app: merge share methods

This significantly increases readability and makes order of ops more obvious.

Signed-off-by: Ophestra <cat@gensokyo.uk>

1 files changed, 335 insertions, 0 deletions

diff --git a/internal/app/share.go b/internal/app/share.go
new file mode 100644
index 00000000..dea55a87
--- /dev/null
+++ b/internal/app/share.go
@@ -0,0 +1,335 @@
+package app
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"path"
+
+	"git.gensokyo.uk/security/fortify/acl"
+	"git.gensokyo.uk/security/fortify/dbus"
+	"git.gensokyo.uk/security/fortify/fst"
+	"git.gensokyo.uk/security/fortify/internal/fmsg"
+	"git.gensokyo.uk/security/fortify/internal/linux"
+	"git.gensokyo.uk/security/fortify/internal/system"
+)
+
+const (
+	home  = "HOME"
+	shell = "SHELL"
+
+	xdgConfigHome   = "XDG_CONFIG_HOME"
+	xdgRuntimeDir   = "XDG_RUNTIME_DIR"
+	xdgSessionClass = "XDG_SESSION_CLASS"
+	xdgSessionType  = "XDG_SESSION_TYPE"
+
+	term    = "TERM"
+	display = "DISPLAY"
+
+	// https://manpages.debian.org/experimental/libwayland-doc/wl_display_connect.3.en.html
+	waylandDisplay = "WAYLAND_DISPLAY"
+
+	pulseServer = "PULSE_SERVER"
+	pulseCookie = "PULSE_COOKIE"
+
+	dbusSessionBusAddress = "DBUS_SESSION_BUS_ADDRESS"
+	dbusSystemBusAddress  = "DBUS_SYSTEM_BUS_ADDRESS"
+)
+
+var (
+	ErrWayland  = errors.New(waylandDisplay + " unset")
+	ErrXDisplay = errors.New(display + " unset")
+
+	ErrPulseCookie = errors.New("pulse cookie not present")
+	ErrPulseSocket = errors.New("pulse socket not present")
+	ErrPulseMode   = errors.New("unexpected pulse socket mode")
+)
+
+func (seal *appSeal) setupShares(bus [2]*dbus.Config, os linux.System) error {
+	if seal.shared {
+		panic("seal shared twice")
+	}
+	seal.shared = true
+
+	/*
+		Tmpdir-based share directory
+	*/
+
+	// ensure Share (e.g. `/tmp/fortify.%d`)
+	// acl is unnecessary as this directory is world executable
+	seal.sys.Ensure(seal.SharePath, 0711)
+
+	// ensure process-specific share (e.g. `/tmp/fortify.%d/%s`)
+	// acl is unnecessary as this directory is world executable
+	seal.share = path.Join(seal.SharePath, seal.id)
+	seal.sys.Ephemeral(system.Process, seal.share, 0711)
+
+	// ensure child tmpdir parent directory (e.g. `/tmp/fortify.%d/tmpdir`)
+	targetTmpdirParent := path.Join(seal.SharePath, "tmpdir")
+	seal.sys.Ensure(targetTmpdirParent, 0700)
+	seal.sys.UpdatePermType(system.User, targetTmpdirParent, acl.Execute)
+
+	// ensure child tmpdir (e.g. `/tmp/fortify.%d/tmpdir/%d`)
+	targetTmpdir := path.Join(targetTmpdirParent, seal.sys.user.as)
+	seal.sys.Ensure(targetTmpdir, 01700)
+	seal.sys.UpdatePermType(system.User, targetTmpdir, acl.Read, acl.Write, acl.Execute)
+	seal.sys.bwrap.Bind(targetTmpdir, "/tmp", false, true)
+
+	/*
+		XDG runtime directory
+	*/
+
+	// mount tmpfs on inner runtime (e.g. `/run/user/%d`)
+	seal.sys.bwrap.Tmpfs("/run/user", 1*1024*1024)
+	seal.sys.bwrap.Tmpfs(seal.sys.runtime, 8*1024*1024)
+
+	// point to inner runtime path `/run/user/%d`
+	seal.sys.bwrap.SetEnv[xdgRuntimeDir] = seal.sys.runtime
+	seal.sys.bwrap.SetEnv[xdgSessionClass] = "user"
+	seal.sys.bwrap.SetEnv[xdgSessionType] = "tty"
+
+	// ensure RunDir (e.g. `/run/user/%d/fortify`)
+	seal.sys.Ensure(seal.RunDirPath, 0700)
+	seal.sys.UpdatePermType(system.User, seal.RunDirPath, acl.Execute)
+
+	// ensure runtime directory ACL (e.g. `/run/user/%d`)
+	seal.sys.Ensure(seal.RuntimePath, 0700) // ensure this dir in case XDG_RUNTIME_DIR is unset
+	seal.sys.UpdatePermType(system.User, seal.RuntimePath, acl.Execute)
+
+	// ensure process-specific share local to XDG_RUNTIME_DIR (e.g. `/run/user/%d/fortify/%s`)
