/* -------------------------------------------------------------------------
 *
 * contrib/sepgsql/label.c
 *
 * Routines to support SELinux labels (security context)
 *
 * Copyright (c) 2010-2019, PostgreSQL Global Development Group
 *
 * -------------------------------------------------------------------------
 */
#include "postgres.h"

#include <selinux/label.h>

#include "access/genam.h"
#include "access/htup_details.h"
#include "access/table.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/pg_attribute.h"
#include "catalog/pg_class.h"
#include "catalog/pg_database.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_proc.h"
#include "commands/dbcommands.h"
#include "commands/seclabel.h"
#include "libpq/auth.h"
#include "libpq/libpq-be.h"
#include "miscadmin.h"
#include "sepgsql.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/rel.h"

/*
 * Saved hook entries (if stacked)
 */
static ClientAuthentication_hook_type next_client_auth_hook = NULL;
static needs_fmgr_hook_type next_needs_fmgr_hook = NULL;
static fmgr_hook_type next_fmgr_hook = NULL;

/*
 * client_label_*
 *
 * security label of the database client.  Initially the client security label
 * is equal to client_label_peer, and can be changed by one or more calls to
 * sepgsql_setcon(), and also be temporarily overridden during execution of a
 * trusted-procedure.
 *
 * sepgsql_setcon() is a transaction-aware operation; a (sub-)transaction
 * rollback should also rollback the current client security label.  Therefore
 * we use the list client_label_pending of pending_label to keep track of which
 * labels were set during the (sub-)transactions.
 */
static char *client_label_peer = NULL;	/* set by getpeercon(3) */
static List *client_label_pending = NIL;	/* pending list being set by
											 * sepgsql_setcon() */
static char *client_label_committed = NULL; /* set by sepgsql_setcon(), and
											 * already committed */
static char *client_label_func = NULL;	/* set by trusted procedure */

typedef struct
{
	SubTransactionId subid;
	char	   *label;
}			pending_label;

/*
 * sepgsql_get_client_label
 *
 * Returns the current security label of the client.  All code should use this
 * routine to get the current label, instead of referring to the client_label_*
 * variables above.
 */
char *
sepgsql_get_client_label(void)
{
	/* trusted procedure client label override */
	if (client_label_func)
		return client_label_func;

	/* uncommitted sepgsql_setcon() value */
	if (client_label_pending)
	{
		pending_label *plabel = llast(client_label_pending);

		if (plabel->label)
			return plabel->label;
	}
	else if (client_label_committed)
		return client_label_committed;	/* set by sepgsql_setcon() committed */

	/* default label */
	Assert(client_label_peer != NULL);
	return client_label_peer;
}

/*
 * sepgsql_set_client_label
 *
 * This routine tries to switch the current security label of the client, and
 * checks related permissions.  The supplied new label shall be added to the
 * client_label_pending list, then saved at transaction-commit time to ensure
 * transaction-awareness.
 */
static void
sepgsql_set_client_label(const char *new_label)
{
	const char *tcontext;
	MemoryContext oldcxt;
	pending_label *plabel;

	/* Reset to the initial client label, if NULL */
	if (!new_label)
		tcontext = client_label_peer;
	else
	{
		if (security_check_context_raw((security_context_t) new_label) < 0)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_NAME),
					 errmsg("SELinux: invalid security label: \"%s\"",
							new_label)));
		tcontext = new_label;
	}

	/* Check process:{setcurrent} permission. */
	sepgsql_avc_check_perms_label(sepgsql_get_client_label(),
								  SEPG_CLASS_PROCESS,
								  SEPG_PROCESS__SETCURRENT,
								  NULL,
								  true);
	/* Check process:{dyntransition} permission. */
	sepgsql_avc_check_perms_label(tcontext,
								  SEPG_CLASS_PROCESS,
								  SEPG_PROCESS__DYNTRANSITION,
								  NULL,
								  true);

	/*
	 * Append the supplied new_label on the pending list until the current
	 * transaction is committed.
	 */
	oldcxt = MemoryContextSwitchTo(CurTransactionContext);

	plabel = palloc0(sizeof(pending_label));
	plabel->subid = GetCurrentSubTransactionId();
	if (new_label)
		plabel->label = pstrdup(new_label);
	client_label_pending = lappend(client_label_pending, plabel);

