logind: Properly unescape names of lingering users

Filenames to store user linger requests are created with C-escaping.
When we enumerate the files to acquire ligering users, we use the
filenames verbatim. In the case C-escaping is not an identity map (such
as "DOMAIN\User"), we won't be able to start user instances of
such mangled users.

Unescape filenames when we treat them as usernames again.

Fixes: #25448

src/login/logind.c

@@ -18,6 +18,7 @@
 #include "daemon-util.h"
 #include "device-util.h"
 #include "dirent-util.h"
+#include "escape.h"
 #include "fd-util.h"
 #include "format-util.h"
 #include "fs-util.h"
@@ -299,11 +300,16 @@ static int manager_enumerate_linger_users(Manager *m) {
 
         FOREACH_DIRENT(de, d, return -errno) {
                 int k;
+                _cleanup_free_ char *n = NULL;
 
                 if (!dirent_is_file(de))
                         continue;
-
-                k = manager_add_user_by_name(m, de->d_name, NULL);
+                k = cunescape(de->d_name, 0, &n);
+                if (k < 0) {
+                        r = log_warning_errno(k, "Failed to unescape username '%s', ignoring: %m", de->d_name);
+                        continue;
+                }
+                k = manager_add_user_by_name(m, n, NULL);
                 if (k < 0)
                         r = log_warning_errno(k, "Couldn't add lingering user %s, ignoring: %m", de->d_name);
         }