limit_manager.h

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// Copyright (C) 2022-2025 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
#ifndef ISC_LIMITS_RATE_LIMIT_MANAGER_H
#define ISC_LIMITS_RATE_LIMIT_MANAGER_H
 
#include <database/audit_entry.h>
#include <dhcp/classify.h>
#include <dhcp/pkt_template.h>
#include <dhcpsrv/cfgmgr.h>
#include <dhcpsrv/lease.h>
#include <dhcpsrv/lease_mgr_factory.h>
#include <dhcpsrv/srv_config.h>
#include <dhcpsrv/subnet.h>
#include <dhcpsrv/subnet_id.h>
#include <hooks/hooks.h>
#include <limits/configuration.h>
#include <limits/limits_logger.h>
#include <util/dhcp_space.h>
#include <util/multi_threading_mgr.h>
 
#include <boost/circular_buffer.hpp>
 
#include <chrono>
#include <unordered_map>
#include <vector>
 
namespace isc {
namespace limits {

using TimePoint = std::chrono::time_point<std::chrono::system_clock>;

using TimeSeries = boost::circular_buffer<TimePoint>;

struct ProtectedTimeSeries {
    std::mutex mutex_;

    TimeSeries time_points_;
};

typedef std::shared_ptr<ProtectedTimeSeries> ProtectedTimeSeriesPtr;

struct LimitManager {
    static LimitManager& instance();

    void clear();

    void initialize(isc::dhcp::SrvConfigPtr const& config);

    void parse(isc::dhcp::SrvConfigPtr const& config);

    template <isc::util::DhcpSpace D>
    int cb_updated(isc::hooks::CalloutHandle& handle) {
        isc::hooks::CalloutHandle::CalloutNextStep const status(handle.getStatus());
        if (status == isc::hooks::CalloutHandle::NEXT_STEP_DROP ||
            status == isc::hooks::CalloutHandle::NEXT_STEP_SKIP) {
            return (0);
        }
 
        isc::db::AuditEntryCollectionPtr audit_entries;
        handle.getArgument("audit_entries", audit_entries);
        if (!audit_entries) {
            isc_throw(Unexpected, "null audit_entries in LimitManager::cb_updated");
        }
 
        auto const& object_type_index(audit_entries->get<isc::db::AuditEntryObjectTypeTag>());
        auto const& client_class_range(object_type_index.equal_range(
            isc::util::formatDhcpSpace<D>("dhcp{}_client_class")));
        auto const& subnet_range(object_type_index.equal_range(
            isc::util::formatDhcpSpace<D>("dhcp{}_subnet")));
 
        // If any client classes or subnets changed, reparse the entire configuration.
        if (std::distance(client_class_range.first, client_class_range.second) ||
            std::distance(subnet_range.first, subnet_range.second)) {
            LimitManager::instance().parse(isc::dhcp::CfgMgr::instance().getCurrentCfg());
        }
 
        return (0);
    }

    template <isc::util::DhcpSpace D>
    int dhcp_srv_configured(isc::hooks::CalloutHandle& handle) {
        isc::hooks::CalloutHandle::CalloutNextStep const status(handle.getStatus());
        if (status == isc::hooks::CalloutHandle::NEXT_STEP_DROP ||
            status == isc::hooks::CalloutHandle::NEXT_STEP_SKIP) {
            return (0);
        }
 
        if (isc::dhcp::LeaseMgrFactory::haveInstance()) {
            // If lease limiting is used, make sure the database has JSON support.
            if (!isc::dhcp::LeaseMgrFactory::instance().isJsonSupported()) {
                const std::string error("The lease database you have configured "
                    "does not support JSON operations which are required for lease "
                    "limiting.");
                handle.setArgument("error", error);
                handle.setStatus(isc::hooks::CalloutHandle::NEXT_STEP_DROP);
                return (1);
            }
 