+	seal.shareLocal = path.Join(seal.RunDirPath, seal.id)
+	seal.sys.Ephemeral(system.Process, seal.shareLocal, 0700)
+	seal.sys.UpdatePerm(seal.shareLocal, acl.Execute)
+
+	/*
+		Inner passwd database
+	*/
+
+	// look up shell
+	sh := "/bin/sh"
+	if s, ok := os.LookupEnv(shell); ok {
+		seal.sys.bwrap.SetEnv[shell] = s
+		sh = s
+	}
+
+	// generate /etc/passwd
+	passwdPath := path.Join(seal.share, "passwd")
+	username := "chronos"
+	if seal.sys.user.username != "" {
+		username = seal.sys.user.username
+	}
+	homeDir := "/var/empty"
+	if seal.sys.user.home != "" {
+		homeDir = seal.sys.user.home
+	}
+
+	// bind home directory
+	seal.sys.bwrap.Bind(seal.sys.user.data, homeDir, false, true)
+	seal.sys.bwrap.Chdir = homeDir
+
+	seal.sys.bwrap.SetEnv["USER"] = username
+	seal.sys.bwrap.SetEnv["HOME"] = homeDir
+
+	passwd := username + ":x:" + seal.sys.mappedIDString + ":" + seal.sys.mappedIDString + ":Fortify:" + homeDir + ":" + sh + "\n"
+	seal.sys.Write(passwdPath, passwd)
+
+	// write /etc/group
+	groupPath := path.Join(seal.share, "group")
+	seal.sys.Write(groupPath, "fortify:x:"+seal.sys.mappedIDString+":\n")
+
+	// bind /etc/passwd and /etc/group
+	seal.sys.bwrap.Bind(passwdPath, "/etc/passwd")
+	seal.sys.bwrap.Bind(groupPath, "/etc/group")
+
+	/*
+		Display servers
+	*/
+
+	// pass $TERM to launcher
+	if t, ok := os.LookupEnv(term); ok {
+		seal.sys.bwrap.SetEnv[term] = t
+	}
+
+	// set up wayland
+	if seal.et.Has(system.EWayland) {
+		var wp string
+		if wd, ok := os.LookupEnv(waylandDisplay); !ok {
+			return fmsg.WrapError(ErrWayland,
+				"WAYLAND_DISPLAY is not set")
+		} else {
+			wp = path.Join(seal.RuntimePath, wd)
+		}
+
+		w := path.Join(seal.sys.runtime, "wayland-0")
+		seal.sys.bwrap.SetEnv[waylandDisplay] = w
+
+		if !seal.directWayland { // set up security-context-v1
+			wc := path.Join(seal.SharePath, "wayland")
+			wt := path.Join(wc, seal.id)
+			seal.sys.Ensure(wc, 0711)
+			appID := seal.fid
+			if appID == "" {
+				// use instance ID in case app id is not set
+				appID = "moe.ophivana.fortify." + seal.id
+			}
+			seal.sys.Wayland(wt, wp, appID, seal.id)
+			seal.sys.bwrap.Bind(wt, w)
+		} else { // bind mount wayland socket (insecure)
+			// hardlink wayland socket
+			wpi := path.Join(seal.shareLocal, "wayland")
+			seal.sys.Link(wp, wpi)
+			seal.sys.bwrap.Bind(wpi, w)
+
+			// ensure Wayland socket ACL (e.g. `/run/user/%d/wayland-%d`)
+			seal.sys.UpdatePermType(system.EWayland, wp, acl.Read, acl.Write, acl.Execute)
+		}
+	}
+
+	// set up X11
+	if seal.et.Has(system.EX11) {
+		// discover X11 and grant user permission via the `ChangeHosts` command
+		if d, ok := os.LookupEnv(display); !ok {
+			return fmsg.WrapError(ErrXDisplay,
+				"DISPLAY is not set")
+		} else {
+			seal.sys.ChangeHosts("#" + seal.sys.user.us)
+			seal.sys.bwrap.SetEnv[display] = d
+			seal.sys.bwrap.Bind("/tmp/.X11-unix", "/tmp/.X11-unix")
+		}
+	}
+
+	/*
+		PulseAudio server and authentication
+	*/
+
+	if seal.et.Has(system.EPulse) {
+		// check PulseAudio directory presence (e.g. `/run/user/%d/pulse`)
+		pd := path.Join(seal.RuntimePath, "pulse")
+		ps := path.Join(pd, "native")
+		if _, err := os.Stat(pd); err != nil {
+			if !errors.Is(err, fs.ErrNotExist) {
+				return fmsg.WrapErrorSuffix(err,
+					fmt.Sprintf("cannot access PulseAudio directory %q:", pd))
+			}
+			return fmsg.WrapError(ErrPulseSocket,
+				fmt.Sprintf("PulseAudio directory %q not found", pd))
+		}
+
+		// check PulseAudio socket permission (e.g. `/run/user/%d/pulse/native`)
+		if s, err := os.Stat(ps); err != nil {
