spec_opts.go

/*
   Copyright The containerd Authors.

   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 oci

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"

	"github.com/containerd/containerd/containers"
	"github.com/containerd/containerd/content"
	"github.com/containerd/containerd/images"
	"github.com/containerd/containerd/mount"
	"github.com/containerd/containerd/namespaces"
	"github.com/containerd/containerd/platforms"
	"github.com/containerd/continuity/fs"
	v1 "github.com/opencontainers/image-spec/specs-go/v1"
	"github.com/opencontainers/runc/libcontainer/user"
	"github.com/opencontainers/runtime-spec/specs-go"
)

// SpecOpts sets spec specific information to a newly generated OCI spec
type SpecOpts func(context.Context, Client, *containers.Container, *Spec) error

// Compose converts a sequence of spec operations into a single operation
func Compose(opts ...SpecOpts) SpecOpts {
	return func(ctx context.Context, client Client, c *containers.Container, s *Spec) error {
		for _, o := range opts {
			if err := o(ctx, client, c, s); err != nil {
				return err
			}
		}
		return nil
	}
}

// setProcess sets Process to empty if unset
func setProcess(s *Spec) {
	if s.Process == nil {
		s.Process = &specs.Process{}
	}
}

// setRoot sets Root to empty if unset
func setRoot(s *Spec) {
	if s.Root == nil {
		s.Root = &specs.Root{}
	}
}

// setLinux sets Linux to empty if unset
func setLinux(s *Spec) {
	if s.Linux == nil {
		s.Linux = &specs.Linux{}
	}
}

// nolint
func setResources(s *Spec) {
	if s.Linux != nil {
		if s.Linux.Resources == nil {
			s.Linux.Resources = &specs.LinuxResources{}
		}
	}
	if s.Windows != nil {
		if s.Windows.Resources == nil {
			s.Windows.Resources = &specs.WindowsResources{}
		}
	}
}

// nolint
func setCPU(s *Spec) {
	setResources(s)
	if s.Linux != nil {
		if s.Linux.Resources.CPU == nil {
			s.Linux.Resources.CPU = &specs.LinuxCPU{}
		}
	}
	if s.Windows != nil {
		if s.Windows.Resources.CPU == nil {
			s.Windows.Resources.CPU = &specs.WindowsCPUResources{}
		}
	}
}

// setCapabilities sets Linux Capabilities to empty if unset
func setCapabilities(s *Spec) {
	setProcess(s)
	if s.Process.Capabilities == nil {
		s.Process.Capabilities = &specs.LinuxCapabilities{}
	}
}

// WithDefaultSpec returns a SpecOpts that will populate the spec with default
// values.
//
// Use as the first option to clear the spec, then apply options afterwards.
func WithDefaultSpec() SpecOpts {
	return func(ctx context.Context, _ Client, c *containers.Container, s *Spec) error {
		return generateDefaultSpecWithPlatform(ctx, platforms.DefaultString(), c.ID, s)
	}
}

// WithDefaultSpecForPlatform returns a SpecOpts that will populate the spec
// with default values for a given platform.
//
// Use as the first option to clear the spec, then apply options afterwards.
func WithDefaultSpecForPlatform(platform string) SpecOpts {
	return func(ctx context.Context, _ Client, c *containers.Container, s *Spec) error {
		return generateDefaultSpecWithPlatform(ctx, platform, c.ID, s)
	}
}

// WithSpecFromBytes loads the spec from the provided byte slice.
func WithSpecFromBytes(p []byte) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		*s = Spec{} // make sure spec is cleared.
		if err := json.Unmarshal(p, s); err != nil {
			return fmt.Errorf("decoding spec config file failed, current supported OCI runtime-spec : v%s: %w", specs.Version, err)
		}
		return nil
	}
}

// WithSpecFromFile loads the specification from the provided filename.
func WithSpecFromFile(filename string) SpecOpts {
	return func(ctx context.Context, c Client, container *containers.Container, s *Spec) error {
		p, err := os.ReadFile(filename)
		if err != nil {
			return fmt.Errorf("cannot load spec config file: %w", err)
		}
		return WithSpecFromBytes(p)(ctx, c, container, s)
	}
}

// WithEnv appends environment variables
func WithEnv(environmentVariables []string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		if len(environmentVariables) > 0 {
			setProcess(s)
			s.Process.Env = replaceOrAppendEnvValues(s.Process.Env, environmentVariables)
		}
		return nil
	}
}

// WithDefaultPathEnv sets the $PATH environment variable to the
// default PATH defined in this package.
func WithDefaultPathEnv(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	s.Process.Env = replaceOrAppendEnvValues(s.Process.Env, defaultUnixEnv)
	return nil
}

