Bluetooth: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
int stuff;
struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Marcel Holtmann <[e-mail]>

drivers/bluetooth/btqca.h

···
 struct edl_event_hdr {
 	__u8 cresp;
 	__u8 rtype;
-	__u8 data[0];
+	__u8 data[];
 } __packed;
 
 struct qca_btsoc_version {
···
 	__le16 tag_len;
 	__le32 reserve1;
 	__le32 reserve2;
-	__u8   data[0];
+	__u8   data[];
 } __packed;
 
 struct tlv_type_hdr {
 	__le32 type_len;
-	__u8   data[0];
+	__u8   data[];
 } __packed;
 
 enum qca_btsoc_type {

drivers/bluetooth/btrtl.h

···
 struct rtl_vendor_config_entry {
 	__le16 offset;
 	__u8 len;
-	__u8 data[0];
+	__u8 data[];
 } __packed;
 
 struct rtl_vendor_config {
 	__le32 signature;
 	__le16 total_len;
-	struct rtl_vendor_config_entry entry[0];
+	struct rtl_vendor_config_entry entry[];
 } __packed;
 
 #if IS_ENABLED(CONFIG_BT_RTL)

include/net/bluetooth/hci.h

···
 struct hci_cp_set_event_flt {
 	__u8     flt_type;
 	__u8     cond_type;
-	__u8     condition[0];
+	__u8     condition[];
 } __packed;
 
 /* Filter types */
···
 	__u8     status;
 	__u8     phy_handle;
 	__le16   rem_len;
-	__u8     frag[0];
+	__u8     frag[];
 } __packed;
 
 #define HCI_OP_WRITE_REMOTE_AMP_ASSOC	0x140b
···
 	__u8     phy_handle;
 	__le16   len_so_far;
 	__le16   rem_len;
-	__u8     frag[0];
+	__u8     frag[];
 } __packed;
 struct hci_rp_write_remote_amp_assoc {
 	__u8     status;
···
 	__u8    own_addr_type;
 	__u8    filter_policy;
 	__u8    scanning_phys;
-	__u8    data[0];
+	__u8    data[];
 } __packed;
 
 #define LE_SCAN_PHY_1M		0x01
···
 	__u8      peer_addr_type;
 	bdaddr_t  peer_addr;
 	__u8      phys;
-	__u8      data[0];
+	__u8      data[];
 } __packed;
 
 struct hci_cp_le_ext_conn_param {
···
 struct hci_cp_le_set_ext_adv_enable {
 	__u8  enable;
 	__u8  num_of_sets;
-	__u8  data[0];
+	__u8  data[];
 } __packed;
 
 struct hci_cp_ext_adv_set {
···
 	__le16  m_latency;
 	__le16  s_latency;
 	__u8    num_cis;
-	struct hci_cis_params cis[0];
+	struct hci_cis_params cis[];
 } __packed;
 
 struct hci_rp_le_set_cig_params {
 	__u8    status;
 	__u8    cig_id;
 	__u8    num_handles;
-	__le16  handle[0];
+	__le16  handle[];
 } __packed;
 
 #define HCI_OP_LE_CREATE_CIS			0x2064
···
 
 struct hci_cp_le_create_cis {
 	__u8    num_cis;
-	struct hci_cis cis[0];
+	struct hci_cis cis[];
 } __packed;
 
 #define HCI_OP_LE_REMOVE_CIG			0x2065
···
 
 struct hci_ev_num_comp_pkts {
 	__u8     num_hndl;
-	struct hci_comp_pkts_info handles[0];
+	struct hci_comp_pkts_info handles[];
 } __packed;
 
 #define HCI_EV_MODE_CHANGE		0x14
···
 struct hci_ev_num_comp_blocks {
 	__le16   num_blocks;
 	__u8     num_hndl;
-	struct hci_comp_blocks_info handles[0];
+	struct hci_comp_blocks_info handles[];
 } __packed;
 
 #define HCI_EV_SYNC_TRAIN_COMPLETE	0x4F
···
 	__u8	 bdaddr_type;
 	bdaddr_t bdaddr;
 	__u8	 length;
-	__u8	 data[0];
+	__u8	 data[];
 } __packed;
 
 #define HCI_EV_LE_CONN_UPDATE_COMPLETE	0x03
···
 	__u8  	 direct_addr_type;
 	bdaddr_t direct_addr;
 	__u8  	 length;
-	__u8	 data[0];
+	__u8	 data[];
 } __packed;
 
