s4:dsdb/subtree_delete: do the recursive delete AS_SYSTEM/TRUSTED (bug #7711)

[Samba/gebeck_regimport.git] / source4 / dsdb / samdb / ldb_modules / linked_attributes.c

/*
   ldb database library

   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2007
   Copyright (C) Simo Sorce <idra@samba.org> 2008
   Copyright (C) Matthieu Patou <mat@matws.net> 2011

   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/>.
*/

/*
 *  Name: ldb
 *
 *  Component: ldb linked_attributes module
 *
 *  Description: Module to ensure linked attribute pairs remain in sync
 *
 *  Author: Andrew Bartlett
 */

#include "includes.h"
#include "ldb_module.h"
#include "util/dlinklist.h"
#include "dsdb/samdb/samdb.h"
#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;
};

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 *mod_dn;
        struct replace_context *rc;
        struct la_op_store *ops;
        struct ldb_extended *op_response;
        struct ldb_control **op_controls;
        /*
         * For futur use
         * will tell which GC to use for resolving links
         */
        char *gc_dns_name;
};


static int handle_verify_name_control(TALLOC_CTX *ctx, struct ldb_context *ldb,
                                        struct ldb_control *control, struct la_context *ac)
{
        /*
         * If we are a GC let's remove the control,
         * if there is a specified GC check that is us.
         */
        struct ldb_verify_name_control *lvnc = (struct ldb_verify_name_control *)control->data;
        if (samdb_is_gc(ldb)) {
                /* Because we can't easily talloc a struct ldb_dn*/
                struct ldb_dn **dn = talloc_array(ctx, struct ldb_dn *, 1);
                int ret = samdb_server_reference_dn(ldb, ctx, dn);
                const char *dns;

                if (ret != LDB_SUCCESS) {
                        return ldb_operr(ldb);
                }

                dns = samdb_dn_to_dnshostname(ldb, ctx, *dn);
                if (!dns) {
                        return ldb_operr(ldb);
                }
                if (!lvnc->gc || strcasecmp(dns, lvnc->gc) == 0) {
                        if (!ldb_save_controls(control, ctx, NULL)) {
                                return ldb_operr(ldb);
                        }
                } else {
                        control->critical = true;
                }
                talloc_free(dn);
        } else {
                /* For the moment we don't remove the control is this case in order
                 * to fail the request. It's better than having the client thinking
                 * that we honnor its control.
                 * Hopefully only a very small set of usecase should hit this problem.
                 */
                if (lvnc->gc) {
                        ac->gc_dns_name = talloc_strdup(ac, lvnc->gc);
                }
                control->critical = true;
        }

        return LDB_SUCCESS;
}

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)
{
        NTSTATUS status;
        int ret;

        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_operr(ldb_module_get_ctx(ac->module));
        }

        ret = dsdb_module_guid_by_dn(ac->module, dn, guid, ac->req);
        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) {
                return ldb_oom(ldb);
        }

        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) {
                return ldb_oom(ldb);
        }

        /* 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;
        unsigned int i, j;
        struct ldb_control *control;
        int ret;

        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);
        }

        ac = linked_attributes_init(module, req);
        if (!ac) {
                return ldb_operr(ldb);
        }

        control = ldb_request_get_control(req, LDB_CONTROL_VERIFY_NAME_OID);
        if (control != NULL && control->data != NULL) {
                ret = handle_verify_name_control(req, ldb, control, ac);
                if (ret != LDB_SUCCESS) {
                        return ldb_operr(ldb);
                }
        }

        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 */
                talloc_free(ac);
                return ldb_next_request(module, req);
        }
        ctrl->critical = false;

        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,
                                               "%s: attribute %s is not a valid attribute in schema",
                                               __FUNCTION__,
                                               el->name);
                        return LDB_ERR_OBJECT_CLASS_VIOLATION;
                }

                /* this could be a link with no partner, in which case
                   there is no special work to do */
                if (schema_attr->linkID == 0) {
                        continue;
                }

                /* this part of the code should only be handling forward links */
                SMB_ASSERT((schema_attr->linkID & 1) == 0);