// replaceOrAppendEnvValues returns the defaults with the overrides either
// replaced by env key or appended to the list
func replaceOrAppendEnvValues(defaults, overrides []string) []string {
	cache := make(map[string]int, len(defaults))
	results := make([]string, 0, len(defaults))
	for i, e := range defaults {
		parts := strings.SplitN(e, "=", 2)
		results = append(results, e)
		cache[parts[0]] = i
	}

	for _, value := range overrides {
		// Values w/o = means they want this env to be removed/unset.
		if !strings.Contains(value, "=") {
			if i, exists := cache[value]; exists {
				results[i] = "" // Used to indicate it should be removed
			}
			continue
		}

		// Just do a normal set/update
		parts := strings.SplitN(value, "=", 2)
		if i, exists := cache[parts[0]]; exists {
			results[i] = value
		} else {
			results = append(results, value)
		}
	}

	// Now remove all entries that we want to "unset"
	for i := 0; i < len(results); i++ {
		if results[i] == "" {
			results = append(results[:i], results[i+1:]...)
			i--
		}
	}

	return results
}

// WithProcessArgs replaces the args on the generated spec
func WithProcessArgs(args ...string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setProcess(s)
		s.Process.Args = args
		return nil
	}
}

// WithProcessCwd replaces the current working directory on the generated spec
func WithProcessCwd(cwd string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setProcess(s)
		s.Process.Cwd = cwd
		return nil
	}
}

// WithTTY sets the information on the spec as well as the environment variables for
// using a TTY
func WithTTY(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	setProcess(s)
	s.Process.Terminal = true
	if s.Linux != nil {
		s.Process.Env = append(s.Process.Env, "TERM=xterm")
	}

	return nil
}

// WithTTYSize sets the information on the spec as well as the environment variables for
// using a TTY
func WithTTYSize(width, height int) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setProcess(s)
		if s.Process.ConsoleSize == nil {
			s.Process.ConsoleSize = &specs.Box{}
		}
		s.Process.ConsoleSize.Width = uint(width)
		s.Process.ConsoleSize.Height = uint(height)
		return nil
	}
}

// WithHostname sets the container's hostname
func WithHostname(name string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		s.Hostname = name
		return nil
	}
}

// WithMounts appends mounts
func WithMounts(mounts []specs.Mount) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		s.Mounts = append(s.Mounts, mounts...)
		return nil
	}
}

// WithoutMounts removes mounts
func WithoutMounts(dests ...string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		var (
			mounts  []specs.Mount
			current = s.Mounts
		)
	mLoop:
		for _, m := range current {
			mDestination := filepath.Clean(m.Destination)
			for _, dest := range dests {
				if mDestination == dest {
					continue mLoop
				}
			}
			mounts = append(mounts, m)
		}
		s.Mounts = mounts
		return nil
	}
}

// WithHostNamespace allows a task to run inside the host's linux namespace
func WithHostNamespace(ns specs.LinuxNamespaceType) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setLinux(s)
		for i, n := range s.Linux.Namespaces {
			if n.Type == ns {
				s.Linux.Namespaces = append(s.Linux.Namespaces[:i], s.Linux.Namespaces[i+1:]...)
				return nil
			}
		}
		return nil
	}
}

// WithLinuxNamespace uses the passed in namespace for the spec. If a namespace of the same type already exists in the
// spec, the existing namespace is replaced by the one provided.
func WithLinuxNamespace(ns specs.LinuxNamespace) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setLinux(s)
		for i, n := range s.Linux.Namespaces {
			if n.Type == ns.Type {
				s.Linux.Namespaces[i] = ns
				return nil
			}
		}
		s.Linux.Namespaces = append(s.Linux.Namespaces, ns)
		return nil
	}
}

// WithNewPrivileges turns off the NoNewPrivileges feature flag in the spec
func WithNewPrivileges(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	setProcess(s)
	s.Process.NoNewPrivileges = false

	return nil
}

// WithImageConfig configures the spec to from the configuration of an Image
func WithImageConfig(image Image) SpecOpts {
	return WithImageConfigArgs(image, nil)
}

