wcn36xx: Avoid memset() beyond end of struct field

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring array fields.

Instead of writing past the end of the header to reach the rest of
the body, replace the redundant function with existing macro to wipe
struct contents and set field values. Additionally adjusts macro to add
missing parens.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210617171058.3410494-1-keescook@chromium.org

drivers/net/wireless/ath/wcn36xx/smd.c

@@ -445,22 +445,12 @@ static int wcn36xx_smd_send_and_wait(struct wcn36xx *wcn, size_t len)
 	return ret;
 }
 
-static void init_hal_msg(struct wcn36xx_hal_msg_header *hdr,
-			 enum wcn36xx_hal_host_msg_type msg_type,
-			 size_t msg_size)
-{
-	memset(hdr, 0, msg_size + sizeof(*hdr));
-	hdr->msg_type = msg_type;
-	hdr->msg_version = WCN36XX_HAL_MSG_VERSION0;
-	hdr->len = msg_size + sizeof(*hdr);
-}
-
 #define __INIT_HAL_MSG(msg_body, type, version) \
 	do {								\
-		memset(&msg_body, 0, sizeof(msg_body));			\
-		msg_body.header.msg_type = type;			\
-		msg_body.header.msg_version = version;			\
-		msg_body.header.len = sizeof(msg_body);			\
+		memset(&(msg_body), 0, sizeof(msg_body));		\
+		(msg_body).header.msg_type = type;			\
+		(msg_body).header.msg_version = version;		\
+		(msg_body).header.len = sizeof(msg_body);		\
 	} while (0)							\
 
 #define INIT_HAL_MSG(msg_body, type)	\
@@ -2729,8 +2719,7 @@ int wcn36xx_smd_set_mc_list(struct wcn36xx *wcn,
 
 	msg_body = (struct wcn36xx_hal_rcv_flt_pkt_set_mc_list_req_msg *)
 		   wcn->hal_buf;
-	init_hal_msg(&msg_body->header, WCN36XX_HAL_8023_MULTICAST_LIST_REQ,
-		     sizeof(msg_body->mc_addr_list));
+	INIT_HAL_MSG(*msg_body, WCN36XX_HAL_8023_MULTICAST_LIST_REQ);
 
 	/* An empty list means all mc traffic will be received */
 	if (fp)