Bluetooth: hci_conn: Use __counted_by() and avoid -Wfamnae warning

Prepare for the coming implementation by GCC and Clang of the
__counted_by attribute. Flexible array members annotated with
__counted_by can have their accesses bounds-checked at run-time
via CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE
(for strcpy/memcpy-family functions).

Also, -Wflex-array-member-not-at-end is coming in GCC-14, and we are
getting ready to enable it globally.

So, use the `DEFINE_FLEX()` helper for an on-stack definition of
a flexible structure where the size of the flexible-array member
is known at compile-time, and refactor the rest of the code,
accordingly.

With these changes, fix the following warning:
net/bluetooth/hci_conn.c:669:41: warning: structure containing a
flexible array member is not at the end of another structure
[-Wflex-array-member-not-at-end]

Link: KSPP#202
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Author: GustavoARSilva

include/net/bluetooth/hci.h

@@ -2143,7 +2143,7 @@ struct hci_cp_le_set_cig_params {
 	__le16  c_latency;
 	__le16  p_latency;
 	__u8    num_cis;
-	struct hci_cis_params cis[];
+	struct hci_cis_params cis[] __counted_by(num_cis);
 } __packed;
 
 struct hci_rp_le_set_cig_params {

net/bluetooth/hci_conn.c

@@ -664,11 +664,6 @@ static void le_conn_timeout(struct work_struct *work)
 	hci_abort_conn(conn, HCI_ERROR_REMOTE_USER_TERM);
 }
 
-struct iso_cig_params {
-	struct hci_cp_le_set_cig_params cp;
-	struct hci_cis_params cis[0x1f];
-};
-
 struct iso_list_data {
 	union {
 		u8  cig;
@@ -1722,34 +1717,33 @@ static int hci_le_create_big(struct hci_conn *conn, struct bt_iso_qos *qos)
 
 static int set_cig_params_sync(struct hci_dev *hdev, void *data)
 {
+	DEFINE_FLEX(struct hci_cp_le_set_cig_params, pdu, cis, num_cis, 0x1f);
 	u8 cig_id = PTR_UINT(data);
 	struct hci_conn *conn;
 	struct bt_iso_qos *qos;
-	struct iso_cig_params pdu;
+	u8 aux_num_cis = 0;
 	u8 cis_id;
 
 	conn = hci_conn_hash_lookup_cig(hdev, cig_id);
 	if (!conn)
 		return 0;
 
-	memset(&pdu, 0, sizeof(pdu));
-
 	qos = &conn->iso_qos;
-	pdu.cp.cig_id = cig_id;
-	hci_cpu_to_le24(qos->ucast.out.interval, pdu.cp.c_interval);
-	hci_cpu_to_le24(qos->ucast.in.interval, pdu.cp.p_interval);
-	pdu.cp.sca = qos->ucast.sca;
-	pdu.cp.packing = qos->ucast.packing;
-	pdu.cp.framing = qos->ucast.framing;
-	pdu.cp.c_latency = cpu_to_le16(qos->ucast.out.latency);
-	pdu.cp.p_latency = cpu_to_le16(qos->ucast.in.latency);
+	pdu->cig_id = cig_id;
+	hci_cpu_to_le24(qos->ucast.out.interval, pdu->c_interval);
+	hci_cpu_to_le24(qos->ucast.in.interval, pdu->p_interval);
+	pdu->sca = qos->ucast.sca;
+	pdu->packing = qos->ucast.packing;
+	pdu->framing = qos->ucast.framing;
+	pdu->c_latency = cpu_to_le16(qos->ucast.out.latency);
+	pdu->p_latency = cpu_to_le16(qos->ucast.in.latency);
 
 	/* Reprogram all CIS(s) with the same CIG, valid range are:
 	 * num_cis: 0x00 to 0x1F
 	 * cis_id: 0x00 to 0xEF
 	 */
 	for (cis_id = 0x00; cis_id < 0xf0 &&
-	     pdu.cp.num_cis < ARRAY_SIZE(pdu.cis); cis_id++) {
+	     aux_num_cis < pdu->num_cis; cis_id++) {
 		struct hci_cis_params *cis;
 
 		conn = hci_conn_hash_lookup_cis(hdev, NULL, 0, cig_id, cis_id);
@@ -1758,7 +1752,7 @@ static int set_cig_params_sync(struct hci_dev *hdev, void *data)
 
 		qos = &conn->iso_qos;
 
-		cis = &pdu.cis[pdu.cp.num_cis++];
+		cis = &pdu->cis[aux_num_cis++];
 		cis->cis_id = cis_id;
 		cis->c_sdu  = cpu_to_le16(conn->iso_qos.ucast.out.sdu);
 		cis->p_sdu  = cpu_to_le16(conn->iso_qos.ucast.in.sdu);
@@ -1769,14 +1763,14 @@ static int set_cig_params_sync(struct hci_dev *hdev, void *data)
 		cis->c_rtn  = qos->ucast.out.rtn;
 		cis->p_rtn  = qos->ucast.in.rtn;
 	}
+	pdu->num_cis = aux_num_cis;
 
-	if (!pdu.cp.num_cis)
+	if (!pdu->num_cis)
 		return 0;
 
 	return __hci_cmd_sync_status(hdev, HCI_OP_LE_SET_CIG_PARAMS,
-				     sizeof(pdu.cp) +
-				     pdu.cp.num_cis * sizeof(pdu.cis[0]), &pdu,
-				     HCI_CMD_TIMEOUT);
+				     struct_size(pdu, cis, pdu->num_cis),
+				     pdu, HCI_CMD_TIMEOUT);
 }
 
 static bool hci_le_set_cig_params(struct hci_conn *conn, struct bt_iso_qos *qos)