// WithImageConfigArgs configures the spec to from the configuration of an Image with additional args that
// replaces the CMD of the image
func WithImageConfigArgs(image Image, args []string) SpecOpts {
	return func(ctx context.Context, client Client, c *containers.Container, s *Spec) error {
		ic, err := image.Config(ctx)
		if err != nil {
			return err
		}
		var (
			ociimage v1.Image
			config   v1.ImageConfig
		)
		switch ic.MediaType {
		case v1.MediaTypeImageConfig, images.MediaTypeDockerSchema2Config:
			p, err := content.ReadBlob(ctx, image.ContentStore(), ic)
			if err != nil {
				return err
			}

			if err := json.Unmarshal(p, &ociimage); err != nil {
				return err
			}
			config = ociimage.Config
		default:
			return fmt.Errorf("unknown image config media type %s", ic.MediaType)
		}

		setProcess(s)
		if s.Linux != nil {
			defaults := config.Env
			if len(defaults) == 0 {
				defaults = defaultUnixEnv
			}
			s.Process.Env = replaceOrAppendEnvValues(defaults, s.Process.Env)
			cmd := config.Cmd
			if len(args) > 0 {
				cmd = args
			}
			s.Process.Args = append(config.Entrypoint, cmd...)

			cwd := config.WorkingDir
			if cwd == "" {
				cwd = "/"
			}
			s.Process.Cwd = cwd
			if config.User != "" {
				if err := WithUser(config.User)(ctx, client, c, s); err != nil {
					return err
				}
				return WithAdditionalGIDs(fmt.Sprintf("%d", s.Process.User.UID))(ctx, client, c, s)
			}
			// we should query the image's /etc/group for additional GIDs
			// even if there is no specified user in the image config
			return WithAdditionalGIDs("root")(ctx, client, c, s)
		} else if s.Windows != nil {
			s.Process.Env = replaceOrAppendEnvValues(config.Env, s.Process.Env)
			cmd := config.Cmd
			if len(args) > 0 {
				cmd = args
			}
			s.Process.Args = append(config.Entrypoint, cmd...)

			s.Process.Cwd = config.WorkingDir
			s.Process.User = specs.User{
				Username: config.User,
			}
		} else {
			return errors.New("spec does not contain Linux or Windows section")
		}
		return nil
	}
}

// WithRootFSPath specifies unmanaged rootfs path.
func WithRootFSPath(path string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setRoot(s)
		s.Root.Path = path
		// Entrypoint is not set here (it's up to caller)
		return nil
	}
}

// WithRootFSReadonly sets specs.Root.Readonly to true
func WithRootFSReadonly() SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setRoot(s)
		s.Root.Readonly = true
		return nil
	}
}

// WithNoNewPrivileges sets no_new_privileges on the process for the container
func WithNoNewPrivileges(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	setProcess(s)
	s.Process.NoNewPrivileges = true
	return nil
}

// WithHostHostsFile bind-mounts the host's /etc/hosts into the container as readonly
func WithHostHostsFile(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	s.Mounts = append(s.Mounts, specs.Mount{
		Destination: "/etc/hosts",
		Type:        "bind",
		Source:      "/etc/hosts",
		Options:     []string{"rbind", "ro"},
	})
	return nil
}

// WithHostResolvconf bind-mounts the host's /etc/resolv.conf into the container as readonly
func WithHostResolvconf(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	s.Mounts = append(s.Mounts, specs.Mount{
		Destination: "/etc/resolv.conf",
		Type:        "bind",
		Source:      "/etc/resolv.conf",
		Options:     []string{"rbind", "ro"},
	})
	return nil
}

// WithHostLocaltime bind-mounts the host's /etc/localtime into the container as readonly
func WithHostLocaltime(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	s.Mounts = append(s.Mounts, specs.Mount{
		Destination: "/etc/localtime",
		Type:        "bind",
		Source:      "/etc/localtime",
		Options:     []string{"rbind", "ro"},
	})
	return nil
}

// WithUserNamespace sets the uid and gid mappings for the task
// this can be called multiple times to add more mappings to the generated spec
func WithUserNamespace(uidMap, gidMap []specs.LinuxIDMapping) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		var hasUserns bool
		setLinux(s)
		for _, ns := range s.Linux.Namespaces {
			if ns.Type == specs.UserNamespace {
				hasUserns = true
				break
			}
		}
		if !hasUserns {
			s.Linux.Namespaces = append(s.Linux.Namespaces, specs.LinuxNamespace{
				Type: specs.UserNamespace,
			})
		}
		s.Linux.UIDMappings = append(s.Linux.UIDMappings, uidMap...)
		s.Linux.GIDMappings = append(s.Linux.GIDMappings, gidMap...)
		return nil
	}
}

// WithCgroup sets the container's cgroup path
func WithCgroup(path string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setLinux(s)
		s.Linux.CgroupsPath = path
		return nil
	}
}

// WithNamespacedCgroup uses the namespace set on the context to create a
// root directory for containers in the cgroup with the id as the subcgroup
func WithNamespacedCgroup() SpecOpts {
	return func(ctx context.Context, _ Client, c *containers.Container, s *Spec) error {
		namespace, err := namespaces.NamespaceRequired(ctx)
		if err != nil {
			return err
		}
		setLinux(s)
		s.Linux.CgroupsPath = filepath.Join("/", namespace, c.ID)
		return nil
	}
}

