r12998: A big update to samldb.c

This updates the module to handle both SID allocation and nextRid
updating while importing users.  (As imported users already have a
SID, so don't go via the allocation step).  We also ensure that SIDs
in the database are unquie at create time.

Furthermore, at allocation time, we double-check the SID isn't already
in use, and that we don't create a foriegnSecurityPrincipal for a
'local' sid.

Also create random samAccountName entries for users without one (we
were setting $000000-000000000000).

We may want to seperate the uniqueness code from the rest of samldb,
and into a module with the objectguid code, which needs similar
checks.  These checks also need to apply to modification, or those
modifications denied outright.

Also update part of the testsuite to validate this.

Andrew Bartlett
(This used to be commit 7a9c8eee4bea88f5f0bb7c62f701476384b7dc84)

1 files changed, 433 insertions, 194 deletions

diff --git a/source4/dsdb/samdb/ldb_modules/samldb.c b/source4/dsdb/samdb/ldb_modules/samldb.c
index c10a96a6ad..e92def7ccd 100644
--- a/source4/dsdb/samdb/ldb_modules/samldb.c
+++ b/source4/dsdb/samdb/ldb_modules/samldb.c
@@ -2,6 +2,7 @@
    SAM ldb module
 
    Copyright (C) Simo Sorce  2004
+   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2005
 
    * NOTICE: this module is NOT released under the GNU LGPL license as
    * other ldb code. This module is release under the GNU GPL v2 or
@@ -33,55 +34,95 @@
  */
 
 #include "includes.h"
-#include "lib/ldb/include/ldb.h"
+#include "libcli/ldap/ldap.h"
 #include "lib/ldb/include/ldb_errors.h"
 #include "lib/ldb/include/ldb_private.h"
 #include "dsdb/samdb/samdb.h"
 
-#define SAM_ACCOUNT_NAME_BASE "$000000-000000000000"
+
+/* if value is not null also check for attribute to have exactly that value */
+static struct ldb_message_element *samldb_find_attribute(const struct ldb_message *msg, const char *name, const char *value)
+{
+	int j;
+	struct ldb_message_element *el = ldb_msg_find_element(msg, name);
+	if (!el) {
+		return NULL;
+	}
+
+	if (!value) {
+		return el;
+	}
+
+	for (j = 0; j < el->num_values; j++) {
+		if (strcasecmp(value, 
+			       (char *)el->values[j].data) == 0) {
+			return el;
+		}
+	}
+
+	return NULL;
+}
+
+static BOOL samldb_msg_add_string(struct ldb_module *module, struct ldb_message *msg, const char *name, const char *value)
+{
+	char *aval = talloc_strdup(msg, value);
+
+	if (aval == NULL) {
+		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_msg_add_string: talloc_strdup failed!\n");
+		return False;
+	}
+
+	if (ldb_msg_add_string(msg, name, aval) != 0) {
+		return False;
+	}
+
+	return True;
+}
+
+static BOOL samldb_msg_add_sid(struct ldb_module *module, struct ldb_message *msg, const char *name, const struct dom_sid *sid)
+{
+	struct ldb_val v;
+	NTSTATUS status;
+	status = ndr_push_struct_blob(&v, msg, sid, 
+				      (ndr_push_flags_fn_t)ndr_push_dom_sid);
+	if (!NT_STATUS_IS_OK(status)) {
+		return -1;
+	}
+	return (ldb_msg_add_value(msg, name, &v) == 0);
+}
+
+static BOOL samldb_find_or_add_attribute(struct ldb_module *module, struct ldb_message *msg, const char *name, const char *value, const char *set_value)
+{
+	if (samldb_find_attribute(msg, name, value) == NULL) {
+		return samldb_msg_add_string(module, msg, name, set_value);
+	}
+	return True;
+}
 
 /*
   allocate a new id, attempting to do it atomically
   return 0 on failure, the id on success
 */
-static int samldb_allocate_next_rid(struct ldb_context *ldb, TALLOC_CTX *mem_ctx,
-				   const struct ldb_dn *dn, uint32_t *id)
+static int samldb_set_next_rid(struct ldb_context *ldb, TALLOC_CTX *mem_ctx,
+			       const struct ldb_dn *dn, uint32_t old_id, uint32_t new_id)
 {
-	const char * const attrs[2] = { "nextRid", NULL };
-	struct ldb_result *res = NULL;
 	struct ldb_message msg;
 	int ret;
-	const char *str;
 	struct ldb_val vals[2];
 	struct ldb_message_element els[2];
 
