core: fix security and concurrency issues found in a backend audit (#2805)

* core: fix security and concurrency issues found in backend audit

Security:
- privesc: pipe the sudo password via stdin (sudo -S) instead of
  embedding it in the command string, so it no longer appears in argv
  (readable by any local user via /proc/<pid>/cmdline or ps)
- greeter: tokenize a session .desktop Exec= line into argv and execve
  directly instead of running it through /bin/sh -c, closing a command-
  injection path via user-writable ~/.local/share/wayland-sessions
- plugins: reject path-separator/.. in plugin id/name before joining
  into a filesystem path, closing an arbitrary-directory-delete in the
  uninstall/update fallback
- keybinds/hyprland: always quote unrecognized bind actions/keys when
  writing generated Lua; only re-emit genuine round-tripped custom Lua
  verbatim (tracked via an explicit flag), closing a Lua-injection path
- desktop/mimeapps: reject newline/bracket in mime/desktop-id fields so
  they can't inject fake sections into the shared mimeapps.list

Robustness / concurrency:
- server: recover panics in the request-dispatch path so one bad
  handler can't crash the daemon and drop every client
- go-wayland: recover panics in the shared dispatch choke point so a
  malformed compositor event can't crash CLI tools / the daemon
- server: per-connection D-Bus client ID instead of a shared constant,
  fixing cross-client signal delivery and subscription teardown
- network: guard the NetworkManager device maps with a mutex (a
  concurrent map read/write here is an unrecoverable fatal error)
- cups: close the event channel on Stop() so Unsubscribe() of the last
  subscriber no longer deadlocks; allocate the fresh channel in Start()
- freedesktop: reuse the shared session conn for the settings watcher
  and tear it down in Close(), fixing a per-Manager conn+goroutine leak
- clipboard: mutex-guard lazy dbusConn creation
- geolocation: use WithMatchMember for the GeoClue2 LocationUpdated
  signal (was WithMatchSender with an interface.member string, so the
  match never fired and live location updates never arrived)
- screenshot: set failed=true on buffer/pool creation errors so the
  dispatch loop doesn't wait forever for a ready/failed that never comes

* apply code review comments

---------

Co-authored-by: bbedward <bbedward@gmail.com>
(cherry picked from commit ca89e12963)

core/internal/greeter/session_launcher.go

@@ -3,6 +3,7 @@ package greeter
 import (
 	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"strings"
 	"syscall"
@@ -93,18 +94,95 @@ func resolveSessionExecInDirs(sessionID string, dirs []string) (string, error) {
 	return "", fmt.Errorf("session desktop file %q was not found", id)
 }
 
+// parseExecString splits a Desktop Entry Exec= value into argv without
+// involving a shell, mirroring quickshell's DesktopEntry::parseExecString
+// (string quoting, value escapes, field code stripping).
+func parseExecString(execLine string) []string {
+	var args []string
+	var cur strings.Builder
+	inString := false
+	escape := 0
+	percent := false
+
+	for _, c := range execLine {
+		switch {
+		case escape == 0 && c == '\\':
+			escape = 1
+		case inString:
+			switch {
+			case c == '\\':
+				escape++
+				if escape == 4 {
+					cur.WriteByte('\\')
+					escape = 0
+				}
+			case escape == 2:
+				cur.WriteRune(c)
+				escape = 0
+			case escape != 0:
+				switch c {
+				case 's':
+					cur.WriteByte(' ')
+				case 'n':
+					cur.WriteByte('\n')
+				case 't':
+					cur.WriteByte('\t')
+				case 'r':
+					cur.WriteByte('\r')
+				default:
+					cur.WriteRune(c)
+				}
+				escape = 0
+			case c == '"' || c == '\'':
+				inString = false
+			default:
+				cur.WriteRune(c)
+			}
+		case escape != 0:
+			cur.WriteRune(c)
+			escape = 0
+		case percent:
+			if c == '%' {
+				cur.WriteByte('%')
+			}
+			percent = false
+		case c == '%':
+			percent = true
+		case c == '"' || c == '\'':
+			inString = true
+		case c == ' ':
+			if cur.Len() > 0 {
+				args = append(args, cur.String())
+				cur.Reset()
+			}
+		default:
+			cur.WriteRune(c)
+		}
+	}
+	if cur.Len() > 0 {
+		args = append(args, cur.String())
+	}
+	return args
+}
+
 func LaunchSessionByID(sessionID string) error {
 	execLine, err := ResolveSessionExec(sessionID)
 	if err != nil {
 		return err
 	}
-	execLine = strings.TrimSpace(stripDesktopExecCodes(execLine))
-	if execLine == "" {
+
+	argv := parseExecString(strings.TrimSpace(execLine))
+	if len(argv) == 0 {
 		return fmt.Errorf("session %q has an empty Exec command", sessionID)
 	}
 
+	resolved, err := exec.LookPath(argv[0])
+	if err != nil {
+		return fmt.Errorf("session %q command %q not found: %w", sessionID, argv[0], err)
+	}
+
 	env := append(os.Environ(), "XDG_SESSION_TYPE=wayland")
-	return syscall.Exec("/bin/sh", []string{"sh", "-c", "exec " + execLine}, env)
+	return syscall.Exec(resolved, argv, env)
 }
 
 func LaunchSessionFromMemory(cacheDir, homeDir string) error {