rowsecurity.c

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/*
 * rewrite/rowsecurity.c
 *    Routines to support policies for row-level security (aka RLS).
 *
 * Policies in PostgreSQL provide a mechanism to limit what records are
 * returned to a user and what records a user is permitted to add to a table.
 *
 * Policies can be defined for specific roles, specific commands, or provided
 * by an extension.  Row security can also be enabled for a table without any
 * policies being explicitly defined, in which case a default-deny policy is
 * applied.
 *
 * Any part of the system which is returning records back to the user, or
 * which is accepting records from the user to add to a table, needs to
 * consider the policies associated with the table (if any).  For normal
 * queries, this is handled by calling get_row_security_policies() during
 * rewrite, for each RTE in the query.  This returns the expressions defined
 * by the table's policies as a list that is prepended to the securityQuals
 * list for the RTE.  For queries which modify the table, any WITH CHECK
 * clauses from the table's policies are also returned and prepended to the
 * list of WithCheckOptions for the Query to check each row that is being
 * added to the table.  Other parts of the system (eg: COPY) simply construct
 * a normal query and use that, if RLS is to be applied.
 *
 * The check to see if RLS should be enabled is provided through
 * check_enable_rls(), which returns an enum (defined in rowsecurity.h) to
 * indicate if RLS should be enabled (RLS_ENABLED), or bypassed (RLS_NONE or
 * RLS_NONE_ENV).  RLS_NONE_ENV indicates that RLS should be bypassed
 * in the current environment, but that may change if the row_security GUC or
 * the current role changes.
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 */
#include "postgres.h"
 
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "catalog/pg_class.h"
#include "catalog/pg_inherits.h"
#include "catalog/pg_policy.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/pg_list.h"
#include "nodes/plannodes.h"
#include "parser/parsetree.h"
#include "parser/parse_relation.h"
#include "rewrite/rewriteDefine.h"
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "rewrite/rowsecurity.h"
#include "tcop/utility.h"
#include "utils/acl.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/rls.h"
#include "utils/syscache.h"
 
static void get_policies_for_relation(Relation relation,
                                      CmdType cmd, Oid user_id,
                                      List **permissive_policies,
                                      List **restrictive_policies);
 
static void sort_policies_by_name(List *policies);
 
static int  row_security_policy_cmp(const ListCell *a, const ListCell *b);
 
static void add_security_quals(int rt_index,
                               List *permissive_policies,
                               List *restrictive_policies,
                               List **securityQuals,
                               bool *hasSubLinks);
 
static void add_with_check_options(Relation rel,
                                   int rt_index,
                                   WCOKind kind,
                                   List *permissive_policies,
                                   List *restrictive_policies,
                                   List **withCheckOptions,
                                   bool *hasSubLinks,
                                   bool force_using);
 
static bool check_role_for_policy(ArrayType *policy_roles, Oid user_id);
 
/*
 * hooks to allow extensions to add their own security policies
 *
 * row_security_policy_hook_permissive can be used to add policies which
 * are combined with the other permissive policies, using OR.
 *
 * row_security_policy_hook_restrictive can be used to add policies which
 * are enforced, regardless of other policies (they are combined using AND).
 */
row_security_policy_hook_type row_security_policy_hook_permissive = NULL;
row_security_policy_hook_type row_security_policy_hook_restrictive = NULL;
 
/*
 * Get any row security quals and WithCheckOption checks that should be
 * applied to the specified RTE.
 *
 * In addition, hasRowSecurity is set to true if row-level security is enabled
 * (even if this RTE doesn't have any row security quals), and hasSubLinks is
 * set to true if any of the quals returned contain sublinks.
 */
void
get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
                          List **securityQuals, List **withCheckOptions,
                          bool *hasRowSecurity, bool *hasSubLinks)
{
    Oid         user_id;
    int         rls_status;
    Relation    rel;
    CmdType     commandType;
    List       *permissive_policies;
    List       *restrictive_policies;
    RTEPermissionInfo *perminfo;
 
    /* Defaults for the return values */
    *securityQuals = NIL;
    *withCheckOptions = NIL;
    *hasRowSecurity = false;
    *hasSubLinks = false;
 
    Assert(rte->rtekind == RTE_RELATION);
 
