policy.c

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/*-------------------------------------------------------------------------
 *
 * policy.c
 *    Commands for manipulating policies.
 *
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/backend/commands/policy.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup.h"
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_policy.h"
#include "catalog/pg_type.h"
#include "commands/policy.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/pg_list.h"
#include "parser/parse_clause.h"
#include "parser/parse_collate.h"
#include "parser/parse_node.h"
#include "parser/parse_relation.h"
#include "rewrite/rewriteManip.h"
#include "rewrite/rowsecurity.h"
#include "storage/lock.h"
#include "utils/acl.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/syscache.h"

static void RangeVarCallbackForPolicy(const RangeVar *rv,
                          Oid relid, Oid oldrelid, void *arg);
static char parse_policy_command(const char *cmd_name);
static Datum *policy_role_list_to_array(List *roles, int *num_roles);

/*
 * Callback to RangeVarGetRelidExtended().
 *
 * Checks the following:
 *  - the relation specified is a table.
 *  - current user owns the table.
 *  - the table is not a system table.
 *
 * If any of these checks fails then an error is raised.
 */
static void
RangeVarCallbackForPolicy(const RangeVar *rv, Oid relid, Oid oldrelid,
                          void *arg)
{
    HeapTuple   tuple;
    Form_pg_class classform;
    char        relkind;

    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        return;

    classform = (Form_pg_class) GETSTRUCT(tuple);
    relkind = classform->relkind;

    /* Must own relation. */
    if (!pg_class_ownercheck(relid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(get_rel_relkind(relid)), rv->relname);

    /* No system table modifications unless explicitly allowed. */
    if (!allowSystemTableMods && IsSystemClass(relid, classform))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        rv->relname)));

    /* Relation type MUST be a table. */
    if (relkind != RELKIND_RELATION && relkind != RELKIND_PARTITIONED_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table", rv->relname)));

    ReleaseSysCache(tuple);
}

/*
 * parse_policy_command -
 *   helper function to convert full command strings to their char
 *   representation.
 *
 * cmd_name - full string command name. Valid values are 'all', 'select',
 *            'insert', 'update' and 'delete'.
 *
 */
static char
parse_policy_command(const char *cmd_name)
{
    char        polcmd;

    if (!cmd_name)
        elog(ERROR, "unrecognized policy command");

    if (strcmp(cmd_name, "all") == 0)
        polcmd = '*';
    else if (strcmp(cmd_name, "select") == 0)
        polcmd = ACL_SELECT_CHR;
    else if (strcmp(cmd_name, "insert") == 0)
        polcmd = ACL_INSERT_CHR;
    else if (strcmp(cmd_name, "update") == 0)
        polcmd = ACL_UPDATE_CHR;
    else if (strcmp(cmd_name, "delete") == 0)
        polcmd = ACL_DELETE_CHR;
    else
        elog(ERROR, "unrecognized policy command");

    return polcmd;
}

/*
 * policy_role_list_to_array
 *   helper function to convert a list of RoleSpecs to an array of
 *   role id Datums.
 */
static Datum *
policy_role_list_to_array(List *roles, int *num_roles)
{
    Datum      *role_oids;
    ListCell   *cell;
    int         i = 0;

    /* Handle no roles being passed in as being for public */
    if (roles == NIL)
    {
        *num_roles = 1;
        role_oids = (Datum *) palloc(*num_roles * sizeof(Datum));
        role_oids[0] = ObjectIdGetDatum(ACL_ID_PUBLIC);

        return role_oids;
    }

    *num_roles = list_length(roles);
    role_oids = (Datum *) palloc(*num_roles * sizeof(Datum));

    foreach(cell, roles)
    {
        RoleSpec   *spec = lfirst(cell);

        /*
         * PUBLIC covers all roles, so it only makes sense alone.
         */
        if (spec->roletype == ROLESPEC_PUBLIC)
        {
            if (*num_roles != 1)
            {
                ereport(WARNING,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("ignoring specified roles other than PUBLIC"),
                         errhint("All roles are members of the PUBLIC role.")));
                *num_roles = 1;
            }
            role_oids[0] = ObjectIdGetDatum(ACL_ID_PUBLIC);

            return role_oids;
        }
        else
            role_oids[i++] =
                ObjectIdGetDatum(get_rolespec_oid(spec, false));
    }

    return role_oids;
}

/*
 * Load row security policy from the catalog, and store it in
 * the relation's relcache entry.
 */
void
RelationBuildRowSecurity(Relation relation)
{
    MemoryContext rscxt;
    MemoryContext oldcxt = CurrentMemoryContext;
    RowSecurityDesc *volatile rsdesc = NULL;

    /*
     * Create a memory context to hold everything associated with this
     * relation's row security policy.  This makes it easy to clean up during
     * a relcache flush.
     */
    rscxt = AllocSetContextCreate(CacheMemoryContext,
                                  "row security descriptor",
                                  ALLOCSET_SMALL_SIZES);

    /*
     * Since rscxt lives under CacheMemoryContext, it is long-lived.  Use a
     * PG_TRY block to ensure it'll get freed if we fail partway through.
     */
    PG_TRY();
    {
        Relation    catalog;
        ScanKeyData skey;
        SysScanDesc sscan;
        HeapTuple   tuple;

        MemoryContextCopyAndSetIdentifier(rscxt,
                                          RelationGetRelationName(relation));

        rsdesc = MemoryContextAllocZero(rscxt, sizeof(RowSecurityDesc));
        rsdesc->rscxt = rscxt;

        catalog = heap_open(PolicyRelationId, AccessShareLock);

