/* -------------------------------------------------------------------------
 *
 * contrib/sepgsql/hooks.c
 *
 * Entrypoints of the hooks in PostgreSQL, and dispatches the callbacks.
 *
 * Copyright (c) 2010-2012, PostgreSQL Global Development Group
 *
 * -------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/dependency.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_class.h"
#include "catalog/pg_database.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_proc.h"
#include "commands/seclabel.h"
#include "executor/executor.h"
#include "fmgr.h"
#include "miscadmin.h"
#include "tcop/utility.h"
#include "utils/guc.h"

#include "sepgsql.h"

PG_MODULE_MAGIC;

/*
 * Declarations
 */
void		_PG_init(void);

/*
 * Saved hook entries (if stacked)
 */
static object_access_hook_type next_object_access_hook = NULL;
static ExecutorCheckPerms_hook_type next_exec_check_perms_hook = NULL;
static ProcessUtility_hook_type next_ProcessUtility_hook = NULL;
static ExecutorStart_hook_type next_ExecutorStart_hook = NULL;

/*
 * Contextual information on DDL commands
 */
typedef struct
{
	NodeTag		cmdtype;

	/*
	 * Name of the template database given by users on CREATE DATABASE
	 * command. Elsewhere (including the case of default) NULL.
	 */
	const char *createdb_dtemplate;
}	sepgsql_context_info_t;

static sepgsql_context_info_t sepgsql_context_info;

/*
 * GUC: sepgsql.permissive = (on|off)
 */
static bool sepgsql_permissive;

bool
sepgsql_get_permissive(void)
{
	return sepgsql_permissive;
}

/*
 * GUC: sepgsql.debug_audit = (on|off)
 */
static bool sepgsql_debug_audit;

bool
sepgsql_get_debug_audit(void)
{
	return sepgsql_debug_audit;
}

/*
 * sepgsql_object_access
 *
 * Entrypoint of the object_access_hook. This routine performs as
 * a dispatcher of invocation based on access type and object classes.
 */
static void
sepgsql_object_access(ObjectAccessType access,
					  Oid classId,
					  Oid objectId,
					  int subId,
					  void *arg)
{
	if (next_object_access_hook)
		(*next_object_access_hook) (access, classId, objectId, subId, arg);

	switch (access)
	{
		case OAT_POST_CREATE:
			switch (classId)
			{
				case DatabaseRelationId:
					sepgsql_database_post_create(objectId,
									sepgsql_context_info.createdb_dtemplate);
					break;

				case NamespaceRelationId:
					sepgsql_schema_post_create(objectId);
					break;

				case RelationRelationId:
					if (subId == 0)
					{
						/*
						 * All cases we want to apply permission checks on
						 * creation of a new relation are invocation of the
						 * heap_create_with_catalog via DefineRelation or
						 * OpenIntoRel. Elsewhere, we need neither assignment
						 * of security label nor permission checks.
						 */
						switch (sepgsql_context_info.cmdtype)
						{
							case T_CreateStmt:
							case T_ViewStmt:
							case T_CreateSeqStmt:
							case T_CompositeTypeStmt:
							case T_CreateForeignTableStmt:
							case T_SelectStmt:
								sepgsql_relation_post_create(objectId);
								break;
							default:
								/* via make_new_heap() */
								break;
						}
					}
					else
						sepgsql_attribute_post_create(objectId, subId);
					break;

				case ProcedureRelationId:
					sepgsql_proc_post_create(objectId);
					break;

				default:
					/* Ignore unsupported object classes */
					break;
			}
			break;

		case OAT_DROP:
			{
				ObjectAccessDrop *drop_arg = (ObjectAccessDrop *) arg;

				/*
				 * No need to apply permission checks on object deletion due
				 * to internal cleanups; such as removal of temporary database
				 * object on session closed.
				 */
				if ((drop_arg->dropflags & PERFORM_DELETION_INTERNAL) != 0)
					break;

				switch (classId)
				{
					case DatabaseRelationId:
						sepgsql_database_drop(objectId);
						break;

					case NamespaceRelationId:
						sepgsql_schema_drop(objectId);
						break;

					case RelationRelationId:
						if (subId == 0)
							sepgsql_relation_drop(objectId);
						else
							sepgsql_attribute_drop(objectId, subId);
						break;

					case ProcedureRelationId:
						sepgsql_proc_drop(objectId);
						break;

					default:
						/* Ignore unsupported object classes */
						break;
				}
			}
			break;

		default:
			elog(ERROR, "unexpected object access type: %d", (int) access);
			break;
	}
}

/*
 * sepgsql_exec_check_perms
 *
 * Entrypoint of DML permissions
 */
static bool
sepgsql_exec_check_perms(List *rangeTabls, bool abort)
{
	/*
	 * If security provider is stacking and one of them replied 'false' at
	 * least, we don't need to check any more.
	 */
	if (next_exec_check_perms_hook &&
		!(*next_exec_check_perms_hook) (rangeTabls, abort))
		return false;

	if (!sepgsql_dml_privileges(rangeTabls, abort))
		return false;

	return true;
}

/*
 * sepgsql_executor_start
 *
 * It saves contextual information during ExecutorStart to distinguish
 * a case with/without permission checks later.
 */
static void
sepgsql_executor_start(QueryDesc *queryDesc, int eflags)
{
	sepgsql_context_info_t saved_context_info = sepgsql_context_info;

	PG_TRY();
	{
		if (queryDesc->operation == CMD_SELECT)
			sepgsql_context_info.cmdtype = T_SelectStmt;
		else if (queryDesc->operation == CMD_INSERT)
			sepgsql_context_info.cmdtype = T_InsertStmt;
		else if (queryDesc->operation == CMD_DELETE)
			sepgsql_context_info.cmdtype = T_DeleteStmt;
		else if (queryDesc->operation == CMD_UPDATE)
			sepgsql_context_info.cmdtype = T_UpdateStmt;