    /* If this is not a normal relation, just return immediately */
    if (rte->relkind != RELKIND_RELATION &&
        rte->relkind != RELKIND_PARTITIONED_TABLE)
        return;
 
    perminfo = getRTEPermissionInfo(root->rteperminfos, rte);
 
    /* Switch to checkAsUser if it's set */
    user_id = OidIsValid(perminfo->checkAsUser) ?
        perminfo->checkAsUser : GetUserId();
 
    /* Determine the state of RLS for this, pass checkAsUser explicitly */
    rls_status = check_enable_rls(rte->relid, perminfo->checkAsUser, false);
 
    /* If there is no RLS on this table at all, nothing to do */
    if (rls_status == RLS_NONE)
        return;
 
    /*
     * RLS_NONE_ENV means we are not doing any RLS now, but that may change
     * with changes to the environment, so we mark it as hasRowSecurity to
     * force a re-plan when the environment changes.
     */
    if (rls_status == RLS_NONE_ENV)
    {
        /*
         * Indicate that this query may involve RLS and must therefore be
         * replanned if the environment changes (GUCs, role), but we are not
         * adding anything here.
         */
        *hasRowSecurity = true;
 
        return;
    }
 
    /*
     * RLS is enabled for this relation.
     *
     * Get the security policies that should be applied, based on the command
     * type.  Note that if this isn't the target relation, we actually want
     * the relation's SELECT policies, regardless of the query command type,
     * for example in UPDATE t1 ... FROM t2 we need to apply t1's UPDATE
     * policies and t2's SELECT policies.
     */
    rel = table_open(rte->relid, NoLock);
 
    commandType = rt_index == root->resultRelation ?
        root->commandType : CMD_SELECT;
 
    /*
     * In some cases, we need to apply USING policies (which control the
     * visibility of records) associated with multiple command types (see
     * specific cases below).
     *
     * When considering the order in which to apply these USING policies, we
     * prefer to apply higher privileged policies, those which allow the user
     * to lock records (UPDATE and DELETE), first, followed by policies which
     * don't (SELECT).
     *
     * Note that the optimizer is free to push down and reorder quals which
     * use leakproof functions.
     *
     * In all cases, if there are no policy clauses allowing access to rows in
     * the table for the specific type of operation, then a single
     * always-false clause (a default-deny policy) will be added (see
     * add_security_quals).
     */
 
    /*
     * For a SELECT, if UPDATE privileges are required (eg: the user has
     * specified FOR [KEY] UPDATE/SHARE), then add the UPDATE USING quals
     * first.
     *
     * This way, we filter out any records from the SELECT FOR SHARE/UPDATE
     * which the user does not have access to via the UPDATE USING policies,
     * similar to how we require normal UPDATE rights for these queries.
     */
    if (commandType == CMD_SELECT && perminfo->requiredPerms & ACL_UPDATE)
    {
        List       *update_permissive_policies;
        List       *update_restrictive_policies;
 
        get_policies_for_relation(rel, CMD_UPDATE, user_id,
                                  &update_permissive_policies,
                                  &update_restrictive_policies);
 
        add_security_quals(rt_index,
                           update_permissive_policies,
                           update_restrictive_policies,
                           securityQuals,
                           hasSubLinks);
    }
 
    /*
     * For SELECT, UPDATE and DELETE, add security quals to enforce the USING
     * policies.  These security quals control access to existing table rows.
     * Restrictive policies are combined together using AND, and permissive
     * policies are combined together using OR.
     */
 
    get_policies_for_relation(rel, commandType, user_id, &permissive_policies,
                              &restrictive_policies);
 
    if (commandType == CMD_SELECT ||
        commandType == CMD_UPDATE ||
        commandType == CMD_DELETE)
        add_security_quals(rt_index,
                           permissive_policies,
                           restrictive_policies,
                           securityQuals,
                           hasSubLinks);
 
