s4:dsdb Handle backlinks for Windows 2000 level linked attributes

This revives the code from 5964acfa741d691c0196f91c0796122ec025f177,
before tridge and I simplified this too much, and removed the Windows
2000 functional level linked attribute support.

By telling the linked_attributes module that repl_meta_data has
handled the links, we avoid a conflict for the new style (functional
level 2003 and above) linked attributes.  However, we still need
backlinks for 2000 style linked attributes, so this allows that code
in the linked_attributes module to be revived to handle those.

Andrew Bartlett

2 files changed, 928 insertions, 12 deletions

diff --git a/source4/dsdb/samdb/ldb_modules/linked_attributes.c b/source4/dsdb/samdb/ldb_modules/linked_attributes.c
index 876ada6d2c..2da5a82583 100644
--- a/source4/dsdb/samdb/ldb_modules/linked_attributes.c
+++ b/source4/dsdb/samdb/ldb_modules/linked_attributes.c
@@ -35,6 +35,548 @@
 #include "librpc/gen_ndr/ndr_misc.h"
 #include "dsdb/samdb/ldb_modules/util.h"
 
+struct la_private {
+	struct la_context *la_list;
+};
+
+struct la_op_store {
+	struct la_op_store *next;
+	struct la_op_store *prev;
+	enum la_op {LA_OP_ADD, LA_OP_DEL} op;
+	struct GUID guid;
+	char *name;
+	char *value;
+};
+
+struct replace_context {
+	struct la_context *ac;
+	unsigned int num_elements;
+	struct ldb_message_element *el;
+};
+
+struct la_context {
+	struct la_context *next, *prev;
+	const struct dsdb_schema *schema;
+	struct ldb_module *module;
+	struct ldb_request *req;
+	struct ldb_dn *add_dn;
+	struct ldb_dn *del_dn;
+	struct replace_context *rc;
+	struct la_op_store *ops;
+	struct ldb_extended *op_response;
+	struct ldb_control **op_controls;
+};
+
+static struct la_context *linked_attributes_init(struct ldb_module *module,
+						 struct ldb_request *req)
+{
+	struct ldb_context *ldb;
+	struct la_context *ac;
+
+	ldb = ldb_module_get_ctx(module);
+
+	ac = talloc_zero(req, struct la_context);
+	if (ac == NULL) {
+		ldb_oom(ldb);
+		return NULL;
+	}
+
+	ac->schema = dsdb_get_schema(ldb, ac);
+	ac->module = module;
+	ac->req = req;
+
+	return ac;
+}
+
+/*
+  turn a DN into a GUID
+ */
+static int la_guid_from_dn(struct la_context *ac, struct ldb_dn *dn, struct GUID *guid)
+{
+	int ret;
+	NTSTATUS status;
+
+	status = dsdb_get_extended_dn_guid(dn, guid, "GUID");
+	if (NT_STATUS_IS_OK(status)) {
+		return LDB_SUCCESS;
+	}
+	if (!NT_STATUS_EQUAL(status, NT_STATUS_OBJECT_NAME_NOT_FOUND)) {
+		DEBUG(4,(__location__ ": Unable to parse GUID for dn %s\n",
+			 ldb_dn_get_linearized(dn)));
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	ret = dsdb_find_guid_by_dn(ldb_module_get_ctx(ac->module), dn, guid);
+	if (ret != LDB_SUCCESS) {
+		DEBUG(4,(__location__ ": Failed to find GUID for dn %s\n",
+			 ldb_dn_get_linearized(dn)));
+		return ret;
+	}
+	return LDB_SUCCESS;
+}
+
+
+/* Common routine to handle reading the attributes and creating a
+ * series of modify requests */
+static int la_store_op(struct la_context *ac,
+		       enum la_op op, struct ldb_val *dn,
+		       const char *name)
+{
+	struct ldb_context *ldb;
+	struct la_op_store *os;
+	struct ldb_dn *op_dn;
+	int ret;
+
+	ldb = ldb_module_get_ctx(ac->module);
+
+	op_dn = ldb_dn_from_ldb_val(ac, ldb, dn);
+	if (!op_dn) {
+		ldb_asprintf_errstring(ldb, 
+				       "could not parse attribute as a DN");
+		return LDB_ERR_INVALID_DN_SYNTAX;
+	}
+
+	os = talloc_zero(ac, struct la_op_store);
+	if (!os) {
+		ldb_oom(ldb);
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	os->op = op;
+
+	ret = la_guid_from_dn(ac, op_dn, &os->guid);
+	talloc_free(op_dn);
+	if (ret == LDB_ERR_NO_SUCH_OBJECT && ac->req->operation == LDB_DELETE) {
+		/* we are deleting an object, and we've found it has a
+		 * forward link to a target that no longer
+		 * exists. This is not an error in the delete, and we
+		 * should just not do the deferred delete of the