        ScanKeyInit(&skey,
                    Anum_pg_policy_polrelid,
                    BTEqualStrategyNumber, F_OIDEQ,
                    ObjectIdGetDatum(RelationGetRelid(relation)));

        sscan = systable_beginscan(catalog, PolicyPolrelidPolnameIndexId, true,
                                   NULL, 1, &skey);

        /*
         * Loop through the row level security policies for this relation, if
         * any.
         */
        while (HeapTupleIsValid(tuple = systable_getnext(sscan)))
        {
            Datum       value_datum;
            char        cmd_value;
            bool        permissive_value;
            Datum       roles_datum;
            char       *qual_value;
            Expr       *qual_expr;
            char       *with_check_value;
            Expr       *with_check_qual;
            char       *policy_name_value;
            bool        isnull;
            RowSecurityPolicy *policy;

            /*
             * Note: all the pass-by-reference data we collect here is either
             * still stored in the tuple, or constructed in the caller's
             * short-lived memory context.  We must copy it into rscxt
             * explicitly below.
             */

            /* Get policy command */
            value_datum = heap_getattr(tuple, Anum_pg_policy_polcmd,
                                       RelationGetDescr(catalog), &isnull);
            Assert(!isnull);
            cmd_value = DatumGetChar(value_datum);

            /* Get policy permissive or restrictive */
            value_datum = heap_getattr(tuple, Anum_pg_policy_polpermissive,
                                       RelationGetDescr(catalog), &isnull);
            Assert(!isnull);
            permissive_value = DatumGetBool(value_datum);

            /* Get policy name */
            value_datum = heap_getattr(tuple, Anum_pg_policy_polname,
                                       RelationGetDescr(catalog), &isnull);
            Assert(!isnull);
            policy_name_value = NameStr(*(DatumGetName(value_datum)));

            /* Get policy roles */
            roles_datum = heap_getattr(tuple, Anum_pg_policy_polroles,
                                       RelationGetDescr(catalog), &isnull);
            /* shouldn't be null, but initdb doesn't mark it so, so check */
            if (isnull)
                elog(ERROR, "unexpected null value in pg_policy.polroles");

            /* Get policy qual */
            value_datum = heap_getattr(tuple, Anum_pg_policy_polqual,
                                       RelationGetDescr(catalog), &isnull);
            if (!isnull)
            {
                qual_value = TextDatumGetCString(value_datum);
                qual_expr = (Expr *) stringToNode(qual_value);
            }
            else
                qual_expr = NULL;

            /* Get WITH CHECK qual */
            value_datum = heap_getattr(tuple, Anum_pg_policy_polwithcheck,
                                       RelationGetDescr(catalog), &isnull);
            if (!isnull)
            {
                with_check_value = TextDatumGetCString(value_datum);
                with_check_qual = (Expr *) stringToNode(with_check_value);
            }
            else
                with_check_qual = NULL;

            /* Now copy everything into the cache context */
            MemoryContextSwitchTo(rscxt);

            policy = palloc0(sizeof(RowSecurityPolicy));
            policy->policy_name = pstrdup(policy_name_value);
            policy->polcmd = cmd_value;
            policy->permissive = permissive_value;
            policy->roles = DatumGetArrayTypePCopy(roles_datum);
            policy->qual = copyObject(qual_expr);
            policy->with_check_qual = copyObject(with_check_qual);
            policy->hassublinks = checkExprHasSubLink((Node *) qual_expr) ||
                checkExprHasSubLink((Node *) with_check_qual);

            rsdesc->policies = lcons(policy, rsdesc->policies);

            MemoryContextSwitchTo(oldcxt);

            /* clean up some (not all) of the junk ... */
            if (qual_expr != NULL)
                pfree(qual_expr);
            if (with_check_qual != NULL)
                pfree(with_check_qual);
        }

        systable_endscan(sscan);
        heap_close(catalog, AccessShareLock);
    }
    PG_CATCH();
    {
        /* Delete rscxt, first making sure it isn't active */
        MemoryContextSwitchTo(oldcxt);
        MemoryContextDelete(rscxt);
        PG_RE_THROW();
    }
    PG_END_TRY();

    /* Success --- attach the policy descriptor to the relcache entry */
    relation->rd_rsdesc = rsdesc;
}

/*
 * RemovePolicyById -
 *   remove a policy by its OID.  If a policy does not exist with the provided
 *   oid, then an error is raised.
 *
 * policy_id - the oid of the policy.
 */
void
RemovePolicyById(Oid policy_id)
{
    Relation    pg_policy_rel;
    SysScanDesc sscan;
    ScanKeyData skey[1];
    HeapTuple   tuple;
    Oid         relid;
    Relation    rel;

    pg_policy_rel = heap_open(PolicyRelationId, RowExclusiveLock);

    /*
     * Find the policy to delete.
     */
    ScanKeyInit(&skey[0],
                ObjectIdAttributeNumber,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(policy_id));

    sscan = systable_beginscan(pg_policy_rel, PolicyOidIndexId, true,
                               NULL, 1, skey);

    tuple = systable_getnext(sscan);

    /* If the policy exists, then remove it, otherwise raise an error. */
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "could not find tuple for policy %u", policy_id);