// WithUser sets the user to be used within the container.
// It accepts a valid user string in OCI Image Spec v1.0.0:
//   user, uid, user:group, uid:gid, uid:group, user:gid
func WithUser(userstr string) SpecOpts {
	return func(ctx context.Context, client Client, c *containers.Container, s *Spec) error {
		setProcess(s)

		// For LCOW it's a bit harder to confirm that the user actually exists on the host as a rootfs isn't
		// mounted on the host and shared into the guest, but rather the rootfs is constructed entirely in the
		// guest itself. To accommodate this, a spot to place the user string provided by a client as-is is needed.
		// The `Username` field on the runtime spec is marked by Platform as only for Windows, and in this case it
		// *is* being set on a Windows host at least, but will be used as a temporary holding spot until the guest
		// can use the string to perform these same operations to grab the uid:gid inside.
		if s.Windows != nil && s.Linux != nil {
			s.Process.User.Username = userstr
			return nil
		}

		parts := strings.Split(userstr, ":")
		switch len(parts) {
		case 1:
			v, err := strconv.Atoi(parts[0])
			if err != nil {
				// if we cannot parse as a uint they try to see if it is a username
				return WithUsername(userstr)(ctx, client, c, s)
			}
			return WithUserID(uint32(v))(ctx, client, c, s)
		case 2:
			var (
				username  string
				groupname string
			)
			var uid, gid uint32
			v, err := strconv.Atoi(parts[0])
			if err != nil {
				username = parts[0]
			} else {
				uid = uint32(v)
			}
			if v, err = strconv.Atoi(parts[1]); err != nil {
				groupname = parts[1]
			} else {
				gid = uint32(v)
			}
			if username == "" && groupname == "" {
				s.Process.User.UID, s.Process.User.GID = uid, gid
				return nil
			}
			f := func(root string) error {
				if username != "" {
					user, err := UserFromPath(root, func(u user.User) bool {
						return u.Name == username
					})
					if err != nil {
						return err
					}
					uid = uint32(user.Uid)
				}
				if groupname != "" {
					gid, err = GIDFromPath(root, func(g user.Group) bool {
						return g.Name == groupname
					})
					if err != nil {
						return err
					}
				}
				s.Process.User.UID, s.Process.User.GID = uid, gid
				return nil
			}
			if c.Snapshotter == "" && c.SnapshotKey == "" {
				if !isRootfsAbs(s.Root.Path) {
					return errors.New("rootfs absolute path is required")
				}
				return f(s.Root.Path)
			}
			if c.Snapshotter == "" {
				return errors.New("no snapshotter set for container")
			}
			if c.SnapshotKey == "" {
				return errors.New("rootfs snapshot not created for container")
			}
			snapshotter := client.SnapshotService(c.Snapshotter)
			mounts, err := snapshotter.Mounts(ctx, c.SnapshotKey)
			if err != nil {
				return err
			}

			mounts = tryReadonlyMounts(mounts)
			return mount.WithTempMount(ctx, mounts, f)
		default:
			return fmt.Errorf("invalid USER value %s", userstr)
		}
	}
}

// WithUIDGID allows the UID and GID for the Process to be set
func WithUIDGID(uid, gid uint32) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setProcess(s)
		s.Process.User.UID = uid
		s.Process.User.GID = gid
		return nil
	}
}

// WithUserID sets the correct UID and GID for the container based
// on the image's /etc/passwd contents. If /etc/passwd does not exist,
// or uid is not found in /etc/passwd, it sets the requested uid,
// additionally sets the gid to 0, and does not return an error.
func WithUserID(uid uint32) SpecOpts {
	return func(ctx context.Context, client Client, c *containers.Container, s *Spec) (err error) {
		setProcess(s)
		if c.Snapshotter == "" && c.SnapshotKey == "" {
			if !isRootfsAbs(s.Root.Path) {
				return errors.New("rootfs absolute path is required")
			}
			user, err := UserFromPath(s.Root.Path, func(u user.User) bool {
				return u.Uid == int(uid)
			})
			if err != nil {
				if os.IsNotExist(err) || err == ErrNoUsersFound {
					s.Process.User.UID, s.Process.User.GID = uid, 0
					return nil
				}
				return err
			}
			s.Process.User.UID, s.Process.User.GID = uint32(user.Uid), uint32(user.Gid)
			return nil

