s4-ldbmodules: Added new module aclread to handle access checks on LDAP search

It is currently enabled only if the request comes from the LDAP server, and is
disabled  by default. Use acl:search=true in smb.conf to enable it.
It filters out all objects the user is not allowed to see, and all attributes
the user does not have RP on. Extended access not supported yet.

4 files changed, 327 insertions, 0 deletions

diff --git a/source4/dsdb/samdb/ldb_modules/acl_read.c b/source4/dsdb/samdb/ldb_modules/acl_read.c
new file mode 100644
index 0000000000..49d9095d1c
--- /dev/null
+++ b/source4/dsdb/samdb/ldb_modules/acl_read.c
@@ -0,0 +1,307 @@
+/*
+  ldb database library
+
+  Copyright (C) Simo Sorce 2006-2008
+  Copyright (C) Nadezhda Ivanova 2010
+
+  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 ACL Read module
+ *
+ *  Description: Module that performs authorisation access checks on read requests
+ *               Only DACL checks implemented at this point
+ *
+ *  Author: Nadezhda Ivanova
+ */
+
+#include "includes.h"
+#include "ldb_module.h"
+#include "auth/auth.h"
+#include "libcli/security/security.h"
+#include "dsdb/samdb/samdb.h"
+#include "librpc/gen_ndr/ndr_security.h"
+#include "param/param.h"
+#include "dsdb/samdb/ldb_modules/util.h"
+
+
+struct aclread_context {
+	struct ldb_module *module;
+	struct ldb_request *req;
+	const char * const *attrs;
+	const struct dsdb_schema *schema;
+};
+
+struct aclread_private {
+	bool enabled;
+};
+
+static int aclread_callback(struct ldb_request *req, struct ldb_reply *ares)
+{
+	 struct ldb_context *ldb;
+	 struct aclread_context *ac;
+	 struct ldb_result *acl_res;
+	 struct ldb_message_element *parent;
+	 static const char *acl_attrs[] = {
+		 "nTSecurityDescriptor",
+		 "objectSid",
+		 "parentGUID",
+		 NULL
+	 };
+	 int i, ret;
+	 struct security_descriptor *sd;
+	 struct dom_sid *sid = NULL;
+	 TALLOC_CTX *tmp_ctx;
+	 ac = talloc_get_type(req->context, struct aclread_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);
+	 }
+	 tmp_ctx = talloc_new(ac);
+	 switch (ares->type) {
+	 case LDB_REPLY_ENTRY:
+		 ret = dsdb_module_search_dn(ac->module, tmp_ctx, &acl_res, ares->message->dn,
+					     acl_attrs,
+					     DSDB_FLAG_NEXT_MODULE |
+					     DSDB_SEARCH_SHOW_DELETED);
+		 if (ret != LDB_SUCCESS) {
+			 goto fail;
+		 }
+		 ret = dsdb_get_sd_from_ldb_message(ldb, tmp_ctx, acl_res->msgs[0], &sd);
+		 if (ret != LDB_SUCCESS) {
+			 DEBUG(10, ("acl_read: cannot get descriptor\n"));
+			 ret = LDB_ERR_OPERATIONS_ERROR;
+			 goto fail;
+		 }
+		 sid = samdb_result_dom_sid(tmp_ctx, acl_res->msgs[0], "objectSid");
+		 /* get the parent guid */
+		 parent = ldb_msg_find_element(acl_res->msgs[0], "parentGUID");
+		 if (parent) {
+			 /* the object has a parent, so we have to check for visibility */
+			 struct GUID parent_guid = samdb_result_guid(acl_res->msgs[0], "parentGUID");
+			 ret = dsdb_module_check_access_on_guid(ac->module,
+								tmp_ctx,
+								&parent_guid,
+								SEC_ADS_LIST,
+								NULL);
+			 if (ret == LDB_ERR_INSUFFICIENT_ACCESS_RIGHTS) {
+				 talloc_free(tmp_ctx);
+				 return LDB_SUCCESS;
+			 } else if (ret != LDB_SUCCESS) {
+				 goto fail;
+			 }
+		 }
+		 /* for every element in the message check RP */
+		 i = 0;
+		 while (i < ares->message->num_elements) {
+			 char *p, *new_attr;
+			 const struct dsdb_attribute *attr;
+			 p = strchr(ares->message->elements[i].name, ';');
+			 if (!p) {
+				 attr =  dsdb_attribute_by_lDAPDisplayName(ac->schema,
+									   ares->message->elements[i].name);
+			 } else {
+				 new_attr = talloc_strndup(tmp_ctx,
+							   ares->message->elements[i].name,
+							   (size_t)(p -ares->message->elements[i].name));
+				 if (!new_attr) {
+					 ldb_oom(ldb);
+					 ret = LDB_ERR_OPERATIONS_ERROR;
