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@@ -0,0 +1,141 @@
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+ From fd6736eb357100ce121762c386592e7703db71e0 Mon Sep 17 00:00:00 2001
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+ From: Benjamin Berg <bberg@redhat.com>
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+ Date: Wed, 25 Sep 2019 14:51:40 +0200
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+ Subject: [PATCH] gdm-session-worker: Drop login_vt assuming it is
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+ GDM_INITIAL_VT
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+
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+ When a session ends, its "session worker" is closed. Since
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+ 3e8220921bb608afd06ed677104fd2244b901a28 (3.33.4), we uninitialise PAM
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+ when this happens. As part of this procedure, we jump back to the login
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+ screen, if the screen being killed is not itself the login screen.
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+
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+ This has broken fast user switching. It goes like this - this
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+ explanation is a bit complicated, bear with us:
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+
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+ We want to jump back to the login screen when a normal user session
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+ ends, so that people can log in again. We do not want to do this when a
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+ login screen itself ends. When session workers start up, they query for
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+ the *currently active VT* and save this in `login_vt`. Then later on, we
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+ check if our session ID is the same as `login_vt`, and jump to
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+ `login_vt` if they are different - this means that it was a user session
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+ not a login session. Querying the currently active VT is fine for the
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+ first greeter, but when initiating a user switch it's wrong as this
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+ gives the user VT.
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+
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+ GDM greeters are killed once they have spawned a session. They are
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+ associated with a logind session, and therefore a PAM session. There are
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+ some actions performed when unregistering PAM sessions, including the
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+ previously mentioned VT jump. Before
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+ 3e8220921bb608afd06ed677104fd2244b901a28 we only uninitialised PAM when
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+ the session itself exited so the bug was masked, but now (since this
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+ commit), if the login screen's *worker* exits first - as happens in the
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+ normal case when GDM kills it - we also do this uninitialisation. Since
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+ we falsely recorded the login screen as the first user's VT, this means
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+ that checking `login_vt != session_vt` returns `TRUE` and we jump back
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+ to the previous user's session immediately after logging into the new
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+ session: fast user switching is broken.
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+
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+ Since the work on shutting down the GDM session has been finished, we
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+ can assume that the login_vt is always on GDM_INITIAL_VT (see
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+ example c71bc5d6c3bc2ec448b5c72ce9a811d9c0c7905e
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+ "local-display-factory: Remove initial VT is in use check" and
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+ 39fb4ff64e6a0653e70a3bfab31da47b49227d59 "manager: don't run autologin
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+ display on tty1"). So simply replace all usages of login_vt with
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+ GDM_INITIAL_VT to solve the above problem.
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+
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+ Note that in the case where ENABLE_USER_DISPLAY_SERVER is not enabled,
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+ the login_vt is always the same as the session_vt. We can simply remove
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+ the VT switching magic there and everything should be working as
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+ expected.
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+
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+ This is a simpler version of the patch by Iain Lane <iainl@gnome.org>,
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+ taking into account that we can make the assumption about the login_vt.
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+
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+ Closes #515
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+ ---
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+ daemon/gdm-session-worker.c | 43 +++++++------------------------------
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+ 1 file changed, 8 insertions(+), 35 deletions(-)
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+
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+ diff --git a/daemon/gdm-session-worker.c b/daemon/gdm-session-worker.c
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+ index 0e854158..4f9083c3 100644
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+ --- a/daemon/gdm-session-worker.c
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+ +++ b/daemon/gdm-session-worker.c
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+ @@ -146,7 +146,6 @@ struct GdmSessionWorkerPrivate
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+ char **extensions;
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+
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+ int cred_flags;
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+ - int login_vt;
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+ int session_vt;
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+ int session_tty_fd;
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+
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+ @@ -1052,13 +1051,15 @@ gdm_session_worker_uninitialize_pam (GdmSessionWorker *worker,
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+
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+ gdm_session_worker_stop_auditor (worker);
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+
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+ +#ifdef ENABLE_USER_DISPLAY_SERVER
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+ if (g_strcmp0 (worker->priv->display_seat_id, "seat0") == 0) {
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+ - if (worker->priv->login_vt != worker->priv->session_vt) {
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+ - jump_to_vt (worker, worker->priv->login_vt);
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+ + /* Switch to the login VT if we are not the login screen. */
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+ + if (worker->priv->session_vt != GDM_INITIAL_VT) {
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+ + jump_to_vt (worker, GDM_INITIAL_VT);
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+ }
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+ }
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+ +#endif
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+
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+ - worker->priv->login_vt = 0;
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+ worker->priv->session_vt = 0;
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+
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+ g_debug ("GdmSessionWorker: state NONE");
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+ @@ -1107,32 +1108,6 @@ _get_xauth_for_pam (const char *x11_authority_file)
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+ }
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+ #endif
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+
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+ -static gboolean
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+ -ensure_login_vt (GdmSessionWorker *worker)
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+ -{
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+ - int fd;
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+ - struct vt_stat vt_state = { 0 };
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+ - gboolean got_login_vt = FALSE;
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+ -
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+ - fd = open ("/dev/tty0", O_RDWR | O_NOCTTY);
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+ -
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+ - if (fd < 0) {
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+ - g_debug ("GdmSessionWorker: couldn't open VT master: %m");
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+ - return FALSE;
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+ - }
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+ -
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+ - if (ioctl (fd, VT_GETSTATE, &vt_state) < 0) {
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+ - g_debug ("GdmSessionWorker: couldn't get current VT: %m");
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+ - goto out;
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+ - }
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+ -
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+ - worker->priv->login_vt = vt_state.v_active;
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+ - got_login_vt = TRUE;
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+ -out:
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+ - close (fd);
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+ - return got_login_vt;
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+ -}
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+ -
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+ static gboolean
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+ gdm_session_worker_initialize_pam (GdmSessionWorker *worker,
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+ const char *service,
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+ @@ -1227,12 +1202,10 @@ gdm_session_worker_initialize_pam (GdmSessionWorker *worker,
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+ g_debug ("GdmSessionWorker: state SETUP_COMPLETE");
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+ gdm_session_worker_set_state (worker, GDM_SESSION_WORKER_STATE_SETUP_COMPLETE);
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+
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+ - /* Temporarily set PAM_TTY with the currently active VT (login screen)
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+ + /* Temporarily set PAM_TTY with the login VT,
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+ PAM_TTY will be reset with the users VT right before the user session is opened */
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+ - if (ensure_login_vt (worker)) {
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+ - g_snprintf (tty_string, 256, "/dev/tty%d", worker->priv->login_vt);
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+ - pam_set_item (worker->priv->pam_handle, PAM_TTY, tty_string);
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+ - }
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+ + g_snprintf (tty_string, 256, "/dev/tty%d", GDM_INITIAL_VT);
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+ + pam_set_item (worker->priv->pam_handle, PAM_TTY, tty_string);
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+ if (!display_is_local)
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+ worker->priv->password_is_required = TRUE;
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+
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+ --
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+ 2.21.0
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+
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benzea
commented 4 years ago
https://gitlab.gnome.org/GNOME/gdm/merge_requests/86
Resolves: #1751673