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

commit 4376c946 upstream.

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>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
[bwh: Backported to 3.2:
 - In dev_remove(), msg is a structure not a pointer to it]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/nfs/blocklayout/blocklayoutdm.c

@@ -52,7 +52,8 @@ static void dev_remove(dev_t dev)
 	dprintk("Entering %s\n", __func__);
 
 	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;
 
@@ -63,7 +64,6 @@ static void dev_remove(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(&bl_wq, &wq);
 	if (rpc_queue_upcall(bl_device_pipe->d_inode, &msg) < 0) {