    /*
     * Open and exclusive-lock the relation the policy belongs to.  (We need
     * exclusive lock to lock out queries that might otherwise depend on the
     * set of policies the rel has; furthermore we've got to hold the lock
     * till commit.)
     */
    relid = ((Form_pg_policy) GETSTRUCT(tuple))->polrelid;

    rel = heap_open(relid, AccessExclusiveLock);
    if (rel->rd_rel->relkind != RELKIND_RELATION &&
        rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table",
                        RelationGetRelationName(rel))));

    if (!allowSystemTableMods && IsSystemRelation(rel))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        RelationGetRelationName(rel))));

    CatalogTupleDelete(pg_policy_rel, &tuple->t_self);

    systable_endscan(sscan);

    /*
     * Note that, unlike some of the other flags in pg_class, relrowsecurity
     * is not just an indication of if policies exist.  When relrowsecurity is
     * set by a user, then all access to the relation must be through a
     * policy.  If no policy is defined for the relation then a default-deny
     * policy is created and all records are filtered (except for queries from
     * the owner).
     */
    CacheInvalidateRelcache(rel);

    heap_close(rel, NoLock);

    /* Clean up */
    heap_close(pg_policy_rel, RowExclusiveLock);
}

/*
 * RemoveRoleFromObjectPolicy -
 *   remove a role from a policy by its OID.  If the role is not a member of
 *   the policy then an error is raised.  False is returned to indicate that
 *   the role could not be removed due to being the only role on the policy
 *   and therefore the entire policy should be removed.
 *
 * Note that a warning will be thrown and true will be returned on a
 * permission error, as the policy should not be removed in that case.
 *
 * roleid - the oid of the role to remove
 * classid - should always be PolicyRelationId
 * policy_id - the oid of the policy.
 */
bool
RemoveRoleFromObjectPolicy(Oid roleid, Oid classid, Oid policy_id)
{
    Relation    pg_policy_rel;
    SysScanDesc sscan;
    ScanKeyData skey[1];
    HeapTuple   tuple;
    Oid         relid;
    Relation    rel;
    ArrayType  *policy_roles;
    int         num_roles;
    Datum       roles_datum;
    bool        attr_isnull;
    bool        noperm = true;

    Assert(classid == PolicyRelationId);

    pg_policy_rel = heap_open(PolicyRelationId, RowExclusiveLock);

    /*
     * Find the policy to update.
     */
    ScanKeyInit(&skey[0],
                ObjectIdAttributeNumber,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(policy_id));

    sscan = systable_beginscan(pg_policy_rel, PolicyOidIndexId, true,
                               NULL, 1, skey);

    tuple = systable_getnext(sscan);

    /* Raise an error if we don't find the policy. */
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "could not find tuple for policy %u", policy_id);

    /*
     * Open and exclusive-lock the relation the policy belongs to.
     */
    relid = ((Form_pg_policy) GETSTRUCT(tuple))->polrelid;

    rel = relation_open(relid, AccessExclusiveLock);

    if (rel->rd_rel->relkind != RELKIND_RELATION &&
        rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table",
                        RelationGetRelationName(rel))));

    if (!allowSystemTableMods && IsSystemRelation(rel))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        RelationGetRelationName(rel))));

    /* Get the current set of roles */
    roles_datum = heap_getattr(tuple,
                               Anum_pg_policy_polroles,
                               RelationGetDescr(pg_policy_rel),
                               &attr_isnull);

    Assert(!attr_isnull);

    policy_roles = DatumGetArrayTypePCopy(roles_datum);

    /* We should be removing exactly one entry from the roles array */
    num_roles = ARR_DIMS(policy_roles)[0] - 1;

    Assert(num_roles >= 0);

    /* Must own relation. */
    if (pg_class_ownercheck(relid, GetUserId()))
        noperm = false;         /* user is allowed to modify this policy */
    else
        ereport(WARNING,
                (errcode(ERRCODE_WARNING_PRIVILEGE_NOT_REVOKED),
                 errmsg("role \"%s\" could not be removed from policy \"%s\" on \"%s\"",
                        GetUserNameFromId(roleid, false),
                        NameStr(((Form_pg_policy) GETSTRUCT(tuple))->polname),
                        RelationGetRelationName(rel))));

    /*
     * If multiple roles exist on this policy, then remove the one we were
     * asked to and leave the rest.
     */
    if (!noperm && num_roles > 0)
    {
        int         i,
                    j;
        Oid        *roles = (Oid *) ARR_DATA_PTR(policy_roles);
        Datum      *role_oids;
        char       *qual_value;
        Node       *qual_expr;
        List       *qual_parse_rtable = NIL;
        char       *with_check_value;
        Node       *with_check_qual;
        List       *with_check_parse_rtable = NIL;
        Datum       values[Natts_pg_policy];
        bool        isnull[Natts_pg_policy];
        bool        replaces[Natts_pg_policy];
        Datum       value_datum;
        ArrayType  *role_ids;
        HeapTuple   new_tuple;
        ObjectAddress target;
        ObjectAddress myself;

        /* zero-clear */
        memset(values, 0, sizeof(values));
        memset(replaces, 0, sizeof(replaces));
        memset(isnull, 0, sizeof(isnull));

        /*
         * All of the dependencies will be removed from the policy and then
         * re-added.  In order to get them correct, we need to extract out the
         * expressions in the policy and construct a parsestate just enough to
         * build the range table(s) to then pass to recordDependencyOnExpr().
         */

