service: add minimal access control logic for notifcation socket

fixme

@@ -63,8 +63,6 @@
 
 * abstract namespace dbus socket
 
-* discuss NOTIFY_SOCKET, make it configurable? security implications?
-
 Regularly:
 
 * look for close() vs. close_nointr() vs. close_nointr_nofail()

src/load-fragment.c

@@ -1204,6 +1204,8 @@ finish:
         return r;
 }
 
+DEFINE_CONFIG_PARSE_ENUM(config_parse_notify_access, notify_access, NotifyAccess, "Failed to parse notify access specifier");
+
 #define FOLLOW_MAX 8
 
 static int open_follow(char **filename, FILE **_f, Set *names, char **_final) {
@@ -1360,6 +1362,9 @@ static void dump_items(FILE *f, const ConfigItem *items) {
                 { config_parse_description,      "DESCRIPTION" },
                 { config_parse_timer,            "TIMER" },
                 { config_parse_timer_unit,       "NAME" },
+                { config_parse_path_spec,        "PATH" },
+                { config_parse_path_unit,        "UNIT" },
+                { config_parse_notify_access,    "ACCESS" }
         };
 
         assert(f);
@@ -1491,6 +1496,7 @@ static int load_from_path(Unit *u, const char *path) {
                 { "KillMode",               config_parse_kill_mode,       &u->service.kill_mode,                           "Service" },
                 { "NonBlocking",            config_parse_bool,            &u->service.exec_context.non_blocking,           "Service" },
                 { "BusName",                config_parse_string,          &u->service.bus_name,                            "Service" },
+                { "NotifyAccess",           config_parse_notify_access,   &u->service.notify_access,                       "Service" },
                 EXEC_CONTEXT_CONFIG_ITEMS(u->service.exec_context, "Service"),
 
                 { "ListenStream",           config_parse_listen,          &u->socket,                                      "Socket"  },

src/manager.c

@@ -70,7 +70,6 @@ static int manager_setup_notify(Manager *m) {
                 struct sockaddr_un un;
         } sa;
         struct epoll_event ev;
-        char *ne[2], **t;
         int one = 1;
 
         assert(m);
@@ -106,19 +105,9 @@ static int manager_setup_notify(Manager *m) {
         if (epoll_ctl(m->epoll_fd, EPOLL_CTL_ADD, m->notify_watch.fd, &ev) < 0)
                 return -errno;
 
-        if (asprintf(&ne[0], "NOTIFY_SOCKET=@%s", sa.un.sun_path+1) < 0)
+        if (!(m->notify_socket = strdup(sa.un.sun_path+1)))
                 return -ENOMEM;
 
-        ne[1] = NULL;
-        t = strv_env_merge(2, m->environment, ne);
-        free(ne[0]);
-
-        if (!t)
-                return -ENOMEM;
-
-        strv_free(m->environment);
-        m->environment = t;
-
         return 0;
 }
 
@@ -451,6 +440,8 @@ void manager_free(Manager *m) {
         if (m->notify_watch.fd >= 0)
                 close_nointr_nofail(m->notify_watch.fd);
 
+        free(m->notify_socket);
+
         lookup_paths_free(&m->lookup_paths);
         strv_free(m->environment);
 
@@ -1672,7 +1663,7 @@ static int manager_process_notify_fd(Manager *m) {
                 log_debug("Got notification message for unit %s", u->meta.id);
 
                 if (UNIT_VTABLE(u)->notify_message)
-                        UNIT_VTABLE(u)->notify_message(u, tags);
+                        UNIT_VTABLE(u)->notify_message(u, ucred->pid, tags);
 
                 strv_free(tags);
         }

src/manager.h

@@ -125,6 +125,8 @@ struct Manager {
 
         Hashmap *watch_pids;  /* pid => Unit object n:1 */
 
+        char *notify_socket;
+
         Watch notify_watch;
         Watch signal_watch;
 