+		 * target attribute
+		 */
+		talloc_free(os);
+		return LDB_SUCCESS;
+	}
+	if (ret != LDB_SUCCESS) {
+		return ret;
+	}
+
+	os->name = talloc_strdup(os, name);
+	if (!os->name) {
+		ldb_oom(ldb);
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	/* Do deletes before adds */
+	if (op == LA_OP_ADD) {
+		DLIST_ADD_END(ac->ops, os, struct la_op_store *);
+	} else {
+		/* By adding to the head of the list, we do deletes before
+		 * adds when processing a replace */
+		DLIST_ADD(ac->ops, os);
+	}
+
+	return LDB_SUCCESS;
+}
+
+static int la_queue_mod_request(struct la_context *ac);
+static int la_down_req(struct la_context *ac);
+
+
+
+/* add */
+static int linked_attributes_add(struct ldb_module *module, struct ldb_request *req)
+{
+	struct ldb_context *ldb;
+	const struct dsdb_attribute *target_attr;
+	struct la_context *ac;
+	const char *attr_name;
+	struct ldb_control *ctrl;
+	int ret;
+	int i, j;
+
+	ldb = ldb_module_get_ctx(module);
+
+	if (ldb_dn_is_special(req->op.add.message->dn)) {
+		/* do not manipulate our control entries */
+		return ldb_next_request(module, req);
+	}
+
+	if (!(ctrl = ldb_request_get_control(req, DSDB_CONTROL_APPLY_LINKS))) {
+		/* don't do anything special for linked attributes, repl_meta_data has done it */
+		return ldb_next_request(module, req);
+	}
+	ctrl->critical = false;
+
+	ac = linked_attributes_init(module, req);
+	if (!ac) {
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	if (!ac->schema) {
+		/* without schema, this doesn't make any sense */
+		talloc_free(ac);
+		return ldb_next_request(module, req);
+	}
+
+	/* Need to ensure we only have forward links being specified */
+	for (i=0; i < req->op.add.message->num_elements; i++) {
+		const struct ldb_message_element *el = &req->op.add.message->elements[i];
+		const struct dsdb_attribute *schema_attr
+			= dsdb_attribute_by_lDAPDisplayName(ac->schema, el->name);
+		if (!schema_attr) {
+			ldb_asprintf_errstring(ldb, 
+					       "attribute %s is not a valid attribute in schema", el->name);
+			return LDB_ERR_OBJECT_CLASS_VIOLATION;			
+		}
+		/* We have a valid attribute, now find out if it is a forward link */
+		if ((schema_attr->linkID == 0) || ((schema_attr->linkID & 1) == 1)) {
+			continue;
+		}
+		
+		/* Even link IDs are for the originating attribute */
+		target_attr = dsdb_attribute_by_linkID(ac->schema, schema_attr->linkID + 1);
+		if (!target_attr) {
+			/*
+			 * windows 2003 has a broken schema where
+			 * the definition of msDS-IsDomainFor
+			 * is missing (which is supposed to be
+			 * the backlink of the msDS-HasDomainNCs
+			 * attribute
+			 */
+			continue;
+		}
+
+		attr_name = target_attr->lDAPDisplayName;
+
+		for (j = 0; j < el->num_values; j++) {
+			ret = la_store_op(ac, LA_OP_ADD,
+					  &el->values[j],
+					  attr_name);
+			if (ret != LDB_SUCCESS) {
+				return ret;
+			}
+		}
+	}
+
+	/* if no linked attributes are present continue */
+	if (ac->ops == NULL) {
+		/* nothing to do for this module, proceed */
+		talloc_free(ac);
+		return ldb_next_request(module, req);
+	}
+
+	/* start with the original request */
+	return la_down_req(ac);
+}
+
+/* For a delete or rename, we need to find out what linked attributes
+ * are currently on this DN, and then deal with them.  This is the
+ * callback to the base search */
+
+static int la_mod_search_callback(struct ldb_request *req, struct ldb_reply *ares)
+{
+	struct ldb_context *ldb;
+	const struct dsdb_attribute *schema_attr;
+	const struct dsdb_attribute *target_attr;
+	struct ldb_message_element *search_el;
+	struct replace_context *rc;
+	struct la_context *ac;
+	const char *attr_name;
+	int i, j;
+	int ret = LDB_SUCCESS;
+
+	ac = talloc_get_type(req->context, struct la_context);
+	ldb = ldb_module_get_ctx(ac->module);
+	rc = ac->rc;
+
+	if (!ares) {
+		return ldb_module_done(ac->req, NULL, NULL,
+					LDB_ERR_OPERATIONS_ERROR);
+	}