            // Recount the leases by class.
            recountClassLeases<D>();
        } else {
            std::string const lease_db_access_string(isc::dhcp::CfgMgr::instance()
                                                         .getStagingCfg()
                                                         ->getCfgDbAccess()
                                                         ->getLeaseDbAccessString());
            if (lease_db_access_string.find("retry-on-startup=true") &&
                (lease_db_access_string.find("type=mysql") ||
                 lease_db_access_string.find("type=postgresql"))) {
                LOG_WARN(limits_logger, LIMITS_CONFIGURATION_LEASE_BACKEND_NOT_AVAILABLE);
            } else {
                LOG_ERROR(limits_logger,
                          LIMITS_CONFIGURATION_LEASE_BACKEND_SHOULD_HAVE_BEEN_AVAILABLE);
            }
        }
 
        return (0);
    }

    template <isc::util::DhcpSpace D>
    int pkt_receive(isc::hooks::CalloutHandle& handle) {
        isc::hooks::CalloutHandle::CalloutNextStep const status(handle.getStatus());
        if (status == isc::hooks::CalloutHandle::NEXT_STEP_DROP ||
            status == isc::hooks::CalloutHandle::NEXT_STEP_SKIP) {
            return (0);
        }
 
        // Get the client classes.
        isc::dhcp::PktTPtr<D> packet;
        handle.getArgument(isc::util::formatDhcpSpace<D>("query{}"), packet);
        if (!packet) {
            isc_throw(Unexpected, "null packet in LimitManager::pkt_receive");
        }
        auto const& classes(packet->getClasses());
 
        // To be able to iterate over client classes and template classes, all
        // regular classes must be added to a SubClassContainer with subclass
        // name set to the same value as template class name.
        auto const& relations = packet->getSubClassesRelations();
 
        // Get the current time.
        TimePoint const now(std::chrono::system_clock::now());
 
        // Should contain client classes that are both in the packet and that are limited.
        std::vector<isc::dhcp::ClientClass> common_client_classes;
 
        // Lock a global-wide mutex for all client classes. It's not a necessary condition, but it's
        // sufficient. Locking per client class, similarly to how it happens for subnet IDs would
        // have been more efficient in a more heterogeneous class-to-packet distribution, but that
        // situation is not guaranteed.
        isc::util::MultiThreadingLock lock(mutex_);
 
        // Check if the rate limit is respected.
        for (auto const& c : relations) {
            auto const& class_def = isc::dhcp::CfgMgr::instance().getCurrentCfg()->getClientClassDictionary()->findClass(c.class_def_);
            if (!class_def) {
                continue;
            }
 
            auto const &limit_cfg = rate_limit_configuration_.parseUserContext(class_def->getContext());
 
            if (!limit_cfg) {
                continue;
            }
 
            // Get the limit.
            RateLimit const& limit(limit_cfg->stringValue());
 
            // Get the time series. Create a list on this class if not already added to the map.
            TimeSeries& time_series(clocked_in_times_by_class_[c.class_]);
 
            time_series.set_capacity(limit.allowed_packets_);
 
            // Remove all expired times.
            while (!time_series.empty()) {
                if (time_series.back() + limit.time_unit_ < now) {
                    time_series.pop_back();
                } else {
                    // This is an optimization. Job is finished at the first time point that is not
                    // expired. The rest are sorted and higher in value, thus not expired.
                    break;
                }
            }
 
            // Effectively check the limit.
            if (time_series.size() == limit.allowed_packets_) {
                // Drop the packet.
                handle.setStatus(isc::hooks::CalloutHandle::NEXT_STEP_DROP);
 
                LOG_DEBUG(limits_logger, isc::log::DBGLVL_TRACE_BASIC,
                          LIMITS_PACKET_WITH_CLIENT_CLASSES_RATE_LIMIT_DROPPED)
                    .arg(classes.toText())
                    .arg(limit.text_)
                    .arg(c.class_);
 
                // No need to check other client classes since packet is dropped.
                break;
            }
 
            // Cache the set of client classes that are both in the packet and limited. If packet is
            // not dropped, they will be iterated through one more time further below. As such, the
            // configuration lookup for each client class at the beginning of this loop will no
            // longer be required.
            common_client_classes.push_back(c.class_);
        }
 
        if (handle.getStatus() != isc::hooks::CalloutHandle::NEXT_STEP_DROP) {
            // Honor the packet and keep track of it.
            for (auto const& c : common_client_classes) {
                TimeSeries& time_series(clocked_in_times_by_class_.at(c));
                time_series.push_front(now);
            }
 