+					 goto fail;
+				 }
+				 attr =  dsdb_attribute_by_lDAPDisplayName(ac->schema,
+									   new_attr);
+				 talloc_free(new_attr);
+			 }
+
+			 if (!attr) {
+				 DEBUG(2, ("acl_read: cannot find attribute %s in schema\n",
+					   ares->message->elements[i].name));
+				 ret = LDB_ERR_OPERATIONS_ERROR;
+				 goto fail;
+			 }
+			 /* nTSecurityDescriptor is a special case */
+			 if (ldb_attr_cmp("nTSecurityDescriptor",
+					  ares->message->elements[i].name) == 0) {
+				 ret = acl_check_access_on_attribute(ac->module,
+								     tmp_ctx,
+								     sd,
+								     sid,
+								     SEC_FLAG_SYSTEM_SECURITY,
+								     attr);
+			 } else {
+				 ret = acl_check_access_on_attribute(ac->module,
+								     tmp_ctx,
+								     sd,
+								     sid,
+								     SEC_ADS_READ_PROP,
+								     attr);
+			 }
+			 if (ret == LDB_SUCCESS) {
+				 i++;
+			 } else if (ret == LDB_ERR_INSUFFICIENT_ACCESS_RIGHTS) {
+				 /* do not return this entry if attribute is
+					    part of the search filter */
+				 if (dsdb_attr_in_parse_tree(ac->req->op.search.tree,
+							     ares->message->elements[i].name)) {
+					 talloc_free(tmp_ctx);
+					 return LDB_SUCCESS;
+				 }
+				 ldb_msg_remove_attr(ares->message, ares->message->elements[i].name);
+			 } else {
+				 goto fail;
+			 }
+		 }
+		 talloc_free(tmp_ctx);
+		 return ldb_module_send_entry(ac->req, ares->message, ares->controls);
+	 case LDB_REPLY_REFERRAL:
+		 return ldb_module_send_referral(ac->req, ares->referral);
+	 case LDB_REPLY_DONE:
+		 return ldb_module_done(ac->req, ares->controls,
+					ares->response, LDB_SUCCESS);
+
+	 }
+	 return LDB_SUCCESS;
+fail:
+	 talloc_free(tmp_ctx);
+	 return ldb_module_done(ac->req, NULL, NULL, ret);
+}
+
+
+static int aclread_search(struct ldb_module *module, struct ldb_request *req)
+{
+	struct ldb_context *ldb;
+	int ret;
+	bool block_anonymous;
+	struct aclread_context *ac;
+	struct ldb_request *down_req;
+	struct ldb_control *as_system = ldb_request_get_control(req, LDB_CONTROL_AS_SYSTEM_OID);
+	struct ldb_control *apply_access = ldb_request_get_control(req, DSDB_CONTROL_SEARCH_APPLY_ACCESS);
+	struct auth_session_info *session_info;
+	struct ldb_result *res;
+	struct ldb_message_element *parent;
+	struct aclread_private *p;
+	static const char *acl_attrs[] = {
+		 "parentGUID",
+		 NULL
+	 };
+	ldb = ldb_module_get_ctx(module);
+	p = talloc_get_type(ldb_module_get_private(module), struct aclread_private);
+	if (apply_access != NULL) {
+		apply_access->critical = 0;
+	}
+	/* skip access checks if we are system or system control is supplied
+	 * or this is not LDAP server request */
+	if (!p || !p->enabled ||
+	    dsdb_module_am_system(module)
+	    || as_system || !apply_access) {
+		return ldb_next_request(module, req);
+	}
+	/* no checks on special dn */
+	if (ldb_dn_is_special(req->op.search.base)) {
+		return ldb_next_request(module, req);
+	}
+	/* allow all access to rootDSE */
+	if (req->op.search.scope == LDB_SCOPE_BASE && ldb_dn_is_null(req->op.search.base)) {
+		return ldb_next_request(module, req);
+	}
+
+	session_info = (struct auth_session_info *)ldb_get_opaque(ldb, "sessionInfo");
+	if (session_info && security_token_is_anonymous(session_info->security_token)) {
+		block_anonymous = dsdb_block_anonymous_ops(module, req);
+		if (block_anonymous) {
+			return ldb_error(ldb, LDB_ERR_OPERATIONS_ERROR,
+					 "This request is not allowed to an anonymous connection.");
+		}
+	}
+
+	/* check accessibility of base */
+	if (!ldb_dn_is_null(req->op.search.base)) {
+		ret = dsdb_module_search_dn(module, req, &res, req->op.search.base,
+					    acl_attrs,
+					    DSDB_FLAG_NEXT_MODULE |
+					    DSDB_SEARCH_SHOW_DELETED);
+		if (ret != LDB_SUCCESS) {
+			return ldb_error(ldb, ret,