		}
		if c.Snapshotter == "" {
			return errors.New("no snapshotter set for container")
		}
		if c.SnapshotKey == "" {
			return errors.New("rootfs snapshot not created for container")
		}
		snapshotter := client.SnapshotService(c.Snapshotter)
		mounts, err := snapshotter.Mounts(ctx, c.SnapshotKey)
		if err != nil {
			return err
		}

		mounts = tryReadonlyMounts(mounts)
		return mount.WithTempMount(ctx, mounts, func(root string) error {
			user, err := UserFromPath(root, func(u user.User) bool {
				return u.Uid == int(uid)
			})
			if err != nil {
				if os.IsNotExist(err) || err == ErrNoUsersFound {
					s.Process.User.UID, s.Process.User.GID = uid, 0
					return nil
				}
				return err
			}
			s.Process.User.UID, s.Process.User.GID = uint32(user.Uid), uint32(user.Gid)
			return nil
		})
	}
}

// WithUsername sets the correct UID and GID for the container
// based on the image's /etc/passwd contents. If /etc/passwd
// does not exist, or the username is not found in /etc/passwd,
// it returns error. On Windows this sets the username as provided,
// the operating system will validate the user when going to run
// the container.
func WithUsername(username string) SpecOpts {
	return func(ctx context.Context, client Client, c *containers.Container, s *Spec) (err error) {
		setProcess(s)
		if s.Linux != nil {
			if c.Snapshotter == "" && c.SnapshotKey == "" {
				if !isRootfsAbs(s.Root.Path) {
					return errors.New("rootfs absolute path is required")
				}
				user, err := UserFromPath(s.Root.Path, func(u user.User) bool {
					return u.Name == username
				})
				if err != nil {
					return err
				}
				s.Process.User.UID, s.Process.User.GID = uint32(user.Uid), uint32(user.Gid)
				return nil
			}
			if c.Snapshotter == "" {
				return errors.New("no snapshotter set for container")
			}
			if c.SnapshotKey == "" {
				return errors.New("rootfs snapshot not created for container")
			}
			snapshotter := client.SnapshotService(c.Snapshotter)
			mounts, err := snapshotter.Mounts(ctx, c.SnapshotKey)
			if err != nil {
				return err
			}

			mounts = tryReadonlyMounts(mounts)
			return mount.WithTempMount(ctx, mounts, func(root string) error {
				user, err := UserFromPath(root, func(u user.User) bool {
					return u.Name == username
				})
				if err != nil {
					return err
				}
				s.Process.User.UID, s.Process.User.GID = uint32(user.Uid), uint32(user.Gid)
				return nil
			})
		} else if s.Windows != nil {
			s.Process.User.Username = username
		} else {
			return errors.New("spec does not contain Linux or Windows section")
		}
		return nil
	}
}

// WithAdditionalGIDs sets the OCI spec's additionalGids array to any additional groups listed
// for a particular user in the /etc/groups file of the image's root filesystem
// The passed in user can be either a uid or a username.
func WithAdditionalGIDs(userstr string) SpecOpts {
	return func(ctx context.Context, client Client, c *containers.Container, s *Spec) (err error) {
		// For LCOW or on Darwin additional GID's not supported
		if s.Windows != nil || runtime.GOOS == "darwin" {
			return nil
		}
		setProcess(s)
		setAdditionalGids := func(root string) error {
			var username string
			uid, err := strconv.Atoi(userstr)
			if err == nil {
				user, err := UserFromPath(root, func(u user.User) bool {
					return u.Uid == uid
				})
				if err != nil {
					if os.IsNotExist(err) || err == ErrNoUsersFound {
						return nil
					}
					return err
				}
				username = user.Name
			} else {
				username = userstr
			}
			gids, err := getSupplementalGroupsFromPath(root, func(g user.Group) bool {
				// we only want supplemental groups
				if g.Name == username {
					return false
				}
				for _, entry := range g.List {
					if entry == username {
						return true
					}
				}
				return false
			})
			if err != nil {
				if os.IsNotExist(err) {
					return nil
				}
				return err
			}
			s.Process.User.AdditionalGids = gids
			return nil
		}
		if c.Snapshotter == "" && c.SnapshotKey == "" {
			if !isRootfsAbs(s.Root.Path) {
				return errors.New("rootfs absolute path is required")
			}
			return setAdditionalGids(s.Root.Path)
		}
		if c.Snapshotter == "" {
			return errors.New("no snapshotter set for container")
		}
		if c.SnapshotKey == "" {
			return errors.New("rootfs snapshot not created for container")
		}
		snapshotter := client.SnapshotService(c.Snapshotter)
		mounts, err := snapshotter.Mounts(ctx, c.SnapshotKey)
		if err != nil {
			return err
		}

		mounts = tryReadonlyMounts(mounts)
		return mount.WithTempMount(ctx, mounts, setAdditionalGids)
	}
}

