ksmbd: ipc: use kzalloc_flex and __counted_by

The former is just a nice macro and the latter allows runtime analysis
of the allocation and its size.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: neheb

fs/smb/server/transport_ipc.c

@@ -55,7 +55,7 @@ static bool ksmbd_ipc_validate_version(struct genl_info *m)
 struct ksmbd_ipc_msg {
 	unsigned int		type;
 	unsigned int		sz;
-	unsigned char		payload[];
+	unsigned char		payload[] __counted_by(sz);
 };
 
 struct ipc_msg_table_entry {
@@ -242,9 +242,8 @@ static void ipc_update_last_active(void)
 static struct ksmbd_ipc_msg *ipc_msg_alloc(size_t sz)
 {
 	struct ksmbd_ipc_msg *msg;
-	size_t msg_sz = sz + sizeof(struct ksmbd_ipc_msg);
 
-	msg = kvzalloc(msg_sz, KSMBD_DEFAULT_GFP);
+	msg = kvzalloc_flex(*msg, payload, sz, KSMBD_DEFAULT_GFP);
 	if (msg)
 		msg->sz = sz;
 	return msg;