+	if (ares->error != LDB_SUCCESS) {
+		return ldb_module_done(ac->req, ares->controls,
+					ares->response, ares->error);
+	}
+
+	/* Only entries are interesting, and we only want the olddn */
+	switch (ares->type) {
+	case LDB_REPLY_ENTRY:
+
+		if (ldb_dn_compare(ares->message->dn, ac->req->op.mod.message->dn) != 0) {
+			ldb_asprintf_errstring(ldb, 
+					       "linked_attributes: %s is not the DN we were looking for", 
+					       ldb_dn_get_linearized(ares->message->dn));
+			/* Guh?  We only asked for this DN */
+			talloc_free(ares);
+			return ldb_module_done(ac->req, NULL, NULL,
+						LDB_ERR_OPERATIONS_ERROR);
+		}
+
+		ac->add_dn = ac->del_dn = talloc_steal(ac, ares->message->dn);
+
+		/* We don't populate 'rc' for ADD - it can't be deleting elements anyway */
+		for (i = 0; rc && i < rc->num_elements; i++) {
+
+			schema_attr = dsdb_attribute_by_lDAPDisplayName(ac->schema, rc->el[i].name);
+			if (!schema_attr) {
+				ldb_asprintf_errstring(ldb,
+					"attribute %s is not a valid attribute in schema",
+					rc->el[i].name);
+				talloc_free(ares);
+				return ldb_module_done(ac->req, NULL, NULL,
+						LDB_ERR_OBJECT_CLASS_VIOLATION);
+			}
+
+			search_el = ldb_msg_find_element(ares->message,
+							 rc->el[i].name);
+
+			/* See if this element already exists */
+			/* otherwise just ignore as
+			 * the add has already been scheduled */
+			if ( ! search_el) {
+				continue;
+			}
+
+			target_attr = dsdb_attribute_by_linkID(ac->schema, schema_attr->linkID + 1);
+			if (!target_attr) {
+				/*
+				 * windows 2003 has a broken schema where
+				 * the definition of msDS-IsDomainFor
+				 * is missing (which is supposed to be
+				 * the backlink of the msDS-HasDomainNCs
+				 * attribute
+				 */
+				continue;
+			}
+			attr_name = target_attr->lDAPDisplayName;
+
+			/* Now we know what was there, we can remove it for the re-add */
+			for (j = 0; j < search_el->num_values; j++) {
+				ret = la_store_op(ac, LA_OP_DEL,
+						  &search_el->values[j],
+						  attr_name);
+				if (ret != LDB_SUCCESS) {
+					talloc_free(ares);
+					return ldb_module_done(ac->req,
+							       NULL, NULL, ret);
+				}
+			}
+		}
+
+		break;
+
+	case LDB_REPLY_REFERRAL:
+		/* ignore */
+		break;
+
+	case LDB_REPLY_DONE:
+
+		talloc_free(ares);
+
+		if (ac->req->operation == LDB_ADD) {
+			/* Start the modifies to the backlinks */
+			ret = la_queue_mod_request(ac);
+
+			if (ret != LDB_SUCCESS) {
+				return ldb_module_done(ac->req, NULL, NULL,
+						       ret);
+			}
+		} else {
+			/* Start with the original request */
+			ret = la_down_req(ac);
+			if (ret != LDB_SUCCESS) {
+				return ldb_module_done(ac->req, NULL, NULL, ret);
+			}
+		}
+		return LDB_SUCCESS;
+	}
+
+	talloc_free(ares);
+	return ret;
+}
+
+
+/* modify */
+static int linked_attributes_modify(struct ldb_module *module, struct ldb_request *req)
+{
+	/* Look over list of modifications */
+	/* Find if any are for linked attributes */
+	/* Determine the effect of the modification */
+	/* Apply the modify to the linked entry */
+
+	struct ldb_context *ldb;
+	int i, j;
+	struct la_context *ac;
+	struct ldb_request *search_req;
+	const char **attrs;
+	struct ldb_control *ctrl;
+
+	int ret;
+
+	ldb = ldb_module_get_ctx(module);
+
+	if (ldb_dn_is_special(req->op.mod.message->dn)) {
+		/* do not manipulate our control entries */
+		return ldb_next_request(module, req);
+	}
+
+	if (!(ctrl = ldb_request_get_control(req, DSDB_CONTROL_APPLY_LINKS))) {
+		/* don't do anything special for linked attributes, repl_meta_data has done it */
+		return ldb_next_request(module, req);
+	}
+	ctrl->critical = false;
+
+	ac = linked_attributes_init(module, req);
+	if (!ac) {
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	if (!ac->schema) {
+		/* without schema, this doesn't make any sense */
+		return ldb_next_request(module, req);
+	}
+
+	ac->rc = talloc_zero(ac, struct replace_context);
