Fix setupDev logic in rootfs_linux.go

setupDev was introduced in #96, but broken since #536 because spec 0.3.0 introduced default devices.

Fix #80 again
Fix docker/docker#21808

Signed-off-by: Akihiro Suda <suda.kyoto@gmail.com>
Signed-off-by: Alexander Morozov <lk4d4@docker.com>

libcontainer/rootfs_linux.go

@@ -25,6 +25,16 @@ import (
 
 const defaultMountFlags = syscall.MS_NOEXEC | syscall.MS_NOSUID | syscall.MS_NODEV
 
+// setupDev returns true if /dev needs to be set up.
+func needsSetupDev(config *configs.Config) bool {
+	for _, m := range config.Mounts {
+		if m.Device == "bind" && (m.Destination == "/dev" || m.Destination == "/dev/") {
+			return false
+		}
+	}
+	return true
+}
+
 // setupRootfs sets up the devices, mount points, and filesystems for use inside a
 // new mount namespace.
 func setupRootfs(config *configs.Config, console *linuxConsole, pipe io.ReadWriter) (err error) {
@@ -32,7 +42,7 @@ func setupRootfs(config *configs.Config, console *linuxConsole, pipe io.ReadWrit
 		return newSystemError(err)
 	}
 
-	setupDev := len(config.Devices) != 0
+	setupDev := needsSetupDev(config)
 	for _, m := range config.Mounts {
 		for _, precmd := range m.PremountCmds {
 			if err := mountCmd(precmd); err != nil {

libcontainer/rootfs_linux_test.go

@@ -2,7 +2,11 @@
 
 package libcontainer
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/opencontainers/runc/libcontainer/configs"
+)
 
 func TestCheckMountDestOnProc(t *testing.T) {
 	dest := "/rootfs/proc/"
@@ -35,3 +39,63 @@ func TestCheckMountRoot(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestNeedsSetupDev(t *testing.T) {
+	config := &configs.Config{
+		Mounts: []*configs.Mount{
+			{
+				Device:      "bind",
+				Source:      "/dev",
+				Destination: "/dev",
+			},
+		},
+	}
+	if needsSetupDev(config) {
+		t.Fatal("expected needsSetupDev to be false, got true")
+	}
+}
+
+func TestNeedsSetupDevStrangeSource(t *testing.T) {
+	config := &configs.Config{
+		Mounts: []*configs.Mount{
+			{
+				Device:      "bind",
+				Source:      "/devx",
+				Destination: "/dev",
+			},
+		},
+	}
+	if needsSetupDev(config) {
+		t.Fatal("expected needsSetupDev to be false, got true")
+	}
+}
+
+func TestNeedsSetupDevStrangeDest(t *testing.T) {
+	config := &configs.Config{
+		Mounts: []*configs.Mount{
+			{
+				Device:      "bind",
+				Source:      "/dev",
+				Destination: "/devx",
+			},
+		},
+	}
+	if !needsSetupDev(config) {
+		t.Fatal("expected needsSetupDev to be true, got false")
+	}
+}
+
+func TestNeedsSetupDevStrangeSourceDest(t *testing.T) {
+	config := &configs.Config{
+		Mounts: []*configs.Mount{
+			{
+				Device:      "bind",
+				Source:      "/devx",
+				Destination: "/devx",
+			},
+		},
+	}
+	if !needsSetupDev(config) {
+		t.Fatal("expected needsSetupDev to be true, got false")
+	}
+}