pnfs-block: removing DM device maybe cause oops when call dev_remove

when pnfs block using device mapper,if umounting later,it maybe
cause oops. we apply "1 + sizeof(bl_umount_request)" memory for
msg->data, the memory maybe overflow when we do "memcpy(&dataptr
[sizeof(bl_msg)], &bl_umount_request, sizeof(bl_umount_request))",
because the size of bl_msg is more than 1 byte.

Signed-off-by: fanchaoting<fanchaoting@cn.fujitsu.com>
Cc: stable@vger.kernel.org
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/blocklayout/blocklayoutdm.c

@@ -55,7 +55,8 @@ static void dev_remove(struct net *net, dev_t dev)
 
 	bl_pipe_msg.bl_wq = &nn->bl_wq;
 	memset(msg, 0, sizeof(*msg));
-	msg->data = kzalloc(1 + sizeof(bl_umount_request), GFP_NOFS);
+	msg->len = sizeof(bl_msg) + bl_msg.totallen;
+	msg->data = kzalloc(msg->len, GFP_NOFS);
 	if (!msg->data)
 		goto out;
 
@@ -66,7 +67,6 @@ static void dev_remove(struct net *net, dev_t dev)
 	memcpy(msg->data, &bl_msg, sizeof(bl_msg));
 	dataptr = (uint8_t *) msg->data;
 	memcpy(&dataptr[sizeof(bl_msg)], &bl_umount_request, sizeof(bl_umount_request));
-	msg->len = sizeof(bl_msg) + bl_msg.totallen;
 
 	add_wait_queue(&nn->bl_wq, &wq);
 	if (rpc_queue_upcall(nn->bl_device_pipe, msg) < 0) {