// WithCapabilities sets Linux capabilities on the process
func WithCapabilities(caps []string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setCapabilities(s)

		s.Process.Capabilities.Bounding = caps
		s.Process.Capabilities.Effective = caps
		s.Process.Capabilities.Permitted = caps
		s.Process.Capabilities.Inheritable = caps

		return nil
	}
}

func capsContain(caps []string, s string) bool {
	for _, c := range caps {
		if c == s {
			return true
		}
	}
	return false
}

func removeCap(caps *[]string, s string) {
	var newcaps []string
	for _, c := range *caps {
		if c == s {
			continue
		}
		newcaps = append(newcaps, c)
	}
	*caps = newcaps
}

// WithAddedCapabilities adds the provided capabilities
func WithAddedCapabilities(caps []string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setCapabilities(s)
		for _, c := range caps {
			for _, cl := range []*[]string{
				&s.Process.Capabilities.Bounding,
				&s.Process.Capabilities.Effective,
				&s.Process.Capabilities.Permitted,
				&s.Process.Capabilities.Inheritable,
			} {
				if !capsContain(*cl, c) {
					*cl = append(*cl, c)
				}
			}
		}
		return nil
	}
}

// WithDroppedCapabilities removes the provided capabilities
func WithDroppedCapabilities(caps []string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setCapabilities(s)
		for _, c := range caps {
			for _, cl := range []*[]string{
				&s.Process.Capabilities.Bounding,
				&s.Process.Capabilities.Effective,
				&s.Process.Capabilities.Permitted,
				&s.Process.Capabilities.Inheritable,
			} {
				removeCap(cl, c)
			}
		}
		return nil
	}
}

// WithAmbientCapabilities set the Linux ambient capabilities for the process
// Ambient capabilities should only be set for non-root users or the caller should
// understand how these capabilities are used and set
func WithAmbientCapabilities(caps []string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setCapabilities(s)

		s.Process.Capabilities.Ambient = caps
		return nil
	}
}

// ErrNoUsersFound can be returned from UserFromPath
var ErrNoUsersFound = errors.New("no users found")

// UserFromPath inspects the user object using /etc/passwd in the specified rootfs.
// filter can be nil.
func UserFromPath(root string, filter func(user.User) bool) (user.User, error) {
	ppath, err := fs.RootPath(root, "/etc/passwd")
	if err != nil {
		return user.User{}, err
	}
	users, err := user.ParsePasswdFileFilter(ppath, filter)
	if err != nil {
		return user.User{}, err
	}
	if len(users) == 0 {
		return user.User{}, ErrNoUsersFound
	}
	return users[0], nil
}

// ErrNoGroupsFound can be returned from GIDFromPath
var ErrNoGroupsFound = errors.New("no groups found")

// GIDFromPath inspects the GID using /etc/passwd in the specified rootfs.
// filter can be nil.
func GIDFromPath(root string, filter func(user.Group) bool) (gid uint32, err error) {
	gpath, err := fs.RootPath(root, "/etc/group")
	if err != nil {
		return 0, err
	}
	groups, err := user.ParseGroupFileFilter(gpath, filter)
	if err != nil {
		return 0, err
	}
	if len(groups) == 0 {
		return 0, ErrNoGroupsFound
	}
	g := groups[0]
	return uint32(g.Gid), nil
}

func getSupplementalGroupsFromPath(root string, filter func(user.Group) bool) ([]uint32, error) {
	gpath, err := fs.RootPath(root, "/etc/group")
	if err != nil {
		return []uint32{}, err
	}
	groups, err := user.ParseGroupFileFilter(gpath, filter)
	if err != nil {
		return []uint32{}, err
	}
	if len(groups) == 0 {
		// if there are no additional groups; just return an empty set
		return []uint32{}, nil
	}
	addlGids := []uint32{}
	for _, grp := range groups {
		addlGids = append(addlGids, uint32(grp.Gid))
	}
	return addlGids, nil
}

func isRootfsAbs(root string) bool {
	return filepath.IsAbs(root)
}

// WithMaskedPaths sets the masked paths option
func WithMaskedPaths(paths []string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setLinux(s)
		s.Linux.MaskedPaths = paths
		return nil
	}
}

// WithReadonlyPaths sets the read only paths option
func WithReadonlyPaths(paths []string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setLinux(s)
		s.Linux.ReadonlyPaths = paths
		return nil
	}
}

