gdm-session: set PAM_TTY when initialising pam

Temporarily set this to the VT that the login screen is currently active on so that pam modules that require this
information early can have access to it. Debian/Ubuntu use this to detect if the login is coming from a local tty.
PAM_TTY will get reset to the users VT right before the user session is opened.

https://bugzilla.gnome.org/show_bug.cgi?id=764669

1 files changed, 33 insertions, 7 deletions

diff --git a/daemon/gdm-session-worker.c b/daemon/gdm-session-worker.c
index f2581ae0..b97c688a 100644
--- a/daemon/gdm-session-worker.c
+++ b/daemon/gdm-session-worker.c
@@ -963,6 +963,32 @@ _get_xauth_for_pam (const char *x11_authority_file)
 #endif
 
 static gboolean
+ensure_login_vt (GdmSessionWorker *worker)
+{
+        int fd;
+        struct vt_stat vt_state = { 0 };
+        gboolean got_login_vt = FALSE;
+
+        fd = open ("/dev/tty0", O_RDWR | O_NOCTTY);
+
+        if (fd < 0) {
+                g_debug ("GdmSessionWorker: couldn't open VT master: %m");
+                return FALSE;
+        }
+
+        if (ioctl (fd, VT_GETSTATE, &vt_state) < 0) {
+                g_debug ("GdmSessionWorker: couldn't get current VT: %m");
+                goto out;
+        }
+
+        worker->priv->login_vt = vt_state.v_active;
+        got_login_vt = TRUE;
+out:
+        close (fd);
+        return got_login_vt;
+}
+
+static gboolean
 gdm_session_worker_initialize_pam (GdmSessionWorker *worker,
                                    const char       *service,
                                    const char       *username,
@@ -976,6 +1002,7 @@ gdm_session_worker_initialize_pam (GdmSessionWorker *worker,
 {
         struct pam_conv        pam_conversation;
         int                    error_code;
+        char tty_string[256];
 
         g_assert (worker->priv->pam_handle == NULL);
 
@@ -1048,6 +1075,12 @@ gdm_session_worker_initialize_pam (GdmSessionWorker *worker,
         g_debug ("GdmSessionWorker: state SETUP_COMPLETE");
         worker->priv->state = GDM_SESSION_WORKER_STATE_SETUP_COMPLETE;
 
+        /* Temporarily set PAM_TTY with the currently active VT (login screen) 
+           PAM_TTY will be reset with the users VT right before the user session is opened */
+        ensure_login_vt (worker);
+        g_snprintf (tty_string, 256, "/dev/tty%d", worker->priv->login_vt);
+        pam_set_item (worker->priv->pam_handle, PAM_TTY, tty_string);
+
  out:
         if (error_code != PAM_SUCCESS) {
                 gdm_session_worker_uninitialize_pam (worker, error_code);
@@ -2020,7 +2053,6 @@ set_up_for_new_vt (GdmSessionWorker *worker)
 {
         int fd;
         char vt_string[256], tty_string[256];
-        struct vt_stat vt_state = { 0 };
         int session_vt = 0;
 
         fd = open ("/dev/tty0", O_RDWR | O_NOCTTY);
@@ -2030,11 +2062,6 @@ set_up_for_new_vt (GdmSessionWorker *worker)
                 return FALSE;
         }
 
-        if (ioctl (fd, VT_GETSTATE, &vt_state) < 0) {
-                g_debug ("GdmSessionWorker: couldn't get current VT: %m");
-                goto fail;
-        }
-
         if (worker->priv->display_is_initial) {
                 session_vt = atoi (GDM_INITIAL_VT);
         } else {
@@ -2044,7 +2071,6 @@ set_up_for_new_vt (GdmSessionWorker *worker)
                 }
         }
 
-        worker->priv->login_vt = vt_state.v_active;
         worker->priv->session_vt = session_vt;
 
         close (fd);