-	ret = ldb_search(ldb, dn, LDB_SCOPE_BASE, "nextRid=*", attrs, &res);
-	if (ret != LDB_SUCCESS || res->count != 1) {
-		if (res) talloc_free(res);
-		return -1;
-	}
-	str = ldb_msg_find_string(res->msgs[0], "nextRid", NULL);
-	if (str == NULL) {
-		ldb_debug(ldb, LDB_DEBUG_FATAL, "attribute nextRid not found in %s\n", ldb_dn_linearize(res, dn));
-		talloc_free(res);
-		return -1;
-	}
-
-	*id = strtol(str, NULL, 0);
-	if ((*id)+1 == 0) {
+	if (new_id == 0) {
 		/* out of IDs ! */
 		ldb_debug(ldb, LDB_DEBUG_FATAL, "Are we out of valid IDs ?\n");
-		talloc_free(res);
-		return -1;
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
-	talloc_free(res);
 
 	/* we do a delete and add as a single operation. That prevents
-	   a race */
+	   a race, in case we are not actually on a transaction db */
 	ZERO_STRUCT(msg);
 	msg.dn = ldb_dn_copy(mem_ctx, dn);
 	if (!msg.dn) {
-		return -1;
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 	msg.num_elements = 2;
 	msg.elements = els;
@@ -91,7 +132,7 @@ static int samldb_allocate_next_rid(struct ldb_context *ldb, TALLOC_CTX *mem_ctx
 	els[0].flags = LDB_FLAG_MOD_DELETE;
 	els[0].name = talloc_strdup(mem_ctx, "nextRid");
 	if (!els[0].name) {
-		return -1;
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 
 	els[1].num_values = 1;
@@ -99,26 +140,103 @@ static int samldb_allocate_next_rid(struct ldb_context *ldb, TALLOC_CTX *mem_ctx
 	els[1].flags = LDB_FLAG_MOD_ADD;
 	els[1].name = els[0].name;
 
-	vals[0].data = (uint8_t *)talloc_asprintf(mem_ctx, "%u", *id);
+	vals[0].data = (uint8_t *)talloc_asprintf(mem_ctx, "%u", old_id);
 	if (!vals[0].data) {
-		return -1;
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 	vals[0].length = strlen((char *)vals[0].data);
 
-	vals[1].data = (uint8_t *)talloc_asprintf(mem_ctx, "%u", (*id)+1);
+	vals[1].data = (uint8_t *)talloc_asprintf(mem_ctx, "%u", new_id);
 	if (!vals[1].data) {
-		return -1;
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 	vals[1].length = strlen((char *)vals[1].data);
 
 	ret = ldb_modify(ldb, &msg);
-	if (ret != 0) {
-		return 1;
+	return ret;
+}
+
+/*
+  allocate a new id, attempting to do it atomically
+  return 0 on failure, the id on success
+*/
+static int samldb_find_next_rid(struct ldb_module *module, TALLOC_CTX *mem_ctx,
+				const struct ldb_dn *dn, uint32_t *old_rid)
+{
+	const char * const attrs[2] = { "nextRid", NULL };
+	struct ldb_result *res = NULL;
+	int ret;
+	const char *str;
+
+	ret = ldb_search(module->ldb, dn, LDB_SCOPE_BASE, "nextRid=*", attrs, &res);
+	if (ret != LDB_SUCCESS) {
+		return ret;
+	}
+	talloc_steal(mem_ctx, res);
+	if (res->count != 1) {
+		talloc_free(res);
+		return -1;
+	}
+
+	str = ldb_msg_find_string(res->msgs[0], "nextRid", NULL);
+	if (str == NULL) {
+		ldb_set_errstring(module, talloc_asprintf(mem_ctx, "attribute nextRid not found in %s\n", ldb_dn_linearize(res, dn)));
+		talloc_free(res);
+		return -1;
 	}
 
