Samba.org patch source is referenced below.
WiKi page is:
https://wiki.samba.org/index.php/VFS/vfs_worm
changes against the community version:
 - removed support of grace time on file
 - slightly modified to run on VFS rev.28
-- Jiri Sasek

From 2004317c09d781a4ec1275aaa4a29289e798eff3 Mon Sep 17 00:00:00 2001
From: Volker Lendecke <[email protected]>
Date: Wed, 20 Nov 2013 12:09:47 +0100
Subject: [PATCH] s3-modules: add new vfs_worm module

VFS module to disallow writes for older files.

Signed-off-by: Volker Lendecke <[email protected]>
Reviewed-by: Stefan Metzmacher <[email protected]>
Reviewed-by: Jeremy Allison <[email protected]>
---
 source3/modules/vfs_worm.c |   97 ++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 97 insertions(+), 0 deletions(-)
 create mode 100644 source3/modules/vfs_worm.c

diff --git a/source3/modules/vfs_worm.c b/source3/modules/vfs_worm.c
new file mode 100644
index 0000000..77a18ca
--- /dev/null
+++ b/source3/modules/vfs_worm.c
@@ -0,0 +1,93 @@
+/*
+ * VFS module to disallow writes for older files
+ *
+ * Copyright (C) 2013, Volker Lendecke
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "includes.h"
+#include "smbd/smbd.h"
+#include "system/filesys.h"
+#include "libcli/security/security.h"
+
+static NTSTATUS vfs_worm_create_file(vfs_handle_struct *handle,
+				     struct smb_request *req,
+				     uint16_t root_dir_fid,
+				     struct smb_filename *smb_fname,
+				     uint32_t access_mask,
+				     uint32_t share_access,
+				     uint32_t create_disposition,
+				     uint32_t create_options,
+				     uint32_t file_attributes,
+				     uint32_t oplock_request,
+				     uint64_t allocation_size,
+				     uint32_t private_flags,
+				     struct security_descriptor *sd,
+				     struct ea_list *ea_list,
+				     files_struct **result,
+				     int *pinfo)
+{
+	bool readonly = false;
+	const uint32_t write_access_flags =
+		FILE_WRITE_DATA | FILE_APPEND_DATA |
+		FILE_WRITE_ATTRIBUTES | DELETE_ACCESS |
+		WRITE_DAC_ACCESS | WRITE_OWNER_ACCESS;
+	NTSTATUS status;
+
+	if (VALID_STAT(smb_fname->st)) {
+		/* no grace_period supported */
+		readonly = true;
+	}
+
+	if (readonly && (access_mask & write_access_flags)) {
+		return NT_STATUS_ACCESS_DENIED;
+	}
+
+	status = SMB_VFS_NEXT_CREATE_FILE(
+		handle, req, root_dir_fid, smb_fname, access_mask,
+		share_access, create_disposition, create_options,
+		file_attributes, oplock_request, allocation_size,
+		private_flags, sd, ea_list, result, pinfo);
+	if (!NT_STATUS_IS_OK(status)) {
+		return status;
+	}
+
+	/*
+	 * Access via MAXIMUM_ALLOWED_ACCESS?
+	 */
+	if (readonly && ((*result)->access_mask & write_access_flags)) {
+		close_file(req, *result, NORMAL_CLOSE);
+		return NT_STATUS_ACCESS_DENIED;
+	}
+	return NT_STATUS_OK;
+}
+
+static struct vfs_fn_pointers vfs_worm_fns = {
+	.create_file = vfs_worm_create_file,
+};
+
+NTSTATUS vfs_worm_init(void);
+NTSTATUS vfs_worm_init(void)
+{
+	NTSTATUS ret;
+
+	ret = smb_register_vfs(SMB_VFS_INTERFACE_VERSION, "worm",
+			       &vfs_worm_fns);
+	if (!NT_STATUS_IS_OK(ret)) {
+		return ret;
+	}
+
+	return ret;
+}
-- 
1.7.0.4

   Makefile.in and configure.in adds