BUG/MINOR: mux-quic: fix free on qcs-new fail alloc

qcs_new() allocates several elements in intermediary steps. All elements
must first be properly initialized to be able to free qcs instance in
case of an intermediary failure.

Previously, qc_stream_desc allocation was done in the middle of
qcs_new() before some elements initializations. In case this fails, a
crash can happened as some elements are left uninitialized.

To fix this, move qc_stream_desc allocation at the end of qcs_new().
This ensures that all qcs elements are initialized first.

This should be backported up to 2.6.

src/mux_quic.c

@@ -112,16 +112,6 @@ static struct qcs *qcs_new(struct qcc *qcc, uint64_t id, enum qcs_type type)
 	qcs->id = qcs->by_id.key = id;
 	eb64_insert(&qcc->streams_by_id, &qcs->by_id);
 
-	/* Allocate transport layer stream descriptor. Only needed for TX. */
-	if (!quic_stream_is_uni(id) || !quic_stream_is_remote(qcc, id)) {
-		struct quic_conn *qc = qcc->conn->handle.qc;
-		qcs->stream = qc_stream_desc_new(id, type, qcs, qc);
-		if (!qcs->stream) {
-			TRACE_ERROR("qc_stream_desc alloc failure", QMUX_EV_QCS_NEW, qcc->conn, qcs);
-			goto err;
-		}
-	}
-
 	/* If stream is local, use peer remote-limit, or else the opposite. */
 	if (quic_stream_is_bidi(id)) {
 		qcs->tx.msd = quic_stream_is_local(qcc, id) ? qcc->rfctl.msd_bidi_r :
@@ -158,6 +148,16 @@ static struct qcs *qcs_new(struct qcc *qcc, uint64_t id, enum qcs_type type)
 
 	qcs->err = 0;
 
+	/* Allocate transport layer stream descriptor. Only needed for TX. */
+	if (!quic_stream_is_uni(id) || !quic_stream_is_remote(qcc, id)) {
+		struct quic_conn *qc = qcc->conn->handle.qc;
+		qcs->stream = qc_stream_desc_new(id, type, qcs, qc);
+		if (!qcs->stream) {
+			TRACE_ERROR("qc_stream_desc alloc failure", QMUX_EV_QCS_NEW, qcc->conn, qcs);
+			goto err;
+		}
+	}
+
 	if (qcc->app_ops->attach && qcc->app_ops->attach(qcs, qcc->ctx)) {
 		TRACE_ERROR("app proto failure", QMUX_EV_QCS_NEW, qcc->conn, qcs);
 		goto err;