 #define HCI_EV_LE_ENHANCED_CONN_COMPLETE    0x0a
···
 #define HCI_EV_STACK_INTERNAL	0xfd
 struct hci_ev_stack_internal {
 	__u16    type;
-	__u8     data[0];
+	__u8     data[];
 } __packed;
 
 #define HCI_EV_SI_DEVICE	0x01
···
 struct hci_iso_hdr {
 	__le16	handle;
 	__le16	dlen;
-	__u8	data[0];
+	__u8	data[];
 } __packed;
 
 /* ISO data packet status flags */

include/net/bluetooth/hci_sock.h

···
 
 struct hci_dev_list_req {
 	__u16  dev_num;
-	struct hci_dev_req dev_req[0];	/* hci_dev_req structures */
+	struct hci_dev_req dev_req[];	/* hci_dev_req structures */
 };
 
 struct hci_conn_list_req {
 	__u16  dev_id;
 	__u16  conn_num;
-	struct hci_conn_info conn_info[0];
+	struct hci_conn_info conn_info[];
 };
 
 struct hci_conn_info_req {
 	bdaddr_t bdaddr;
 	__u8     type;
-	struct   hci_conn_info conn_info[0];
+	struct   hci_conn_info conn_info[];
 };
 
 struct hci_auth_info_req {

include/net/bluetooth/l2cap.h

···
 struct l2cap_conf_req {
 	__le16     dcid;
 	__le16     flags;
-	__u8       data[0];
+	__u8       data[];
 } __packed;
 
 struct l2cap_conf_rsp {
 	__le16     scid;
 	__le16     flags;
 	__le16     result;
-	__u8       data[0];
+	__u8       data[];
 } __packed;
 
 #define L2CAP_CONF_SUCCESS	0x0000
···
 struct l2cap_conf_opt {
 	__u8       type;
 	__u8       len;
-	__u8       val[0];
+	__u8       val[];
 } __packed;
 #define L2CAP_CONF_OPT_SIZE	2
 
···
 struct l2cap_info_rsp {
 	__le16      type;
 	__le16      result;
-	__u8        data[0];
+	__u8        data[];
 } __packed;
 
 struct l2cap_create_chan_req {

include/net/bluetooth/rfcomm.h

···
 
 struct rfcomm_dev_list_req {
 	u16      dev_num;
-	struct   rfcomm_dev_info dev_info[0];
+	struct   rfcomm_dev_info dev_info[];
 };
 
 int  rfcomm_dev_ioctl(struct sock *sk, unsigned int cmd, void __user *arg);

net/bluetooth/a2mp.h

···
 	__u8	code;
 	__u8	ident;
 	__le16	len;
-	__u8	data[0];
+	__u8	data[];
 } __packed;
 
 /* A2MP command codes */
 #define A2MP_COMMAND_REJ         0x01
 struct a2mp_cmd_rej {
 	__le16	reason;
-	__u8	data[0];
+	__u8	data[];
 } __packed;
 
 #define A2MP_DISCOVER_REQ        0x02
···
 struct a2mp_discov_rsp {
 	__le16     mtu;
 	__le16     ext_feat;
-	struct a2mp_cl cl[0];
+	struct a2mp_cl cl[];
 } __packed;
 
 #define A2MP_CHANGE_NOTIFY       0x04
···
 struct a2mp_amp_assoc_rsp {
 	__u8	id;
 	__u8	status;
-	__u8	amp_assoc[0];
+	__u8	amp_assoc[];
 } __packed;
 
 #define A2MP_CREATEPHYSLINK_REQ  0x0A
···
 struct a2mp_physlink_req {
 	__u8	local_id;
 	__u8	remote_id;
-	__u8	amp_assoc[0];
+	__u8	amp_assoc[];
 } __packed;
 
 #define A2MP_CREATEPHYSLINK_RSP  0x0B

net/bluetooth/bnep/bnep.h

···
 	__u8 type;
 	__u8 ctrl;
 	__u8 uuid_size;
-	__u8 service[0];
+	__u8 service[];
 } __packed;
 
 struct bnep_set_filter_req {
 	__u8 type;
 	__u8 ctrl;
 	__be16 len;
-	__u8 list[0];
+	__u8 list[];
 } __packed;
 
 struct bnep_control_rsp {
···
 struct bnep_ext_hdr {
 	__u8 type;
 	__u8 len;
-	__u8 data[0];
+	__u8 data[];
 } __packed;
 
 /* BNEP ioctl defines */