server/IdletimerController.cpp

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * MODUS OPERANDI
 * --------------
 *
 * IPTABLES command sequence:
 *
 * iptables -F
 *
 * iptables -t raw -F idletimer_PREROUTING
 * iptables -t mangle -F idletimer_POSTROUTING
 *
 *
 * iptables -t raw -N idletimer_PREROUTING
 * iptables -t mangle -N idletimer_POSTROUTING
 *
 * iptables -t raw -D PREROUTING -j idletimer_PREROUTING
 * iptables -t mangle -D POSTROUTING -j idletimer_POSTROUTING
 *
 *
 * iptables -t raw -I PREROUTING -j idletimer_PREROUTING
 * iptables -t mangle -I POSTROUTING -j idletimer_POSTROUTING
 *
 * # For notifications to work the lable name must match the name of a valid interface.
 * # If the label name does match an interface, the rules will be a no-op.
 *
 * iptables -t raw -A idletimer_PREROUTING -i rmnet0 -j IDLETIMER  --timeout 5 --label test-chain --send_nl_msg 1
 * iptables -t mangle -A idletimer_POSTROUTING -o rmnet0 -j IDLETIMER  --timeout 5 --label test-chain --send_nl_msg 1
 *
 * iptables -nxvL -t raw
 * iptables -nxvL -t mangle
 *
 * =================
 *
 * ndc command sequence
 * ------------------
 * ndc idletimer enable
 * ndc idletimer add <iface> <timeout> <class label>
 * ndc idletimer remove <iface> <timeout> <class label>
 *
 * Monitor effect on the iptables chains after each step using:
 *     iptables -nxvL -t raw
 *     iptables -nxvL -t mangle
 *
 * Remember that the timeout value has to be same at the time of the
 * removal.
 *
 * =================
 *
 * Verifying the iptables rule
 * ---------------------------
 * We want to make sure the iptable rules capture every packet. It can be
 * verified with tcpdump. First take a note of the pkts count for the two rules:
 *
 * adb shell iptables -t mangle -L idletimer_mangle_POSTROUTING -v && adb shell iptables -t raw -L idletimer_raw_PREROUTING -v
 *
 * And then, before any network traffics happen on the device, run tcpdump:
 *
 * adb shell tcpdump | tee tcpdump.log
 *
 * After a while run iptables commands again, you could then count the number
 * of incoming and outgoing packets captured by tcpdump, and compare that with
 * the numbers reported by iptables command. There shouldn't be too much
 * difference on these numbers, i.e., with 2000 packets captured it should
 * differ by less than 5.
 *
 * =================
 *
 * Note that currently if the name of the iface is incorrect, iptables
 * will setup rules without checking if it is the name of a valid
 * interface (although no notifications will ever be received).  It is
 * the responsibility of code in Java land to ensure that the interface name
 * is correct. The benefit of this, is that idletimers can be setup on
 * interfaces than come and go.
 *
 * A remove should be called for each add command issued during cleanup, as duplicate
 * entries of the rule may exist and will all have to removed.
 *
 */

#define LOG_NDEBUG 0

#include <string>
#include <vector>

#include <stdint.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <cutils/properties.h>

#include <android-base/strings.h>
#include <android-base/stringprintf.h>

#define LOG_TAG "IdletimerController"
#include <log/log.h>

#include "IdletimerController.h"
#include "NetdConstants.h"

using android::base::Join;
using android::base::StringPrintf;

const char* IdletimerController::LOCAL_RAW_PREROUTING = "idletimer_raw_PREROUTING";
const char* IdletimerController::LOCAL_MANGLE_POSTROUTING = "idletimer_mangle_POSTROUTING";

auto IdletimerController::execIptablesRestore = ::execIptablesRestore;

IdletimerController::IdletimerController() {
}

IdletimerController::~IdletimerController() {
}

bool IdletimerController::setupIptablesHooks() {
    return true;
}

int IdletimerController::modifyInterfaceIdletimer(IptOp op, const char *iface,
                                                  uint32_t timeout,
                                                  const char *classLabel) {
    if (!isIfaceName(iface)) {
        errno = ENOENT;
        return -1;
    }

    const char *addRemove = (op == IptOpAdd) ? "-A" : "-D";
    std::vector<std::string> cmds = {
        "*raw",
        StringPrintf("%s %s -i %s -j IDLETIMER --timeout %u --label %s --send_nl_msg 1",
                    addRemove, LOCAL_RAW_PREROUTING, iface, timeout, classLabel),
        "COMMIT",
        "*mangle",
        StringPrintf("%s %s -o %s -j IDLETIMER --timeout %u --label %s --send_nl_msg 1",
                    addRemove, LOCAL_MANGLE_POSTROUTING, iface, timeout, classLabel),
        "COMMIT\n",
    };

    return (execIptablesRestore(V4V6, Join(cmds, '\n')) == 0) ? 0 : -EREMOTEIO;
}

int IdletimerController::addInterfaceIdletimer(const char *iface,
                                               uint32_t timeout,
                                               const char *classLabel) {
    return modifyInterfaceIdletimer(IptOpAdd, iface, timeout, classLabel);
}

int IdletimerController::removeInterfaceIdletimer(const char *iface,
                                                  uint32_t timeout,
                                                  const char *classLabel) {
    return modifyInterfaceIdletimer(IptOpDelete, iface, timeout, classLabel);
}