+	*old_rid = strtol(str, NULL, 0);
+	talloc_free(res);
 	return 0;
 }
 
+static int samldb_allocate_next_rid(struct ldb_module *module, TALLOC_CTX *mem_ctx,
+				    const struct ldb_dn *dn, const struct dom_sid *dom_sid, 
+				    struct dom_sid **new_sid)
+{
+	struct dom_sid *obj_sid;
+	uint32_t old_rid;
+	int ret;
+	struct ldb_message **sid_msgs;
+	const char *sid_attrs[] = { NULL };
+	
+	do {
+		ret = samldb_find_next_rid(module, mem_ctx, dn, &old_rid);	
+		if (ret) {
+			return ret;
+		}
+		
+		/* return the new object sid */
+		obj_sid = dom_sid_add_rid(mem_ctx, dom_sid, old_rid);
+		
+		ret = samldb_set_next_rid(module->ldb, mem_ctx, dn, old_rid, old_rid + 1);
+		if (ret != 0) {
+			return ret;
+		}
+
+		*new_sid = dom_sid_add_rid(mem_ctx, dom_sid, old_rid + 1);
+		if (!*new_sid) {
+			return LDB_ERR_OPERATIONS_ERROR;
+		}
+
+		ret = gendb_search(module->ldb,
+				   mem_ctx, NULL, &sid_msgs, sid_attrs,
+				   "objectSid=%s",
+				   ldap_encode_ndr_dom_sid(mem_ctx, *new_sid));
+		if (ret == 0) {
+			/* Great. There are no conflicting users/groups/etc */
+			return 0;
+		} else if (ret == -1) {
+			/* Bugger, there is a problem, and we don't know what it is until gendb_search improves */
+			return ret;
+		} else {
+                        /* gah, there are conflicting sids, lets move around the loop again... */
+		}
+	} while (1);
+	return ret;
+}
+
+/* Find a domain object in the parents of a particular DN.  */
 static struct ldb_dn *samldb_search_domain(struct ldb_module *module, TALLOC_CTX *mem_ctx, const struct ldb_dn *dn)
 {
 	TALLOC_CTX *local_ctx;
@@ -158,18 +276,11 @@ static struct dom_sid *samldb_get_new_sid(struct ldb_module *module,
 	const char * const attrs[2] = { "objectSid", NULL };
 	struct ldb_result *res = NULL;
 	const struct ldb_dn *dom_dn;
-	uint32_t rid;
 	int ret;
 	struct dom_sid *dom_sid, *obj_sid;
 
 	/* get the domain component part of the provided dn */
 
-	/* FIXME: quick search here, I think we should use something like
-	   ldap_parse_dn here to be 100% sure we get the right domain dn */
-
-	/* FIXME: "dc=" is probably not utf8 safe either,
-	   we need a multibyte safe substring search function here */
-	
 	dom_dn = samldb_search_domain(module, mem_ctx, obj_dn);
 	if (dom_dn == NULL) {
 		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "Invalid dn (%s) not child of a domain object!\n", ldb_dn_linearize(mem_ctx, obj_dn));
@@ -193,87 +304,148 @@ static struct dom_sid *samldb_get_new_sid(struct ldb_module *module,
 	}
 
 	/* allocate a new Rid for the domain */
-	ret = samldb_allocate_next_rid(module->ldb, mem_ctx, dom_dn, &rid);
+	ret = samldb_allocate_next_rid(module, mem_ctx, dom_dn, dom_sid, &obj_sid);
 	if (ret != 0) {
 		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "Failed to increment nextRid of %s\n", ldb_dn_linearize(mem_ctx, dom_dn));
 		talloc_free(res);
 		return NULL;
 	}
 
-	/* return the new object sid */
-	obj_sid = dom_sid_add_rid(mem_ctx, dom_sid, rid);
-
 	talloc_free(res);
 
 	return obj_sid;
 }
 
-static char *samldb_generate_samAccountName(const void *mem_ctx) {
-	char *name;
-
-	name = talloc_strdup(mem_ctx, SAM_ACCOUNT_NAME_BASE);
-	/* TODO: randomize name */	
-
-	return name;
-}
+/* If we are adding new users/groups, we need to update the nextRid
+ * attribute to be 'above' all incoming users RIDs.  This tries to
+ * avoid clashes in future */
 
-/* if value is not null also check for attribute to have exactly that value */
-static struct ldb_message_element *samldb_find_attribute(const struct ldb_message *msg, const char *name, const char *value)
+int samldb_notice_sid(struct ldb_module *module, 
+		      TALLOC_CTX *mem_ctx, const struct dom_sid *sid)
 {
-	int i, j;
+	int ret;
+	struct ldb_dn *dom_dn;
+	struct dom_sid *dom_sid;
+	const char *dom_attrs[] = { NULL };
+	struct ldb_message **dom_msgs;
+	uint32_t old_rid;
+
+	/* find the domain DN */
+
+	ret = gendb_search(module->ldb,
+			   mem_ctx, NULL, &dom_msgs, dom_attrs,
+			   "objectSid=%s",
+			   ldap_encode_ndr_dom_sid(mem_ctx, sid));
+	if (ret > 0) {
+		ldb_set_errstring(module, talloc_asprintf(mem_ctx, "Attempt to add record with SID %s rejected, because this SID is already in the database", dom_sid_string(mem_ctx, sid)));
+		/* We have a duplicate SID, we must reject the add */
+		talloc_free(dom_msgs);
+		return LDB_ERR_CONSTRAINT_VIOLATION;
+	}
+	
+	if (ret == -1) {
+		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_get_new_sid: error searching for proposed sid!\n");
+		return -1;
+	}
 