    /*
     * Similar to above, during an UPDATE, DELETE, or MERGE, if SELECT rights
     * are also required (eg: when a RETURNING clause exists, or the user has
     * provided a WHERE clause which involves columns from the relation), we
     * collect up CMD_SELECT policies and add them via add_security_quals
     * first.
     *
     * This way, we filter out any records which are not visible through an
     * ALL or SELECT USING policy.
     */
    if ((commandType == CMD_UPDATE || commandType == CMD_DELETE ||
         commandType == CMD_MERGE) &&
        perminfo->requiredPerms & ACL_SELECT)
    {
        List       *select_permissive_policies;
        List       *select_restrictive_policies;
 
        get_policies_for_relation(rel, CMD_SELECT, user_id,
                                  &select_permissive_policies,
                                  &select_restrictive_policies);
 
        add_security_quals(rt_index,
                           select_permissive_policies,
                           select_restrictive_policies,
                           securityQuals,
                           hasSubLinks);
    }
 
    /*
     * For INSERT and UPDATE, add withCheckOptions to verify that any new
     * records added are consistent with the security policies.  This will use
     * each policy's WITH CHECK clause, or its USING clause if no explicit
     * WITH CHECK clause is defined.
     */
    if (commandType == CMD_INSERT || commandType == CMD_UPDATE)
    {
        /* This should be the target relation */
        Assert(rt_index == root->resultRelation);
 
        add_with_check_options(rel, rt_index,
                               commandType == CMD_INSERT ?
                               WCO_RLS_INSERT_CHECK : WCO_RLS_UPDATE_CHECK,
                               permissive_policies,
                               restrictive_policies,
                               withCheckOptions,
                               hasSubLinks,
                               false);
 
        /*
         * Get and add ALL/SELECT policies, if SELECT rights are required for
         * this relation (eg: when RETURNING is used).  These are added as WCO
         * policies rather than security quals to ensure that an error is
         * raised if a policy is violated; otherwise, we might end up silently
         * dropping rows to be added.
         */
        if (perminfo->requiredPerms & ACL_SELECT)
        {
            List       *select_permissive_policies = NIL;
            List       *select_restrictive_policies = NIL;
 
            get_policies_for_relation(rel, CMD_SELECT, user_id,
                                      &select_permissive_policies,
                                      &select_restrictive_policies);
            add_with_check_options(rel, rt_index,
                                   commandType == CMD_INSERT ?
                                   WCO_RLS_INSERT_CHECK : WCO_RLS_UPDATE_CHECK,
                                   select_permissive_policies,
                                   select_restrictive_policies,
                                   withCheckOptions,
                                   hasSubLinks,
                                   true);
        }
 
        /*
         * For INSERT ... ON CONFLICT DO UPDATE we need additional policy
         * checks for the UPDATE which may be applied to the same RTE.
         */
        if (commandType == CMD_INSERT &&
            root->onConflict && root->onConflict->action == ONCONFLICT_UPDATE)
        {
            List       *conflict_permissive_policies;
            List       *conflict_restrictive_policies;
            List       *conflict_select_permissive_policies = NIL;
            List       *conflict_select_restrictive_policies = NIL;
 
            /* Get the policies that apply to the auxiliary UPDATE */
            get_policies_for_relation(rel, CMD_UPDATE, user_id,
                                      &conflict_permissive_policies,
                                      &conflict_restrictive_policies);
 
            /*
             * Enforce the USING clauses of the UPDATE policies using WCOs
             * rather than security quals.  This ensures that an error is
             * raised if the conflicting row cannot be updated due to RLS,
             * rather than the change being silently dropped.
             */
            add_with_check_options(rel, rt_index,
                                   WCO_RLS_CONFLICT_CHECK,
                                   conflict_permissive_policies,
                                   conflict_restrictive_policies,
                                   withCheckOptions,
                                   hasSubLinks,
                                   true);
 
            /*
             * Get and add ALL/SELECT policies, as WCO_RLS_CONFLICT_CHECK WCOs
             * to ensure they are considered when taking the UPDATE path of an
             * INSERT .. ON CONFLICT DO UPDATE, if SELECT rights are required
             * for this relation, also as WCO policies, again, to avoid
             * silently dropping data.  See above.
             */
            if (perminfo->requiredPerms & ACL_SELECT)
            {
                get_policies_for_relation(rel, CMD_SELECT, user_id,
                                          &conflict_select_permissive_policies,
                                          &conflict_select_restrictive_policies);
                add_with_check_options(rel, rt_index,
                                       WCO_RLS_CONFLICT_CHECK,
                                       conflict_select_permissive_policies,
                                       conflict_select_restrictive_policies,
                                       withCheckOptions,
                                       hasSubLinks,
                                       true);
            }
 