        /* Get policy qual, to update dependencies */
        value_datum = heap_getattr(tuple, Anum_pg_policy_polqual,
                                   RelationGetDescr(pg_policy_rel), &attr_isnull);
        if (!attr_isnull)
        {
            ParseState *qual_pstate;

            /* parsestate is built just to build the range table */
            qual_pstate = make_parsestate(NULL);

            qual_value = TextDatumGetCString(value_datum);
            qual_expr = stringToNode(qual_value);

            /* Add this rel to the parsestate's rangetable, for dependencies */
            addRangeTableEntryForRelation(qual_pstate, rel, NULL, false, false);

            qual_parse_rtable = qual_pstate->p_rtable;
            free_parsestate(qual_pstate);
        }
        else
            qual_expr = NULL;

        /* Get WITH CHECK qual, to update dependencies */
        value_datum = heap_getattr(tuple, Anum_pg_policy_polwithcheck,
                                   RelationGetDescr(pg_policy_rel), &attr_isnull);
        if (!attr_isnull)
        {
            ParseState *with_check_pstate;

            /* parsestate is built just to build the range table */
            with_check_pstate = make_parsestate(NULL);

            with_check_value = TextDatumGetCString(value_datum);
            with_check_qual = stringToNode(with_check_value);

            /* Add this rel to the parsestate's rangetable, for dependencies */
            addRangeTableEntryForRelation(with_check_pstate, rel, NULL, false,
                                          false);

            with_check_parse_rtable = with_check_pstate->p_rtable;
            free_parsestate(with_check_pstate);
        }
        else
            with_check_qual = NULL;

        /* Rebuild the roles array to then update the pg_policy tuple with */
        role_oids = (Datum *) palloc(num_roles * sizeof(Datum));
        for (i = 0, j = 0; i < ARR_DIMS(policy_roles)[0]; i++)
            /* Copy over all of the roles which are not the one being removed */
            if (roles[i] != roleid)
                role_oids[j++] = ObjectIdGetDatum(roles[i]);

        /* We should have only removed the one role */
        Assert(j == num_roles);

        /* This is the array for the new tuple */
        role_ids = construct_array(role_oids, num_roles, OIDOID,
                                   sizeof(Oid), true, 'i');

        replaces[Anum_pg_policy_polroles - 1] = true;
        values[Anum_pg_policy_polroles - 1] = PointerGetDatum(role_ids);

        new_tuple = heap_modify_tuple(tuple,
                                      RelationGetDescr(pg_policy_rel),
                                      values, isnull, replaces);
        CatalogTupleUpdate(pg_policy_rel, &new_tuple->t_self, new_tuple);

        /* Remove all old dependencies. */
        deleteDependencyRecordsFor(PolicyRelationId, policy_id, false);

        /* Record the new set of dependencies */
        target.classId = RelationRelationId;
        target.objectId = relid;
        target.objectSubId = 0;

        myself.classId = PolicyRelationId;
        myself.objectId = policy_id;
        myself.objectSubId = 0;

        recordDependencyOn(&myself, &target, DEPENDENCY_AUTO);

        if (qual_expr)
            recordDependencyOnExpr(&myself, qual_expr, qual_parse_rtable,
                                   DEPENDENCY_NORMAL);

        if (with_check_qual)
            recordDependencyOnExpr(&myself, with_check_qual,
                                   with_check_parse_rtable,
                                   DEPENDENCY_NORMAL);

        /* Remove all the old shared dependencies (roles) */
        deleteSharedDependencyRecordsFor(PolicyRelationId, policy_id, 0);

        /* Record the new shared dependencies (roles) */
        target.classId = AuthIdRelationId;
        target.objectSubId = 0;
        for (i = 0; i < num_roles; i++)
        {
            target.objectId = DatumGetObjectId(role_oids[i]);
            /* no need for dependency on the public role */
            if (target.objectId != ACL_ID_PUBLIC)
                recordSharedDependencyOn(&myself, &target,
                                         SHARED_DEPENDENCY_POLICY);
        }

        InvokeObjectPostAlterHook(PolicyRelationId, policy_id, 0);

        heap_freetuple(new_tuple);

        /* Invalidate Relation Cache */
        CacheInvalidateRelcache(rel);
    }

    /* Clean up. */
    systable_endscan(sscan);

    relation_close(rel, NoLock);

    heap_close(pg_policy_rel, RowExclusiveLock);

    return (noperm || num_roles > 0);
}

/*
 * CreatePolicy -
 *   handles the execution of the CREATE POLICY command.
 *
 * stmt - the CreatePolicyStmt that describes the policy to create.
 */
ObjectAddress
CreatePolicy(CreatePolicyStmt *stmt)
{
    Relation    pg_policy_rel;
    Oid         policy_id;
    Relation    target_table;
    Oid         table_id;
    char        polcmd;
    Datum      *role_oids;
    int         nitems = 0;
    ArrayType  *role_ids;
    ParseState *qual_pstate;
    ParseState *with_check_pstate;
    RangeTblEntry *rte;
    Node       *qual;
    Node       *with_check_qual;
    ScanKeyData skey[2];
    SysScanDesc sscan;
    HeapTuple   policy_tuple;
    Datum       values[Natts_pg_policy];
    bool        isnull[Natts_pg_policy];
    ObjectAddress target;
    ObjectAddress myself;
    int         i;

    /* Parse command */
    polcmd = parse_policy_command(stmt->cmd_name);