-	for (i = 0; i < msg->num_elements; i++) {
-		if (ldb_attr_cmp(name, msg->elements[i].name) == 0) {
-			if (!value) {
-				return &msg->elements[i];
-			}
-			for (j = 0; j < msg->elements[i].num_values; j++) {
-				if (strcasecmp(value, 
-					       (char *)msg->elements[i].values[j].data) == 0) {
-					return &msg->elements[i];
-				}
-			}
-		}
+	dom_sid = dom_sid_dup(mem_ctx, sid);
+	if (!dom_sid) {
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
+	/* get the domain component part of the provided SID */
+	dom_sid->num_auths--;
 
-	return NULL;
-}
+	/* find the domain DN */
 
-static BOOL samldb_msg_add_string(struct ldb_module *module, struct ldb_message *msg, const char *name, const char *value)
-{
-	char *aname = talloc_strdup(msg, name);
-	char *aval = talloc_strdup(msg, value);
+	ret = gendb_search(module->ldb,
+			   mem_ctx, NULL, &dom_msgs, dom_attrs,
+			   "(&(objectSid=%s)(objectclass=domain))",
+			   ldap_encode_ndr_dom_sid(mem_ctx, dom_sid));
+	if (ret == 0) {
+		/* This isn't an operation on a domain we know about, so nothing to update */
+		return 0;
+	}
 
-	if (aname == NULL || aval == NULL) {
-		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_msg_add_string: talloc_strdup failed!\n");
-		return False;
+	if (ret > 1) {
+		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_get_new_sid: error retrieving domain from sid: duplicate domains!\n");
+		talloc_free(dom_msgs);
+		return -1;
 	}
 
-	if (ldb_msg_add_string(msg, aname, aval) != 0) {
-		return False;
+	if (ret != 1) {
+		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_get_new_sid: error retrieving domain sid!\n");
+		return -1;
 	}
 
-	return True;
+	dom_dn = dom_msgs[0]->dn;
+
+	ret = samldb_find_next_rid(module, mem_ctx, 
+				   dom_dn, &old_rid);
+	if (ret) {
+		talloc_free(dom_msgs);
+		return ret;
+	}
+
+	if (old_rid <= sid->sub_auths[sid->num_auths - 1]) {
+		ret = samldb_set_next_rid(module->ldb, mem_ctx, dom_dn, old_rid, 
+					  sid->sub_auths[sid->num_auths - 1] + 1);
+	}
+	talloc_free(dom_msgs);
+	return ret;
 }
 
-static BOOL samldb_msg_add_sid(struct ldb_module *module, struct ldb_message *msg, const char *name, const struct dom_sid *sid)
+static int samldb_handle_sid(struct ldb_module *module, 
+					 TALLOC_CTX *mem_ctx, struct ldb_message *msg2)
 {
-	struct ldb_val v;
-	NTSTATUS status;
-	status = ndr_push_struct_blob(&v, msg, sid, 
-				      (ndr_push_flags_fn_t)ndr_push_dom_sid);
-	if (!NT_STATUS_IS_OK(status)) {
-		return -1;
+	int ret;
+	
+	struct dom_sid *sid = samdb_result_dom_sid(mem_ctx, msg2, "objectSid");
+	if (sid == NULL) { 
+		sid = samldb_get_new_sid(module, msg2, msg2->dn);
+		if (sid == NULL) {
+			ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_user_or_computer_object: internal error! Can't generate new sid\n");
+			return LDB_ERR_OPERATIONS_ERROR;
+		}
+
+		if ( ! samldb_msg_add_sid(module, msg2, "objectSid", sid)) {
+			talloc_free(sid);
+			return LDB_ERR_OPERATIONS_ERROR;
+		}
+		talloc_free(sid);
+		ret = 0;
+	} else {
+		ret = samldb_notice_sid(module, msg2, sid);
 	}
-	return (ldb_msg_add_value(msg, name, &v) == 0);
+	return ret;
 }
 