            // Only log that the packet is within the limit if this packet is being rate limited.
            if (!common_client_classes.empty()) {
                LOG_DEBUG(limits_logger, isc::log::DBGLVL_TRACE_DETAIL_DATA,
                          LIMITS_PACKET_WITH_CLIENT_CLASSES_RATE_LIMIT_HONORED)
                    .arg(classes.toText());
            }
        }
 
        return (0);
    }

    template <isc::util::DhcpSpace D>
    int subnet_select(isc::hooks::CalloutHandle& handle) {
        isc::hooks::CalloutHandle::CalloutNextStep const status(handle.getStatus());
        if (status == isc::hooks::CalloutHandle::NEXT_STEP_DROP ||
            status == isc::hooks::CalloutHandle::NEXT_STEP_SKIP) {
            return (0);
        }
 
        // Get the subnet ID.
        isc::dhcp::ConstSubnetTPtr<D> subnet;
        handle.getArgument(isc::util::formatDhcpSpace<D>("subnet{}"), subnet);
        if (!subnet) {
            LOG_DEBUG(limits_logger, isc::log::DBGLVL_TRACE_DETAIL_DATA,
                      LIMITS_PACKET_WIIH_SUBNET_ID_RATE_NO_SUBNET);
            return (0);
        }
        isc::dhcp::SubnetID const subnet_id(subnet->getID());
 
        RateLimit limit;
        auto const& limit_cfg = subnetRateLimit<D>(subnet_id);
        if (limit_cfg) {
            // Get the limit.
            limit = RateLimit(limit_cfg->stringValue());
        } else {
            return (0);
        }
 
        ProtectedTimeSeriesPtr time_series;
 
        // Lock a global-wide mutex while configuration can be read-to and written-from.
        {
            isc::util::MultiThreadingLock lock(mutex_);
 
            // Create a time series on this subnet ID if not already added to the map.
            ProtectedTimeSeriesPtr& time_series_ref(clocked_in_times_by_subnet_id_[subnet_id]);
            if (!time_series_ref) {
                time_series_ref = std::make_shared<ProtectedTimeSeries>();
            }
            time_series = time_series_ref;
        }
 
        // Get the current time.
        TimePoint const now(std::chrono::system_clock::now());
 
        // Lock the mutex on this subnet ID.
        isc::util::MultiThreadingLock lock(time_series->mutex_);
 
        time_series->time_points_.set_capacity(limit.allowed_packets_);
 
        // Remove all expired times.
        while (!time_series->time_points_.empty()) {
            if (time_series->time_points_.back() + limit.time_unit_ < now) {
                time_series->time_points_.pop_back();
            } else {
                // This is an optimization. Job is finished at the first time point that is not
                // expired. The rest are sorted and higher in value, thus not expired.
                break;
            }
        }
 
        // Check the limit.
        if (time_series->time_points_.size() < limit.allowed_packets_) {
            // Honor the packet and keep track of it.
            time_series->time_points_.push_front(now);
        } else {
            // Drop the packet.
            handle.setStatus(isc::hooks::CalloutHandle::NEXT_STEP_DROP);
 
            LOG_DEBUG(limits_logger, isc::log::DBGLVL_TRACE_BASIC,
                      LIMITS_PACKET_WITH_SUBNET_ID_RATE_LIMIT_DROPPED)
                .arg(subnet_id)
                .arg(limit.text_);
 
            return (0);
        }
 
        LOG_DEBUG(limits_logger, isc::log::DBGLVL_TRACE_DETAIL_DATA,
                  LIMITS_PACKET_WITH_SUBNET_ID_RATE_LIMIT_HONORED)
            .arg(subnet_id)
            .arg(limit.text_);
 
        return (0);
    }

    template <isc::util::DhcpSpace D>
    int lease_callout(isc::hooks::CalloutHandle& handle, bool lease_update = false) {
        isc::hooks::CalloutHandle::CalloutNextStep const status(handle.getStatus());
        if (status == isc::hooks::CalloutHandle::NEXT_STEP_DROP ||
            status == isc::hooks::CalloutHandle::NEXT_STEP_SKIP) {
            return (0);
        }
 
        // Get the lease.
        isc::dhcp::LeaseTPtr<D> lease;
        handle.getArgument(isc::util::formatDhcpSpace<D>("lease{}"), lease);
        if (!lease) {
            isc_throw(Unexpected, "null lease in LimitManager::lease_callout");
        }
        isc::dhcp::SubnetID const subnet_id(lease->subnet_id_);
 