src/service.c

@@ -850,6 +850,9 @@ static int service_load(Unit *u) {
                         if ((r = unit_watch_bus_name(u, s->bus_name)) < 0)
                             return r;
                 }
+
+                if (s->type == SERVICE_NOTIFY && s->notify_access == NOTIFY_NONE)
+                        s->notify_access = NOTIFY_MAIN;
         }
 
         return service_verify(s);
@@ -873,13 +876,15 @@ static void service_dump(Unit *u, FILE *f, const char *prefix) {
                 "%sRootDirectoryStartOnly: %s\n"
                 "%sValidNoProcess: %s\n"
                 "%sKillMode: %s\n"
-                "%sType: %s\n",
+                "%sType: %s\n"
+                "%sNotifyAccess: %s\n",
                 prefix, service_state_to_string(s->state),
                 prefix, yes_no(s->permissions_start_only),
                 prefix, yes_no(s->root_directory_start_only),
                 prefix, yes_no(s->valid_no_process),
                 prefix, kill_mode_to_string(s->kill_mode),
-                prefix, service_type_to_string(s->type));
+                prefix, service_type_to_string(s->type),
+                prefix, notify_access_to_string(s->notify_access));
 
         if (s->control_pid > 0)
                 fprintf(f,
@@ -1245,13 +1250,14 @@ static int service_spawn(
                 bool pass_fds,
                 bool apply_permissions,
                 bool apply_chroot,
+                bool set_notify_socket,
                 pid_t *_pid) {
 
         pid_t pid;
         int r;
         int *fds = NULL;
         unsigned n_fds = 0;
-        char **argv;
+        char **argv = NULL, **env = NULL;
 
         assert(s);
         assert(c);
@@ -1276,11 +1282,29 @@ static int service_spawn(
                 goto fail;
         }
 
+        if (set_notify_socket) {
+                char *t;
+
+                if (asprintf(&t, "NOTIFY_SOCKET=@%s", s->meta.manager->notify_socket) < 0) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+
+                env = strv_env_set(s->meta.manager->environment, t);
+                free(t);
+
+                if (!env) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+        } else
+                env = s->meta.manager->environment;
+
         r = exec_spawn(c,
                        argv,
                        &s->exec_context,
                        fds, n_fds,
-                       s->meta.manager->environment,
+                       env,
                        apply_permissions,
                        apply_chroot,
                        UNIT(s)->meta.manager->confirm_spawn,
@@ -1288,6 +1312,12 @@ static int service_spawn(
                        &pid);
 
         strv_free(argv);
+        argv = NULL;
+
+        if (set_notify_socket)
+                strv_free(env);
+        env = NULL;
+
         if (r < 0)
                 goto fail;
 
@@ -1309,6 +1339,11 @@ static int service_spawn(
 fail:
         free(fds);
 
+        strv_free(argv);
+
+        if (set_notify_socket)
+                strv_free(env);
+
         if (timeout)
                 unit_unwatch_timer(UNIT(s), &s->timer_watch);
 
@@ -1395,6 +1430,7 @@ static void service_enter_stop_post(Service *s, bool success) {
                                        false,
                                        !s->permissions_start_only,
                                        !s->root_directory_start_only,
+                                       false,
                                        &s->control_pid)) < 0)
                         goto fail;
 
@@ -1493,6 +1529,7 @@ static void service_enter_stop(Service *s, bool success) {
                                        false,
                                        !s->permissions_start_only,
                                        !s->root_directory_start_only,
+                                       false,
                                        &s->control_pid)) < 0)
                         goto fail;
 
@@ -1537,6 +1574,7 @@ static void service_enter_start_post(Service *s) {
                                        false,
                                        !s->permissions_start_only,
                                        !s->root_directory_start_only,
+                                       false,
                                        &s->control_pid)) < 0)
                         goto fail;
 
@@ -1571,6 +1609,7 @@ static void service_enter_start(Service *s) {
                                true,
                                true,
                                true,
+                               s->notify_access != NOTIFY_NONE,
                                &pid)) < 0)
                 goto fail;
 
