logind: close FIFO before ending sessions cleanly

For clean session endings ask logind explicitly to get rid of the FIFO
before closing it so that the FIFO logic doesn't result in su/sudo to be
terminated immediately.

src/login/logind-dbus.c

@@ -80,6 +80,9 @@
         "   <arg name=\"seat\" type=\"s\" direction=\"out\"/>\n"        \
         "   <arg name=\"vtnr\" type=\"u\" direction=\"out\"/>\n"        \
         "  </method>\n"                                                 \
+        "  <method name=\"ReleaseSession\">\n"                          \
+        "   <arg name=\"id\" type=\"s\" direction=\"in\"/>\n"           \
+        "  </method>\n"                                                 \
         "  <method name=\"ActivateSession\">\n"                         \
         "   <arg name=\"id\" type=\"s\" direction=\"in\"/>\n"           \
         "  </method>\n"                                                 \
@@ -1075,6 +1078,33 @@ static DBusHandlerResult manager_message_handler(
                 if (r < 0)
                         return bus_send_error_reply(connection, message, &error, r);
 
+        } else if (dbus_message_is_method_call(message, "org.freedesktop.login1.Manager", "ReleaseSession")) {
+                const char *name;
+                Session *session;
+
+                if (!dbus_message_get_args(
+                                    message,
+                                    &error,
+                                    DBUS_TYPE_STRING, &name,
+                                    DBUS_TYPE_INVALID))
+                        return bus_send_error_reply(connection, message, &error, -EINVAL);
+
+                session = hashmap_get(m->sessions, name);
+                if (!session)
+                        return bus_send_error_reply(connection, message, &error, -ENOENT);
+
+                /* We use the FIFO to detect stray sessions where the
+                process invoking PAM dies abnormally. We need to make
+                sure that that process is not killed if at the clean
+                end of the session it closes the FIFO. Hence, with
+                this call explicitly turn off the FIFO logic, so that
+                the PAM code can finish clean up on its own */
+                session_remove_fifo(session);
+
+                reply = dbus_message_new_method_return(message);
+                if (!reply)
+                        goto oom;
+
         } else if (dbus_message_is_method_call(message, "org.freedesktop.login1.Manager", "ActivateSession")) {
                 const char *name;
                 Session *session;

src/login/pam-module.c

@@ -414,7 +414,6 @@ _public_ PAM_EXTERN int pam_sm_open_session(
                         "/org/freedesktop/login1",
                         "org.freedesktop.login1.Manager",
                         "CreateSession");
-
         if (!m) {
                 pam_syslog(handle, LOG_ERR, "Could not allocate create session message.");
                 r = PAM_BUF_ERR;
@@ -620,11 +619,77 @@ _public_ PAM_EXTERN int pam_sm_close_session(
                 int argc, const char **argv) {
 
         const void *p = NULL;
+        const char *id;
+        DBusConnection *bus = NULL;
+        DBusMessage *m = NULL, *reply = NULL;
+        DBusError error;
+        int r;
 
+        assert(handle);
+
+        dbus_error_init(&error);
+
+        id = pam_getenv(handle, "XDG_SESSION_ID");
+        if (id) {
+
+                /* Before we go and close the FIFO we need to tell
+                 * logind that this is a clean session shutdown, so
+                 * that it doesn't just go and slaughter us
+                 * immediately after closing the fd */
+
+                bus = dbus_bus_get_private(DBUS_BUS_SYSTEM, &error);
+                if (!bus) {
+                        pam_syslog(handle, LOG_ERR, "Failed to connect to system bus: %s", bus_error_message(&error));
+                        r = PAM_SESSION_ERR;
+                        goto finish;
+                }
+
+                m = dbus_message_new_method_call(
+                                "org.freedesktop.login1",
+                                "/org/freedesktop/login1",
+                                "org.freedesktop.login1.Manager",
+                                "ReleaseSession");
+                if (!m) {
+                        pam_syslog(handle, LOG_ERR, "Could not allocate release session message.");
+                        r = PAM_BUF_ERR;
+                        goto finish;
+                }
+
+                if (!dbus_message_append_args(m,
+                                              DBUS_TYPE_STRING, &id,
+                                              DBUS_TYPE_INVALID)) {
+                        pam_syslog(handle, LOG_ERR, "Could not attach parameters to message.");
+                        r = PAM_BUF_ERR;
+                        goto finish;
+                }
+
+                reply = dbus_connection_send_with_reply_and_block(bus, m, -1, &error);
+                if (!reply) {
+                        pam_syslog(handle, LOG_ERR, "Failed to release session: %s", bus_error_message(&error));
+                        r = PAM_SESSION_ERR;
+                        goto finish;
+                }
+        }
+
+        r = PAM_SUCCESS;
+
+finish:
         pam_get_data(handle, "systemd.session-fd", &p);
-
         if (p)
                 close_nointr(PTR_TO_INT(p) - 1);
 
-        return PAM_SUCCESS;
+        dbus_error_free(&error);
+
+        if (bus) {
+                dbus_connection_close(bus);
+                dbus_connection_unref(bus);
+        }
+
+        if (m)
+                dbus_message_unref(m);
+
+        if (reply)
+                dbus_message_unref(reply);
+
+        return r;
 }