+	if (!ac->rc) {
+		ldb_oom(ldb);
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	for (i=0; i < req->op.mod.message->num_elements; i++) {
+		bool store_el = false;
+		const char *attr_name;
+		const struct dsdb_attribute *target_attr;
+		const struct ldb_message_element *el = &req->op.mod.message->elements[i];
+		const struct dsdb_attribute *schema_attr
+			= dsdb_attribute_by_lDAPDisplayName(ac->schema, el->name);
+		if (!schema_attr) {
+			ldb_asprintf_errstring(ldb, 
+					       "attribute %s is not a valid attribute in schema", el->name);
+			return LDB_ERR_OBJECT_CLASS_VIOLATION;			
+		}
+		/* We have a valid attribute, now find out if it is a forward link
+		   (Even link IDs are for the originating attribute) */
+		if ((schema_attr->linkID == 0) || ((schema_attr->linkID & 1) == 1)) {
+			continue;
+		}
+
+		/* Now find the target attribute */
+		target_attr = dsdb_attribute_by_linkID(ac->schema, schema_attr->linkID + 1);
+		if (!target_attr) {
+			/*
+			 * windows 2003 has a broken schema where
+			 * the definition of msDS-IsDomainFor
+			 * is missing (which is supposed to be
+			 * the backlink of the msDS-HasDomainNCs
+			 * attribute
+			 */
+			continue;
+		}
+
+		attr_name = target_attr->lDAPDisplayName;
+	
+		switch (el->flags & LDB_FLAG_MOD_MASK) {
+		case LDB_FLAG_MOD_REPLACE:
+			/* treat as just a normal add the delete part is handled by the callback */
+			store_el = true;
+
+			/* break intentionally missing */
+
+		case LDB_FLAG_MOD_ADD:
+
+			/* For each value being added, we need to setup the adds */
+			for (j = 0; j < el->num_values; j++) {
+				ret = la_store_op(ac, LA_OP_ADD,
+						  &el->values[j],
+						  attr_name);
+				if (ret != LDB_SUCCESS) {
+					return ret;
+				}
+			}
+			break;
+
+		case LDB_FLAG_MOD_DELETE:
+
+			if (el->num_values) {
+				/* For each value being deleted, we need to setup the delete */
+				for (j = 0; j < el->num_values; j++) {
+					ret = la_store_op(ac, LA_OP_DEL,
+							  &el->values[j],
+							  attr_name);
+					if (ret != LDB_SUCCESS) {
+						return ret;
+					}
+				}
+			} else {
+				/* Flag that there was a DELETE
+				 * without a value specified, so we
+				 * need to look for the old value */
+				store_el = true;
+			}
+
+			break;
+		}
+
+		if (store_el) {
+			struct ldb_message_element *search_el;
+
+			search_el = talloc_realloc(ac->rc, ac->rc->el,
+						   struct ldb_message_element,
+						   ac->rc->num_elements +1);
+			if (!search_el) {
+				ldb_oom(ldb);
+				return LDB_ERR_OPERATIONS_ERROR;
+			}
+			ac->rc->el = search_el;
+
+			ac->rc->el[ac->rc->num_elements] = *el;
+			ac->rc->num_elements++;
+		}
+	}
+	
+	if (ac->ops || ac->rc->el) {
+		/* both replace and delete without values are handled in the callback
+		 * after the search on the entry to be modified is performed */
+		
+		attrs = talloc_array(ac->rc, const char *, ac->rc->num_elements + 1);
+		if (!attrs) {
+			ldb_oom(ldb);
+			return LDB_ERR_OPERATIONS_ERROR;
+		}
+		for (i = 0; ac->rc && i < ac->rc->num_elements; i++) {
+			attrs[i] = ac->rc->el[i].name;
+		}
+		attrs[i] = NULL;
+		
+		/* The callback does all the hard work here */
+		ret = ldb_build_search_req(&search_req, ldb, ac,
+					   req->op.mod.message->dn,
+					   LDB_SCOPE_BASE,
+					   "(objectClass=*)", attrs,
+					   NULL,
+					   ac, la_mod_search_callback,
+					   req);
+
+		/* We need to figure out our own extended DN, to fill in as the backlink target */
+		if (ret == LDB_SUCCESS) {
+			ret = ldb_request_add_control(search_req,
+						      LDB_CONTROL_EXTENDED_DN_OID,
+						      false, NULL);
+		}
+		if (ret == LDB_SUCCESS) {
+			talloc_steal(search_req, attrs);
+			
+			ret = ldb_next_request(module, search_req);
+		}
+
+	} else {
+		/* nothing to do for this module, proceed */
+		talloc_free(ac);
+		ret = ldb_next_request(module, req);
+	}
+
+	return ret;
+}
 
