treewide: Replace 0-element memcpy() destinations with flexible arrays

The 0-element arrays that are used as memcpy() destinations are actually
flexible arrays. Adjust their structures accordingly so that memcpy()
can better reason able their destination size (i.e. they need to be seen
as "unknown" length rather than "zero").

In some cases, use of the DECLARE_FLEX_ARRAY() helper is needed when a
flexible array is alone in a struct.

Cc: "Gustavo A. R. Silva" <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Kalle Valo <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: Jakub Kicinski <[e-mail]>
Cc: Nilesh Javali <[e-mail]>
Cc: Manish Rangankar <[e-mail]>
Cc: [e-mail]
Cc: "James E.J. Bottomley" <[e-mail]>
Cc: "Martin K. Petersen" <[e-mail]>
Cc: Larry Finger <[e-mail]>
Cc: Phillip Potter <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Florian Schilhabel <[e-mail]>
Cc: Johannes Berg <[e-mail]>
Cc: Christophe JAILLET <[e-mail]>
Cc: Fabio Aiuto <[e-mail]>
Cc: Ross Schmidt <[e-mail]>
Cc: Marco Cesati <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>

drivers/net/wireless/ath/ath10k/bmi.h

···
 		struct {
 			__le32 addr;
 			__le32 len;
-			u8 payload[0];
+			u8 payload[];
 		} write_mem;
 		struct {
 			__le32 addr;
···
 		} rompatch_uninstall;
 		struct {
 			__le32 count;
-			__le32 patch_ids[0]; /* length of @count */
+			__le32 patch_ids[]; /* length of @count */
 		} rompatch_activate;
 		struct {
 			__le32 count;
-			__le32 patch_ids[0]; /* length of @count */
+			__le32 patch_ids[]; /* length of @count */
 		} rompatch_deactivate;
 		struct {
 			__le32 addr;
 		} lz_start;
 		struct {
 			__le32 len; /* max BMI_MAX_DATA_SIZE */
-			u8 payload[0]; /* length of @len */
+			u8 payload[]; /* length of @len */
 		} lz_data;
 		struct {
 			u8 name[BMI_NVRAM_SEG_NAME_SZ];
···
 
 union bmi_resp {
 	struct {
-		u8 payload[0];
+		DECLARE_FLEX_ARRAY(u8, payload);
 	} read_mem;
 	struct {
 		__le32 result;

drivers/scsi/qla4xxx/ql4_def.h

···
 		struct {
 			enum iscsi_host_event_code code;
 			uint32_t data_size;
-			uint8_t data[0];
+			uint8_t data[];
 		} aen;
 		struct {
 			uint32_t status;
 			uint32_t pid;
 			uint32_t data_size;
-			uint8_t data[0];
+			uint8_t data[];
 		} ping;
 	} u;
 };

drivers/staging/r8188eu/include/ieee80211.h

···
 		struct {
 			u32 len;
 			u8 reserved[32];
-			u8 data[0];
+			u8 data[];
 		} wpa_ie;
 		struct {
 			int command;
···
 			u8 idx;
 			u8 seq[8]; /* sequence counter (set: RX, get: TX) */
 			u16 key_len;
-			u8 key[0];
+			u8 key[];
 		} crypt;
 #ifdef CONFIG_88EU_AP_MODE
 		struct {
···
 		} add_sta;
 		struct {
 			u8	reserved[2];/* for set max_num_sta */
-			u8	buf[0];
+			u8	buf[];
 		} bcn_ie;
 #endif
 

drivers/staging/rtl8712/ieee80211.h

···
 		struct {
 			u32 len;
 			u8 reserved[32];
-			u8 data[0];
+			u8 data[];
 		} wpa_ie;
 		struct {
 			int command;
···
 			u8 idx;
 			u8 seq[8]; /* sequence counter (set: RX, get: TX) */
 			u16 key_len;
-			u8 key[0];
+			u8 key[];
 		} crypt;
 	} u;
 };