            /* Enforce the WITH CHECK clauses of the UPDATE policies */
            add_with_check_options(rel, rt_index,
                                   WCO_RLS_UPDATE_CHECK,
                                   conflict_permissive_policies,
                                   conflict_restrictive_policies,
                                   withCheckOptions,
                                   hasSubLinks,
                                   false);
 
            /*
             * Add ALL/SELECT policies as WCO_RLS_UPDATE_CHECK WCOs, to ensure
             * that the final updated row is visible when taking the UPDATE
             * path of an INSERT .. ON CONFLICT DO UPDATE, if SELECT rights
             * are required for this relation.
             */
            if (perminfo->requiredPerms & ACL_SELECT)
                add_with_check_options(rel, rt_index,
                                       WCO_RLS_UPDATE_CHECK,
                                       conflict_select_permissive_policies,
                                       conflict_select_restrictive_policies,
                                       withCheckOptions,
                                       hasSubLinks,
                                       true);
        }
    }
 
    /*
     * FOR MERGE, we fetch policies for UPDATE, DELETE and INSERT (and ALL)
     * and set them up so that we can enforce the appropriate policy depending
     * on the final action we take.
     *
     * We already fetched the SELECT policies above.
     *
     * We don't push the UPDATE/DELETE USING quals to the RTE because we don't
     * really want to apply them while scanning the relation since we don't
     * know whether we will be doing an UPDATE or a DELETE at the end. We
     * apply the respective policy once we decide the final action on the
     * target tuple.
     *
     * XXX We are setting up USING quals as WITH CHECK. If RLS prohibits
     * UPDATE/DELETE on the target row, we shall throw an error instead of
     * silently ignoring the row. This is different than how normal
     * UPDATE/DELETE works and more in line with INSERT ON CONFLICT DO UPDATE
     * handling.
     */
    if (commandType == CMD_MERGE)
    {
        List       *merge_permissive_policies;
        List       *merge_restrictive_policies;
 
        /*
         * Fetch the UPDATE policies and set them up to execute on the
         * existing target row before doing UPDATE.
         */
        get_policies_for_relation(rel, CMD_UPDATE, user_id,
                                  &merge_permissive_policies,
                                  &merge_restrictive_policies);
 
        /*
         * WCO_RLS_MERGE_UPDATE_CHECK is used to check UPDATE USING quals on
         * the existing target row.
         */
        add_with_check_options(rel, rt_index,
                               WCO_RLS_MERGE_UPDATE_CHECK,
                               merge_permissive_policies,
                               merge_restrictive_policies,
                               withCheckOptions,
                               hasSubLinks,
                               true);
 
        /*
         * Same with DELETE policies.
         */
        get_policies_for_relation(rel, CMD_DELETE, user_id,
                                  &merge_permissive_policies,
                                  &merge_restrictive_policies);
 
        add_with_check_options(rel, rt_index,
                               WCO_RLS_MERGE_DELETE_CHECK,
                               merge_permissive_policies,
                               merge_restrictive_policies,
                               withCheckOptions,
                               hasSubLinks,
                               true);
 
        /*
         * No special handling is required for INSERT policies. They will be
         * checked and enforced during ExecInsert(). But we must add them to
         * withCheckOptions.
         */
        get_policies_for_relation(rel, CMD_INSERT, user_id,
                                  &merge_permissive_policies,
                                  &merge_restrictive_policies);
 
        add_with_check_options(rel, rt_index,
                               WCO_RLS_INSERT_CHECK,
                               merge_permissive_policies,
                               merge_restrictive_policies,
                               withCheckOptions,
                               hasSubLinks,
                               false);
 
        /* Enforce the WITH CHECK clauses of the UPDATE policies */
        add_with_check_options(rel, rt_index,
                               WCO_RLS_UPDATE_CHECK,
                               merge_permissive_policies,
                               merge_restrictive_policies,
                               withCheckOptions,
                               hasSubLinks,
                               false);
    }
 
    table_close(rel, NoLock);
 
    /*
     * Copy checkAsUser to the row security quals and WithCheckOption checks,
     * in case they contain any subqueries referring to other relations.
     */
    setRuleCheckAsUser((Node *) *securityQuals, perminfo->checkAsUser);
    setRuleCheckAsUser((Node *) *withCheckOptions, perminfo->checkAsUser);
 