	MemoryContextSwitchTo(oldcxt);
}

/*
 * sepgsql_xact_callback
 *
 * A callback routine of transaction commit/abort/prepare.  Commit or abort
 * changes in the client_label_pending list.
 */
static void
sepgsql_xact_callback(XactEvent event, void *arg)
{
	if (event == XACT_EVENT_COMMIT)
	{
		if (client_label_pending != NIL)
		{
			pending_label *plabel = llast(client_label_pending);
			char	   *new_label;

			if (plabel->label)
				new_label = MemoryContextStrdup(TopMemoryContext,
												plabel->label);
			else
				new_label = NULL;

			if (client_label_committed)
				pfree(client_label_committed);

			client_label_committed = new_label;

			/*
			 * XXX - Note that items of client_label_pending are allocated on
			 * CurTransactionContext, thus, all acquired memory region shall
			 * be released implicitly.
			 */
			client_label_pending = NIL;
		}
	}
	else if (event == XACT_EVENT_ABORT)
		client_label_pending = NIL;
}

/*
 * sepgsql_subxact_callback
 *
 * A callback routine of sub-transaction start/abort/commit.  Releases all
 * security labels that are set within the sub-transaction that is aborted.
 */
static void
sepgsql_subxact_callback(SubXactEvent event, SubTransactionId mySubid,
						 SubTransactionId parentSubid, void *arg)
{
	ListCell   *cell;

	if (event == SUBXACT_EVENT_ABORT_SUB)
	{
		foreach(cell, client_label_pending)
		{
			pending_label *plabel = lfirst(cell);

			if (plabel->subid == mySubid)
				client_label_pending
					= foreach_delete_current(client_label_pending, cell);
		}
	}
}

/*
 * sepgsql_client_auth
 *
 * Entrypoint of the client authentication hook.
 * It switches the client label according to getpeercon(), and the current
 * performing mode according to the GUC setting.
 */
static void
sepgsql_client_auth(Port *port, int status)
{
	if (next_client_auth_hook)
		(*next_client_auth_hook) (port, status);

	/*
	 * In the case when authentication failed, the supplied socket shall be
	 * closed soon, so we don't need to do anything here.
	 */
	if (status != STATUS_OK)
		return;

	/*
	 * Getting security label of the peer process using API of libselinux.
	 */
	if (getpeercon_raw(port->sock, &client_label_peer) < 0)
		ereport(FATAL,
				(errcode(ERRCODE_INTERNAL_ERROR),
				 errmsg("SELinux: unable to get peer label: %m")));

	/*
	 * Switch the current performing mode from INTERNAL to either DEFAULT or
	 * PERMISSIVE.
	 */
	if (sepgsql_get_permissive())
		sepgsql_set_mode(SEPGSQL_MODE_PERMISSIVE);
	else
		sepgsql_set_mode(SEPGSQL_MODE_DEFAULT);
}

/*
 * sepgsql_needs_fmgr_hook
 *
 * It informs the core whether the supplied function is trusted procedure,
 * or not. If true, sepgsql_fmgr_hook shall be invoked at start, end, and
 * abort time of function invocation.
 */
static bool
sepgsql_needs_fmgr_hook(Oid functionId)
{
	ObjectAddress object;

	if (next_needs_fmgr_hook &&
		(*next_needs_fmgr_hook) (functionId))
		return true;

	/*
	 * SELinux needs the function to be called via security_definer wrapper,
	 * if this invocation will take a domain-transition. We call these
	 * functions as trusted-procedure, if the security policy has a rule that
	 * switches security label of the client on execution.
	 */
	if (sepgsql_avc_trusted_proc(functionId) != NULL)
		return true;

	/*
	 * Even if not a trusted-procedure, this function should not be inlined
	 * unless the client has db_procedure:{execute} permission. Please note
	 * that it shall be actually failed later because of same reason with
	 * ACL_EXECUTE.
	 */
	object.classId = ProcedureRelationId;
	object.objectId = functionId;
	object.objectSubId = 0;
	if (!sepgsql_avc_check_perms(&object,
								 SEPG_CLASS_DB_PROCEDURE,
								 SEPG_DB_PROCEDURE__EXECUTE |
								 SEPG_DB_PROCEDURE__ENTRYPOINT,
								 SEPGSQL_AVC_NOAUDIT, false))
		return true;

	return false;
}

/*
 * sepgsql_fmgr_hook
 *
 * It switches security label of the client on execution of trusted
 * procedures.
 */
static void
sepgsql_fmgr_hook(FmgrHookEventType event,
				  FmgrInfo *flinfo, Datum *private)
{
	struct
	{
		char	   *old_label;
		char	   *new_label;
		Datum		next_private;
	}		   *stack;

	switch (event)
	{
		case FHET_START:
			stack = (void *) DatumGetPointer(*private);
			if (!stack)
			{
				MemoryContext oldcxt;

				oldcxt = MemoryContextSwitchTo(flinfo->fn_mcxt);
				stack = palloc(sizeof(*stack));
				stack->old_label = NULL;
				stack->new_label = sepgsql_avc_trusted_proc(flinfo->fn_oid);
				stack->next_private = 0;