// WithWriteableSysfs makes any sysfs mounts writeable
func WithWriteableSysfs(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	for _, m := range s.Mounts {
		if m.Type == "sysfs" {
			for i, o := range m.Options {
				if o == "ro" {
					m.Options[i] = "rw"
				}
			}
		}
	}
	return nil
}

// WithWriteableCgroupfs makes any cgroup mounts writeable
func WithWriteableCgroupfs(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	for _, m := range s.Mounts {
		if m.Type == "cgroup" {
			for i, o := range m.Options {
				if o == "ro" {
					m.Options[i] = "rw"
				}
			}
		}
	}
	return nil
}

// WithSelinuxLabel sets the process SELinux label
func WithSelinuxLabel(label string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setProcess(s)
		s.Process.SelinuxLabel = label
		return nil
	}
}

// WithApparmorProfile sets the Apparmor profile for the process
func WithApparmorProfile(profile string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setProcess(s)
		s.Process.ApparmorProfile = profile
		return nil
	}
}

// WithSeccompUnconfined clears the seccomp profile
func WithSeccompUnconfined(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	setLinux(s)
	s.Linux.Seccomp = nil
	return nil
}

// WithParentCgroupDevices uses the default cgroup setup to inherit the container's parent cgroup's
// allowed and denied devices
func WithParentCgroupDevices(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	setLinux(s)
	if s.Linux.Resources == nil {
		s.Linux.Resources = &specs.LinuxResources{}
	}
	s.Linux.Resources.Devices = nil
	return nil
}

// WithAllDevicesAllowed permits READ WRITE MKNOD on all devices nodes for the container
func WithAllDevicesAllowed(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	setLinux(s)
	if s.Linux.Resources == nil {
		s.Linux.Resources = &specs.LinuxResources{}
	}
	s.Linux.Resources.Devices = []specs.LinuxDeviceCgroup{
		{
			Allow:  true,
			Access: rwm,
		},
	}
	return nil
}

// WithDefaultUnixDevices adds the default devices for unix such as /dev/null, /dev/random to
// the container's resource cgroup spec
func WithDefaultUnixDevices(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	setLinux(s)
	if s.Linux.Resources == nil {
		s.Linux.Resources = &specs.LinuxResources{}
	}
	intptr := func(i int64) *int64 {
		return &i
	}
	s.Linux.Resources.Devices = append(s.Linux.Resources.Devices, []specs.LinuxDeviceCgroup{
		{
			// "/dev/null",
			Type:   "c",
			Major:  intptr(1),
			Minor:  intptr(3),
			Access: rwm,
			Allow:  true,
		},
		{
			// "/dev/random",
			Type:   "c",
			Major:  intptr(1),
			Minor:  intptr(8),
			Access: rwm,
			Allow:  true,
		},
		{
			// "/dev/full",
			Type:   "c",
			Major:  intptr(1),
			Minor:  intptr(7),
			Access: rwm,
			Allow:  true,
		},
		{
			// "/dev/tty",
			Type:   "c",
			Major:  intptr(5),
			Minor:  intptr(0),
			Access: rwm,
			Allow:  true,
		},
		{
			// "/dev/zero",
			Type:   "c",
			Major:  intptr(1),
			Minor:  intptr(5),
			Access: rwm,
			Allow:  true,
		},
		{
			// "/dev/urandom",
			Type:   "c",
			Major:  intptr(1),
			Minor:  intptr(9),
			Access: rwm,
			Allow:  true,
		},
		{
			// "/dev/console",
			Type:   "c",
			Major:  intptr(5),
			Minor:  intptr(1),
			Access: rwm,
			Allow:  true,
		},
		// /dev/pts/ - pts namespaces are "coming soon"
		{
			Type:   "c",
			Major:  intptr(136),
			Access: rwm,
			Allow:  true,
		},
		{
			Type:   "c",
			Major:  intptr(5),
			Minor:  intptr(2),
			Access: rwm,
			Allow:  true,
		},
		{
			// tuntap
			Type:   "c",
			Major:  intptr(10),
			Minor:  intptr(200),
			Access: rwm,
			Allow:  true,
		},
	}...)
	return nil
}

// WithPrivileged sets up options for a privileged container
var WithPrivileged = Compose(
	WithAllCurrentCapabilities,
	WithMaskedPaths(nil),
	WithReadonlyPaths(nil),
	WithWriteableSysfs,
	WithWriteableCgroupfs,
	WithSelinuxLabel(""),
	WithApparmorProfile(""),
	WithSeccompUnconfined,
)

// WithWindowsHyperV sets the Windows.HyperV section for HyperV isolation of containers.
func WithWindowsHyperV(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
	if s.Windows == nil {
		s.Windows = &specs.Windows{}
	}
	if s.Windows.HyperV == nil {
		s.Windows.HyperV = &specs.WindowsHyperV{}
	}
	return nil
}