drivers/staging/rtl8723bs/include/ieee80211.h

···
 		struct {
 			u32 len;
 			u8 reserved[32];
-			u8 data[0];
+			u8 data[];
 		} wpa_ie;
 	        struct{
 			int command;
···
 			u8 idx;
 			u8 seq[8]; /* sequence counter (set: RX, get: TX) */
 			u16 key_len;
-			u8 key[0];
+			u8 key[];
 		} crypt;
 		struct {
 			u16 aid;
···
 		} add_sta;
 		struct {
 			u8 reserved[2];/* for set max_num_sta */
-			u8 buf[0];
+			u8 buf[];
 		} bcn_ie;
 	} u;
 };

include/linux/ieee80211.h

···
 			__le16 auth_transaction;
 			__le16 status_code;
 			/* possibly followed by Challenge text */
-			u8 variable[0];
+			u8 variable[];
 		} __packed auth;
 		struct {
 			__le16 reason_code;
···
 			__le16 capab_info;
 			__le16 listen_interval;
 			/* followed by SSID and Supported rates */
-			u8 variable[0];
+			u8 variable[];
 		} __packed assoc_req;
 		struct {
 			__le16 capab_info;
 			__le16 status_code;
 			__le16 aid;
 			/* followed by Supported rates */
-			u8 variable[0];
+			u8 variable[];
 		} __packed assoc_resp, reassoc_resp;
 		struct {
 			__le16 capab_info;
 			__le16 status_code;
-			u8 variable[0];
+			u8 variable[];
 		} __packed s1g_assoc_resp, s1g_reassoc_resp;
 		struct {
 			__le16 capab_info;
 			__le16 listen_interval;
 			u8 current_ap[ETH_ALEN];
 			/* followed by SSID and Supported rates */
-			u8 variable[0];
+			u8 variable[];
 		} __packed reassoc_req;
 		struct {
 			__le16 reason_code;
···
 			__le16 capab_info;
 			/* followed by some of SSID, Supported rates,
 			 * FH Params, DS Params, CF Params, IBSS Params, TIM */
-			u8 variable[0];
+			u8 variable[];
 		} __packed beacon;
 		struct {
 			/* only variable items: SSID, Supported rates */
-			u8 variable[0];
+			DECLARE_FLEX_ARRAY(u8, variable);
 		} __packed probe_req;
 		struct {
 			__le64 timestamp;
···
 			__le16 capab_info;
 			/* followed by some of SSID, Supported rates,
 			 * FH Params, DS Params, CF Params, IBSS Params */
-			u8 variable[0];
+			u8 variable[];
 		} __packed probe_resp;
 		struct {
 			u8 category;
···
 					u8 action_code;
 					u8 dialog_token;
 					u8 status_code;
-					u8 variable[0];
+					u8 variable[];
 				} __packed wme_action;
 				struct{
 					u8 action_code;
-					u8 variable[0];
+					u8 variable[];
 				} __packed chan_switch;
 				struct{
 					u8 action_code;
 					struct ieee80211_ext_chansw_ie data;
-					u8 variable[0];
+					u8 variable[];
 				} __packed ext_chan_switch;
 				struct{
 					u8 action_code;
···
 					__le16 timeout;
 					__le16 start_seq_num;
 					/* followed by BA Extension */
-					u8 variable[0];
+					u8 variable[];
 				} __packed addba_req;
 				struct{
 					u8 action_code;
···
 				} __packed delba;
 				struct {
 					u8 action_code;
-					u8 variable[0];
+					u8 variable[];
 				} __packed self_prot;
 				struct{
 					u8 action_code;
-					u8 variable[0];
+					u8 variable[];
 				} __packed mesh_action;
 				struct {
 					u8 action;
···
 					u8 toa[6];
 					__le16 tod_error;
 					__le16 toa_error;
-					u8 variable[0];
+					u8 variable[];
 				} __packed ftm;
 				struct {
 					u8 action_code;

include/uapi/linux/dlm_device.h

···
 	void __user *bastaddr;
 	struct dlm_lksb __user *lksb;
 	char lvb[DLM_USER_LVB_LEN];
-	char name[0];
+	char name[];
 };
 
 struct dlm_lspace_params {
 	__u32 flags;
 	__u32 minor;
-	char name[0];
+	char name[];
 };
 
 struct dlm_purge_params {