                /* 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;
        unsigned 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->mod_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,
                                        "%s: attribute %s is not a valid attribute in schema",
                                        __FUNCTION__,
                                        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_control *control;
        struct ldb_context *ldb;
        unsigned 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);
        }

        ac = linked_attributes_init(module, req);
        if (!ac) {
                return ldb_operr(ldb);
        }

        control = ldb_request_get_control(req, LDB_CONTROL_VERIFY_NAME_OID);
        if (control != NULL && control->data != NULL) {
                ret = handle_verify_name_control(req, ldb, control, ac);
                if (ret != LDB_SUCCESS) {
                        return ldb_operr(ldb);
                }
        }

        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 */
                talloc_free(ac);
                return ldb_next_request(module, req);
        }
        ctrl->critical = false;

        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) {
                return ldb_oom(ldb);
        }

        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,
                                               "%s: attribute %s is not a valid attribute in schema",
                                               __FUNCTION__,
                                               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) {
                        continue;
                }

                /* this part of the code should only be handling forward links */
                SMB_ASSERT((schema_attr->linkID & 1) == 0);

                /* 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) {
                                return ldb_oom(ldb);
                        }
                        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) {
                        return ldb_oom(ldb);
                }
                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);
                LDB_REQ_SET_LOCATION(search_req);

                /* We need to figure out our own extended DN, to fill in as the backlink target */
                if (ret == LDB_SUCCESS) {
                        ret = dsdb_request_add_controls(search_req,
                                                        DSDB_SEARCH_SHOW_DELETED |
                                                        DSDB_SEARCH_SHOW_EXTENDED_DN);
                }
                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,
                                       struct ldb_message_element *el, struct dsdb_schema *schema,
                                       const struct dsdb_attribute *schema_attr,
                                       struct ldb_request *parent)
{
        unsigned int i, j;
        TALLOC_CTX *tmp_ctx = talloc_new(module);
        struct ldb_context *ldb = ldb_module_get_ctx(module);
        const struct dsdb_attribute *target;
        const char *attrs[2];
        int ret;

        target = dsdb_attribute_by_linkID(schema, schema_attr->linkID ^ 1);
        if (target == NULL) {
                /* there is no counterpart link to change */
                return LDB_SUCCESS;
        }

        attrs[0] = target->lDAPDisplayName;
        attrs[1] = NULL;

        for (i=0; i<el->num_values; i++) {
                struct dsdb_dn *dsdb_dn;
                struct ldb_result *res;
                struct ldb_message *msg;
                struct ldb_message_element *el2;

                dsdb_dn = dsdb_dn_parse(tmp_ctx, ldb, &el->values[i], schema_attr->syntax->ldap_oid);
                if (dsdb_dn == NULL) {
                        talloc_free(tmp_ctx);
                        return LDB_ERR_INVALID_DN_SYNTAX;
                }

                ret = dsdb_module_search_dn(module, tmp_ctx, &res, dsdb_dn->dn,
                                            attrs,
                                            DSDB_FLAG_NEXT_MODULE |
                                            DSDB_SEARCH_SHOW_RECYCLED |
                                            DSDB_SEARCH_SHOW_DN_IN_STORAGE_FORMAT |
                                            DSDB_SEARCH_REVEAL_INTERNALS, parent);
                if (ret != LDB_SUCCESS) {
                        ldb_asprintf_errstring(ldb, "Linked attribute %s->%s between %s and %s - remote not found - %s",
                                               el->name, target->lDAPDisplayName,
                                               ldb_dn_get_linearized(old_dn),
                                               ldb_dn_get_linearized(dsdb_dn->dn),
                                               ldb_errstring(ldb));
                        talloc_free(tmp_ctx);
                        return ret;
                }
                msg = res->msgs[0];