-static BOOL samldb_find_or_add_attribute(struct ldb_module *module, struct ldb_message *msg, const char *name, const char *value, const char *set_value)
+static char *samldb_generate_samAccountName(struct ldb_module *module, TALLOC_CTX *mem_ctx) 
 {
-	if (samldb_find_attribute(msg, name, value) == NULL) {
-		return samldb_msg_add_string(module, msg, name, set_value);
-	}
-	return True;
+	char *name;
+	const char *attrs[] = { NULL };
+	struct ldb_message **msgs;
+	int ret;
+	
+	/* Format: $000000-000000000000 */
+	
+	do {
+		name = talloc_asprintf(mem_ctx, "$%.6X-%.6X%.6X", (unsigned int)random(), (unsigned int)random(), (unsigned int)random());
+		/* TODO: Figure out exactly what this is meant to conflict with */
+		ret = gendb_search(module->ldb,
+				   mem_ctx, NULL, &msgs, attrs,
+				   "samAccountName=%s",
+				   ldb_binary_encode_string(mem_ctx, name));
+		if (ret == 0) {
+			/* Great. There are no conflicting users/groups/etc */
+			return name;
+		} else if (ret == -1) {
+			/* Bugger, there is a problem, and we don't know what it is until gendb_search improves */
+			return NULL;
+		} else {
+			talloc_free(name);
+                        /* gah, there are conflicting sids, lets move around the loop again... */
+		}
+	} while (1);
 }
 
 static int samldb_copy_template(struct ldb_module *module, struct ldb_message *msg, const char *filter)
@@ -335,185 +507,236 @@ static int samldb_copy_template(struct ldb_module *module, struct ldb_message *m
 	return 0;
 }
 
-static struct ldb_message *samldb_fill_group_object(struct ldb_module *module, const struct ldb_message *msg)
+static int samldb_fill_group_object(struct ldb_module *module, const struct ldb_message *msg,
+						    struct ldb_message **ret_msg)
 {
+	int ret;
+	const char *name;
 	struct ldb_message *msg2;
-	struct ldb_message_element *attribute;
 	struct ldb_dn_component *rdn;
-
-	if (samldb_find_attribute(msg, "objectclass", "group") == NULL) {
-		return NULL;
+	TALLOC_CTX *mem_ctx = talloc_new(msg);
+	if (!mem_ctx) {
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 
-	ldb_debug(module->ldb, LDB_DEBUG_TRACE, "samldb_fill_group_object\n");
-
 	/* build the new msg */
-	msg2 = ldb_msg_copy(module->ldb, msg);
+	msg2 = ldb_msg_copy(mem_ctx, msg);
 	if (!msg2) {
 		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_group_object: ldb_msg_copy failed!\n");
-		return NULL;
+		talloc_free(mem_ctx);
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 
-	if (samldb_copy_template(module, msg2, "(&(CN=TemplateGroup)(objectclass=groupTemplate))") != 0) {
+	ret = samldb_copy_template(module, msg2, "(&(CN=TemplateGroup)(objectclass=groupTemplate))");
+	if (ret != 0) {
 		ldb_debug(module->ldb, LDB_DEBUG_WARNING, "samldb_fill_group_object: Error copying template!\n");
-		return NULL;
+		talloc_free(mem_ctx);
+		return ret;
 	}
 
-	if ((rdn = ldb_dn_get_rdn(msg2, msg2->dn)) == NULL) {
-		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_group_object: Bad DN (%s)!\n", ldb_dn_linearize(msg2, msg2->dn));
-		return NULL;
-	}
+	rdn = ldb_dn_get_rdn(msg2, msg2->dn);
+
 	if (strcasecmp(rdn->name, "cn") != 0) {
 		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_group_object: Bad RDN (%s) for group!\n", rdn->name);
-		return NULL;
+		talloc_free(mem_ctx);
+		return LDB_ERR_CONSTRAINT_VIOLATION;
 	}
 
-	if ((attribute = samldb_find_attribute(msg2, "objectSid", NULL)) == NULL ) {
-		struct dom_sid *sid = samldb_get_new_sid(module, msg2, msg2->dn);
-		if (sid == NULL) {
-			ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_group_object: internal error! Can't generate new sid\n");
-			return NULL;
+	/* Generate a random name, if no samAccountName was supplied */
+	if (ldb_msg_find_element(msg2, "samAccountName") == NULL) {
+		name = samldb_generate_samAccountName(module, mem_ctx);
+		if (!name) {
+			talloc_free(mem_ctx);
+			return LDB_ERR_OPERATIONS_ERROR;
 		}
-
-		if (!samldb_msg_add_sid(module, msg2, "objectSid", sid)) {
-			talloc_free(sid);
-			return NULL;
+		if ( ! samldb_find_or_add_attribute(module, msg2, "sAMAccountName", NULL, name)) {
+			talloc_free(mem_ctx);
+			return LDB_ERR_OPERATIONS_ERROR;
 		}
-		talloc_free(sid);
 	}
+	
+	/* Manage SID allocation, conflicts etc */
+	ret = samldb_handle_sid(module, mem_ctx, msg2); 
 