+			if !errors.Is(err, fs.ErrNotExist) {
+				return fmsg.WrapErrorSuffix(err,
+					fmt.Sprintf("cannot access PulseAudio socket %q:", ps))
+			}
+			return fmsg.WrapError(ErrPulseSocket,
+				fmt.Sprintf("PulseAudio directory %q found but socket does not exist", pd))
+		} else {
+			if m := s.Mode(); m&0o006 != 0o006 {
+				return fmsg.WrapError(ErrPulseMode,
+					fmt.Sprintf("unexpected permissions on %q:", ps), m)
+			}
+		}
+
+		// hard link pulse socket into target-executable share
+		psi := path.Join(seal.shareLocal, "pulse")
+		p := path.Join(seal.sys.runtime, "pulse", "native")
+		seal.sys.Link(ps, psi)
+		seal.sys.bwrap.Bind(psi, p)
+		seal.sys.bwrap.SetEnv[pulseServer] = "unix:" + p
+
+		// publish current user's pulse cookie for target user
+		if src, err := discoverPulseCookie(os); err != nil {
+			// not fatal
+			fmsg.VPrintln(err.(*fmsg.BaseError).Message())
+		} else {
+			dst := path.Join(seal.share, "pulse-cookie")
+			innerDst := fst.Tmp + "/pulse-cookie"
+			seal.sys.bwrap.SetEnv[pulseCookie] = innerDst
+			seal.sys.CopyFile(dst, src)
+			seal.sys.bwrap.Bind(dst, innerDst)
+		}
+	}
+
+	/*
+		D-Bus proxy
+	*/
+
+	if seal.et.Has(system.EDBus) {
+		// ensure dbus session bus defaults
+		if bus[0] == nil {
+			bus[0] = dbus.NewConfig(seal.fid, true, true)
+		}
+
+		// downstream socket paths
+		sessionPath, systemPath := path.Join(seal.share, "bus"), path.Join(seal.share, "system_bus_socket")
+
+		// configure dbus proxy
+		if f, err := seal.sys.ProxyDBus(bus[0], bus[1], sessionPath, systemPath); err != nil {
+			return err
+		} else {
+			seal.dbusMsg = f
+		}
+
+		// share proxy sockets
+		sessionInner := path.Join(seal.sys.runtime, "bus")
+		seal.sys.bwrap.SetEnv[dbusSessionBusAddress] = "unix:path=" + sessionInner
+		seal.sys.bwrap.Bind(sessionPath, sessionInner)
+		seal.sys.UpdatePerm(sessionPath, acl.Read, acl.Write)
+		if bus[1] != nil {
+			systemInner := "/run/dbus/system_bus_socket"
+			seal.sys.bwrap.SetEnv[dbusSystemBusAddress] = "unix:path=" + systemInner
+			seal.sys.bwrap.Bind(systemPath, systemInner)
+			seal.sys.UpdatePerm(systemPath, acl.Read, acl.Write)
+		}
+	}
+
+	/*
+		Miscellaneous
+	*/
+
+	// queue overriding tmpfs at the end of seal.sys.bwrap.Filesystem
+	for _, dest := range seal.sys.override {
+		seal.sys.bwrap.Tmpfs(dest, 8*1024)
+	}
+
+	return nil
+}
+
+// discoverPulseCookie attempts various standard methods to discover the current user's PulseAudio authentication cookie
+func discoverPulseCookie(os linux.System) (string, error) {
+	if p, ok := os.LookupEnv(pulseCookie); ok {
+		return p, nil
+	}
+
+	// dotfile $HOME/.pulse-cookie
+	if p, ok := os.LookupEnv(home); ok {
+		p = path.Join(p, ".pulse-cookie")
+		if s, err := os.Stat(p); err != nil {
+			if !errors.Is(err, fs.ErrNotExist) {
+				return p, fmsg.WrapErrorSuffix(err,
+					fmt.Sprintf("cannot access PulseAudio cookie %q:", p))
+			}
+			// not found, try next method
+		} else if !s.IsDir() {
+			return p, nil
+		}
+	}
+
+	// $XDG_CONFIG_HOME/pulse/cookie
+	if p, ok := os.LookupEnv(xdgConfigHome); ok {
+		p = path.Join(p, "pulse", "cookie")
+		if s, err := os.Stat(p); err != nil {
+			if !errors.Is(err, fs.ErrNotExist) {
+				return p, fmsg.WrapErrorSuffix(err,
+					fmt.Sprintf("cannot access PulseAudio cookie %q:", p))
+			}
+			// not found, try next method
+		} else if !s.IsDir() {
+			return p, nil
+		}
+	}
+
+	return "", fmsg.WrapError(ErrPulseCookie,
+		fmt.Sprintf("cannot locate PulseAudio cookie (tried $%s, $%s/pulse/cookie, $%s/.pulse-cookie)",
+			pulseCookie, xdgConfigHome, home))
+}