usercontext.c

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/*-------------------------------------------------------------------------
 *
 * usercontext.c
 *    Convenience functions for running code as a different database user.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/init/usercontext.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "miscadmin.h"
#include "utils/acl.h"
#include "utils/guc.h"
#include "utils/usercontext.h"
 
/*
 * Temporarily switch to a new user ID.
 *
 * If the current user doesn't have permission to SET ROLE to the new user,
 * an ERROR occurs.
 *
 * If the new user doesn't have permission to SET ROLE to the current user,
 * SECURITY_RESTRICTED_OPERATION is imposed and a new GUC nest level is
 * created so that any settings changes can be rolled back.
 */
void
SwitchToUntrustedUser(Oid userid, UserContext *context)
{
    /* Get the current user ID and security context. */
    GetUserIdAndSecContext(&context->save_userid,
                           &context->save_sec_context);
 
    /* Check that we have sufficient privileges to assume the target role. */
    if (!member_can_set_role(context->save_userid, userid))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("role \"%s\" cannot SET ROLE to \"%s\"",
                        GetUserNameFromId(context->save_userid, false),
                        GetUserNameFromId(userid, false))));
 
    /*
     * Try to prevent the user to which we're switching from assuming the
     * privileges of the current user, unless they can SET ROLE to that user
     * anyway.
     */
    if (member_can_set_role(userid, context->save_userid))
    {
        /*
         * Each user can SET ROLE to the other, so there's no point in
         * imposing any security restrictions. Just let the user do whatever
         * they want.
         */
        SetUserIdAndSecContext(userid, context->save_sec_context);
        context->save_nestlevel = -1;
    }
    else
    {
        int         sec_context = context->save_sec_context;
 
        /*
         * This user can SET ROLE to the target user, but not the other way
         * around, so protect ourselves against the target user by setting
         * SECURITY_RESTRICTED_OPERATION to prevent certain changes to the
         * session state. Also set up a new GUC nest level, so that we can
         * roll back any GUC changes that may be made by code running as the
         * target user, inasmuch as they could be malicious.
         */
        sec_context |= SECURITY_RESTRICTED_OPERATION;
        SetUserIdAndSecContext(userid, sec_context);
        context->save_nestlevel = NewGUCNestLevel();
    }
}
 
/*
 * Switch back to the original user ID.
 *
 * If we created a new GUC nest level, also roll back any changes that were
 * made within it.
 */
void
RestoreUserContext(UserContext *context)
{
    if (context->save_nestlevel != -1)
        AtEOXact_GUC(false, context->save_nestlevel);
    SetUserIdAndSecContext(context->save_userid, context->save_sec_context);
}