 static int linked_attributes_fix_links(struct ldb_module *module,
 				       struct ldb_dn *old_dn, struct ldb_dn *new_dn,
@@ -190,7 +732,356 @@ static int linked_attributes_rename(struct ldb_module *module, struct ldb_reques
 }
 
 
+/* queue a linked attributes modify request in the la_private
+   structure */
+static int la_queue_mod_request(struct la_context *ac)
+{
+	struct la_private *la_private = 
+		talloc_get_type(ldb_module_get_private(ac->module), struct la_private);
+
+	if (la_private == NULL) {
+		ldb_debug(ldb_module_get_ctx(ac->module), LDB_DEBUG_ERROR, __location__ ": No la_private transaction setup\n");
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	talloc_steal(la_private, ac);
+	DLIST_ADD(la_private->la_list, ac);
+
+	return ldb_module_done(ac->req, ac->op_controls,
+			       ac->op_response, LDB_SUCCESS);
+}
+
+/* Having done the original operation, then try to fix up all the linked attributes for modify and delete */
+static int la_mod_del_callback(struct ldb_request *req, struct ldb_reply *ares)
+{
+	int ret;
+	struct la_context *ac;
+	struct ldb_context *ldb;
+
+	ac = talloc_get_type(req->context, struct la_context);
+	ldb = ldb_module_get_ctx(ac->module);
+
+	if (!ares) {
+		return ldb_module_done(ac->req, NULL, NULL,
+					LDB_ERR_OPERATIONS_ERROR);
+	}
+	if (ares->error != LDB_SUCCESS) {
+		return ldb_module_done(ac->req, ares->controls,
+					ares->response, ares->error);
+	}
+
+	if (ares->type != LDB_REPLY_DONE) {
+		ldb_set_errstring(ldb,
+				  "invalid ldb_reply_type in callback");
+		talloc_free(ares);
+		return ldb_module_done(ac->req, NULL, NULL,
+					LDB_ERR_OPERATIONS_ERROR);
+	}
+	
+	ac->op_controls = talloc_steal(ac, ares->controls);
+	ac->op_response = talloc_steal(ac, ares->response);
+
+	/* If we have modfies to make, this is the time to do them for modify and delete */
+	ret = la_queue_mod_request(ac);
+	
+	if (ret != LDB_SUCCESS) {
+		return ldb_module_done(ac->req, NULL, NULL, ret);
+	}
+	talloc_free(ares);
+
+	/* la_queue_mod_request has already sent the callbacks */
+	return LDB_SUCCESS;
+
+}
+
+/* Having done the original add, then try to fix up all the linked attributes
+
+  This is done after the add so the links can get the extended DNs correctly.
+ */
+static int la_add_callback(struct ldb_request *req, struct ldb_reply *ares)
+{
+	int ret;
+	struct la_context *ac;
+	struct ldb_context *ldb;
+
+	ac = talloc_get_type(req->context, struct la_context);
+	ldb = ldb_module_get_ctx(ac->module);
+
+	if (!ares) {
+		return ldb_module_done(ac->req, NULL, NULL,
+					LDB_ERR_OPERATIONS_ERROR);
+	}
+	if (ares->error != LDB_SUCCESS) {
+		return ldb_module_done(ac->req, ares->controls,
+					ares->response, ares->error);
+	}
+
+	if (ares->type != LDB_REPLY_DONE) {
+		ldb_set_errstring(ldb,
+				  "invalid ldb_reply_type in callback");
+		talloc_free(ares);
+		return ldb_module_done(ac->req, NULL, NULL,
+					LDB_ERR_OPERATIONS_ERROR);
+	}
+	
+	if (ac->ops) {
+		struct ldb_request *search_req;
+		static const char *attrs[] = { NULL };
+		
+		/* The callback does all the hard work here - we need
+		 * the objectGUID and SID of the added record */
+		ret = ldb_build_search_req(&search_req, ldb, ac,
+					   ac->req->op.add.message->dn,
+					   LDB_SCOPE_BASE,
+					   "(objectClass=*)", attrs,
+					   NULL,
+					   ac, la_mod_search_callback,
+					   ac->req);
+		
+		if (ret == LDB_SUCCESS) {
+			ret = ldb_request_add_control(search_req,
+						      LDB_CONTROL_EXTENDED_DN_OID,
+						      false, NULL);
+		}
+		if (ret != LDB_SUCCESS) {
+			return ldb_module_done(ac->req, NULL, NULL,