@@ -1630,6 +1669,7 @@ static void service_enter_start_pre(Service *s) {
                                        false,
                                        !s->permissions_start_only,
                                        !s->root_directory_start_only,
+                                       false,
                                        &s->control_pid)) < 0)
                         goto fail;
 
@@ -1677,6 +1717,7 @@ static void service_enter_reload(Service *s) {
                                        false,
                                        !s->permissions_start_only,
                                        !s->root_directory_start_only,
+                                       false,
                                        &s->control_pid)) < 0)
                         goto fail;
 
@@ -1711,6 +1752,7 @@ static void service_run_next(Service *s, bool success) {
                                false,
                                !s->permissions_start_only,
                                !s->root_directory_start_only,
+                               false,
                                &s->control_pid)) < 0)
                 goto fail;
 
@@ -2218,12 +2260,24 @@ static void service_cgroup_notify_event(Unit *u) {
         }
 }
 
-static void service_notify_message(Unit *u, char **tags) {
+static void service_notify_message(Unit *u, pid_t pid, char **tags) {
         Service *s = SERVICE(u);
         const char *e;
 
         assert(u);
 
+        if (s->notify_access == NOTIFY_NONE) {
+                log_warning("%s: Got notification message from PID %lu, but reception is disabled.",
+                            u->meta.id, (unsigned long) pid);
+                return;
+        }
+
+        if (s->notify_access == NOTIFY_MAIN && pid != s->main_pid) {
+                log_warning("%s: Got notification message from PID %lu, but reception only permitted for PID %lu",
+                            u->meta.id, (unsigned long) pid, (unsigned long) s->main_pid);
+                return;
+        }
+
         log_debug("%s: Got message", u->meta.id);
 
         /* Interpret MAINPID= */
@@ -2232,7 +2286,6 @@ static void service_notify_message(Unit *u, char **tags) {
              s->state == SERVICE_START_POST ||
              s->state == SERVICE_RUNNING ||
              s->state == SERVICE_RELOAD)) {
-                pid_t pid;
 
                 if (parse_pid(e + 8, &pid) < 0)
                         log_warning("Failed to parse %s", e);
@@ -2545,6 +2598,14 @@ static const char* const service_exec_command_table[_SERVICE_EXEC_COMMAND_MAX] =
 
 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_ALL] = "all"
+};
+
+DEFINE_STRING_TABLE_LOOKUP(notify_access, NotifyAccess);
+
 const UnitVTable service_vtable = {
         .suffix = ".service",
 

src/service.h

@@ -76,12 +76,22 @@ typedef enum ServiceExecCommand {
         _SERVICE_EXEC_COMMAND_INVALID = -1
 } ServiceExecCommand;
 
+typedef enum NotifyAccess {
+        NOTIFY_NONE,
+        NOTIFY_ALL,
+        NOTIFY_MAIN,
+        _NOTIFY_ACCESS_MAX,
+        _NOTIFY_ACCESS_INVALID = -1
+} NotifyAccess;
+
 struct Service {
         Meta meta;
 
         ServiceType type;
         ServiceRestart restart;
 
+        NotifyAccess notify_access;
+
         /* If set we'll read the main daemon PID from this file */
         char *pid_file;
 
@@ -147,4 +157,7 @@ ServiceType service_type_from_string(const char *s);
 const char* service_exec_command_to_string(ServiceExecCommand i);
 ServiceExecCommand service_exec_command_from_string(const char *s);
 
+const char* notify_access_to_string(NotifyAccess i);
+NotifyAccess notify_access_from_string(const char *s);
+
 #endif

src/unit.h

@@ -286,7 +286,7 @@ struct UnitVTable {
         void (*cgroup_notify_empty)(Unit *u);
 
         /* Called whenever a process of this unit sends us a message */
-        void (*notify_message)(Unit *u, char **tags);
+        void (*notify_message)(Unit *u, pid_t pid, char **tags);
 
         /* Called whenever a name thus Unit registered for comes or
          * goes away. */