    /*
     * If the command is SELECT or DELETE then WITH CHECK should be NULL.
     */
    if ((polcmd == ACL_SELECT_CHR || polcmd == ACL_DELETE_CHR)
        && stmt->with_check != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("WITH CHECK cannot be applied to SELECT or DELETE")));

    /*
     * If the command is INSERT then WITH CHECK should be the only expression
     * provided.
     */
    if (polcmd == ACL_INSERT_CHR && stmt->qual != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("only WITH CHECK expression allowed for INSERT")));

    /* Collect role ids */
    role_oids = policy_role_list_to_array(stmt->roles, &nitems);
    role_ids = construct_array(role_oids, nitems, OIDOID,
                               sizeof(Oid), true, 'i');

    /* Parse the supplied clause */
    qual_pstate = make_parsestate(NULL);
    with_check_pstate = make_parsestate(NULL);

    /* zero-clear */
    memset(values, 0, sizeof(values));
    memset(isnull, 0, sizeof(isnull));

    /* Get id of table.  Also handles permissions checks. */
    table_id = RangeVarGetRelidExtended(stmt->table, AccessExclusiveLock,
                                        0,
                                        RangeVarCallbackForPolicy,
                                        (void *) stmt);

    /* Open target_table to build quals. No additional lock is necessary. */
    target_table = relation_open(table_id, NoLock);

    /* Add for the regular security quals */
    rte = addRangeTableEntryForRelation(qual_pstate, target_table,
                                        NULL, false, false);
    addRTEtoQuery(qual_pstate, rte, false, true, true);

    /* Add for the with-check quals */
    rte = addRangeTableEntryForRelation(with_check_pstate, target_table,
                                        NULL, false, false);
    addRTEtoQuery(with_check_pstate, rte, false, true, true);

    qual = transformWhereClause(qual_pstate,
                                copyObject(stmt->qual),
                                EXPR_KIND_POLICY,
                                "POLICY");

    with_check_qual = transformWhereClause(with_check_pstate,
                                           copyObject(stmt->with_check),
                                           EXPR_KIND_POLICY,
                                           "POLICY");

    /* Fix up collation information */
    assign_expr_collations(qual_pstate, qual);
    assign_expr_collations(with_check_pstate, with_check_qual);

    /* Open pg_policy catalog */
    pg_policy_rel = heap_open(PolicyRelationId, RowExclusiveLock);

    /* Set key - policy's relation id. */
    ScanKeyInit(&skey[0],
                Anum_pg_policy_polrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(table_id));

    /* Set key - policy's name. */
    ScanKeyInit(&skey[1],
                Anum_pg_policy_polname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(stmt->policy_name));

    sscan = systable_beginscan(pg_policy_rel,
                               PolicyPolrelidPolnameIndexId, true, NULL, 2,
                               skey);

    policy_tuple = systable_getnext(sscan);

    /* Complain if the policy name already exists for the table */
    if (HeapTupleIsValid(policy_tuple))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
                 errmsg("policy \"%s\" for table \"%s\" already exists",
                        stmt->policy_name, RelationGetRelationName(target_table))));

    values[Anum_pg_policy_polrelid - 1] = ObjectIdGetDatum(table_id);
    values[Anum_pg_policy_polname - 1] = DirectFunctionCall1(namein,
                                                             CStringGetDatum(stmt->policy_name));
    values[Anum_pg_policy_polcmd - 1] = CharGetDatum(polcmd);
    values[Anum_pg_policy_polpermissive - 1] = BoolGetDatum(stmt->permissive);
    values[Anum_pg_policy_polroles - 1] = PointerGetDatum(role_ids);

    /* Add qual if present. */
    if (qual)
        values[Anum_pg_policy_polqual - 1] = CStringGetTextDatum(nodeToString(qual));
    else
        isnull[Anum_pg_policy_polqual - 1] = true;

    /* Add WITH CHECK qual if present */
    if (with_check_qual)
        values[Anum_pg_policy_polwithcheck - 1] = CStringGetTextDatum(nodeToString(with_check_qual));
    else
        isnull[Anum_pg_policy_polwithcheck - 1] = true;

    policy_tuple = heap_form_tuple(RelationGetDescr(pg_policy_rel), values,
                                   isnull);

    policy_id = CatalogTupleInsert(pg_policy_rel, policy_tuple);

    /* Record Dependencies */
    target.classId = RelationRelationId;
    target.objectId = table_id;
    target.objectSubId = 0;

    myself.classId = PolicyRelationId;
    myself.objectId = policy_id;
    myself.objectSubId = 0;

    recordDependencyOn(&myself, &target, DEPENDENCY_AUTO);

    recordDependencyOnExpr(&myself, qual, qual_pstate->p_rtable,
                           DEPENDENCY_NORMAL);

    recordDependencyOnExpr(&myself, with_check_qual,
                           with_check_pstate->p_rtable, DEPENDENCY_NORMAL);

    /* Register role dependencies */
    target.classId = AuthIdRelationId;
    target.objectSubId = 0;
    for (i = 0; i < nitems; i++)
    {
        target.objectId = DatumGetObjectId(role_oids[i]);
        /* no dependency if public */
        if (target.objectId != ACL_ID_PUBLIC)
            recordSharedDependencyOn(&myself, &target,
                                     SHARED_DEPENDENCY_POLICY);
    }

    InvokeObjectPostCreateHook(PolicyRelationId, policy_id, 0);