// WithMemoryLimit sets the `Linux.LinuxResources.Memory.Limit` section to the
// `limit` specified if the `Linux` section is not `nil`. Additionally sets the
// `Windows.WindowsResources.Memory.Limit` section if the `Windows` section is
// not `nil`.
func WithMemoryLimit(limit uint64) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		if s.Linux != nil {
			if s.Linux.Resources == nil {
				s.Linux.Resources = &specs.LinuxResources{}
			}
			if s.Linux.Resources.Memory == nil {
				s.Linux.Resources.Memory = &specs.LinuxMemory{}
			}
			l := int64(limit)
			s.Linux.Resources.Memory.Limit = &l
		}
		if s.Windows != nil {
			if s.Windows.Resources == nil {
				s.Windows.Resources = &specs.WindowsResources{}
			}
			if s.Windows.Resources.Memory == nil {
				s.Windows.Resources.Memory = &specs.WindowsMemoryResources{}
			}
			s.Windows.Resources.Memory.Limit = &limit
		}
		return nil
	}
}

// WithAnnotations appends or replaces the annotations on the spec with the
// provided annotations
func WithAnnotations(annotations map[string]string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		if s.Annotations == nil {
			s.Annotations = make(map[string]string)
		}
		for k, v := range annotations {
			s.Annotations[k] = v
		}
		return nil
	}
}

// WithLinuxDevices adds the provided linux devices to the spec
func WithLinuxDevices(devices []specs.LinuxDevice) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setLinux(s)
		s.Linux.Devices = append(s.Linux.Devices, devices...)
		return nil
	}
}

// WithLinuxDevice adds the device specified by path to the spec
func WithLinuxDevice(path, permissions string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		setLinux(s)
		setResources(s)

		dev, err := DeviceFromPath(path)
		if err != nil {
			return err
		}

		s.Linux.Devices = append(s.Linux.Devices, *dev)

		s.Linux.Resources.Devices = append(s.Linux.Resources.Devices, specs.LinuxDeviceCgroup{
			Type:   dev.Type,
			Allow:  true,
			Major:  &dev.Major,
			Minor:  &dev.Minor,
			Access: permissions,
		})

		return nil
	}
}

// WithEnvFile adds environment variables from a file to the container's spec
func WithEnvFile(path string) SpecOpts {
	return func(_ context.Context, _ Client, _ *containers.Container, s *Spec) error {
		var vars []string
		f, err := os.Open(path)
		if err != nil {
			return err
		}
		defer f.Close()

		sc := bufio.NewScanner(f)
		for sc.Scan() {
			vars = append(vars, sc.Text())
		}
		if err = sc.Err(); err != nil {
			return err
		}
		return WithEnv(vars)(nil, nil, nil, s)
	}
}

// ErrNoShmMount is returned when there is no /dev/shm mount specified in the config
// and an Opts was trying to set a configuration value on the mount.
var ErrNoShmMount = errors.New("no /dev/shm mount specified")

// WithDevShmSize sets the size of the /dev/shm mount for the container.
//
// The size value is specified in kb, kilobytes.
func WithDevShmSize(kb int64) SpecOpts {
	return func(ctx context.Context, _ Client, _ *containers.Container, s *Spec) error {
		for i, m := range s.Mounts {
			if filepath.Clean(m.Destination) == "/dev/shm" && m.Source == "shm" && m.Type == "tmpfs" {
				for i := 0; i < len(m.Options); i++ {
					if strings.HasPrefix(m.Options[i], "size=") {
						m.Options = append(m.Options[:i], m.Options[i+1:]...)
						i--
					}
				}
				s.Mounts[i].Options = append(m.Options, fmt.Sprintf("size=%dk", kb))
				return nil
			}
		}
		return ErrNoShmMount
	}
}

// tryReadonlyMounts is used by the options which are trying to get user/group
// information from container's rootfs. Since the option does read operation
// only, this helper will append ReadOnly mount option to prevent linux kernel
// from syncing whole filesystem in umount syscall.
//
// TODO(fuweid):
//
// Currently, it only works for overlayfs. I think we can apply it to other
// kinds of filesystem. Maybe we can return `ro` option by `snapshotter.Mount`
// API, when the caller passes that experimental annotation
// `containerd.io/snapshot/readonly.mount` something like that.
func tryReadonlyMounts(mounts []mount.Mount) []mount.Mount {
	if len(mounts) == 1 && mounts[0].Type == "overlay" {
		mounts[0].Options = append(mounts[0].Options, "ro")
	}
	return mounts
}