+					 "acl_read: Error retrieving SD for base.");
+		}
+
+		parent = ldb_msg_find_element(res->msgs[0], "parentGUID");
+		if (parent) {
+			/* the object has a parent, so we have to check for visibility */
+			struct GUID parent_guid = samdb_result_guid(res->msgs[0], "parentGUID");
+			ret = dsdb_module_check_access_on_guid(module,
+							       req,
+							       &parent_guid,
+							       SEC_ADS_LIST,
+							       NULL);
+			if (ret == LDB_ERR_INSUFFICIENT_ACCESS_RIGHTS) {
+				return ldb_module_done(req, NULL, NULL, LDB_ERR_NO_SUCH_OBJECT);
+			} else if (ret != LDB_SUCCESS) {
+				return ldb_module_done(req, NULL, NULL, ret);
+			}
+		}
+	}
+	ac = talloc_zero(req, struct aclread_context);
+	if (ac == NULL) {
+		return ldb_oom(ldb);
+	}
+	ac->module = module;
+	ac->req = req;
+	ac->schema = dsdb_get_schema(ldb, req);
+	if (!ac->schema) {
+		return ldb_operr(ldb);
+	}
+
+	ret = ldb_build_search_req_ex(&down_req,
+				      ldb, ac,
+				      req->op.search.base,
+				      req->op.search.scope,
+				      req->op.search.tree,
+				      req->op.search.attrs,
+				      req->controls,
+				      ac, aclread_callback,
+				      req);
+
+	if (ret != LDB_SUCCESS) {
+		return LDB_ERR_OPERATIONS_ERROR;
+	}
+
+	return ldb_next_request(module, down_req);
+}
+
+static int aclread_init(struct ldb_module *module)
+{
+	struct ldb_context *ldb = ldb_module_get_ctx(module);
+	struct aclread_private *p = talloc_zero(module, struct aclread_private);
+	if (p == NULL) {
+		return ldb_module_oom(module);
+	}
+	p->enabled = lpcfg_parm_bool(ldb_get_opaque(ldb, "loadparm"), NULL, "acl", "search", false);
+	ldb_module_set_private(module, p);
+	return ldb_next_init(module);
+}
+
+_PUBLIC_ const struct ldb_module_ops ldb_aclread_module_ops = {
+	.name		   = "aclread",
+	.search            = aclread_search,
+	.init_context      = aclread_init
+};
diff --git a/source4/dsdb/samdb/ldb_modules/config.mk b/source4/dsdb/samdb/ldb_modules/config.mk
index 93ce5645b7..442481fc6b 100644
--- a/source4/dsdb/samdb/ldb_modules/config.mk
+++ b/source4/dsdb/samdb/ldb_modules/config.mk
@@ -452,3 +452,14 @@ INIT_FUNCTION = LDB_MODULE(validate_update)
 ################################################
 
 ldb_validate_update_OBJ_FILES = $(dsdbsrcdir)/samdb/ldb_modules/validate_update.o
+
+################################################
+# Start MODULE ldb_aclread
+[MODULE::ldb_aclread]
+PRIVATE_DEPENDENCIES = LIBTALLOC LIBEVENTS LIBSECURITY SAMDB
+SUBSYSTEM = LIBLDB
+INIT_FUNCTION = LDB_MODULE(aclread)
+# End MODULE ldb_acl
+################################################
+
+ldb_acl_OBJ_FILES = $(dsdbsrcdir)/samdb/ldb_modules/acl_read.o
diff --git a/source4/dsdb/samdb/ldb_modules/samba_dsdb.c b/source4/dsdb/samdb/ldb_modules/samba_dsdb.c
index 1c5abbe23e..4d0f9465b0 100644
--- a/source4/dsdb/samdb/ldb_modules/samba_dsdb.c
+++ b/source4/dsdb/samdb/ldb_modules/samba_dsdb.c
@@ -164,6 +164,7 @@ static int samba_dsdb_init(struct ldb_module *module)
 	*/
 	static const char *modules_list[] = {"resolve_oids",
 					     "rootdse",
+					     "aclread",
 					     "lazy_commit",
 					     "paged_results",
 					     "ranged_results",
diff --git a/source4/dsdb/samdb/ldb_modules/wscript_build b/source4/dsdb/samdb/ldb_modules/wscript_build
index f6b5c28456..e455ae9249 100644
--- a/source4/dsdb/samdb/ldb_modules/wscript_build
+++ b/source4/dsdb/samdb/ldb_modules/wscript_build
@@ -331,3 +331,11 @@ bld.SAMBA_MODULE('ldb_lazy_commit',
 	init_function='LDB_MODULE(lazy_commit)',
 	deps='SAMDB'
 	)
+
+bld.SAMBA_MODULE('ldb_aclread',
+        source='acl_read.c',
+        subsystem='ldb',
+        init_function='LDB_MODULE(aclread)',
+        internal_module=not bld.CONFIG_SET('USING_SYSTEM_LDB'),
+        deps='talloc LIBEVENTS LIBSECURITY SAMDB'
+        )