https://gitlab.gnome.org/GNOME/gdm/-/issues/1089
https://gitlab.gnome.org/GNOME/gdm/-/merge_requests/380
https://gitlab.gnome.org/GNOME/gdm/-/commit/e760c8e4950dfd3de7a1062be0d2c2dc18e70c73

Revert upstream commit e760c8e4950dfd3de7a1062be0d2c2dc18e70c73
("session-worker: Explicitly check and load gdm services"), included
in the 51.beta tarball. It was independently bisected by an upstream
reporter (gdm#1089, comment from darkblaze69, 2026-08-12) as the
commit that introduced a login regression:

Symptom: after selecting a username in the greeter, the password
field intermittently fails to appear at all -- the conversation
switches from gdm-switchable-auth to gdm-password, PAM initializes
and starts authenticating, but the greeter never renders the prompt
or relays a reply. Repeatedly clicking the username, or mashing
Enter, sometimes works around it; eventually GDM tears down the
stalled PAM conversation with error 19 (conversation error).
Reproduced independently on Arch Linux and by the Miezhiko overlay
maintainer.

The commit itself replaces the plain `service` string passed to
pam_start() with an explicitly resolved absolute path, looked up via
synchronous g_file_test() calls against PAM_CONFIG_SERVICES_DIR
(/etc/pam.d) and PAM_SYS_SERVICES_DIR (/usr/lib/pam.d) at PAM-init
time -- introduced as part of MR !380, merged 2026-07-27. As of
2026-08-13 gdm#1089 is still open upstream with no fix or revert
merged yet, so we carry this locally until one lands.

--- a/daemon/gdm-session-worker.c
+++ b/daemon/gdm-session-worker.c
@@ -1200,24 +1200,6 @@
         gdm_session_worker_set_state (worker, GDM_SESSION_WORKER_STATE_NONE);
 }

-static gchar *
-gdm_session_worker_resolve_service_file (const char *service)
-{
-        g_autofree char *service_path = NULL;
-
-        g_set_str (&service_path, g_build_filename (PAM_CONFIG_SERVICES_DIR, service, NULL));
-        if (g_file_test (service_path, G_FILE_TEST_EXISTS|G_FILE_TEST_IS_REGULAR)) {
-                return g_steal_pointer (&service_path);
-        }
-
-        g_set_str (&service_path, g_build_filename (PAM_SYS_SERVICES_DIR, service, NULL));
-        if (g_file_test (service_path, G_FILE_TEST_EXISTS|G_FILE_TEST_IS_REGULAR)) {
-                return g_steal_pointer (&service_path);
-        }
-
-        return NULL;
-}
-
 static gboolean
 gdm_session_worker_initialize_pam (GdmSessionWorker   *worker,
                                    const char         *service,
@@ -1232,7 +1214,6 @@
         struct pam_conv        pam_conversation;
         int                    error_code;
         char tty_string[256];
-        g_autofree char *service_path = NULL;

         g_assert (service != NULL);
         g_assert (worker->pam_handle == NULL);
@@ -1242,25 +1223,6 @@
                  username ? username : "(null)",
                  seat_id ? seat_id : "(null)");

-        service_path = gdm_session_worker_resolve_service_file (service);
-        if (!service_path) {
-                g_debug ("GdmSessionWorker: PAM profile %s was not found", service);
-                g_set_error (error,
-                             GDM_SESSION_WORKER_ERROR,
-                             GDM_SESSION_WORKER_ERROR_SERVICE_UNAVAILABLE,
-                             "PAM profile %s was not found", service);
-
-                /* There is not a specific error for service not found, so we just
-                 * error out as the module is missing, although this is not really
-                 * used since no pam handle is set, thus it's just used to keep
-                 * the same "out" logic.
-                 */
-                error_code = PAM_MODULE_UNKNOWN;
-                goto out;
-        }
-
-        g_debug ("GdmSessionWorker: using PAM profile %s", service_path);
-
 #ifdef SUPPORTS_PAM_EXTENSIONS
         if (extensions != NULL) {
                 gdm_pam_extension_advertise_supported_extensions (gdm_pam_extension_environment_block,
@@ -1273,7 +1235,7 @@
         pam_conversation.appdata_ptr = worker;

         gdm_session_worker_start_auditor (worker);
-        error_code = pam_start (service_path,
+        error_code = pam_start (service,
                                 username,
                                 &pam_conversation,
                                 &worker->pam_handle);