-	if ( ! samldb_find_or_add_attribute(module, msg2, "sAMAccountName", NULL, samldb_generate_samAccountName(msg2))) {
-		return NULL;
+	if (ret == 0) {
+		talloc_steal(msg, msg2);
+		*ret_msg = msg2;
 	}
-
-	talloc_steal(msg, msg2);
-
-	return msg2;
+	talloc_free(mem_ctx);
+	return 0;
 }
 
-static struct ldb_message *samldb_fill_user_or_computer_object(struct ldb_module *module, const struct ldb_message *msg)
+static int samldb_fill_user_or_computer_object(struct ldb_module *module, const struct ldb_message *msg,
+							       struct ldb_message **ret_msg)
 {
+	int ret;
+	char *name;
 	struct ldb_message *msg2;
-	struct ldb_message_element *attribute;
 	struct ldb_dn_component *rdn;
-
-	if ((samldb_find_attribute(msg, "objectclass", "user") == NULL) && 
-	    (samldb_find_attribute(msg, "objectclass", "computer") == NULL)) {
-		return NULL;
+	TALLOC_CTX *mem_ctx = talloc_new(msg);
+	if (!mem_ctx) {
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 
-	ldb_debug(module->ldb, LDB_DEBUG_TRACE, "samldb_fill_user_or_computer_object\n");
-
 	/* build the new msg */
-	msg2 = ldb_msg_copy(module->ldb, msg);
+	msg2 = ldb_msg_copy(mem_ctx, msg);
 	if (!msg2) {
 		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_group_object: ldb_msg_copy failed!\n");
-		return NULL;
+		talloc_free(mem_ctx);
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 
 	if (samldb_find_attribute(msg, "objectclass", "computer") != NULL) {
-		if (samldb_copy_template(module, msg2, "(&(CN=TemplateComputer)(objectclass=userTemplate))") != 0) {
+		ret = samldb_copy_template(module, msg2, "(&(CN=TemplateComputer)(objectclass=userTemplate))");
+		if (ret) {
 			ldb_debug(module->ldb, LDB_DEBUG_WARNING, "samldb_fill_user_or_computer_object: Error copying computer template!\n");
-			return NULL;
+			talloc_free(mem_ctx);
+			return ret;
 		}
 	} else {
-		if (samldb_copy_template(module, msg2, "(&(CN=TemplateUser)(objectclass=userTemplate))") != 0) {
+		ret = samldb_copy_template(module, msg2, "(&(CN=TemplateUser)(objectclass=userTemplate))");
+		if (ret) {
 			ldb_debug(module->ldb, LDB_DEBUG_WARNING, "samldb_fill_user_or_computer_object: Error copying user template!\n");
-			return NULL;
+			talloc_free(mem_ctx);
+			return ret;
 		}
 	}
 
-	if ((rdn = ldb_dn_get_rdn(msg2, msg2->dn)) == NULL) {
-		return NULL;
-	}
+	rdn = ldb_dn_get_rdn(msg2, msg2->dn);
+
 	if (strcasecmp(rdn->name, "cn") != 0) {
-		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_user_or_computer_object: Bad RDN (%s) for user/computer!\n", rdn->name);
-		return NULL;
+		ldb_set_errstring(module, talloc_asprintf(module, "Bad RDN (%s=) for user/computer, should be CN=!\n", rdn->name));
+		talloc_free(mem_ctx);
+		return LDB_ERR_CONSTRAINT_VIOLATION;
 	}
 
 	/* if the only attribute was: "objectclass: computer", then make sure we also add "user" objectclass */
 	if ( ! samldb_find_or_add_attribute(module, msg2, "objectclass", "user", "user")) {
-		return NULL;
+		talloc_free(mem_ctx);
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 
-	if ((attribute = samldb_find_attribute(msg2, "objectSid", NULL)) == NULL ) {
-		struct dom_sid *sid;
-		sid = samldb_get_new_sid(module, msg2, msg2->dn);
-		if (sid == NULL) {
-			ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_user_or_computer_object: internal error! Can't generate new sid\n");
-			return NULL;
-		}
+	/* meddle with objectclass */
 
