logind: refuse operations if the target unit is masked or unavailable

If hibernate.target is masked, and systemctl hibernate is invoked, havoc ensues.
logind starts the hibernation operation, but then doesn't go through with it;
gnome-shell segfaults. Let's be nice to the user and refuse doing anything in
that case.

$ sudo systemctl mask hibernate.target
$ busctl call org.freedesktop.login1 /org/freedesktop/login1 org.freedesktop.login1.Manager CanHibernate
s "no"
$ sudo systemctl hibernate
Failed to hibernate system via logind: Access denied
Failed to start hibernate.target: Unit hibernate.target is masked.

https://bugzilla.redhat.com/show_bug.cgi?id=1468003#c4

1 files changed, 45 insertions, 0 deletions

diff --git a/src/login/logind-dbus.c b/src/login/logind-dbus.c
index e53644f8d..73be87b19 100644
--- a/src/login/logind-dbus.c
+++ b/src/login/logind-dbus.c
@@ -3,6 +3,19 @@
   This file is part of systemd.
 
   Copyright 2011 Lennart Poettering
+
+  elogind is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  elogind is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with elogind; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
 #include <errno.h>
@@ -16,6 +29,7 @@
 #include "audit-util.h"
 #include "bus-common-errors.h"
 #include "bus-error.h"
+//#include "bus-unit-util.h"
 #include "bus-util.h"
 #include "dirent-util.h"
 //#include "efivars.h"
@@ -1741,6 +1755,7 @@ int bus_manager_shutdown_or_sleep_now_or_later(
 #if 0 /// elogind has HandleAction instead of const char* unit_name
                 const char *unit_name,
 
+        _cleanup_free_ char *load_state = NULL;
 #else
                 HandleAction unit_name,
 #endif // 0
@@ -1755,6 +1770,15 @@ int bus_manager_shutdown_or_sleep_now_or_later(
         assert(w > 0);
         assert(w <= _INHIBIT_WHAT_MAX);
         assert(!m->action_job);
+
+        r = unit_load_state(m->bus, unit_name, &load_state);
+        if (r < 0)
+                return r;
+
+        if (!streq(load_state, "loaded")) {
+                log_notice("Unit %s is %s, refusing operation.", unit_name, load_state);
+                return -EACCES;
+        }
 #else
         assert(w > 0);
         assert(w <= _INHIBIT_WHAT_MAX);
@@ -2360,6 +2384,7 @@ static int method_can_shutdown_or_sleep(
                 sd_bus_error *error) {
 
         _cleanup_(sd_bus_creds_unrefp) sd_bus_creds *creds = NULL;
+        HandleAction handle;
         bool multiple_sessions, challenge, blocked;
         const char *result = NULL;
         uid_t uid;
@@ -2400,6 +2425,25 @@ static int method_can_shutdown_or_sleep(
         multiple_sessions = r > 0;
         blocked = manager_is_inhibited(m, w, INHIBIT_BLOCK, NULL, false, true, uid, NULL);
 
+        handle = handle_action_from_string(sleep_verb);
+        if (handle >= 0) {
+                const char *target;
+
+                target = manager_target_for_action(handle);
+                if (target) {
+                        _cleanup_free_ char *load_state = NULL;
+
+                        r = unit_load_state(m->bus, target, &load_state);
+                        if (r < 0)
+                                return r;
+
+                        if (!streq(load_state, "loaded")) {
+                                result = "no";
+                                goto finish;
+                        }
+                }
+        }
+
         if (multiple_sessions) {
                 r = bus_test_polkit(message, CAP_SYS_BOOT, action_multiple_sessions, NULL, UID_INVALID, &challenge, error);
                 if (r < 0)
@@ -2442,6 +2486,7 @@ static int method_can_shutdown_or_sleep(
                         result = "no";
         }
 
+ finish:
         return sd_bus_reply_method_return(message, "s", result);
 }