		/*
		 * XXX - If queryDesc->operation is not above four cases, an error
		 * shall be raised on the following executor stage soon.
		 */
		if (next_ExecutorStart_hook)
			(*next_ExecutorStart_hook) (queryDesc, eflags);
		else
			standard_ExecutorStart(queryDesc, eflags);
	}
	PG_CATCH();
	{
		sepgsql_context_info = saved_context_info;
		PG_RE_THROW();
	}
	PG_END_TRY();
	sepgsql_context_info = saved_context_info;
}

/*
 * sepgsql_utility_command
 *
 * It tries to rough-grained control on utility commands; some of them can
 * break whole of the things if nefarious user would use.
 */
static void
sepgsql_utility_command(Node *parsetree,
						const char *queryString,
						ParamListInfo params,
						bool isTopLevel,
						DestReceiver *dest,
						char *completionTag)
{
	sepgsql_context_info_t saved_context_info = sepgsql_context_info;
	ListCell   *cell;

	PG_TRY();
	{
		/*
		 * Check command tag to avoid nefarious operations, and save the
		 * current contextual information to determine whether we should apply
		 * permission checks here, or not.
		 */
		sepgsql_context_info.cmdtype = nodeTag(parsetree);

		switch (nodeTag(parsetree))
		{
			case T_CreatedbStmt:

				/*
				 * We hope to reference name of the source database, but it
				 * does not appear in system catalog. So, we save it here.
				 */
				foreach(cell, ((CreatedbStmt *) parsetree)->options)
				{
					DefElem    *defel = (DefElem *) lfirst(cell);

					if (strcmp(defel->defname, "template") == 0)
					{
						sepgsql_context_info.createdb_dtemplate
							= strVal(defel->arg);
						break;
					}
				}
				break;

			case T_LoadStmt:

				/*
				 * We reject LOAD command across the board on enforcing mode,
				 * because a binary module can arbitrarily override hooks.
				 */
				if (sepgsql_getenforce())
				{
					ereport(ERROR,
							(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
							 errmsg("SELinux: LOAD is not permitted")));
				}
				break;
			default:

				/*
				 * Right now we don't check any other utility commands,
				 * because it needs more detailed information to make access
				 * control decision here, but we don't want to have two parse
				 * and analyze routines individually.
				 */
				break;
		}

		if (next_ProcessUtility_hook)
			(*next_ProcessUtility_hook) (parsetree, queryString, params,
										 isTopLevel, dest, completionTag);
		else
			standard_ProcessUtility(parsetree, queryString, params,
									isTopLevel, dest, completionTag);
	}
	PG_CATCH();
	{
		sepgsql_context_info = saved_context_info;
		PG_RE_THROW();
	}
	PG_END_TRY();
	sepgsql_context_info = saved_context_info;
}

/*
 * Module load/unload callback
 */
void
_PG_init(void)
{
	/*
	 * We allow to load the SE-PostgreSQL module on single-user-mode or
	 * shared_preload_libraries settings only.
	 */
	if (IsUnderPostmaster)
		ereport(ERROR,
				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
			 errmsg("sepgsql must be loaded via shared_preload_libraries")));

	/*
	 * Check availability of SELinux on the platform. If disabled, we cannot
	 * activate any SE-PostgreSQL features, and we have to skip rest of
	 * initialization.
	 */
	if (is_selinux_enabled() < 1)
	{
		sepgsql_set_mode(SEPGSQL_MODE_DISABLED);
		return;
	}

	/*
	 * sepgsql.permissive = (on|off)
	 *
	 * This variable controls performing mode of SE-PostgreSQL on user's
	 * session.
	 */
	DefineCustomBoolVariable("sepgsql.permissive",
							 "Turn on/off permissive mode in SE-PostgreSQL",
							 NULL,
							 &sepgsql_permissive,
							 false,
							 PGC_SIGHUP,
							 GUC_NOT_IN_SAMPLE,
							 NULL,
							 NULL,
							 NULL);

	/*
	 * sepgsql.debug_audit = (on|off)
	 *
	 * This variable allows users to turn on/off audit logs on access control
	 * decisions, independent from auditallow/auditdeny setting in the
	 * security policy. We intend to use this option for debugging purpose.
	 */
	DefineCustomBoolVariable("sepgsql.debug_audit",
							 "Turn on/off debug audit messages",
							 NULL,
							 &sepgsql_debug_audit,
							 false,
							 PGC_USERSET,
							 GUC_NOT_IN_SAMPLE,
							 NULL,
							 NULL,
							 NULL);

	/* Initialize userspace access vector cache */
	sepgsql_avc_init();

	/* Initialize security label of the client and related stuff */
	sepgsql_init_client_label();

	/* Security label provider hook */
	register_label_provider(SEPGSQL_LABEL_TAG,
							sepgsql_object_relabel);

	/* Object access hook */
	next_object_access_hook = object_access_hook;
	object_access_hook = sepgsql_object_access;

	/* DML permission check */
	next_exec_check_perms_hook = ExecutorCheckPerms_hook;
	ExecutorCheckPerms_hook = sepgsql_exec_check_perms;

	/* ProcessUtility hook */
	next_ProcessUtility_hook = ProcessUtility_hook;
	ProcessUtility_hook = sepgsql_utility_command;

	/* ExecutorStart hook */
	next_ExecutorStart_hook = ExecutorStart_hook;
	ExecutorStart_hook = sepgsql_executor_start;

	/* init contextual info */
	memset(&sepgsql_context_info, 0, sizeof(sepgsql_context_info));
}