-		if ( ! samldb_msg_add_sid(module, msg2, "objectSid", sid)) {
-			talloc_free(sid);
-			return NULL;
+	if (ldb_msg_find_element(msg2, "samAccountName") == NULL) {
+		name = samldb_generate_samAccountName(module, mem_ctx);
+		if (!name) {
+			talloc_free(mem_ctx);
+			return LDB_ERR_OPERATIONS_ERROR;
+		}
+		if ( ! samldb_find_or_add_attribute(module, msg2, "sAMAccountName", NULL, name)) {
+			talloc_free(mem_ctx);
+			return LDB_ERR_OPERATIONS_ERROR;
 		}
-		talloc_free(sid);
-	}
-
-	if ( ! samldb_find_or_add_attribute(module, msg2, "sAMAccountName", NULL, samldb_generate_samAccountName(msg2))) {
-		return NULL;
 	}
 
 	/*
-	  useraccountcontrol: setting value 0 gives 0x200 for users
+	  TODO: useraccountcontrol: setting value 0 gives 0x200 for users
 	*/
 
+	/* Manage SID allocation, conflicts etc */
+	ret = samldb_handle_sid(module, mem_ctx, msg2); 
+
 	/* TODO: objectCategory, userAccountControl, badPwdCount, codePage, countryCode, badPasswordTime, lastLogoff, lastLogon, pwdLastSet, primaryGroupID, accountExpires, logonCount */
 
-	return msg2;
+	if (ret == 0) {
+		*ret_msg = msg2;
+		talloc_steal(msg, msg2);
+	}
+	talloc_free(mem_ctx);
+	return 0;
 }
-
-static struct ldb_message *samldb_fill_foreignSecurityPrincipal_object(struct ldb_module *module, const struct ldb_message *msg)
+	
+static int samldb_fill_foreignSecurityPrincipal_object(struct ldb_module *module, const struct ldb_message *msg, 
+								       struct ldb_message **ret_msg)
 {
 	struct ldb_message *msg2;
-	struct ldb_message_element *attribute;
 	struct ldb_dn_component *rdn;
+	struct dom_sid *dom_sid;
+	struct dom_sid *sid;
+	const char *dom_attrs[] = { "name", NULL };
+	struct ldb_message **dom_msgs;
+	int ret;
 
-	if (samldb_find_attribute(msg, "objectclass", "foreignSecurityPrincipal") == NULL) {
-		return NULL;
+	TALLOC_CTX *mem_ctx = talloc_new(msg);
+	if (!mem_ctx) {
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 
-	ldb_debug(module->ldb, LDB_DEBUG_TRACE, "samldb_fill_foreignSecurityPrincipal_object\n");
-
 	/* build the new msg */
-	msg2 = ldb_msg_copy(module->ldb, msg);
+	msg2 = ldb_msg_copy(mem_ctx, msg);
 	if (!msg2) {
 		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_foreignSecurityPrincpal_object: ldb_msg_copy failed!\n");
-		return NULL;
+		talloc_free(mem_ctx);
+		return LDB_ERR_OPERATIONS_ERROR;
 	}
 
-	talloc_steal(msg, msg2);
-
-	if (samldb_copy_template(module, msg2, "(&(CN=TemplateForeignSecurityPrincipal)(objectclass=foreignSecurityPrincipalTemplate))") != 0) {
+	ret = samldb_copy_template(module, msg2, "(&(CN=TemplateForeignSecurityPrincipal)(objectclass=foreignSecurityPrincipalTemplate))");
+	if (ret != 0) {
 		ldb_debug(module->ldb, LDB_DEBUG_WARNING, "samldb_fill_foreignSecurityPrincipal_object: Error copying template!\n");
-		return NULL;
+		talloc_free(mem_ctx);
+		return ret;
 	}
 
-	if ((rdn = ldb_dn_get_rdn(msg2, msg2->dn)) == NULL) {
-		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_foreignSecurityPrincipal_object: Bad DN (%s)!\n", ldb_dn_linearize(msg2, msg2->dn));
-		return NULL;
-	}
+	rdn = ldb_dn_get_rdn(msg2, msg2->dn);
+
 	if (strcasecmp(rdn->name, "cn") != 0) {
-		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_foreignSecurityPrincipal_object: Bad RDN (%s) for foreignSecurityPrincpal!\n", rdn->name);
-		return NULL;
+		ldb_set_errstring(module, talloc_asprintf(module, "Bad RDN (%s=) for ForeignSecurityPrincipal, should be CN=!", rdn->name));
+		talloc_free(mem_ctx);
+		return LDB_ERR_CONSTRAINT_VIOLATION;
 	}
 