				MemoryContextSwitchTo(oldcxt);

				/*
				 * process:transition permission between old and new label,
				 * when user tries to switch security label of the client on
				 * execution of trusted procedure.
				 *
				 * Also, db_procedure:entrypoint permission should be checked
				 * whether this procedure can perform as an entrypoint of the
				 * trusted procedure, or not. Note that db_procedure:execute
				 * permission shall be checked individually.
				 */
				if (stack->new_label)
				{
					ObjectAddress object;

					object.classId = ProcedureRelationId;
					object.objectId = flinfo->fn_oid;
					object.objectSubId = 0;
					sepgsql_avc_check_perms(&object,
											SEPG_CLASS_DB_PROCEDURE,
											SEPG_DB_PROCEDURE__ENTRYPOINT,
											getObjectDescription(&object),
											true);

					sepgsql_avc_check_perms_label(stack->new_label,
												  SEPG_CLASS_PROCESS,
												  SEPG_PROCESS__TRANSITION,
												  NULL, true);
				}
				*private = PointerGetDatum(stack);
			}
			Assert(!stack->old_label);
			if (stack->new_label)
			{
				stack->old_label = client_label_func;
				client_label_func = stack->new_label;
			}
			if (next_fmgr_hook)
				(*next_fmgr_hook) (event, flinfo, &stack->next_private);
			break;

		case FHET_END:
		case FHET_ABORT:
			stack = (void *) DatumGetPointer(*private);

			if (next_fmgr_hook)
				(*next_fmgr_hook) (event, flinfo, &stack->next_private);

			if (stack->new_label)
			{
				client_label_func = stack->old_label;
				stack->old_label = NULL;
			}
			break;

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

/*
 * sepgsql_init_client_label
 *
 * Initializes the client security label and sets up related hooks for client
 * label management.
 */
void
sepgsql_init_client_label(void)
{
	/*
	 * Set up dummy client label.
	 *
	 * XXX - note that PostgreSQL launches background worker process like
	 * autovacuum without authentication steps. So, we initialize sepgsql_mode
	 * with SEPGSQL_MODE_INTERNAL, and client_label with the security context
	 * of server process. Later, it also launches background of user session.
	 * In this case, the process is always hooked on post-authentication, and
	 * we can initialize the sepgsql_mode and client_label correctly.
	 */
	if (getcon_raw(&client_label_peer) < 0)
		ereport(ERROR,
				(errcode(ERRCODE_INTERNAL_ERROR),
				 errmsg("SELinux: failed to get server security label: %m")));

	/* Client authentication hook */
	next_client_auth_hook = ClientAuthentication_hook;
	ClientAuthentication_hook = sepgsql_client_auth;

	/* Trusted procedure hooks */
	next_needs_fmgr_hook = needs_fmgr_hook;
	needs_fmgr_hook = sepgsql_needs_fmgr_hook;

	next_fmgr_hook = fmgr_hook;
	fmgr_hook = sepgsql_fmgr_hook;

	/* Transaction/Sub-transaction callbacks */
	RegisterXactCallback(sepgsql_xact_callback, NULL);
	RegisterSubXactCallback(sepgsql_subxact_callback, NULL);
}

/*
 * sepgsql_get_label
 *
 * It returns a security context of the specified database object.
 * If unlabeled or incorrectly labeled, the system "unlabeled" label
 * shall be returned.
 */
char *
sepgsql_get_label(Oid classId, Oid objectId, int32 subId)
{
	ObjectAddress object;
	char	   *label;

	object.classId = classId;
	object.objectId = objectId;
	object.objectSubId = subId;

	label = GetSecurityLabel(&object, SEPGSQL_LABEL_TAG);
	if (!label || security_check_context_raw((security_context_t) label))
	{
		security_context_t unlabeled;

		if (security_get_initial_context_raw("unlabeled", &unlabeled) < 0)
			ereport(ERROR,
					(errcode(ERRCODE_INTERNAL_ERROR),
					 errmsg("SELinux: failed to get initial security label: %m")));
		PG_TRY();
		{
			label = pstrdup(unlabeled);
		}
		PG_FINALLY();
		{
			freecon(unlabeled);
		}
		PG_END_TRY();
	}
	return label;
}