+					       ret);
+		}
+
+		ac->op_controls = talloc_steal(ac, ares->controls);
+		ac->op_response = talloc_steal(ac, ares->response);
+
+		return ldb_next_request(ac->module, search_req);
+		
+	} else {
+		return ldb_module_done(ac->req, ares->controls,
+				       ares->response, ares->error);
+	}
+}
+
+/* Reconstruct the original request, but pointing at our local callback to finish things off */
+static int la_down_req(struct la_context *ac)
+{
+	struct ldb_request *down_req;
+	int ret;
+	struct ldb_context *ldb;
+
+	ldb = ldb_module_get_ctx(ac->module);
+
+	switch (ac->req->operation) {
+	case LDB_ADD:
+		ret = ldb_build_add_req(&down_req, ldb, ac,
+					ac->req->op.add.message,
+					ac->req->controls,
+					ac, la_add_callback,
+					ac->req);
+		break;
+	case LDB_MODIFY:
+		ret = ldb_build_mod_req(&down_req, ldb, ac,
+					ac->req->op.mod.message,
+					ac->req->controls,
+					ac, la_mod_del_callback,
+					ac->req);
+		break;
+	default:
+		ret = LDB_ERR_OPERATIONS_ERROR;
+	}
+	if (ret != LDB_SUCCESS) {
+		return ret;
+	}
+
+	return ldb_next_request(ac->module, down_req);
+}
+
+/*
+  use the GUID part of an extended DN to find the target DN, in case
+  it has moved
+ */
+static int la_find_dn_target(struct ldb_module *module, struct la_context *ac, 
+			     struct GUID *guid, struct ldb_dn **dn)
+{
+	return dsdb_find_dn_by_guid(ldb_module_get_ctx(ac->module), ac, guid, dn);
+}
+
+/* apply one la_context op change */
+static int la_do_op_request(struct ldb_module *module, struct la_context *ac, struct la_op_store *op)
+{
+	struct ldb_message_element *ret_el;
+	struct ldb_request *mod_req;
+	struct ldb_message *new_msg;
+	struct ldb_context *ldb;
+	int ret;
+
+	ldb = ldb_module_get_ctx(ac->module);
+
+	/* Create the modify request */
+	new_msg = ldb_msg_new(ac);
+	if (!new_msg) {
+		ldb_oom(ldb);
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	ret = la_find_dn_target(module, ac, &op->guid, &new_msg->dn);
+	if (ret != LDB_SUCCESS) {
+		return ret;
+	}
+
+	if (op->op == LA_OP_ADD) {
+		ret = ldb_msg_add_empty(new_msg, op->name,
+					LDB_FLAG_MOD_ADD, &ret_el);
+	} else {
+		ret = ldb_msg_add_empty(new_msg, op->name,
+					LDB_FLAG_MOD_DELETE, &ret_el);
+	}
+	if (ret != LDB_SUCCESS) {
+		return ret;
+	}
+	ret_el->values = talloc_array(new_msg, struct ldb_val, 1);
+	if (!ret_el->values) {
+		ldb_oom(ldb);
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+	ret_el->num_values = 1;
+	if (op->op == LA_OP_ADD) {
+		ret_el->values[0] = data_blob_string_const(ldb_dn_get_extended_linearized(new_msg, ac->add_dn, 1));
+	} else {
+		ret_el->values[0] = data_blob_string_const(ldb_dn_get_extended_linearized(new_msg, ac->del_dn, 1));
+	}
+
+#if 0
+	ldb_debug(ldb, LDB_DEBUG_WARNING,
+		  "link on %s %s: %s %s\n", 
+		  ldb_dn_get_linearized(new_msg->dn), ret_el->name, 
+		  ret_el->values[0].data, ac->ops->op == LA_OP_ADD ? "added" : "deleted");
+#endif	
+
+	ret = ldb_build_mod_req(&mod_req, ldb, op,
+				new_msg,
+				NULL,
+				NULL, 
+				ldb_op_default_callback,
+				NULL);
+	if (ret != LDB_SUCCESS) {
+		return ret;
+	}
+	talloc_steal(mod_req, new_msg);
+
+	if (DEBUGLVL(4)) {
+		DEBUG(4,("Applying linked attribute change:\n%s\n",
+			 ldb_ldif_message_string(ldb, op, LDB_CHANGETYPE_MODIFY, new_msg)));
+	}
+
+	/* Run the new request */
+	ret = ldb_next_request(module, mod_req);
+
+	/* we need to wait for this to finish, as we are being called
+	   from the synchronous end_transaction hook of this module */
+	if (ret == LDB_SUCCESS) {
+		ret = ldb_wait(mod_req->handle, LDB_WAIT_ALL);
+	}
+
+	if (ret != LDB_SUCCESS) {