    /* Invalidate Relation Cache */
    CacheInvalidateRelcache(target_table);

    /* Clean up. */
    heap_freetuple(policy_tuple);
    free_parsestate(qual_pstate);
    free_parsestate(with_check_pstate);
    systable_endscan(sscan);
    relation_close(target_table, NoLock);
    heap_close(pg_policy_rel, RowExclusiveLock);

    return myself;
}

/*
 * AlterPolicy -
 *   handles the execution of the ALTER POLICY command.
 *
 * stmt - the AlterPolicyStmt that describes the policy and how to alter it.
 */
ObjectAddress
AlterPolicy(AlterPolicyStmt *stmt)
{
    Relation    pg_policy_rel;
    Oid         policy_id;
    Relation    target_table;
    Oid         table_id;
    Datum      *role_oids = NULL;
    int         nitems = 0;
    ArrayType  *role_ids = NULL;
    List       *qual_parse_rtable = NIL;
    List       *with_check_parse_rtable = NIL;
    Node       *qual = NULL;
    Node       *with_check_qual = NULL;
    ScanKeyData skey[2];
    SysScanDesc sscan;
    HeapTuple   policy_tuple;
    HeapTuple   new_tuple;
    Datum       values[Natts_pg_policy];
    bool        isnull[Natts_pg_policy];
    bool        replaces[Natts_pg_policy];
    ObjectAddress target;
    ObjectAddress myself;
    Datum       polcmd_datum;
    char        polcmd;
    bool        polcmd_isnull;
    int         i;

    /* Parse role_ids */
    if (stmt->roles != NULL)
    {
        role_oids = policy_role_list_to_array(stmt->roles, &nitems);
        role_ids = construct_array(role_oids, nitems, OIDOID,
                                   sizeof(Oid), true, 'i');
    }

    /* Get id of table.  Also handles permissions checks. */
    table_id = RangeVarGetRelidExtended(stmt->table, AccessExclusiveLock,
                                        0,
                                        RangeVarCallbackForPolicy,
                                        (void *) stmt);

    target_table = relation_open(table_id, NoLock);

    /* Parse the using policy clause */
    if (stmt->qual)
    {
        RangeTblEntry *rte;
        ParseState *qual_pstate = make_parsestate(NULL);

        rte = addRangeTableEntryForRelation(qual_pstate, target_table,
                                            NULL, false, false);

        addRTEtoQuery(qual_pstate, rte, false, true, true);

        qual = transformWhereClause(qual_pstate, copyObject(stmt->qual),
                                    EXPR_KIND_POLICY,
                                    "POLICY");

        /* Fix up collation information */
        assign_expr_collations(qual_pstate, qual);

        qual_parse_rtable = qual_pstate->p_rtable;
        free_parsestate(qual_pstate);
    }

    /* Parse the with-check policy clause */
    if (stmt->with_check)
    {
        RangeTblEntry *rte;
        ParseState *with_check_pstate = make_parsestate(NULL);

        rte = addRangeTableEntryForRelation(with_check_pstate, target_table,
                                            NULL, false, false);

        addRTEtoQuery(with_check_pstate, rte, false, true, true);

        with_check_qual = transformWhereClause(with_check_pstate,
                                               copyObject(stmt->with_check),
                                               EXPR_KIND_POLICY,
                                               "POLICY");

        /* Fix up collation information */
        assign_expr_collations(with_check_pstate, with_check_qual);

        with_check_parse_rtable = with_check_pstate->p_rtable;
        free_parsestate(with_check_pstate);
    }

    /* zero-clear */
    memset(values, 0, sizeof(values));
    memset(replaces, 0, sizeof(replaces));
    memset(isnull, 0, sizeof(isnull));

    /* Find policy to update. */
    pg_policy_rel = heap_open(PolicyRelationId, RowExclusiveLock);

    /* Set key - policy's relation id. */
    ScanKeyInit(&skey[0],
                Anum_pg_policy_polrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(table_id));

    /* Set key - policy's name. */
    ScanKeyInit(&skey[1],
                Anum_pg_policy_polname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(stmt->policy_name));

    sscan = systable_beginscan(pg_policy_rel,
                               PolicyPolrelidPolnameIndexId, true, NULL, 2,
                               skey);

    policy_tuple = systable_getnext(sscan);

    /* Check that the policy is found, raise an error if not. */
    if (!HeapTupleIsValid(policy_tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("policy \"%s\" for table \"%s\" does not exist",
                        stmt->policy_name,
                        RelationGetRelationName(target_table))));

    /* Get policy command */
    polcmd_datum = heap_getattr(policy_tuple, Anum_pg_policy_polcmd,
                                RelationGetDescr(pg_policy_rel),
                                &polcmd_isnull);
    Assert(!polcmd_isnull);
    polcmd = DatumGetChar(polcmd_datum);

    /*
     * If the command is SELECT or DELETE then WITH CHECK should be NULL.
     */
    if ((polcmd == ACL_SELECT_CHR || polcmd == ACL_DELETE_CHR)
        && stmt->with_check != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("only USING expression allowed for SELECT, DELETE")));

    /*
     * If the command is INSERT then WITH CHECK should be the only expression
     * provided.
     */
    if ((polcmd == ACL_INSERT_CHR)
        && stmt->qual != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("only WITH CHECK expression allowed for INSERT")));

    policy_id = HeapTupleGetOid(policy_tuple);

    if (role_ids != NULL)
    {
        replaces[Anum_pg_policy_polroles - 1] = true;
        values[Anum_pg_policy_polroles - 1] = PointerGetDatum(role_ids);
    }
    else
    {
        Oid        *roles;
        Datum       roles_datum;
        bool        attr_isnull;
        ArrayType  *policy_roles;