    /*
     * Mark this query as having row security, so plancache can invalidate it
     * when necessary (eg: role changes)
     */
    *hasRowSecurity = true;
}
 
/*
 * get_policies_for_relation
 *
 * Returns lists of permissive and restrictive policies to be applied to the
 * specified relation, based on the command type and role.
 *
 * This includes any policies added by extensions.
 */
static void
get_policies_for_relation(Relation relation, CmdType cmd, Oid user_id,
                          List **permissive_policies,
                          List **restrictive_policies)
{
    ListCell   *item;
 
    *permissive_policies = NIL;
    *restrictive_policies = NIL;
 
    /* First find all internal policies for the relation. */
    foreach(item, relation->rd_rsdesc->policies)
    {
        bool        cmd_matches = false;
        RowSecurityPolicy *policy = (RowSecurityPolicy *) lfirst(item);
 
        /* Always add ALL policies, if they exist. */
        if (policy->polcmd == '*')
            cmd_matches = true;
        else
        {
            /* Check whether the policy applies to the specified command type */
            switch (cmd)
            {
                case CMD_SELECT:
                    if (policy->polcmd == ACL_SELECT_CHR)
                        cmd_matches = true;
                    break;
                case CMD_INSERT:
                    if (policy->polcmd == ACL_INSERT_CHR)
                        cmd_matches = true;
                    break;
                case CMD_UPDATE:
                    if (policy->polcmd == ACL_UPDATE_CHR)
                        cmd_matches = true;
                    break;
                case CMD_DELETE:
                    if (policy->polcmd == ACL_DELETE_CHR)
                        cmd_matches = true;
                    break;
                case CMD_MERGE:
 
                    /*
                     * We do not support a separate policy for MERGE command.
                     * Instead it derives from the policies defined for other
                     * commands.
                     */
                    break;
                default:
                    elog(ERROR, "unrecognized policy command type %d",
                         (int) cmd);
                    break;
            }
        }
 
        /*
         * Add this policy to the relevant list of policies if it applies to
         * the specified role.
         */
        if (cmd_matches && check_role_for_policy(policy->roles, user_id))
        {
            if (policy->permissive)
                *permissive_policies = lappend(*permissive_policies, policy);
            else
                *restrictive_policies = lappend(*restrictive_policies, policy);
        }
    }
 
    /*
     * We sort restrictive policies by name so that any WCOs they generate are
     * checked in a well-defined order.
     */
    sort_policies_by_name(*restrictive_policies);
 
    /*
     * Then add any permissive or restrictive policies defined by extensions.
     * These are simply appended to the lists of internal policies, if they
     * apply to the specified role.
     */
    if (row_security_policy_hook_restrictive)
    {
        List       *hook_policies =
            (*row_security_policy_hook_restrictive) (cmd, relation);
 
        /*
         * As with built-in restrictive policies, we sort any hook-provided
         * restrictive policies by name also.  Note that we also intentionally
         * always check all built-in restrictive policies, in name order,
         * before checking restrictive policies added by hooks, in name order.
         */
        sort_policies_by_name(hook_policies);
 
        foreach(item, hook_policies)
        {
            RowSecurityPolicy *policy = (RowSecurityPolicy *) lfirst(item);
 
            if (check_role_for_policy(policy->roles, user_id))
                *restrictive_policies = lappend(*restrictive_policies, policy);
        }
    }
 
    if (row_security_policy_hook_permissive)
    {
        List       *hook_policies =
            (*row_security_policy_hook_permissive) (cmd, relation);
 
        foreach(item, hook_policies)
        {
            RowSecurityPolicy *policy = (RowSecurityPolicy *) lfirst(item);
 
            if (check_role_for_policy(policy->roles, user_id))
                *permissive_policies = lappend(*permissive_policies, policy);
        }
    }
}
 
/*
 * sort_policies_by_name
 *
 * This is only used for restrictive policies, ensuring that any
 * WithCheckOptions they generate are applied in a well-defined order.
 * This is not necessary for permissive policies, since they are all combined
 * together using OR into a single WithCheckOption check.
 */
static void
sort_policies_by_name(List *policies)
{
    list_sort(policies, row_security_policy_cmp);
}
 