+		ldb_debug(ldb, LDB_DEBUG_WARNING, "Failed to apply linked attribute change '%s' %s\n",
+			  ldb_errstring(ldb),
+			  ldb_ldif_message_string(ldb, op, LDB_CHANGETYPE_MODIFY, new_msg));
+	}
+
+	return ret;
+}
+
+/* apply one set of la_context changes */
+static int la_do_mod_request(struct ldb_module *module, struct la_context *ac)
+{
+	struct la_op_store *op;
+
+	for (op = ac->ops; op; op=op->next) {
+		int ret = la_do_op_request(module, ac, op);
+		if (ret != LDB_SUCCESS) {
+			if (ret != LDB_ERR_NO_SUCH_OBJECT) {
+				return ret;
+			}
+		}
+	}
+
+	return LDB_SUCCESS;
+}
+
+
+/*
+  we hook into the transaction operations to allow us to 
+  perform the linked attribute updates at the end of the whole
+  transaction. This allows a forward linked attribute to be created
+  before the target is created, as long as the target is created
+  in the same transaction
+ */
+static int linked_attributes_start_transaction(struct ldb_module *module)
+{
+	/* create our private structure for this transaction */
+	struct la_private *la_private = talloc_get_type(ldb_module_get_private(module),
+							struct la_private);
+	talloc_free(la_private);
+	la_private = talloc(module, struct la_private);
+	if (la_private == NULL) {
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+	la_private->la_list = NULL;
+	ldb_module_set_private(module, la_private);
+	return ldb_next_start_trans(module);
+}
+
+/*
+  on prepare commit we loop over our queued la_context structures
+  and apply each of them
+ */
+static int linked_attributes_prepare_commit(struct ldb_module *module)
+{
+	struct la_private *la_private = 
+		talloc_get_type(ldb_module_get_private(module), struct la_private);
+	struct la_context *ac;
+
+	if (!la_private) {
+		/* prepare commit without begin_transaction - let someone else return the error, just don't segfault */
+		return ldb_next_prepare_commit(module);
+	}
+	/* walk the list backwards, to do the first entry first, as we
+	 * added the entries with DLIST_ADD() which puts them at the
+	 * start of the list */
+	for (ac = la_private->la_list; ac && ac->next; ac=ac->next) ;
+
+	for (; ac; ac=ac->prev) {
+		int ret;
+		ac->req = NULL;
+		ret = la_do_mod_request(module, ac);
+		if (ret != LDB_SUCCESS) {
+			DEBUG(0,(__location__ ": Failed mod request ret=%d\n", ret));
+			talloc_free(la_private);
+			ldb_module_set_private(module, NULL);	
+			return ret;
+		}
+	}
+
+	talloc_free(la_private);
+	ldb_module_set_private(module, NULL);	
+
+	return ldb_next_prepare_commit(module);
+}
+
+static int linked_attributes_del_transaction(struct ldb_module *module)
+{
+	struct la_private *la_private = 
+		talloc_get_type(ldb_module_get_private(module), struct la_private);
+	talloc_free(la_private);
+	ldb_module_set_private(module, NULL);
+	return ldb_next_del_trans(module);
+}
+
+
 _PUBLIC_ const struct ldb_module_ops ldb_linked_attributes_module_ops = {
 	.name		   = "linked_attributes",
-	.rename	  	   = linked_attributes_rename,
+	.add               = linked_attributes_add,
+	.modify            = linked_attributes_modify,
+	.rename            = linked_attributes_rename,
+	.start_transaction = linked_attributes_start_transaction,
+	.prepare_commit    = linked_attributes_prepare_commit,
+	.del_transaction   = linked_attributes_del_transaction,
 };
diff --git a/source4/dsdb/samdb/ldb_modules/repl_meta_data.c b/source4/dsdb/samdb/ldb_modules/repl_meta_data.c
index db2415b397..8994ee4014 100644
--- a/source4/dsdb/samdb/ldb_modules/repl_meta_data.c
+++ b/source4/dsdb/samdb/ldb_modules/repl_meta_data.c
@@ -50,8 +50,6 @@
 #include "libcli/security/security.h"
 #include "lib/util/tsort.h"
 