                if (msg->num_elements == 0) {
                        /* Forward link without backlink remaining - nothing to do here */
                        continue;
                } else if (msg->num_elements != 1) {
                        ldb_asprintf_errstring(ldb, "Bad msg elements - got %u elements, expected one element to be returned in linked_attributes_fix_links for %s",
                                               msg->num_elements, ldb_dn_get_linearized(msg->dn));
                        talloc_free(tmp_ctx);
                        return LDB_ERR_OPERATIONS_ERROR;
                }
                if (ldb_attr_cmp(msg->elements[0].name, target->lDAPDisplayName) != 0) {
                        ldb_asprintf_errstring(ldb, "Bad returned attribute in linked_attributes_fix_links: got %s, expected %s for %s", msg->elements[0].name, target->lDAPDisplayName, ldb_dn_get_linearized(msg->dn));
                        talloc_free(tmp_ctx);
                        return LDB_ERR_OPERATIONS_ERROR;
                }
                el2 = &msg->elements[0];

                el2->flags = LDB_FLAG_MOD_REPLACE;

                /* find our DN in the values */
                for (j=0; j<el2->num_values; j++) {
                        struct dsdb_dn *dsdb_dn2;
                        dsdb_dn2 = dsdb_dn_parse(msg, ldb, &el2->values[j], target->syntax->ldap_oid);
                        if (dsdb_dn2 == NULL) {
                                talloc_free(tmp_ctx);
                                return LDB_ERR_INVALID_DN_SYNTAX;
                        }
                        if (ldb_dn_compare(old_dn, dsdb_dn2->dn) != 0) {
                                continue;
                        }
                        ret = ldb_dn_update_components(dsdb_dn2->dn, new_dn);
                        if (ret != LDB_SUCCESS) {
                                talloc_free(tmp_ctx);
                                return ret;
                        }

                        el2->values[j] = data_blob_string_const(
                                dsdb_dn_get_extended_linearized(el2->values, dsdb_dn2, 1));
                }

                ret = dsdb_check_single_valued_link(target, el2);
                if (ret != LDB_SUCCESS) {
                        talloc_free(tmp_ctx);
                        return ret;
                }

                /* we may be putting multiple values in an attribute -
                   disable checking for this attribute */
                el2->flags |= LDB_FLAG_INTERNAL_DISABLE_SINGLE_VALUE_CHECK;

                ret = dsdb_module_modify(module, msg, DSDB_FLAG_NEXT_MODULE, parent);
                if (ret != LDB_SUCCESS) {
                        ldb_asprintf_errstring(ldb, "Linked attribute %s->%s between %s and %s - update failed - %s",
                                               el->name, target->lDAPDisplayName,
                                               ldb_dn_get_linearized(old_dn),
                                               ldb_dn_get_linearized(dsdb_dn->dn),
                                               ldb_errstring(ldb));
                        talloc_free(tmp_ctx);
                        return ret;
                }
        }

        talloc_free(tmp_ctx);
        return LDB_SUCCESS;
}


/* rename */
static int linked_attributes_rename(struct ldb_module *module, struct ldb_request *req)
{
        struct ldb_result *res;
        struct ldb_message *msg;
        unsigned int i;
        struct ldb_context *ldb = ldb_module_get_ctx(module);
        struct dsdb_schema *schema;
        int ret;
        /*
           - load the current msg
           - find any linked attributes
           - if its a link then find the target object
           - modify the target linked attributes with the new DN
        */
        ret = dsdb_module_search_dn(module, req, &res, req->op.rename.olddn,
                                    NULL,
                                    DSDB_FLAG_NEXT_MODULE |
                                    DSDB_SEARCH_SHOW_RECYCLED, req);
        if (ret != LDB_SUCCESS) {
                return ret;
        }

        schema = dsdb_get_schema(ldb, res);
        if (!schema) {
                return ldb_oom(ldb);
        }

        msg = res->msgs[0];

        for (i=0; i<msg->num_elements; i++) {
                struct ldb_message_element *el = &msg->elements[i];
                const struct dsdb_attribute *schema_attr
                        = dsdb_attribute_by_lDAPDisplayName(schema, el->name);
                if (!schema_attr || schema_attr->linkID == 0) {
                        continue;
                }
                ret = linked_attributes_fix_links(module, msg->dn, req->op.rename.newdn, el,
                                                  schema, schema_attr, req);
                if (ret != LDB_SUCCESS) {
                        talloc_free(res);
                        return ret;
                }
        }

        talloc_free(res);

        return ldb_next_request(module, req);
}


/* 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_operr(ldb_module_get_ctx(ac->module));
        }