/*
 * list_sort comparator to sort RowSecurityPolicy entries by name
 */
static int
row_security_policy_cmp(const ListCell *a, const ListCell *b)
{
    const RowSecurityPolicy *pa = (const RowSecurityPolicy *) lfirst(a);
    const RowSecurityPolicy *pb = (const RowSecurityPolicy *) lfirst(b);
 
    /* Guard against NULL policy names from extensions */
    if (pa->policy_name == NULL)
        return pb->policy_name == NULL ? 0 : 1;
    if (pb->policy_name == NULL)
        return -1;
 
    return strcmp(pa->policy_name, pb->policy_name);
}
 
/*
 * add_security_quals
 *
 * Add security quals to enforce the specified RLS policies, restricting
 * access to existing data in a table.  If there are no policies controlling
 * access to the table, then all access is prohibited --- i.e., an implicit
 * default-deny policy is used.
 *
 * New security quals are added to securityQuals, and hasSubLinks is set to
 * true if any of the quals added contain sublink subqueries.
 */
static void
add_security_quals(int rt_index,
                   List *permissive_policies,
                   List *restrictive_policies,
                   List **securityQuals,
                   bool *hasSubLinks)
{
    ListCell   *item;
    List       *permissive_quals = NIL;
    Expr       *rowsec_expr;
 
    /*
     * First collect up the permissive quals.  If we do not find any
     * permissive policies then no rows are visible (this is handled below).
     */
    foreach(item, permissive_policies)
    {
        RowSecurityPolicy *policy = (RowSecurityPolicy *) lfirst(item);
 
        if (policy->qual != NULL)
        {
            permissive_quals = lappend(permissive_quals,
                                       copyObject(policy->qual));
            *hasSubLinks |= policy->hassublinks;
        }
    }
 
    /*
     * We must have permissive quals, always, or no rows are visible.
     *
     * If we do not, then we simply return a single 'false' qual which results
     * in no rows being visible.
     */
    if (permissive_quals != NIL)
    {
        /*
         * We now know that permissive policies exist, so we can now add
         * security quals based on the USING clauses from the restrictive
         * policies.  Since these need to be combined together using AND, we
         * can just add them one at a time.
         */
        foreach(item, restrictive_policies)
        {
            RowSecurityPolicy *policy = (RowSecurityPolicy *) lfirst(item);
            Expr       *qual;
 
            if (policy->qual != NULL)
            {
                qual = copyObject(policy->qual);
                ChangeVarNodes((Node *) qual, 1, rt_index, 0);
 
                *securityQuals = list_append_unique(*securityQuals, qual);
                *hasSubLinks |= policy->hassublinks;
            }
        }
 
        /*
         * Then add a single security qual combining together the USING
         * clauses from all the permissive policies using OR.
         */
        if (list_length(permissive_quals) == 1)
            rowsec_expr = (Expr *) linitial(permissive_quals);
        else
            rowsec_expr = makeBoolExpr(OR_EXPR, permissive_quals, -1);
 
        ChangeVarNodes((Node *) rowsec_expr, 1, rt_index, 0);
        *securityQuals = list_append_unique(*securityQuals, rowsec_expr);
    }
    else
 
        /*
         * A permissive policy must exist for rows to be visible at all.
         * Therefore, if there were no permissive policies found, return a
         * single always-false clause.
         */
        *securityQuals = lappend(*securityQuals,
                                 makeConst(BOOLOID, -1, InvalidOid,
                                           sizeof(bool), BoolGetDatum(false),
                                           false, true));
}
 
/*
 * add_with_check_options
 *
 * Add WithCheckOptions of the specified kind to check that new records
 * added by an INSERT or UPDATE are consistent with the specified RLS
 * policies.  Normally new data must satisfy the WITH CHECK clauses from the
 * policies.  If a policy has no explicit WITH CHECK clause, its USING clause
 * is used instead.  In the special case of an UPDATE arising from an
 * INSERT ... ON CONFLICT DO UPDATE, existing records are first checked using
 * a WCO_RLS_CONFLICT_CHECK WithCheckOption, which always uses the USING
 * clauses from RLS policies.
 *
 * New WCOs are added to withCheckOptions, and hasSubLinks is set to true if
 * any of the check clauses added contain sublink subqueries.
 */
static void
add_with_check_options(Relation rel,
                       int rt_index,
                       WCOKind kind,
                       List *permissive_policies,
                       List *restrictive_policies,
                       List **withCheckOptions,
                       bool *hasSubLinks,
                       bool force_using)
{
    ListCell   *item;
    List       *permissive_quals = NIL;
 
