service: new NotifyAccess= value for control processes (#4212)

Setting NotifyAccess=exec allows notifications coming directly from any
control process.

man/systemd.service.xml

@@ -798,11 +798,14 @@
         notification socket, as accessible via the
         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
         call. Takes one of <option>none</option> (the default),
-        <option>main</option> or <option>all</option>. If
-        <option>none</option>, no daemon status updates are accepted
-        from the service processes, all status update messages are
-        ignored. If <option>main</option>, only service updates sent
-        from the main process of the service are accepted. If
+        <option>main</option>, <option>exec</option> or
+        <option>all</option>. If <option>none</option>, no daemon status
+        updates are accepted from the service processes, all status
+        update messages are ignored. If <option>main</option>, only
+        service updates sent from the main process of the service are
+        accepted. If <option>exec</option>, only service updates sent
+        from any of the control processes originating from one of the
+        <varname>Exec*=</varname> commands are accepted. If
         <option>all</option>, all services updates from all members of
         the service's control group are accepted. This option should
         be set to open access to the notification socket when using

src/core/service.c

@@ -1252,7 +1252,8 @@ static int service_spawn(
         if (!our_env)
                 return -ENOMEM;
 
-        if ((flags & EXEC_IS_CONTROL) ? s->notify_access == NOTIFY_ALL : s->notify_access != NOTIFY_NONE)
+        if ((flags & EXEC_IS_CONTROL) ? IN_SET(s->notify_access, NOTIFY_ALL, NOTIFY_EXEC)
+                                      : s->notify_access != NOTIFY_NONE)
                 if (asprintf(our_env + n_env++, "NOTIFY_SOCKET=%s", UNIT(s)->manager->notify_socket) < 0)
                         return -ENOMEM;
 
@@ -3059,6 +3060,16 @@ static void service_notify_message(Unit *u, pid_t pid, char **tags, FDSet *fds)
                 else
                         log_unit_debug(u, "Got notification message from PID "PID_FMT", but reception only permitted for main PID which is currently not known", pid);
                 return;
+        } else if (s->notify_access == NOTIFY_EXEC && pid != s->main_pid && pid != s->control_pid) {
+                if (s->main_pid != 0 && s->control_pid != 0)
+                        log_unit_warning(u, "Got notification message from PID "PID_FMT", but reception only permitted for main PID "PID_FMT" and control PID "PID_FMT,
+                                         pid, s->main_pid, s->control_pid);
+                else if (s->main_pid != 0 || s->control_pid != 0)
+                        log_unit_warning(u, "Got notification message from PID "PID_FMT", but reception only permitted for %s PID "PID_FMT,
+                                         pid, s->main_pid ? "main" : "control", s->main_pid | s->control_pid);
+                else
+                        log_unit_debug(u, "Got notification message from PID "PID_FMT", but reception only permitted for main PID and control PID which are currently not known", pid);
+                return;
         } else
                 log_unit_debug(u, "Got notification message from PID "PID_FMT" (%s)", pid, isempty(cc) ? "n/a" : cc);
 
@@ -3384,6 +3395,7 @@ DEFINE_STRING_TABLE_LOOKUP(service_exec_command, ServiceExecCommand);
 static const char* const notify_access_table[_NOTIFY_ACCESS_MAX] = {
         [NOTIFY_NONE] = "none",
         [NOTIFY_MAIN] = "main",
+        [NOTIFY_EXEC] = "exec",
         [NOTIFY_ALL] = "all"
 };
 

src/core/service.h

@@ -65,6 +65,7 @@ typedef enum NotifyAccess {
         NOTIFY_NONE,
         NOTIFY_ALL,
         NOTIFY_MAIN,
+        NOTIFY_EXEC,
         _NOTIFY_ACCESS_MAX,
         _NOTIFY_ACCESS_INVALID = -1
 } NotifyAccess;