Configure the network namespace before executing jailer

Right now there is a bug when trying to start a Firecracker VM with
jailer using a CNI where the VM is never joined to the correct network
namespace. This is because in its current form, the CNI execution occurs
when `fcinit.SetupNetwork` runs, which occurs _after_ the jailer has
already created a chroot and dropped privleges.

This fixes the problem by executing the `fcinit.SetupNetwork` call
_before_ running jailer and removing that hook from the `FcInit`
functions later on. It also passes through the UID and GID options to
the `tc-redirect-tap` plugin and includes the `IgnoreUnknown` directive
so that chained CNI plugins work.

Signed-off-by: Dan Norris <[email protected]>

machine.go

@@ -376,6 +376,26 @@ func NewMachine(ctx context.Context, cfg Config, opts ...Opt) (*Machine, error)
 
 	if cfg.JailerCfg != nil {
 		m.Handlers.Validation = m.Handlers.Validation.Append(JailerConfigValidationHandler)
+
+		if cfg.NetNS == "" && cfg.NetworkInterfaces.cniInterface() != nil {
+			cfg.NetNS = filepath.Join(defaultNetNSDir, cfg.VMID)
+
+			// If the network namespace is set, we need to setup the network prior to running the jailer.
+			err := cfg.ValidateNetwork()
+			if err != nil {
+				return nil, fmt.Errorf("failed to validate network configuration: %w", err)
+			}
+			m.Handlers.Validation = m.Handlers.Validation.Remove(ValidateNetworkCfgHandlerName)
+			m.Handlers.FcInit = m.Handlers.FcInit.Remove(SetupNetworkHandlerName)
+
+			jailLog := log.New()
+			err, cleanupFuncs := cfg.NetworkInterfaces.setupNetwork(ctx, cfg.VMID, cfg.NetNS, log.NewEntry(jailLog), cfg.JailerCfg.UID, cfg.JailerCfg.GID)
+			m.cleanupFuncs = append(m.cleanupFuncs, cleanupFuncs...)
+			if err != nil {
+				return nil, fmt.Errorf("failed to setup network prior to jailing: %w", err)
+			}
+		}
+
 		if err := jail(ctx, m, &cfg); err != nil {
 			return nil, err
 		}
@@ -492,7 +512,7 @@ func (m *Machine) GetFirecrackerVersion(ctx context.Context) (string, error) {
 }
 
 func (m *Machine) setupNetwork(ctx context.Context) error {
-	err, cleanupFuncs := m.Cfg.NetworkInterfaces.setupNetwork(ctx, m.Cfg.VMID, m.Cfg.NetNS, m.logger)
+	err, cleanupFuncs := m.Cfg.NetworkInterfaces.setupNetwork(ctx, m.Cfg.VMID, m.Cfg.NetNS, m.logger, nil, nil)
 	m.cleanupFuncs = append(m.cleanupFuncs, cleanupFuncs...)
 	return err
 }

network.go

@@ -98,6 +98,8 @@ func (networkInterfaces NetworkInterfaces) setupNetwork(
 	vmID string,
 	netNSPath string,
 	logger *log.Entry,
+	uid *int,
+	gid *int,
 ) (error, []func() error) {
 	var cleanupFuncs []func() error
 
@@ -111,6 +113,22 @@ func (networkInterfaces NetworkInterfaces) setupNetwork(
 	cniNetworkInterface.CNIConfiguration.containerID = vmID
 	cniNetworkInterface.CNIConfiguration.netNSPath = netNSPath
 	cniNetworkInterface.CNIConfiguration.setDefaults()
+	if uid != nil && gid != nil {
+		cniNetworkInterface.CNIConfiguration.Args = [][2]string{
+			{
+				"IgnoreUnknown",
+				"true",
+			},
+			{
+				"TC_REDIRECT_TAP_UID",
+				fmt.Sprintf("%d", *uid),
+			},
+			{
+				"TC_REDIRECT_TAP_GID",
+				fmt.Sprintf("%d", *gid),
+			},
+		}
+	}
 
 	// Make sure the netns is setup. If the path doesn't yet exist, it will be
 	// initialized with a new empty netns.