        // Get the client classes.
        isc::dhcp::PktTPtr<D> packet;
        handle.getArgument(isc::util::formatDhcpSpace<D>("query{}"), packet);
        if (!packet) {
            isc_throw(Unexpected, "null packet in LimitManager::lease_callout");
        }
        auto const& classes(packet->getClasses());
 
        // Add client classes to the lease context.
        addClientClassesToLeaseContext(classes, lease);
 
        // Don't check limits for lease renewals.
        if (lease_update) {
            return (0);
        }
 
        // To be able to iterate over client classes and template classes, all
        // regular classes must be added to a SubClassContainer with subclass
        // name set to the same value as template class name.
        auto const& relations(packet->getSubClassesRelations());
 
        // Create parts of the limits context.
        // Add client class limits to the context.
        isc::data::ElementPtr client_class_limits = clientClassLimitsToElement<D>(relations, lease->getType());
        // Add subnet limits to the context.
        isc::data::ElementPtr subnet_limit = subnetLimitToElement<D>(subnet_id, lease->getType());
 
        // Tie the limits together into an "ISC" context.
        isc::data::ElementPtr limits(isc::data::Element::createMap());
        if (!client_class_limits->empty()) {
            limits->set("client-classes", client_class_limits);
        }
        if (!subnet_limit->empty()) {
            limits->set("subnet", subnet_limit);
        }
        if (limits->empty()) {
            // No limits means we let the lease through by default. Exit here so that we don't check
            // lease limits for nothing and so that we don't log details on non-limited leases.
            return (0);
        }
        isc::data::ElementPtr ISC(isc::data::Element::createMap());
        ISC->set("limits", limits);
        isc::data::ElementPtr context(isc::data::Element::createMap());
        context->set("ISC", ISC);
 
        // Check lease limits.
        std::string const limit_exceeded_text(checkLeaseLimits<D>(context));
        if (limit_exceeded_text.empty()) {
            LOG_DEBUG(limits_logger, isc::log::DBGLVL_TRACE_BASIC, LIMITS_LEASE_WITHIN_LIMITS)
                .arg(lease->addr_);
        } else {
            // Prevent the lease from being allocated.
            handle.setStatus(isc::hooks::CalloutHandle::NEXT_STEP_SKIP);
 
            LOG_DEBUG(limits_logger, isc::log::DBGLVL_TRACE_BASIC, LIMITS_LEASE_LIMIT_EXCEEDED)
                .arg(limit_exceeded_text);
        }
 
        return (0);
    }
 
private:
    void addClientClassesToLeaseContext(isc::dhcp::ClientClasses const& classes,
                                        isc::dhcp::LeasePtr const& lease);

    template <isc::util::DhcpSpace D>
    isc::data::ElementPtr clientClassLimitsToElement(isc::dhcp::SubClassRelationContainer const& classes,
                                                     isc::dhcp::Lease::Type const& lease_type);

    template <isc::util::DhcpSpace D>
    isc::data::ElementPtr subnetLimitToElement(isc::dhcp::SubnetID const subnet_id,
                                               isc::dhcp::Lease::Type const& lease_type);

    template <isc::util::DhcpSpace D>
    isc::data::ConstElementPtr subnetRateLimit(isc::dhcp::SubnetID const subnet_id);

    template <isc::util::DhcpSpace D>
    std::string checkLeaseLimits(isc::data::ConstElementPtr const& context) const;

    template <isc::util::DhcpSpace D>
    void recountClassLeases() const;

    std::unordered_map<isc::dhcp::ClientClass, TimeSeries> clocked_in_times_by_class_;

    std::unordered_map<isc::dhcp::SubnetID, ProtectedTimeSeriesPtr> clocked_in_times_by_subnet_id_;

    std::mutex mutex_;

    AddressLimitConfiguration address_limit_configuration_;

    PrefixLimitConfiguration prefix_limit_configuration_;

    RateLimitConfiguration rate_limit_configuration_;

    LimitManager() = default;
    LimitManager(LimitManager const&) = delete;
    LimitManager& operator=(LimitManager const&) = delete;
};
 
}  // namespace limits
}  // namespace isc
 
#endif  // ISC_LIMITS_RATE_LIMIT_MANAGER_H