Add remount for bind mounts in ro

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

container.go

@@ -716,7 +716,7 @@ func (container *Container) Start() (err error) {
 
 	for r, v := range container.Volumes {
 		mountAs := "ro"
-		if container.VolumesRW[v] {
+		if container.VolumesRW[r] {
 			mountAs = "rw"
 		}
 

mount/mount_test.go

@@ -48,7 +48,7 @@ func TestMounted(t *testing.T) {
 	}
 	f.Close()
 
-	if err := Mount(sourcePath, targetPath, "none", "bind,ro"); err != nil {
+	if err := Mount(sourcePath, targetPath, "none", "bind,rw"); err != nil {
 		t.Fatal(err)
 	}
 	defer func() {
@@ -64,4 +64,47 @@ func TestMounted(t *testing.T) {
 	if !mounted {
 		t.Fatalf("Expected %s to be mounted", targetPath)
 	}
+	if _, err := os.Stat(targetPath); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestMountReadonly(t *testing.T) {
+	tmp := path.Join(os.TempDir(), "mount-tests")
+	if err := os.MkdirAll(tmp, 0777); err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmp)
+
+	var (
+		sourcePath = path.Join(tmp, "sourcefile.txt")
+		targetPath = path.Join(tmp, "targetfile.txt")
+	)
+
+	f, err := os.Create(sourcePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.WriteString("hello")
+	f.Close()
+
+	f, err = os.Create(targetPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	if err := Mount(sourcePath, targetPath, "none", "bind,ro"); err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := Unmount(targetPath); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	f, err = os.OpenFile(targetPath, os.O_RDWR, 0777)
+	if err == nil {
+		t.Fatal("Should not be able to open a ro file as rw")
+	}
 }

mount/mounter_linux.go

@@ -5,7 +5,15 @@ import (
 )
 
 func mount(device, target, mType string, flag uintptr, data string) error {
-	return syscall.Mount(device, target, mType, flag, data)
+	if err := syscall.Mount(device, target, mType, flag, data); err != nil {
+		return err
+	}
+
+	// If we have a bind mount or remount, remount...
+	if flag&syscall.MS_BIND == syscall.MS_BIND && flag&syscall.MS_RDONLY == syscall.MS_RDONLY {
+		return syscall.Mount(device, target, mType, flag|syscall.MS_REMOUNT, data)
+	}
+	return nil
 }
 
 func unmount(target string, flag int) error {