#define QUAL_FOR_WCO(policy) \
    ( !force_using && \
      (policy)->with_check_qual != NULL ? \
      (policy)->with_check_qual : (policy)->qual )
 
    /*
     * First collect up the permissive policy clauses, similar to
     * add_security_quals.
     */
    foreach(item, permissive_policies)
    {
        RowSecurityPolicy *policy = (RowSecurityPolicy *) lfirst(item);
        Expr       *qual = QUAL_FOR_WCO(policy);
 
        if (qual != NULL)
        {
            permissive_quals = lappend(permissive_quals, copyObject(qual));
            *hasSubLinks |= policy->hassublinks;
        }
    }
 
    /*
     * There must be at least one permissive qual found or no rows are allowed
     * to be added.  This is the same as in add_security_quals.
     *
     * If there are no permissive_quals then we fall through and return a
     * single 'false' WCO, preventing all new rows.
     */
    if (permissive_quals != NIL)
    {
        /*
         * Add a single WithCheckOption for all the permissive policy clauses,
         * combining them together using OR.  This check has no policy name,
         * since if the check fails it means that no policy granted permission
         * to perform the update, rather than any particular policy being
         * violated.
         */
        WithCheckOption *wco;
 
        wco = makeNode(WithCheckOption);
        wco->kind = kind;
        wco->relname = pstrdup(RelationGetRelationName(rel));
        wco->polname = NULL;
        wco->cascaded = false;
 
        if (list_length(permissive_quals) == 1)
            wco->qual = (Node *) linitial(permissive_quals);
        else
            wco->qual = (Node *) makeBoolExpr(OR_EXPR, permissive_quals, -1);
 
        ChangeVarNodes(wco->qual, 1, rt_index, 0);
 
        *withCheckOptions = list_append_unique(*withCheckOptions, wco);
 
        /*
         * Now add WithCheckOptions for each of the restrictive policy clauses
         * (which will be combined together using AND).  We use a separate
         * WithCheckOption for each restrictive policy to allow the policy
         * name to be included in error reports if the policy is violated.
         */
        foreach(item, restrictive_policies)
        {
            RowSecurityPolicy *policy = (RowSecurityPolicy *) lfirst(item);
            Expr       *qual = QUAL_FOR_WCO(policy);
 
            if (qual != NULL)
            {
                qual = copyObject(qual);
                ChangeVarNodes((Node *) qual, 1, rt_index, 0);
 
                wco = makeNode(WithCheckOption);
                wco->kind = kind;
                wco->relname = pstrdup(RelationGetRelationName(rel));
                wco->polname = pstrdup(policy->policy_name);
                wco->qual = (Node *) qual;
                wco->cascaded = false;
 
                *withCheckOptions = list_append_unique(*withCheckOptions, wco);
                *hasSubLinks |= policy->hassublinks;
            }
        }
    }
    else
    {
        /*
         * If there were no policy clauses to check new data, add a single
         * always-false WCO (a default-deny policy).
         */
        WithCheckOption *wco;
 
        wco = makeNode(WithCheckOption);
        wco->kind = kind;
        wco->relname = pstrdup(RelationGetRelationName(rel));
        wco->polname = NULL;
        wco->qual = (Node *) makeConst(BOOLOID, -1, InvalidOid,
                                       sizeof(bool), BoolGetDatum(false),
                                       false, true);
        wco->cascaded = false;
 
        *withCheckOptions = lappend(*withCheckOptions, wco);
    }
}
 
/*
 * check_role_for_policy -
 *   determines if the policy should be applied for the current role
 */
static bool
check_role_for_policy(ArrayType *policy_roles, Oid user_id)
{
    int         i;
    Oid        *roles = (Oid *) ARR_DATA_PTR(policy_roles);
 
    /* Quick fall-thru for policies applied to all roles */
    if (roles[0] == ACL_ID_PUBLIC)
        return true;
 
    for (i = 0; i < ARR_DIMS(policy_roles)[0]; i++)
    {
        if (has_privs_of_role(user_id, roles[i]))
            return true;
    }
 
    return false;
}