/*
 * sepgsql_object_relabel
 *
 * An entrypoint of SECURITY LABEL statement
 */
void
sepgsql_object_relabel(const ObjectAddress *object, const char *seclabel)
{
	/*
	 * validate format of the supplied security label, if it is security
	 * context of selinux.
	 */
	if (seclabel &&
		security_check_context_raw((security_context_t) seclabel) < 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_NAME),
				 errmsg("SELinux: invalid security label: \"%s\"", seclabel)));

	/*
	 * Do actual permission checks for each object classes
	 */
	switch (object->classId)
	{
		case DatabaseRelationId:
			sepgsql_database_relabel(object->objectId, seclabel);
			break;

		case NamespaceRelationId:
			sepgsql_schema_relabel(object->objectId, seclabel);
			break;

		case RelationRelationId:
			if (object->objectSubId == 0)
				sepgsql_relation_relabel(object->objectId,
										 seclabel);
			else
				sepgsql_attribute_relabel(object->objectId,
										  object->objectSubId,
										  seclabel);
			break;

		case ProcedureRelationId:
			sepgsql_proc_relabel(object->objectId, seclabel);
			break;

		default:
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("sepgsql provider does not support labels on %s",
							getObjectTypeDescription(object))));
			break;
	}
}

/*
 * TEXT sepgsql_getcon(VOID)
 *
 * It returns the security label of the client.
 */
PG_FUNCTION_INFO_V1(sepgsql_getcon);
Datum
sepgsql_getcon(PG_FUNCTION_ARGS)
{
	char	   *client_label;

	if (!sepgsql_is_enabled())
		PG_RETURN_NULL();

	client_label = sepgsql_get_client_label();

	PG_RETURN_TEXT_P(cstring_to_text(client_label));
}

/*
 * BOOL sepgsql_setcon(TEXT)
 *
 * It switches the security label of the client.
 */
PG_FUNCTION_INFO_V1(sepgsql_setcon);
Datum
sepgsql_setcon(PG_FUNCTION_ARGS)
{
	const char *new_label;

	if (PG_ARGISNULL(0))
		new_label = NULL;
	else
		new_label = TextDatumGetCString(PG_GETARG_DATUM(0));

	sepgsql_set_client_label(new_label);

	PG_RETURN_BOOL(true);
}

/*
 * TEXT sepgsql_mcstrans_in(TEXT)
 *
 * It translate the given qualified MLS/MCS range into raw format
 * when mcstrans daemon is working.
 */
PG_FUNCTION_INFO_V1(sepgsql_mcstrans_in);
Datum
sepgsql_mcstrans_in(PG_FUNCTION_ARGS)
{
	text	   *label = PG_GETARG_TEXT_PP(0);
	char	   *raw_label;
	char	   *result;

	if (!sepgsql_is_enabled())
		ereport(ERROR,
				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
				 errmsg("sepgsql is not enabled")));

	if (selinux_trans_to_raw_context(text_to_cstring(label),
									 &raw_label) < 0)
		ereport(ERROR,
				(errcode(ERRCODE_INTERNAL_ERROR),
				 errmsg("SELinux: could not translate security label: %m")));

	PG_TRY();
	{
		result = pstrdup(raw_label);
	}
	PG_FINALLY();
	{
		freecon(raw_label);
	}
	PG_END_TRY();

	PG_RETURN_TEXT_P(cstring_to_text(result));
}

/*
 * TEXT sepgsql_mcstrans_out(TEXT)
 *
 * It translate the given raw MLS/MCS range into qualified format
 * when mcstrans daemon is working.
 */
PG_FUNCTION_INFO_V1(sepgsql_mcstrans_out);
Datum
sepgsql_mcstrans_out(PG_FUNCTION_ARGS)
{
	text	   *label = PG_GETARG_TEXT_PP(0);
	char	   *qual_label;
	char	   *result;

	if (!sepgsql_is_enabled())
		ereport(ERROR,
				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
				 errmsg("sepgsql is not currently enabled")));

	if (selinux_raw_to_trans_context(text_to_cstring(label),
									 &qual_label) < 0)
		ereport(ERROR,
				(errcode(ERRCODE_INTERNAL_ERROR),
				 errmsg("SELinux: could not translate security label: %m")));

