// Copyright 2018 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package boot loads the kernel and runs the application.
package boot

import (
	"fmt"
	"math/rand"
	"sync/atomic"
	"syscall"
	gtime "time"

	specs "github.com/opencontainers/runtime-spec/specs-go"
	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
	"gvisor.googlesource.com/gvisor/pkg/cpuid"
	"gvisor.googlesource.com/gvisor/pkg/log"
	"gvisor.googlesource.com/gvisor/pkg/sentry/inet"
	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
	"gvisor.googlesource.com/gvisor/pkg/sentry/loader"
	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
	"gvisor.googlesource.com/gvisor/pkg/sentry/platform/kvm"
	"gvisor.googlesource.com/gvisor/pkg/sentry/platform/ptrace"
	"gvisor.googlesource.com/gvisor/pkg/sentry/sighandling"
	slinux "gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux"
	"gvisor.googlesource.com/gvisor/pkg/sentry/time"
	"gvisor.googlesource.com/gvisor/pkg/sentry/watchdog"
	"gvisor.googlesource.com/gvisor/pkg/tcpip/link/sniffer"
	"gvisor.googlesource.com/gvisor/pkg/tcpip/network/arp"
	"gvisor.googlesource.com/gvisor/pkg/tcpip/network/ipv4"
	"gvisor.googlesource.com/gvisor/pkg/tcpip/network/ipv6"
	"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
	"gvisor.googlesource.com/gvisor/pkg/tcpip/transport/tcp"
	"gvisor.googlesource.com/gvisor/pkg/tcpip/transport/udp"
	"gvisor.googlesource.com/gvisor/runsc/boot/filter"
	"gvisor.googlesource.com/gvisor/runsc/specutils"

	// Include supported socket providers.
	"gvisor.googlesource.com/gvisor/pkg/sentry/socket/epsocket"
	"gvisor.googlesource.com/gvisor/pkg/sentry/socket/hostinet"
	_ "gvisor.googlesource.com/gvisor/pkg/sentry/socket/netlink"
	_ "gvisor.googlesource.com/gvisor/pkg/sentry/socket/netlink/route"
	_ "gvisor.googlesource.com/gvisor/pkg/sentry/socket/unix"
)

// Loader keeps state needed to start the kernel and run the application.
type Loader struct {
	// k is the kernel.
	k *kernel.Kernel

	// ctrl is the control server.
	ctrl *controller

	conf *Config

	// console is set to true if terminal is enabled.
	console bool

	watchdog *watchdog.Watchdog

	// stopSignalForwarding disables forwarding of signals to the sandboxed
	// app. It should be called when a sandbox is destroyed.
	stopSignalForwarding func()

	// procArgs refers to the initial application task.
	procArgs kernel.CreateProcessArgs
}

func init() {
	// Initialize the random number generator.
	rand.Seed(gtime.Now().UnixNano())

	// Register the global syscall table.
	kernel.RegisterSyscallTable(slinux.AMD64)
}

// New initializes a new kernel loader configured by spec.
func New(spec *specs.Spec, conf *Config, controllerFD int, ioFDs []int, console bool) (*Loader, error) {
	// Create kernel and platform.
	p, err := createPlatform(conf)
	if err != nil {
		return nil, fmt.Errorf("error creating platform: %v", err)
	}
	k := &kernel.Kernel{
		Platform: p,
	}

	// Create VDSO.
	vdso, err := loader.PrepareVDSO(p)
	if err != nil {
		return nil, fmt.Errorf("error creating vdso: %v", err)
	}

	// Create timekeeper.
	tk, err := kernel.NewTimekeeper(k, vdso.ParamPage.FileRange())
	if err != nil {
		return nil, fmt.Errorf("error creating timekeeper: %v", err)
	}
	tk.SetClocks(time.NewCalibratedClocks())

	// Create initial limits.
	ls, err := createLimitSet(spec)
	if err != nil {
		return nil, fmt.Errorf("error creating limits: %v", err)
	}

	// Create capabilities.
	caps, err := specutils.Capabilities(spec.Process.Capabilities)
	if err != nil {
		return nil, fmt.Errorf("error creating capabilities: %v", err)
	}

