NFSv4: Don't use private xdr_stream fields in decode_getacl

Instead of using the private field xdr->p from struct xdr_stream,
use the public xdr_stream_pos().
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4xdr.c

@@ -5045,10 +5045,10 @@ static int decode_getacl(struct xdr_stream *xdr, struct rpc_rqst *req,
 			 struct nfs_getaclres *res)
 {
 	unsigned int savep;
-	__be32 *bm_p;
 	uint32_t attrlen,
 		 bitmap[3] = {0};
 	int status;
+	unsigned int pg_offset;
 
 	res->acl_len = 0;
 	if ((status = decode_op_hdr(xdr, OP_GETATTR)) != 0)
@@ -5056,7 +5056,8 @@ static int decode_getacl(struct xdr_stream *xdr, struct rpc_rqst *req,
 
 	xdr_enter_page(xdr, xdr->buf->page_len);
 
-	bm_p = xdr->p;
+	/* Calculate the offset of the page data */
+	pg_offset = xdr->buf->head[0].iov_len;
 
 	if ((status = decode_attr_bitmap(xdr, bitmap)) != 0)
 		goto out;
@@ -5070,18 +5071,18 @@ static int decode_getacl(struct xdr_stream *xdr, struct rpc_rqst *req,
 		/* The bitmap (xdr len + bitmaps) and the attr xdr len words
 		 * are stored with the acl data to handle the problem of
 		 * variable length bitmaps.*/
-		res->acl_data_offset = (xdr->p - bm_p) << 2;
+		res->acl_data_offset = xdr_stream_pos(xdr) - pg_offset;
 
 		/* We ignore &savep and don't do consistency checks on
 		 * the attr length.  Let userspace figure it out.... */
 		res->acl_len = attrlen;
-		if (attrlen + res->acl_data_offset > xdr->buf->page_len) {
+		if (attrlen > (xdr->nwords << 2)) {
 			if (res->acl_flags & NFS4_ACL_LEN_REQUEST) {
 				/* getxattr interface called with a NULL buf */
 				goto out;
 			}
 			dprintk("NFS: acl reply: attrlen %u > page_len %u\n",
-					attrlen, xdr->buf->page_len);
+					attrlen, xdr->nwords << 2);
 			return -EINVAL;
 		}
 	} else