        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)
{
        struct la_context *ac;
        struct ldb_context *ldb;
        int ret;

        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)
{
        struct la_context *ac;
        struct ldb_context *ldb;
        int ret;

        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);
                LDB_REQ_SET_LOCATION(search_req);

                if (ret == LDB_SUCCESS) {
                        ret = dsdb_request_add_controls(search_req,
                                                        DSDB_SEARCH_SHOW_DELETED |
                                                        DSDB_SEARCH_SHOW_EXTENDED_DN);
                }
                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;
        struct ldb_context *ldb;
        int ret;

        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);
                LDB_REQ_SET_LOCATION(down_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);
                LDB_REQ_SET_LOCATION(down_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_module_dn_by_guid(ac->module, ac, guid, dn, ac->req);
}

/* 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_message *new_msg;
        struct ldb_context *ldb;
        int ret;

        if (ac->mod_dn == NULL) {
                /* we didn't find the DN that we searched for */
                return LDB_SUCCESS;
        }

        ldb = ldb_module_get_ctx(ac->module);

        /* Create the modify request */
        new_msg = ldb_msg_new(ac);
        if (!new_msg) {
                return ldb_oom(ldb);
        }

        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) {
                return ldb_oom(ldb);
        }
        ret_el->num_values = 1;
        ret_el->values[0] = data_blob_string_const(ldb_dn_get_extended_linearized(new_msg, ac->mod_dn, 1));

        /* a backlink should never be single valued. Unfortunately the
           exchange schema has a attribute
           msExchBridgeheadedLocalConnectorsDNBL which is single
           valued and a backlink. We need to cope with that by
           ignoring the single value flag */
        ret_el->flags |= LDB_FLAG_INTERNAL_DISABLE_SINGLE_VALUE_CHECK;

#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

        if (DEBUGLVL(4)) {
                DEBUG(4,("Applying linked attribute change:\n%s\n",
                         ldb_ldif_message_string(ldb, op, LDB_CHANGETYPE_MODIFY, new_msg)));
        }

        ret = dsdb_module_modify(module, new_msg, DSDB_FLAG_NEXT_MODULE, ac->req);
        if (ret != LDB_SUCCESS) {
                ldb_debug(ldb, LDB_DEBUG_WARNING, __location__ ": failed to apply linked attribute change '%s'\n%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_oom(ldb_module_get_ctx(module));
        }
        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 */

        /* Start at the end of the list - so we can start
         * there, but ensure we don't create a loop by NULLing
         * it out in the first element */
        ac = DLIST_TAIL(la_private->la_list);

        for (; ac; ac=DLIST_PREV(ac)) {
                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);
}

static int linked_attributes_ldb_init(struct ldb_module *module)
{
        int ret;

        ret = ldb_mod_register_control(module, LDB_CONTROL_VERIFY_NAME_OID);
        if (ret != LDB_SUCCESS) {
                ldb_debug(ldb_module_get_ctx(module), LDB_DEBUG_ERROR,
                        "verify_name: Unable to register control with rootdse!\n");
                return ldb_operr(ldb_module_get_ctx(module));
        }

        return ldb_next_init(module);
}


static const struct ldb_module_ops ldb_linked_attributes_module_ops = {
        .name              = "linked_attributes",
        .add               = linked_attributes_add,
        .modify            = linked_attributes_modify,
        .rename            = linked_attributes_rename,
        .init_context      = linked_attributes_ldb_init,
        .start_transaction = linked_attributes_start_transaction,
        .prepare_commit    = linked_attributes_prepare_commit,
        .del_transaction   = linked_attributes_del_transaction,
};

int ldb_linked_attributes_module_init(const char *version)
{
        LDB_MODULE_CHECK_VERSION(version);
        return ldb_register_module(&ldb_linked_attributes_module_ops);
}