	// Convert the spec's additional GIDs to KGIDs.
	extraKGIDs := make([]auth.KGID, 0, len(spec.Process.User.AdditionalGids))
	for _, GID := range spec.Process.User.AdditionalGids {
		extraKGIDs = append(extraKGIDs, auth.KGID(GID))
	}

	// Create credentials.
	creds := auth.NewUserCredentials(
		auth.KUID(spec.Process.User.UID),
		auth.KGID(spec.Process.User.GID),
		extraKGIDs,
		caps,
		auth.NewRootUserNamespace())
	if err != nil {
		return nil, fmt.Errorf("error creating credentials: %v", err)
	}

	// Create user namespace.
	// TODO: Not clear what domain name should be here.  It is
	// not configurable from runtime spec.
	utsns := kernel.NewUTSNamespace(spec.Hostname, "", creds.UserNamespace)

	ipcns := kernel.NewIPCNamespace()

	if err := enableStrace(conf); err != nil {
		return nil, fmt.Errorf("failed to enable strace: %v", err)
	}

	// Get the executable path, which is a bit tricky because we have to
	// inspect the environment PATH which is relative to the root path.
	exec, err := specutils.GetExecutablePath(spec.Process.Args[0], spec.Root.Path, spec.Process.Env)
	if err != nil {
		return nil, fmt.Errorf("error getting executable path: %v", err)
	}

	// Create the process arguments.
	procArgs := kernel.CreateProcessArgs{
		Filename:         exec,
		Argv:             spec.Process.Args,
		Envv:             spec.Process.Env,
		WorkingDirectory: spec.Process.Cwd,
		Credentials:      creds,
		// Creating the FDMap requires that we have kernel.Kernel.fdMapUids, so
		// it must wait until we have a Kernel.
		Umask:                uint(syscall.Umask(0)),
		Limits:               ls,
		MaxSymlinkTraversals: linux.MaxSymlinkTraversals,
		UTSNamespace:         utsns,
		IPCNamespace:         ipcns,
	}

	// Create an empty network stack because the network namespace may be empty at
	// this point. Netns is configured before Run() is called. Netstack is
	// configured using a control uRPC message. Host network is configured inside
	// Run().
	networkStack := newEmptyNetworkStack(conf)

	// Initiate the Kernel object, which is required by the Context passed
	// to createVFS in order to mount (among other things) procfs.
	if err = k.Init(kernel.InitKernelArgs{
		FeatureSet:        cpuid.HostFeatureSet(),
		Timekeeper:        tk,
		RootUserNamespace: creds.UserNamespace,
		NetworkStack:      networkStack,
		ApplicationCores:  8,
		Vdso:              vdso,
		RootUTSNamespace:  utsns,
		RootIPCNamespace:  ipcns,
	}); err != nil {
		return nil, fmt.Errorf("error initializing kernel: %v", err)
	}

	// Turn on packet logging if enabled.
	if conf.LogPackets {
		log.Infof("Packet logging enabled")
		atomic.StoreUint32(&sniffer.LogPackets, 1)
	} else {
		log.Infof("Packet logging disabled")
		atomic.StoreUint32(&sniffer.LogPackets, 0)
	}

	// Create the control server using the provided FD.
	//
	// This must be done *after* we have initialized the kernel since the
	// controller is used to configure the kernel's network stack.
	//
	// This should also be *before* we create the process, since a
	// misconfigured process will cause an error, and we want the control
	// server up before that so that we don't time out trying to connect to
	// it.
	ctrl, err := newController(controllerFD, k)
	if err != nil {
		return nil, fmt.Errorf("error creating control server: %v", err)
	}

	ctx := procArgs.NewContext(k)

	// Create the virtual filesystem.
	mm, err := createMountNamespace(ctx, spec, conf, ioFDs)
	if err != nil {
		return nil, fmt.Errorf("error creating mounts: %v", err)
	}
	k.SetRootMountNamespace(mm)

