sessiond: clarify the role of notification credentials

[lttng-tools.git] / src / bin / lttng-sessiond / notification-thread-events.c

diff --git a/src/bin/lttng-sessiond/notification-thread-events.c b/src/bin/lttng-sessiond/notification-thread-events.c
index 6ccd1fe04abfdc54e3c84aa6e80ceb4edf58c096..6f0ee7d7942cf762b38c6c7edc37ab97caa8972b 100644 (file)
--- a/src/bin/lttng-sessiond/notification-thread-events.c
+++ b/src/bin/lttng-sessiond/notification-thread-events.c
@@ -3094,12 +3094,45 @@ int client_enqueue_dropped_notification(struct notification_client *client)
        return ret;
 }
 
+/*
+ * Permission checks relative to notification channel clients are performed
+ * here. Notice how object, client, and trigger credentials are involved in
+ * this check.
+ *
+ * The `object` credentials are the credentials associated with the "subject"
+ * of a condition. For instance, a `rotation completed` condition applies
+ * to a session. When that condition is met, it will produce an evaluation
+ * against a session. Hence, in this case, the `object` credentials are the
+ * credentials of the "subject" session.
+ *
+ * The `trigger` credentials are the credentials of the user that registered the
+ * trigger.
+ *
+ * The `client` credentials are the credentials of the user that created a given
+ * notification channel.
+ *
+ * In terms of visibility, it is expected that non-privilieged users can only
+ * register triggers against "their" objects (their own sessions and
+ * applications they are allowed to interact with). They can then open a
+ * notification channel and subscribe to notifications associated with those
+ * triggers.
+ *
+ * As for privilieged users, they can register triggers against the objects of
+ * other users. They can then subscribe to the notifications associated to their
+ * triggers. Privilieged users _can't_ subscribe to the notifications of
+ * triggers owned by other users; they must create their own triggers.
+ *
+ * This is more a concern of usability than security. It would be difficult for
+ * a root user reliably subscribe to a specific set of conditions without
+ * interference from external users (those could, for instance, unregister
+ * their triggers).
+ */
 static
 int send_evaluation_to_clients(const struct lttng_trigger *trigger,
                const struct lttng_evaluation *evaluation,
                struct notification_client_list* client_list,
                struct notification_thread_state *state,
-               uid_t channel_uid, gid_t channel_gid)
+               uid_t object_uid, gid_t object_gid)
 {
        int ret = 0;
        struct lttng_payload msg_payload;
@@ -3111,6 +3144,7 @@ int send_evaluation_to_clients(const struct lttng_trigger *trigger,
        struct lttng_notification_channel_message msg_header = {
                .type = (int8_t) LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_NOTIFICATION,
        };
+       const struct lttng_credentials *trigger_creds = lttng_trigger_get_credentials(trigger);
 
        lttng_payload_init(&msg_payload);
 
@@ -3136,10 +3170,15 @@ int send_evaluation_to_clients(const struct lttng_trigger *trigger,
                struct notification_client *client =
                                client_list_element->client;
 
-               if (client->uid != channel_uid && client->gid != channel_gid &&
+               if (client->uid != object_uid && client->gid != object_gid &&
                                client->uid != 0) {
                        /* Client is not allowed to monitor this channel. */
-                       DBG("[notification-thread] Skipping client at it does not have the permission to receive notification for this channel");
+                       DBG("[notification-thread] Skipping client at it does not have the object permission to receive notification for this trigger");
+                       continue;
+               }
+
+               if (client->uid != trigger_creds->uid && client->gid != trigger_creds->gid) {
+                       DBG("[notification-thread] Skipping client at it does not have the permission to receive notification for this trigger");
                        continue;
                }