app: improve WAYLAND_DISPLAY correctness

This now has identical behaviour as wayland C library.

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

6 files changed, 41 insertions, 20 deletions

diff --git a/internal/app/app_nixos_test.go b/internal/app/app_nixos_test.go
index 062bfe0f..18a42e16 100644
--- a/internal/app/app_nixos_test.go
+++ b/internal/app/app_nixos_test.go
@@ -102,7 +102,7 @@ var testCasesNixos = []sealTestCase{
 				"SHELL":                    "/run/current-system/sw/bin/zsh",
 				"TERM":                     "xterm-256color",
 				"USER":                     "u0_a1",
-				"WAYLAND_DISPLAY":          "/run/user/1971/wayland-0",
+				"WAYLAND_DISPLAY":          "wayland-0",
 				"XDG_RUNTIME_DIR":          "/run/user/1971",
 				"XDG_SESSION_CLASS":        "user",
 				"XDG_SESSION_TYPE":         "tty",
diff --git a/internal/app/app_pd_test.go b/internal/app/app_pd_test.go
index 2d042a2c..269c8aa3 100644
--- a/internal/app/app_pd_test.go
+++ b/internal/app/app_pd_test.go
@@ -267,7 +267,7 @@ var testCasesPd = []sealTestCase{
 				"SHELL":                    "/run/current-system/sw/bin/zsh",
 				"TERM":                     "xterm-256color",
 				"USER":                     "chronos",
-				"WAYLAND_DISPLAY":          "/run/user/65534/wayland-0",
+				"WAYLAND_DISPLAY":          "wayland-0",
 				"XDG_RUNTIME_DIR":          "/run/user/65534",
 				"XDG_SESSION_CLASS":        "user",
 				"XDG_SESSION_TYPE":         "tty",
diff --git a/internal/app/share.go b/internal/app/share.go
index f9eec26c..9e7d0f17 100644
--- a/internal/app/share.go
+++ b/internal/app/share.go
@@ -13,6 +13,7 @@ import (
 	"git.gensokyo.uk/security/fortify/internal/fmsg"
 	"git.gensokyo.uk/security/fortify/internal/linux"
 	"git.gensokyo.uk/security/fortify/internal/system"
+	"git.gensokyo.uk/security/fortify/wl"
 )
 
 const (
@@ -27,9 +28,6 @@ const (
 	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"
 
@@ -38,7 +36,6 @@ const (
 )
 
 var (
-	ErrWayland  = errors.New(waylandDisplay + " unset")
 	ErrXDisplay = errors.New(display + " unset")
 
 	ErrPulseCookie = errors.New("pulse cookie not present")
@@ -144,34 +141,36 @@ func (seal *appSeal) setupShares(bus [2]*dbus.Config, os linux.System) error {
 
 	// 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")
+		var socketPath string
+		if name, ok := os.LookupEnv(wl.WaylandDisplay); !ok {
+			fmsg.VPrintln(wl.WaylandDisplay + " is not set, assuming " + wl.FallbackName)
+			socketPath = path.Join(seal.RuntimePath, wl.FallbackName)
+		} else if !path.IsAbs(name) {
+			socketPath = path.Join(seal.RuntimePath, name)
 		} else {
-			wp = path.Join(seal.RuntimePath, wd)
+			socketPath = name
 		}
 
-		w := path.Join(seal.sys.runtime, "wayland-0")
-		seal.sys.bwrap.SetEnv[waylandDisplay] = w
+		innerPath := path.Join(seal.sys.runtime, wl.FallbackName)
+		seal.sys.bwrap.SetEnv[wl.WaylandDisplay] = wl.FallbackName
 
 		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)
+			socketDir := path.Join(seal.SharePath, "wayland")
+			outerPath := path.Join(socketDir, seal.id)
+			seal.sys.Ensure(socketDir, 0711)
 			appID := seal.fid
 			if appID == "" {
 				// use instance ID in case app id is not set
 				appID = "uk.gensokyo.fortify." + seal.id
 			}
-			seal.sys.Wayland(wt, wp, appID, seal.id)
-			seal.sys.bwrap.Bind(wt, w)
+			seal.sys.Wayland(outerPath, socketPath, appID, seal.id)
+			seal.sys.bwrap.Bind(outerPath, innerPath)
 		} else { // bind mount wayland socket (insecure)
 			fmsg.VPrintln("direct wayland access, PROCEED WITH CAUTION")
-			seal.sys.bwrap.Bind(wp, w)
+			seal.sys.bwrap.Bind(socketPath, innerPath)
 
 			// ensure Wayland socket ACL (e.g. `/run/user/%d/wayland-%d`)
-			seal.sys.UpdatePermType(system.EWayland, wp, acl.Read, acl.Write, acl.Execute)
+			seal.sys.UpdatePermType(system.EWayland, socketPath, acl.Read, acl.Write, acl.Execute)
 		}
 	}
 
diff --git a/internal/system/wayland.go b/internal/system/wayland.go
index 7c233472..9646b467 100644
--- a/internal/system/wayland.go
+++ b/internal/system/wayland.go
@@ -38,6 +38,10 @@ func (w Wayland) apply(sys *I) error {
 	}
 
 	if err := w.conn.Attach(w.pair[1]); err != nil {
+		// make console output less nasty
+		if errors.Is(err, os.ErrNotExist) {
+			err = os.ErrNotExist
+		}
 		return fmsg.WrapErrorSuffix(err,
 			fmt.Sprintf("cannot attach to wayland on %q:", w.pair[1]))
 	} else {
diff --git a/test.nix b/test.nix
index 5f41d40a..f71d906d 100644
--- a/test.nix
+++ b/test.nix
@@ -282,6 +282,9 @@ nixosTest {
     if output != "":
         raise Exception(f"unexpected output\n{output}")
 
+    # Verify graceful failure on bad Wayland display name:
+    print(machine.fail("sudo -u alice -i fortify -v run --wayland true"))
+
     # Start fortify permissive defaults within Wayland session:
     fortify('-v run --wayland --dbus notify-send -a "NixOS Tests" "Test notification" "Notification from within sandbox." && touch /tmp/dbus-done')
     machine.wait_for_file("/tmp/dbus-done")
diff --git a/wl/consts.go b/wl/consts.go
new file mode 100644
index 00000000..2ad4028c
--- /dev/null
+++ b/wl/consts.go
@@ -0,0 +1,15 @@
+package wl
+
+const (
+	// WaylandDisplay contains the name of the server socket
+	// (https://gitlab.freedesktop.org/wayland/wayland/-/blob/1.23.1/src/wayland-client.c#L1147)
+	// which is concatenated with XDG_RUNTIME_DIR
+	// (https://gitlab.freedesktop.org/wayland/wayland/-/blob/1.23.1/src/wayland-client.c#L1171)
+	// or used as-is if absolute
+	// (https://gitlab.freedesktop.org/wayland/wayland/-/blob/1.23.1/src/wayland-client.c#L1176).
+	WaylandDisplay = "WAYLAND_DISPLAY"
+
+	// FallbackName is used as the wayland socket name if WAYLAND_DISPLAY is unset
+	// (https://gitlab.freedesktop.org/wayland/wayland/-/blob/1.23.1/src/wayland-client.c#L1149).
+	FallbackName = "wayland-0"
+)