	// Create the FD map, which will set stdin, stdout, and stderr.  If console
	// is true, then ioctl calls will be passed through to the host fd.
	fdm, err := createFDMap(ctx, k, ls, console)
	if err != nil {
		return nil, fmt.Errorf("error importing fds: %v", err)
	}

	// CreateProcess takes a reference on FDMap if successful. We
	// won't need ours either way.
	procArgs.FDMap = fdm

	// We don't care about child signals; some platforms can generate a
	// tremendous number of useless ones (I'm looking at you, ptrace).
	if err := sighandling.IgnoreChildStop(); err != nil {
		return nil, fmt.Errorf("failed to ignore child stop signals: %v", err)
	}
	// Ensure that most signals received in sentry context are forwarded to
	// the emulated kernel.
	stopSignalForwarding := sighandling.StartForwarding(k)

	watchdog := watchdog.New(k, watchdog.DefaultTimeout, watchdog.LogWarning)
	return &Loader{
		k:                    k,
		ctrl:                 ctrl,
		conf:                 conf,
		console:              console,
		watchdog:             watchdog,
		stopSignalForwarding: stopSignalForwarding,
		procArgs:             procArgs,
	}, nil
}

// Destroy cleans up all resources used by the loader.
func (l *Loader) Destroy() {
	if l.ctrl != nil {
		// Shut down control server.
		l.ctrl.srv.Stop()
	}
	l.stopSignalForwarding()
	l.watchdog.Stop()
}

func createPlatform(conf *Config) (platform.Platform, error) {
	switch conf.Platform {
	case PlatformPtrace:
		log.Infof("Platform: ptrace")
		return ptrace.New()
	case PlatformKVM:
		log.Infof("Platform: kvm")
		return kvm.New()
	default:
		return nil, fmt.Errorf("invalid platform %v", conf.Platform)
	}
}

// Run runs the application.
func (l *Loader) Run() error {
	err := l.run()
	l.ctrl.app.startResultChan <- err
	return err
}

func (l *Loader) run() error {
	if l.conf.Network == NetworkHost {
		// Delay host network configuration to this point because network namespace
		// is configured after the loader is created and before Run() is called.
		log.Debugf("Configuring host network")
		stack := l.k.NetworkStack().(*hostinet.Stack)
		if err := stack.Configure(); err != nil {
			return err
		}
	}

	// Finally done with all configuration. Setup filters before user code
	// is loaded.
	if l.conf.DisableSeccomp {
		filter.Report("syscall filter is DISABLED. Running in less secure mode.")
	} else {
		whitelistFS := l.conf.FileAccess == FileAccessDirect
		hostNet := l.conf.Network == NetworkHost
		if err := filter.Install(l.k.Platform, whitelistFS, l.console, hostNet); err != nil {
			return fmt.Errorf("Failed to install seccomp filters: %v", err)
		}
	}

	// Create the initial application task.
	if _, err := l.k.CreateProcess(l.procArgs); err != nil {
		return fmt.Errorf("failed to create init process: %v", err)
	}

	// CreateProcess takes a reference on FDMap if successful.
	l.procArgs.FDMap.DecRef()

	l.watchdog.Start()
	return l.k.Start()
}

// WaitForStartSignal waits for a start signal from the control server.
func (l *Loader) WaitForStartSignal() {
	<-l.ctrl.app.startChan
}

// WaitExit waits for the application to exit, and returns the application's
// exit status.
func (l *Loader) WaitExit() kernel.ExitStatus {
	// Wait for application.
	l.k.WaitExited()

	return l.k.GlobalInit().ExitStatus()
}

func newEmptyNetworkStack(conf *Config) inet.Stack {
	switch conf.Network {
	case NetworkHost:
		return hostinet.NewStack()

	case NetworkNone, NetworkSandbox:
		// NetworkNone sets up loopback using netstack.
		netProtos := []string{ipv4.ProtocolName, ipv6.ProtocolName, arp.ProtocolName}
		protoNames := []string{tcp.ProtocolName, udp.ProtocolName}
		return &epsocket.Stack{stack.New(netProtos, protoNames)}

	default:
		panic(fmt.Sprintf("invalid network configuration: %v", conf.Network))
	}
}