[PATCH] Bluetooth: Replace zero-length array with flexible-array

From: Gustavo A. R. Silva
Date: Thu May 07 2020 - 14:46:27 EST

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]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

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 <gustavoars@xxxxxxxxxx>
---
include/net/bluetooth/l2cap.h | 6 +++---
include/net/bluetooth/mgmt.h | 40 ++++++++++++++++++++--------------------
2 files changed, 23 insertions(+), 23 deletions(-)

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index dada14d0622c..8f1e6a7a2df8 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -499,7 +499,7 @@ struct l2cap_ecred_conn_req {
__le16 mtu;
__le16 mps;
__le16 credits;
- __le16 scid[0];
+ __le16 scid[];
} __packed;

struct l2cap_ecred_conn_rsp {
@@ -507,13 +507,13 @@ struct l2cap_ecred_conn_rsp {
__le16 mps;
__le16 credits;
__le16 result;
- __le16 dcid[0];
+ __le16 dcid[];
};

struct l2cap_ecred_reconf_req {
__le16 mtu;
__le16 mps;
- __le16 scid[0];
+ __le16 scid[];
} __packed;

#define L2CAP_RECONF_SUCCESS 0x0000
diff --git a/include/net/bluetooth/mgmt.h b/include/net/bluetooth/mgmt.h
index f41cd87550dc..e104329e227f 100644
--- a/include/net/bluetooth/mgmt.h
+++ b/include/net/bluetooth/mgmt.h
@@ -70,14 +70,14 @@ struct mgmt_rp_read_version {
struct mgmt_rp_read_commands {
__le16 num_commands;
__le16 num_events;
- __le16 opcodes[0];
+ __le16 opcodes[];
} __packed;

#define MGMT_OP_READ_INDEX_LIST 0x0003
#define MGMT_READ_INDEX_LIST_SIZE 0
struct mgmt_rp_read_index_list {
__le16 num_controllers;
- __le16 index[0];
+ __le16 index[];
} __packed;

/* Reserve one extra byte for names in management messages so that they
@@ -183,7 +183,7 @@ struct mgmt_link_key_info {
struct mgmt_cp_load_link_keys {
__u8 debug_keys;
__le16 key_count;
- struct mgmt_link_key_info keys[0];
+ struct mgmt_link_key_info keys[];
} __packed;
#define MGMT_LOAD_LINK_KEYS_SIZE 3

@@ -206,7 +206,7 @@ struct mgmt_ltk_info {
#define MGMT_OP_LOAD_LONG_TERM_KEYS 0x0013
struct mgmt_cp_load_long_term_keys {
__le16 key_count;
- struct mgmt_ltk_info keys[0];
+ struct mgmt_ltk_info keys[];
} __packed;
#define MGMT_LOAD_LONG_TERM_KEYS_SIZE 2

@@ -223,7 +223,7 @@ struct mgmt_rp_disconnect {
#define MGMT_GET_CONNECTIONS_SIZE 0
struct mgmt_rp_get_connections {
__le16 conn_count;
- struct mgmt_addr_info addr[0];
+ struct mgmt_addr_info addr[];
} __packed;

#define MGMT_OP_PIN_CODE_REPLY 0x0016
@@ -413,7 +413,7 @@ struct mgmt_irk_info {
#define MGMT_OP_LOAD_IRKS 0x0030
struct mgmt_cp_load_irks {
__le16 irk_count;
- struct mgmt_irk_info irks[0];
+ struct mgmt_irk_info irks[];
} __packed;
#define MGMT_LOAD_IRKS_SIZE 2

@@ -465,7 +465,7 @@ struct mgmt_conn_param {
#define MGMT_OP_LOAD_CONN_PARAM 0x0035
struct mgmt_cp_load_conn_param {
__le16 param_count;
- struct mgmt_conn_param params[0];
+ struct mgmt_conn_param params[];
} __packed;
#define MGMT_LOAD_CONN_PARAM_SIZE 2

