fortify/cmd/fpkg/start.go

package main

import (
	"encoding/json"
	"errors"
	"flag"
	"io"
	"os"
	"os/exec"
	"path"

	"git.gensokyo.uk/security/fortify/dbus"
	"git.gensokyo.uk/security/fortify/fst"
	"git.gensokyo.uk/security/fortify/internal"
	"git.gensokyo.uk/security/fortify/internal/fmsg"
	"git.gensokyo.uk/security/fortify/internal/system"
)

const shell = "/run/current-system/sw/bin/bash"

type bundleInfo struct {
	Name    string `json:"name"`
	Version string `json:"version"`

	// passed through to [fst.Config]
	ID string `json:"id"`
	// passed through to [fst.Config]
	AppID int `json:"app_id"`
	// passed through to [fst.Config]
	Groups []string `json:"groups,omitempty"`
	// passed through to [fst.Config]
	UserNS bool `json:"userns,omitempty"`
	// passed through to [fst.Config]
	Net bool `json:"net,omitempty"`
	// passed through to [fst.Config]
	Dev bool `json:"dev,omitempty"`
	// passed through to [fst.Config]
	NoNewSession bool `json:"no_new_session,omitempty"`
	// passed through to [fst.Config]
	MapRealUID bool `json:"map_real_uid,omitempty"`
	// passed through to [fst.Config]
	DirectWayland bool `json:"direct_wayland,omitempty"`
	// passed through to [fst.Config]
	SystemBus *dbus.Config `json:"system_bus,omitempty"`
	// passed through to [fst.Config]
	SessionBus *dbus.Config `json:"session_bus,omitempty"`
	// passed through to [fst.Config]
	Enablements system.Enablements `json:"enablements"`

	// allow gpu access within sandbox
	GPU bool `json:"gpu"`
	// inner nix store path to activate-and-exec script
	Launcher string `json:"launcher"`
	// store path to /run/current-system
	CurrentSystem string `json:"current_system"`
}

func actionStart(args []string) {
	set := flag.NewFlagSet("start", flag.ExitOnError)
	var dropShell bool
	set.BoolVar(&dropShell, "s", false, "Drop to a shell on activation")

	// Ignore errors; set is set for ExitOnError.
	_ = set.Parse(args)

	args = set.Args()

	if len(args) < 1 {
		fmsg.Fatal("invalid argument")
	}
	name := args[0]
	if !path.IsAbs(name) {
		if dir, err := os.Getwd(); err != nil {
			fmsg.Fatalf("cannot get current directory: %v", err)
		} else {
			name = path.Join(dir, name)
		}
	}

	bundle := new(bundleInfo)
	if f, err := os.Open(path.Join(name, "bundle.json")); err != nil {
		fmsg.Fatalf("cannot open bundle: %v", err)
	} else if err = json.NewDecoder(f).Decode(&bundle); err != nil {
		fmsg.Fatalf("cannot parse bundle metadata: %v", err)
	} else if err = f.Close(); err != nil {
		fmsg.Printf("cannot close bundle metadata: %v", err)
	}

	if err := os.Setenv("SHELL", shell); err != nil {
		fmsg.Fatalf("cannot set $SHELL: %v", err)
	}

	command := make([]string, 1, len(args))
	if !dropShell {
		command[0] = bundle.Launcher
	} else {
		command[0] = shell
	}
	command = append(command, args[1:]...)

	baseDir := path.Join(dataHome, bundle.ID)
	homeDir := path.Join(baseDir, "files")
	currentSystem := path.Join(name, bundle.CurrentSystem)
	config := &fst.Config{
		ID:      bundle.ID,
		Command: command,
		Confinement: fst.ConfinementConfig{
			AppID:    bundle.AppID,
			Groups:   bundle.Groups,
			Username: "fortify",
			Inner:    path.Join("/data/data", bundle.ID),
			Outer:    homeDir,
			Sandbox: &fst.SandboxConfig{
				Hostname:      formatHostname(bundle.Name),
				UserNS:        bundle.UserNS,
				Net:           bundle.Net,
				Dev:           bundle.Dev,
				NoNewSession:  bundle.NoNewSession || dropShell,
				MapRealUID:    bundle.MapRealUID,
				DirectWayland: bundle.DirectWayland,
				Filesystem: []*fst.FilesystemConfig{
					{Src: path.Join(name, "nix"), Dst: "/nix", Must: true},
					{Src: currentSystem, Dst: "/run/current-system", Must: true},
					{Src: "/etc/resolv.conf"},
					{Src: "/sys/block"},
					{Src: "/sys/bus"},
					{Src: "/sys/class"},
					{Src: "/sys/dev"},
					{Src: "/sys/devices"},
				},
				Link: [][2]string{
					{"/run/current-system/sw/bin", "/bin"},
					{"/run/current-system/sw/bin", "/usr/bin"},
				},
				Etc:     path.Join(name, "etc"),
				AutoEtc: true,
			},
			ExtraPerms: []*fst.ExtraPermConfig{
				{Ensure: true, Path: baseDir, Read: true, Write: true, Execute: true},
			},
			SystemBus:   bundle.SystemBus,
			SessionBus:  bundle.SessionBus,
			Enablements: bundle.Enablements,
		},
	}

	if bundle.GPU {
		config.Confinement.Sandbox.Filesystem = append(config.Confinement.Sandbox.Filesystem,
			&fst.FilesystemConfig{Src: "/dev/dri", Device: true})
	}

	var (
		cmd *exec.Cmd
		st  io.WriteCloser
	)
	if p, ok := internal.Check(internal.Fortify); !ok {
		fmsg.Fatal("invalid fortify path, this copy of fpkg is not compiled correctly")
		panic("unreachable")
	} else if r, w, err := os.Pipe(); err != nil {
		fmsg.Fatalf("cannot pipe: %v", err)
		panic("unreachable")
	} else {
		if fmsg.Verbose() {
			cmd = exec.Command(p, "-v", "app", "3")
		} else {
			cmd = exec.Command(p, "app", "3")
		}
		cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
		cmd.ExtraFiles = []*os.File{r}
		st = w
	}

	go func() {
		if err := json.NewEncoder(st).Encode(config); err != nil {
			fmsg.Fatalf("cannot send configuration: %v", err)
		}
	}()

	if err := cmd.Start(); err != nil {
		fmsg.Fatalf("cannot start fortify: %v", err)
	}
	if err := cmd.Wait(); err != nil {
		var exitError *exec.ExitError
		if errors.As(err, &exitError) {
			fmsg.Exit(exitError.ExitCode())
		} else {
			fmsg.Fatalf("cannot wait: %v", err)
		}
	}
	fmsg.Exit(0)
}

func formatHostname(name string) string {
	if h, err := os.Hostname(); err != nil {
		fmsg.Printf("cannot get hostname: %v", err)
		return "fortify-" + name
	} else {
		return h + "-" + name
	}
}