        /*
         * We need to pull the set of roles this policy applies to from what's
         * in the catalog, so that we can recreate the dependencies correctly
         * for the policy.
         */

        roles_datum = heap_getattr(policy_tuple, Anum_pg_policy_polroles,
                                   RelationGetDescr(pg_policy_rel),
                                   &attr_isnull);
        Assert(!attr_isnull);

        policy_roles = DatumGetArrayTypePCopy(roles_datum);

        roles = (Oid *) ARR_DATA_PTR(policy_roles);

        nitems = ARR_DIMS(policy_roles)[0];

        role_oids = (Datum *) palloc(nitems * sizeof(Datum));

        for (i = 0; i < nitems; i++)
            role_oids[i] = ObjectIdGetDatum(roles[i]);
    }

    if (qual != NULL)
    {
        replaces[Anum_pg_policy_polqual - 1] = true;
        values[Anum_pg_policy_polqual - 1]
            = CStringGetTextDatum(nodeToString(qual));
    }
    else
    {
        Datum       value_datum;
        bool        attr_isnull;

        /*
         * We need to pull the USING expression and build the range table for
         * the policy from what's in the catalog, so that we can recreate the
         * dependencies correctly for the policy.
         */

        /* Check if the policy has a USING expr */
        value_datum = heap_getattr(policy_tuple, Anum_pg_policy_polqual,
                                   RelationGetDescr(pg_policy_rel),
                                   &attr_isnull);
        if (!attr_isnull)
        {
            char       *qual_value;
            ParseState *qual_pstate;

            /* parsestate is built just to build the range table */
            qual_pstate = make_parsestate(NULL);

            qual_value = TextDatumGetCString(value_datum);
            qual = stringToNode(qual_value);

            /* Add this rel to the parsestate's rangetable, for dependencies */
            addRangeTableEntryForRelation(qual_pstate, target_table, NULL,
                                          false, false);

            qual_parse_rtable = qual_pstate->p_rtable;
            free_parsestate(qual_pstate);
        }
    }

    if (with_check_qual != NULL)
    {
        replaces[Anum_pg_policy_polwithcheck - 1] = true;
        values[Anum_pg_policy_polwithcheck - 1]
            = CStringGetTextDatum(nodeToString(with_check_qual));
    }
    else
    {
        Datum       value_datum;
        bool        attr_isnull;

        /*
         * We need to pull the WITH CHECK expression and build the range table
         * for the policy from what's in the catalog, so that we can recreate
         * the dependencies correctly for the policy.
         */

        /* Check if the policy has a WITH CHECK expr */
        value_datum = heap_getattr(policy_tuple, Anum_pg_policy_polwithcheck,
                                   RelationGetDescr(pg_policy_rel),
                                   &attr_isnull);
        if (!attr_isnull)
        {
            char       *with_check_value;
            ParseState *with_check_pstate;

            /* parsestate is built just to build the range table */
            with_check_pstate = make_parsestate(NULL);

            with_check_value = TextDatumGetCString(value_datum);
            with_check_qual = stringToNode(with_check_value);

            /* Add this rel to the parsestate's rangetable, for dependencies */
            addRangeTableEntryForRelation(with_check_pstate, target_table, NULL,
                                          false, false);

            with_check_parse_rtable = with_check_pstate->p_rtable;
            free_parsestate(with_check_pstate);
        }
    }

    new_tuple = heap_modify_tuple(policy_tuple,
                                  RelationGetDescr(pg_policy_rel),
                                  values, isnull, replaces);
    CatalogTupleUpdate(pg_policy_rel, &new_tuple->t_self, new_tuple);

    /* Update Dependencies. */
    deleteDependencyRecordsFor(PolicyRelationId, policy_id, false);

    /* Record Dependencies */
    target.classId = RelationRelationId;
    target.objectId = table_id;
    target.objectSubId = 0;

    myself.classId = PolicyRelationId;
    myself.objectId = policy_id;
    myself.objectSubId = 0;

    recordDependencyOn(&myself, &target, DEPENDENCY_AUTO);

    recordDependencyOnExpr(&myself, qual, qual_parse_rtable, DEPENDENCY_NORMAL);

    recordDependencyOnExpr(&myself, with_check_qual, with_check_parse_rtable,
                           DEPENDENCY_NORMAL);

    /* Register role dependencies */
    deleteSharedDependencyRecordsFor(PolicyRelationId, policy_id, 0);
    target.classId = AuthIdRelationId;
    target.objectSubId = 0;
    for (i = 0; i < nitems; i++)
    {
        target.objectId = DatumGetObjectId(role_oids[i]);
        /* no dependency if public */
        if (target.objectId != ACL_ID_PUBLIC)
            recordSharedDependencyOn(&myself, &target,
                                     SHARED_DEPENDENCY_POLICY);
    }

    InvokeObjectPostAlterHook(PolicyRelationId, policy_id, 0);

    heap_freetuple(new_tuple);

    /* Invalidate Relation Cache */
    CacheInvalidateRelcache(target_table);