@@ -473,7 +473,7 @@ struct mgmt_cp_load_conn_param {
#define MGMT_READ_UNCONF_INDEX_LIST_SIZE 0
struct mgmt_rp_read_unconf_index_list {
__le16 num_controllers;
- __le16 index[0];
+ __le16 index[];
} __packed;

#define MGMT_OPTION_EXTERNAL_CONFIG 0x00000001
@@ -504,7 +504,7 @@ struct mgmt_cp_start_service_discovery {
__u8 type;
__s8 rssi;
__le16 uuid_count;
- __u8 uuids[0][16];
+ __u8 uuids[][16];
} __packed;
#define MGMT_START_SERVICE_DISCOVERY_SIZE 4

@@ -516,7 +516,7 @@ struct mgmt_cp_read_local_oob_ext_data {
struct mgmt_rp_read_local_oob_ext_data {
__u8 type;
__le16 eir_len;
- __u8 eir[0];
+ __u8 eir[];
} __packed;

#define MGMT_OP_READ_EXT_INDEX_LIST 0x003C
@@ -527,7 +527,7 @@ struct mgmt_rp_read_ext_index_list {
__le16 index;
__u8 type;
__u8 bus;
- } entry[0];
+ } entry[];
} __packed;

#define MGMT_OP_READ_ADV_FEATURES 0x0003D
@@ -538,7 +538,7 @@ struct mgmt_rp_read_adv_features {
__u8 max_scan_rsp_len;
__u8 max_instances;
__u8 num_instances;
- __u8 instance[0];
+ __u8 instance[];
} __packed;

#define MGMT_OP_ADD_ADVERTISING 0x003E
@@ -549,7 +549,7 @@ struct mgmt_cp_add_advertising {
__le16 timeout;
__u8 adv_data_len;
__u8 scan_rsp_len;
- __u8 data[0];
+ __u8 data[];
} __packed;
#define MGMT_ADD_ADVERTISING_SIZE 11
struct mgmt_rp_add_advertising {
@@ -603,7 +603,7 @@ struct mgmt_rp_read_ext_info {
__le32 supported_settings;
__le32 current_settings;
__le16 eir_len;
- __u8 eir[0];
+ __u8 eir[];
} __packed;

#define MGMT_OP_SET_APPEARANCE 0x0043
@@ -668,7 +668,7 @@ struct mgmt_blocked_key_info {

struct mgmt_cp_set_blocked_keys {
__le16 key_count;
- struct mgmt_blocked_key_info keys[0];
+ struct mgmt_blocked_key_info keys[];
} __packed;
#define MGMT_OP_SET_BLOCKED_KEYS_SIZE 2

@@ -678,7 +678,7 @@ struct mgmt_cp_set_blocked_keys {
struct mgmt_ev_cmd_complete {
__le16 opcode;
__u8 status;
- __u8 data[0];
+ __u8 data[];
} __packed;

#define MGMT_EV_CMD_STATUS 0x0002
@@ -726,7 +726,7 @@ struct mgmt_ev_device_connected {
struct mgmt_addr_info addr;
__le32 flags;
__le16 eir_len;
- __u8 eir[0];
+ __u8 eir[];
} __packed;

#define MGMT_DEV_DISCONN_UNKNOWN 0x00
@@ -781,7 +781,7 @@ struct mgmt_ev_device_found {
__s8 rssi;
__le32 flags;
__le16 eir_len;
- __u8 eir[0];
+ __u8 eir[];
} __packed;

#define MGMT_EV_DISCOVERING 0x0013
@@ -876,7 +876,7 @@ struct mgmt_ev_ext_index {
struct mgmt_ev_local_oob_data_updated {
__u8 type;
__le16 eir_len;
- __u8 eir[0];
+ __u8 eir[];
} __packed;

#define MGMT_EV_ADVERTISING_ADDED 0x0023
@@ -892,7 +892,7 @@ struct mgmt_ev_advertising_removed {
#define MGMT_EV_EXT_INFO_CHANGED 0x0025
struct mgmt_ev_ext_info_changed {
__le16 eir_len;
- __u8 eir[0];
+ __u8 eir[];
} __packed;

#define MGMT_EV_PHY_CONFIGURATION_CHANGED 0x0026