-#define W2K3_LINKED_ATTRIBUTES 1
-
 struct replmd_private {
 	TALLOC_CTX *la_ctx;
 	struct la_entry *la_list;
@@ -734,6 +732,7 @@ static int replmd_add(struct ldb_module *module, struct ldb_request *req)
 	char *time_str;
 	int ret;
 	unsigned int i;
+	unsigned int functional_level;
 	uint32_t ni=0;
 	bool allow_add_guid = false;
 	bool remove_current_guid = false;
@@ -753,6 +752,8 @@ static int replmd_add(struct ldb_module *module, struct ldb_request *req)
 
 	ldb = ldb_module_get_ctx(module);
 
+	functional_level = dsdb_functional_level(ldb);
+
 	ldb_debug(ldb, LDB_DEBUG_TRACE, "replmd_add\n");
 
 	ac = replmd_ctx_init(module, req);
@@ -875,8 +876,7 @@ static int replmd_add(struct ldb_module *module, struct ldb_request *req)
 			continue;
 		}
 
-#if W2K3_LINKED_ATTRIBUTES
-		if (sa->linkID != 0 && dsdb_functional_level(ldb) > DS_DOMAIN_FUNCTION_2000) {
+		if (sa->linkID != 0 && functional_level > DS_DOMAIN_FUNCTION_2000) {
 			ret = replmd_add_fix_la(module, e, ac->seq_num, our_invocation_id, t, &guid, sa);
 			if (ret != LDB_SUCCESS) {
 				talloc_free(ac);
@@ -886,7 +886,6 @@ static int replmd_add(struct ldb_module *module, struct ldb_request *req)
 			   replPropertyMetaData in FL above w2k */
 			continue;
 		}
-#endif
 
 		m->attid			= sa->attributeID_id;
 		m->version			= 1;
@@ -974,6 +973,14 @@ static int replmd_add(struct ldb_module *module, struct ldb_request *req)
 		return ret;
 	}
 
+	if (functional_level == DS_DOMAIN_FUNCTION_2000) {
+		ret = ldb_request_add_control(down_req, DSDB_CONTROL_APPLY_LINKS, false, NULL);
+		if (ret != LDB_SUCCESS) {
+			talloc_free(ac);
+			return ret;
+		}
+	}
+
 	/* mark the control done */
 	if (control) {
 		control->critical = 0;
@@ -1021,7 +1028,6 @@ static int replmd_update_rpmd_element(struct ldb_context *ldb,
 		if (a->attributeID_id == omd->ctr.ctr1.array[i].attid) break;
 	}
 
-#if W2K3_LINKED_ATTRIBUTES
 	if (a->linkID != 0 && dsdb_functional_level(ldb) > DS_DOMAIN_FUNCTION_2000) {
 		/* linked attributes are not stored in
 		   replPropertyMetaData in FL above w2k, but we do
@@ -1032,7 +1038,6 @@ static int replmd_update_rpmd_element(struct ldb_context *ldb,
 		}
 		return LDB_SUCCESS;
 	}
-#endif
 
 	if (i == omd->ctr.ctr1.count) {
 		/* we need to add a new one */
@@ -1959,10 +1964,6 @@ static int replmd_modify_handle_linked_attribs(struct ldb_module *module,
 		return LDB_SUCCESS;
 	}
 
-#if !W2K3_LINKED_ATTRIBUTES
-	return LDB_SUCCESS;
-#endif
-
 	if (dsdb_functional_level(ldb) == DS_DOMAIN_FUNCTION_2000) {
 		/* don't do anything special for linked attributes */
 		return LDB_SUCCESS;
@@ -2057,6 +2058,7 @@ static int replmd_modify(struct ldb_module *module, struct ldb_request *req)
 	bool is_urgent = false;
 	struct loadparm_context *lp_ctx;
 	char *referral;
+	unsigned int functional_level;
 
 	/* do not manipulate our control entries */
 	if (ldb_dn_is_special(req->op.mod.message->dn)) {
@@ -2064,6 +2066,8 @@ static int replmd_modify(struct ldb_module *module, struct ldb_request *req)
 	}
 
 	ldb = ldb_module_get_ctx(module);
+	functional_level = dsdb_functional_level(ldb);
+
 	lp_ctx = talloc_get_type(ldb_get_opaque(ldb, "loadparm"),
 				 struct loadparm_context);
 
@@ -2123,6 +2127,18 @@ static int replmd_modify(struct ldb_module *module, struct ldb_request *req)
 		talloc_free(ac);
 		return ret;
 	}
+
+	/* If we are in functional level 2000, then
+	 * replmd_modify_handle_linked_attribs will have done
+	 * nothing */
+	if (functional_level == DS_DOMAIN_FUNCTION_2000) {
+		ret = ldb_request_add_control(down_req, DSDB_CONTROL_APPLY_LINKS, false, NULL);
+		if (ret != LDB_SUCCESS) {
+			talloc_free(ac);
+			return ret;
+		}
+	}
+
 	talloc_steal(down_req, msg);
 
 	/* we only change whenChanged and uSNChanged if the seq_num
@@ -3551,11 +3567,20 @@ static int replmd_extended_replicated_objects(struct ldb_module *module, struct
 		if (!req->controls) return replmd_replicated_request_werror(ar, WERR_NOMEM);
 	}
 
+	/* This allows layers further down to know if a change came in over replication */
 	ret = ldb_request_add_control(req, DSDB_CONTROL_REPLICATED_UPDATE_OID, false, NULL);
 	if (ret != LDB_SUCCESS) {
 		return ret;
 	}
 
+	/* If this change contained linked attributes in the body
+	 * (rather than in the links section) we need to update
+	 * backlinks in linked_attributes */
+	ret = ldb_request_add_control(req, DSDB_CONTROL_APPLY_LINKS, false, NULL);
+	if (ret != LDB_SUCCESS) {
+		return ret;
+	}
+
 	ar->controls = req->controls;
 	req->controls = ctrls;