fortify/internal/system.go

package internal

import (
	"errors"
	"io/fs"
	"os"
	"os/exec"
	"os/user"
	"path"
	"strconv"
	"sync"

	"git.ophivana.moe/security/fortify/internal/fmsg"
)

// System provides safe access to operating system resources.
type System interface {
	// Geteuid provides [os.Geteuid].
	Geteuid() int
	// LookupEnv provides [os.LookupEnv].
	LookupEnv(key string) (string, bool)
	// TempDir provides [os.TempDir].
	TempDir() string
	// LookPath provides [exec.LookPath].
	LookPath(file string) (string, error)
	// Executable provides [os.Executable].
	Executable() (string, error)
	// Lookup provides [user.Lookup].
	Lookup(username string) (*user.User, error)
	// ReadDir provides [os.ReadDir].
	ReadDir(name string) ([]fs.DirEntry, error)
	// Stat provides [os.Stat].
	Stat(name string) (fs.FileInfo, error)
	// Open provides [os.Open]
	Open(name string) (fs.File, error)
	// Exit provides [os.Exit].
	Exit(code int)

	// Paths returns a populated [Paths] struct.
	Paths() Paths
	// SdBooted implements https://www.freedesktop.org/software/systemd/man/sd_booted.html
	SdBooted() bool
}

// Paths contains environment dependent paths used by fortify.
type Paths struct {
	// path to shared directory e.g. /tmp/fortify.%d
	SharePath string `json:"share_path"`
	// XDG_RUNTIME_DIR value e.g. /run/user/%d
	RuntimePath string `json:"runtime_path"`
	// application runtime directory e.g. /run/user/%d/fortify
	RunDirPath string `json:"run_dir_path"`
}

// CopyPaths is a generic implementation of [System.Paths].
func CopyPaths(os System, v *Paths) {
	v.SharePath = path.Join(os.TempDir(), "fortify."+strconv.Itoa(os.Geteuid()))

	fmsg.VPrintf("process share directory at %q", v.SharePath)

	if r, ok := os.LookupEnv(xdgRuntimeDir); !ok || r == "" || !path.IsAbs(r) {
		// fall back to path in share since fortify has no hard XDG dependency
		v.RunDirPath = path.Join(v.SharePath, "run")
		v.RuntimePath = path.Join(v.RunDirPath, "compat")
	} else {
		v.RuntimePath = r
		v.RunDirPath = path.Join(v.RuntimePath, "fortify")
	}

	fmsg.VPrintf("runtime directory at %q", v.RunDirPath)
}

// Std implements System using the standard library.
type Std struct {
	paths     Paths
	pathsOnce sync.Once

	sdBooted     bool
	sdBootedOnce sync.Once
}

func (s *Std) Geteuid() int                               { return os.Geteuid() }
func (s *Std) LookupEnv(key string) (string, bool)        { return os.LookupEnv(key) }
func (s *Std) TempDir() string                            { return os.TempDir() }
func (s *Std) LookPath(file string) (string, error)       { return exec.LookPath(file) }
func (s *Std) Executable() (string, error)                { return os.Executable() }
func (s *Std) Lookup(username string) (*user.User, error) { return user.Lookup(username) }
func (s *Std) ReadDir(name string) ([]os.DirEntry, error) { return os.ReadDir(name) }
func (s *Std) Stat(name string) (fs.FileInfo, error)      { return os.Stat(name) }
func (s *Std) Open(name string) (fs.File, error)          { return os.Open(name) }
func (s *Std) Exit(code int)                              { fmsg.Exit(code) }

const xdgRuntimeDir = "XDG_RUNTIME_DIR"

func (s *Std) Paths() Paths {
	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths) })
	return s.paths
}

func (s *Std) SdBooted() bool {
	s.sdBootedOnce.Do(func() { s.sdBooted = copySdBooted() })
	return s.sdBooted
}

const systemdCheckPath = "/run/systemd/system"

func copySdBooted() bool {
	if v, err := sdBooted(); err != nil {
		fmsg.Println("cannot read systemd marker:", err)
		return false
	} else {
		return v
	}
}

func sdBooted() (bool, error) {
	_, err := os.Stat(systemdCheckPath)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			err = nil
		}
		return false, err
	}

	return true, nil
}