	PG_TRY();
	{
		result = pstrdup(qual_label);
	}
	PG_FINALLY();
	{
		freecon(qual_label);
	}
	PG_END_TRY();

	PG_RETURN_TEXT_P(cstring_to_text(result));
}

/*
 * quote_object_name
 *
 * It tries to quote the supplied identifiers
 */
static char *
quote_object_name(const char *src1, const char *src2,
				  const char *src3, const char *src4)
{
	StringInfoData result;
	const char *temp;

	initStringInfo(&result);

	if (src1)
	{
		temp = quote_identifier(src1);
		appendStringInfoString(&result, temp);
		if (src1 != temp)
			pfree((void *) temp);
	}
	if (src2)
	{
		temp = quote_identifier(src2);
		appendStringInfo(&result, ".%s", temp);
		if (src2 != temp)
			pfree((void *) temp);
	}
	if (src3)
	{
		temp = quote_identifier(src3);
		appendStringInfo(&result, ".%s", temp);
		if (src3 != temp)
			pfree((void *) temp);
	}
	if (src4)
	{
		temp = quote_identifier(src4);
		appendStringInfo(&result, ".%s", temp);
		if (src4 != temp)
			pfree((void *) temp);
	}
	return result.data;
}

/*
 * exec_object_restorecon
 *
 * This routine is a helper called by sepgsql_restorecon; it set up
 * initial security labels of database objects within the supplied
 * catalog OID.
 */
static void
exec_object_restorecon(struct selabel_handle *sehnd, Oid catalogId)
{
	Relation	rel;
	SysScanDesc sscan;
	HeapTuple	tuple;
	char	   *database_name = get_database_name(MyDatabaseId);
	char	   *namespace_name;
	Oid			namespace_id;
	char	   *relation_name;

	/*
	 * Open the target catalog. We don't want to allow writable accesses by
	 * other session during initial labeling.
	 */
	rel = table_open(catalogId, AccessShareLock);

	sscan = systable_beginscan(rel, InvalidOid, false,
							   NULL, 0, NULL);
	while (HeapTupleIsValid(tuple = systable_getnext(sscan)))
	{
		Form_pg_database datForm;
		Form_pg_namespace nspForm;
		Form_pg_class relForm;
		Form_pg_attribute attForm;
		Form_pg_proc proForm;
		char	   *objname;
		int			objtype = 1234;
		ObjectAddress object;
		security_context_t context;

		/*
		 * The way to determine object name depends on object classes. So, any
		 * branches set up `objtype', `objname' and `object' here.
		 */
		switch (catalogId)
		{
			case DatabaseRelationId:
				datForm = (Form_pg_database) GETSTRUCT(tuple);

				objtype = SELABEL_DB_DATABASE;

				objname = quote_object_name(NameStr(datForm->datname),
											NULL, NULL, NULL);

				object.classId = DatabaseRelationId;
				object.objectId = datForm->oid;
				object.objectSubId = 0;
				break;

			case NamespaceRelationId:
				nspForm = (Form_pg_namespace) GETSTRUCT(tuple);

				objtype = SELABEL_DB_SCHEMA;

				objname = quote_object_name(database_name,
											NameStr(nspForm->nspname),
											NULL, NULL);

				object.classId = NamespaceRelationId;
				object.objectId = nspForm->oid;
				object.objectSubId = 0;
				break;

			case RelationRelationId:
				relForm = (Form_pg_class) GETSTRUCT(tuple);

				if (relForm->relkind == RELKIND_RELATION ||
					relForm->relkind == RELKIND_PARTITIONED_TABLE)
					objtype = SELABEL_DB_TABLE;
				else if (relForm->relkind == RELKIND_SEQUENCE)
					objtype = SELABEL_DB_SEQUENCE;
				else if (relForm->relkind == RELKIND_VIEW)
					objtype = SELABEL_DB_VIEW;
				else
					continue;	/* no need to assign security label */

				namespace_name = get_namespace_name(relForm->relnamespace);
				objname = quote_object_name(database_name,
											namespace_name,
											NameStr(relForm->relname),
											NULL);
				pfree(namespace_name);

				object.classId = RelationRelationId;
				object.objectId = relForm->oid;
				object.objectSubId = 0;
				break;

			case AttributeRelationId:
				attForm = (Form_pg_attribute) GETSTRUCT(tuple);

				if (get_rel_relkind(attForm->attrelid) != RELKIND_RELATION &&
					get_rel_relkind(attForm->attrelid) != RELKIND_PARTITIONED_TABLE)
					continue;	/* no need to assign security label */

