix: %s", a.prefix)
 	}
-	a.attached = true
 
-	return newLocalFile(a, f, a.prefix, stat)
+	rv, err := newLocalFile(a, f, a.prefix, stat)
+	if err != nil {
+		return nil, err
+	}
+	a.attached = true
+	return rv, nil
 }
 
 // makeQID returns a unique QID for the given stat buffer.

runsc/fsgofer/fsgofer_test.go

@@ -17,8 +17,10 @@ package fsgofer
 import (
 	"fmt"
 	"io/ioutil"
+	"net"
 	"os"
 	"path"
+	"path/filepath"
 	"syscall"
 	"testing"
 
@@ -621,6 +623,46 @@ func TestAttachFile(t *testing.T) {
 	}
 }
 
+func TestAttachInvalidType(t *testing.T) {
+	dir, err := ioutil.TempDir("", "attach-")
+	if err != nil {
+		t.Fatalf("ioutil.TempDir() failed, err: %v", err)
+	}
+	defer os.RemoveAll(dir)
+
+	fifo := filepath.Join(dir, "fifo")
+	if err := syscall.Mkfifo(fifo, 0755); err != nil {
+		t.Fatalf("Mkfifo(%q): %v", fifo, err)
+	}
+
+	socket := filepath.Join(dir, "socket")
+	l, err := net.Listen("unix", socket)
+	if err != nil {
+		t.Fatalf("net.Listen(unix, %q): %v", socket, err)
+	}
+	defer l.Close()
+
+	for _, tc := range []struct {
+		name string
+		path string
+	}{
+		{name: "fifo", path: fifo},
+		{name: "socket", path: socket},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			conf := Config{ROMount: false}
+			a, err := NewAttachPoint(tc.path, conf)
+			if err != nil {
+				t.Fatalf("NewAttachPoint failed: %v", err)
+			}
+			f, err := a.Attach()
+			if f != nil || err == nil {
+				t.Fatalf("Attach should have failed, got (%v, nil)", f)
+			}
+		})
+	}
+}
+
 func TestDoubleAttachError(t *testing.T) {
 	conf := Config{ROMount: false}
 	root, err := ioutil.TempDir("", "root-")