    /* Clean up. */
    systable_endscan(sscan);
    relation_close(target_table, NoLock);
    heap_close(pg_policy_rel, RowExclusiveLock);

    return myself;
}

/*
 * rename_policy -
 *   change the name of a policy on a relation
 */
ObjectAddress
rename_policy(RenameStmt *stmt)
{
    Relation    pg_policy_rel;
    Relation    target_table;
    Oid         table_id;
    Oid         opoloid;
    ScanKeyData skey[2];
    SysScanDesc sscan;
    HeapTuple   policy_tuple;
    ObjectAddress address;

    /* Get id of table.  Also handles permissions checks. */
    table_id = RangeVarGetRelidExtended(stmt->relation, AccessExclusiveLock,
                                        0,
                                        RangeVarCallbackForPolicy,
                                        (void *) stmt);

    target_table = relation_open(table_id, NoLock);

    pg_policy_rel = heap_open(PolicyRelationId, RowExclusiveLock);

    /* First pass -- check for conflict */

    /* Add key - policy's relation id. */
    ScanKeyInit(&skey[0],
                Anum_pg_policy_polrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(table_id));

    /* Add key - policy's name. */
    ScanKeyInit(&skey[1],
                Anum_pg_policy_polname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(stmt->newname));

    sscan = systable_beginscan(pg_policy_rel,
                               PolicyPolrelidPolnameIndexId, true, NULL, 2,
                               skey);

    if (HeapTupleIsValid(systable_getnext(sscan)))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
                 errmsg("policy \"%s\" for table \"%s\" already exists",
                        stmt->newname, RelationGetRelationName(target_table))));

    systable_endscan(sscan);

    /* Second pass -- find existing policy and update */
    /* Add key - policy's relation id. */
    ScanKeyInit(&skey[0],
                Anum_pg_policy_polrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(table_id));

    /* Add key - policy's name. */
    ScanKeyInit(&skey[1],
                Anum_pg_policy_polname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(stmt->subname));

    sscan = systable_beginscan(pg_policy_rel,
                               PolicyPolrelidPolnameIndexId, true, NULL, 2,
                               skey);

    policy_tuple = systable_getnext(sscan);

    /* Complain if we did not find the policy */
    if (!HeapTupleIsValid(policy_tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("policy \"%s\" for table \"%s\" does not exist",
                        stmt->subname, RelationGetRelationName(target_table))));

    opoloid = HeapTupleGetOid(policy_tuple);

    policy_tuple = heap_copytuple(policy_tuple);

    namestrcpy(&((Form_pg_policy) GETSTRUCT(policy_tuple))->polname,
               stmt->newname);

    CatalogTupleUpdate(pg_policy_rel, &policy_tuple->t_self, policy_tuple);

    InvokeObjectPostAlterHook(PolicyRelationId,
                              HeapTupleGetOid(policy_tuple), 0);

    ObjectAddressSet(address, PolicyRelationId, opoloid);

    /*
     * Invalidate relation's relcache entry so that other backends (and this
     * one too!) are sent SI message to make them rebuild relcache entries.
     * (Ideally this should happen automatically...)
     */
    CacheInvalidateRelcache(target_table);

    /* Clean up. */
    systable_endscan(sscan);
    heap_close(pg_policy_rel, RowExclusiveLock);
    relation_close(target_table, NoLock);

    return address;
}

/*
 * get_relation_policy_oid - Look up a policy by name to find its OID
 *
 * If missing_ok is false, throw an error if policy not found.  If
 * true, just return InvalidOid.
 */
Oid
get_relation_policy_oid(Oid relid, const char *policy_name, bool missing_ok)
{
    Relation    pg_policy_rel;
    ScanKeyData skey[2];
    SysScanDesc sscan;
    HeapTuple   policy_tuple;
    Oid         policy_oid;

    pg_policy_rel = heap_open(PolicyRelationId, AccessShareLock);

    /* Add key - policy's relation id. */
    ScanKeyInit(&skey[0],
                Anum_pg_policy_polrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(relid));

    /* Add key - policy's name. */
    ScanKeyInit(&skey[1],
                Anum_pg_policy_polname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(policy_name));

    sscan = systable_beginscan(pg_policy_rel,
                               PolicyPolrelidPolnameIndexId, true, NULL, 2,
                               skey);

    policy_tuple = systable_getnext(sscan);

    if (!HeapTupleIsValid(policy_tuple))
    {
        if (!missing_ok)
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("policy \"%s\" for table \"%s\" does not exist",
                            policy_name, get_rel_name(relid))));

        policy_oid = InvalidOid;
    }
    else
        policy_oid = HeapTupleGetOid(policy_tuple);

    /* Clean up. */
    systable_endscan(sscan);
    heap_close(pg_policy_rel, AccessShareLock);

    return policy_oid;
}

/*
 * relation_has_policies - Determine if relation has any policies
 */
bool
relation_has_policies(Relation rel)
{
    Relation    catalog;
    ScanKeyData skey;
    SysScanDesc sscan;
    HeapTuple   policy_tuple;
    bool        ret = false;

    catalog = heap_open(PolicyRelationId, AccessShareLock);
    ScanKeyInit(&skey,
                Anum_pg_policy_polrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    sscan = systable_beginscan(catalog, PolicyPolrelidPolnameIndexId, true,
                               NULL, 1, &skey);
    policy_tuple = systable_getnext(sscan);
    if (HeapTupleIsValid(policy_tuple))
        ret = true;

    systable_endscan(sscan);
    heap_close(catalog, AccessShareLock);

    return ret;
}