				objtype = SELABEL_DB_COLUMN;

				namespace_id = get_rel_namespace(attForm->attrelid);
				namespace_name = get_namespace_name(namespace_id);
				relation_name = get_rel_name(attForm->attrelid);
				objname = quote_object_name(database_name,
											namespace_name,
											relation_name,
											NameStr(attForm->attname));
				pfree(namespace_name);
				pfree(relation_name);

				object.classId = RelationRelationId;
				object.objectId = attForm->attrelid;
				object.objectSubId = attForm->attnum;
				break;

			case ProcedureRelationId:
				proForm = (Form_pg_proc) GETSTRUCT(tuple);

				objtype = SELABEL_DB_PROCEDURE;

				namespace_name = get_namespace_name(proForm->pronamespace);
				objname = quote_object_name(database_name,
											namespace_name,
											NameStr(proForm->proname),
											NULL);
				pfree(namespace_name);

				object.classId = ProcedureRelationId;
				object.objectId = proForm->oid;
				object.objectSubId = 0;
				break;

			default:
				elog(ERROR, "unexpected catalog id: %u", catalogId);
				objname = NULL; /* for compiler quiet */
				break;
		}

		if (selabel_lookup_raw(sehnd, &context, objname, objtype) == 0)
		{
			PG_TRY();
			{
				/*
				 * Check SELinux permission to relabel the fetched object,
				 * then do the actual relabeling.
				 */
				sepgsql_object_relabel(&object, context);

				SetSecurityLabel(&object, SEPGSQL_LABEL_TAG, context);
			}
			PG_FINALLY();
			{
				freecon(context);
			}
			PG_END_TRY();
		}
		else if (errno == ENOENT)
			ereport(WARNING,
					(errmsg("SELinux: no initial label assigned for %s (type=%d), skipping",
							objname, objtype)));
		else
			ereport(ERROR,
					(errcode(ERRCODE_INTERNAL_ERROR),
					 errmsg("SELinux: could not determine initial security label for %s (type=%d): %m", objname, objtype)));

		pfree(objname);
	}
	systable_endscan(sscan);

	table_close(rel, NoLock);
}

/*
 * BOOL sepgsql_restorecon(TEXT specfile)
 *
 * This function tries to assign initial security labels on all the object
 * within the current database, according to the system setting.
 * It is typically invoked by sepgsql-install script just after initdb, to
 * assign initial security labels.
 *
 * If @specfile is not NULL, it uses explicitly specified specfile, instead
 * of the system default.
 */
PG_FUNCTION_INFO_V1(sepgsql_restorecon);
Datum
sepgsql_restorecon(PG_FUNCTION_ARGS)
{
	struct selabel_handle *sehnd;
	struct selinux_opt seopts;

	/*
	 * SELinux has to be enabled on the running platform.
	 */
	if (!sepgsql_is_enabled())
		ereport(ERROR,
				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
				 errmsg("sepgsql is not currently enabled")));

	/*
	 * Check DAC permission. Only superuser can set up initial security
	 * labels, like root-user in filesystems
	 */
	if (!superuser())
		ereport(ERROR,
				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
				 errmsg("SELinux: must be superuser to restore initial contexts")));

	/*
	 * Open selabel_lookup(3) stuff. It provides a set of mapping between an
	 * initial security label and object class/name due to the system setting.
	 */
	if (PG_ARGISNULL(0))
	{
		seopts.type = SELABEL_OPT_UNUSED;
		seopts.value = NULL;
	}
	else
	{
		seopts.type = SELABEL_OPT_PATH;
		seopts.value = TextDatumGetCString(PG_GETARG_DATUM(0));
	}
	sehnd = selabel_open(SELABEL_CTX_DB, &seopts, 1);
	if (!sehnd)
		ereport(ERROR,
				(errcode(ERRCODE_INTERNAL_ERROR),
				 errmsg("SELinux: failed to initialize labeling handle: %m")));
	PG_TRY();
	{
		exec_object_restorecon(sehnd, DatabaseRelationId);
		exec_object_restorecon(sehnd, NamespaceRelationId);
		exec_object_restorecon(sehnd, RelationRelationId);
		exec_object_restorecon(sehnd, AttributeRelationId);
		exec_object_restorecon(sehnd, ProcedureRelationId);
	}
	PG_FINALLY();
	{
		selabel_close(sehnd);
	}
	PG_END_TRY();

	PG_RETURN_BOOL(true);
}
