fix: set XDG_CONFIG_DIRS and XDG_DATA_DIRS defaults in tryGetPamEnvVars

When snap or other environments strip XDG_CONFIG_DIRS and XDG_DATA_DIRS,
and PAM env files do not define them, child shells receive no value for
these vars. Apply XDG Base Directory spec defaults (/etc/xdg and
/usr/local/share:/usr/share) following the same pattern already used
for XDG_RUNTIME_DIR.

Fixes #2970

Signed-off-by: majiayu000 <1835304752@qq.com>

Author: majiayu000

pkg/shellexec/shellexec.go

@@ -760,5 +760,11 @@ func tryGetPamEnvVars() map[string]string {
 	if runtime_dir, ok := envVars["XDG_RUNTIME_DIR"]; !ok || runtime_dir == "" {
 		envVars["XDG_RUNTIME_DIR"] = "/run/user/" + fmt.Sprint(os.Getuid())
 	}
+	if configDirs, ok := envVars["XDG_CONFIG_DIRS"]; !ok || configDirs == "" {
+		envVars["XDG_CONFIG_DIRS"] = "/etc/xdg"
+	}
+	if dataDirs, ok := envVars["XDG_DATA_DIRS"]; !ok || dataDirs == "" {
+		envVars["XDG_DATA_DIRS"] = "/usr/local/share:/usr/share"
+	}
 	return envVars
 }