-	if ((attribute = samldb_find_attribute(msg2, "objectSid", NULL)) == NULL ) {
-		struct dom_sid *sid = dom_sid_parse_talloc(msg2, (char *)rdn->value.data);
-		if (sid == NULL) {
-			ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_foreignSecurityPrincipal_object: internal error! Can't parse sid in CN\n");
-			return NULL;
-		}
+	/* Slightly different for the foreign sids.  We don't want
+	 * domain SIDs ending up there, it would cause all sorts of
+	 * pain */
 
-		if (!samldb_msg_add_sid(module, msg2, "objectSid", sid)) {
-			talloc_free(sid);
-			return NULL;
-		}
+	sid = dom_sid_parse_talloc(msg2, (const char *)rdn->value.data);
+	if (!sid) {
+		ldb_set_errstring(module, talloc_asprintf(module, "No valid found SID in ForeignSecurityPrincipal CN!"));
+		talloc_free(mem_ctx);
+		return LDB_ERR_CONSTRAINT_VIOLATION;
+	}
+
+	if ( ! samldb_msg_add_sid(module, msg2, "objectSid", sid)) {
 		talloc_free(sid);
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	dom_sid = dom_sid_dup(mem_ctx, sid);
+	if (!dom_sid) {
+		talloc_free(mem_ctx);
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+	/* get the domain component part of the provided SID */
+	dom_sid->num_auths--;
+
+	/* find the domain DN */
+
+	ret = gendb_search(module->ldb,
+			   mem_ctx, NULL, &dom_msgs, dom_attrs,
+			   "(&(objectSid=%s)(objectclass=domain))",
+			   ldap_encode_ndr_dom_sid(mem_ctx, dom_sid));
+	if (ret >= 1) {
+		const char *name = samdb_result_string(dom_msgs[0], "name", NULL);
+		ldb_set_errstring(module, talloc_asprintf(mem_ctx, "Attempt to add foreign SID record with SID %s rejected, because this domian (%s) is already in the database", dom_sid_string(mem_ctx, sid), name)); 
+		/* We have a duplicate SID, we must reject the add */
+		return LDB_ERR_CONSTRAINT_VIOLATION;
+	} else if (ret == -1) {
+		ldb_debug(module->ldb, LDB_DEBUG_FATAL, "samldb_fill_foreignSecurityPrincipal_object: error searching for a domain with this sid: %s\n", dom_sid_string(mem_ctx, dom_sid));
+		talloc_free(dom_msgs);
+		return -1;
 	}
 
-	return msg2;
+	/* This isn't an operation on a domain we know about, so just
+	 * check for the SID, looking for duplicates via the common
+	 * code */
+	ret = samldb_notice_sid(module, msg2, sid);
+	if (ret == 0) {
+		talloc_steal(msg, msg2);
+		*ret_msg = msg2;
+	}
+	
+	return ret;
 }
 
 /* add_record */
@@ -531,16 +754,32 @@ static int samldb_add(struct ldb_module *module, struct ldb_request *req)
 	}
 
 	/* is user or computer?  add all relevant missing objects */
-	msg2 = samldb_fill_user_or_computer_object(module, msg);
+	if ((samldb_find_attribute(msg, "objectclass", "user") != NULL) || 
+	    (samldb_find_attribute(msg, "objectclass", "computer") != NULL)) {
+		ret = samldb_fill_user_or_computer_object(module, msg, &msg2);
+		if (ret) {
+			return ret;
+		}
+	}
 
 	/* is group? add all relevant missing objects */
 	if ( ! msg2 ) {
-		msg2 = samldb_fill_group_object(module, msg);
+		if (samldb_find_attribute(msg, "objectclass", "group") != NULL) {
+			ret = samldb_fill_group_object(module, msg, &msg2);
+			if (ret) {
+				return ret;
+			}
+		}
 	}
 
 	/* perhaps a foreignSecurityPrincipal? */
 	if ( ! msg2 ) {
-		msg2 = samldb_fill_foreignSecurityPrincipal_object(module, msg);
+		if (samldb_find_attribute(msg, "objectclass", "foreignSecurityPrincipal") != NULL) {
+			ret = samldb_fill_foreignSecurityPrincipal_object(module, msg, &msg2);
+			if (ret) {
+				return ret;
+			}
+		}
 	}
 
 	if (msg2) {