Leakage of mosq->tls_engine in mosquitto_destroy

[CastleOnTheHill]

Issue Description

• Version: v2.0.18
• Platform: Ubuntu 22

Analysis

When a user sets the tls engine using mosquitto_opts_set(mosq, MOSQ_OPT_TLS_ENGINE, engine), Mosquitto copies the engine name and stores it in mosq->tls_engine.

However, when calling mosquitto_destroy, the memory allocated for mosq->tls_engine is not freed.

Suggestions

To address this issue, please ensure that you free mosq->tls_engine in the mosquitto_destroy function.

--- a/lib/mosquitto.c
+++ b/lib/mosquitto.c
@@ -284,6 +284,11 @@ void mosquitto__destroy(struct mosquitto *mosq)
 	mosquitto__free(mosq->tls_psk);
 	mosquitto__free(mosq->tls_psk_identity);
 	mosquitto__free(mosq->tls_alpn);
+
+#ifndef OPENSSL_NO_ENGINE
+	mosquitto__free(mosq->tls_engine);
+	mosq->tls_engine = NULL;
+#endif
 #endif