server/TetherController.cpp

/*
 * Copyright (C) 2008 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.
 */

#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <string.h>

#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>

#include <netinet/in.h>
#include <arpa/inet.h>

#define LOG_TAG "TetherController"
#include <cutils/log.h>
#include <cutils/properties.h>

#include "Fwmark.h"
#include "NetdConstants.h"
#include "Permission.h"
#include "InterfaceController.h"
#include "NetworkController.h"
#include "TetherController.h"

namespace {

const char BP_TOOLS_MODE[] = "bp-tools";
const char IPV4_FORWARDING_PROC_FILE[] = "/proc/sys/net/ipv4/ip_forward";
const char IPV6_FORWARDING_PROC_FILE[] = "/proc/sys/net/ipv6/conf/all/forwarding";
const char SEPARATOR[] = "|";

bool writeToFile(const char* filename, const char* value) {
    int fd = open(filename, O_WRONLY | O_CLOEXEC);
    if (fd < 0) {
        ALOGE("Failed to open %s: %s", filename, strerror(errno));
        return false;
    }

    const ssize_t len = strlen(value);
    if (write(fd, value, len) != len) {
        ALOGE("Failed to write %s to %s: %s", value, filename, strerror(errno));
        close(fd);
        return false;
    }
    close(fd);
    return true;
}

bool configureForIPv6Router(const char *interface) {
    return (InterfaceController::setEnableIPv6(interface, 0) == 0)
            && (InterfaceController::setAcceptIPv6Ra(interface, 0) == 0)
            && (InterfaceController::setAcceptIPv6Dad(interface, 0) == 0)
            && (InterfaceController::setIPv6DadTransmits(interface, "0") == 0)
            && (InterfaceController::setEnableIPv6(interface, 1) == 0);
}

void configureForIPv6Client(const char *interface) {
    InterfaceController::setAcceptIPv6Ra(interface, 1);
    InterfaceController::setAcceptIPv6Dad(interface, 1);
    InterfaceController::setIPv6DadTransmits(interface, "1");
    InterfaceController::setEnableIPv6(interface, 0);
}

bool inBpToolsMode() {
    // In BP tools mode, do not disable IP forwarding
    char bootmode[PROPERTY_VALUE_MAX] = {0};
    property_get("ro.bootmode", bootmode, "unknown");
    return !strcmp(BP_TOOLS_MODE, bootmode);
}

}  // namespace

namespace android {
namespace net {

TetherController::TetherController() {
    mDnsNetId = 0;
    mDaemonFd = -1;
    mDaemonPid = 0;
    if (inBpToolsMode()) {
        enableForwarding(BP_TOOLS_MODE);
    } else {
        setIpFwdEnabled();
    }
}

TetherController::~TetherController() {
    mInterfaces.clear();
    mDnsForwarders.clear();
    mForwardingRequests.clear();
}

bool TetherController::setIpFwdEnabled() {
    bool success = true;
    const char* value = mForwardingRequests.empty() ? "0" : "1";
    ALOGD("Setting IP forward enable = %s", value);
    success &= writeToFile(IPV4_FORWARDING_PROC_FILE, value);
    success &= writeToFile(IPV6_FORWARDING_PROC_FILE, value);
    return success;
}

bool TetherController::enableForwarding(const char* requester) {
    // Don't return an error if this requester already requested forwarding. Only return errors for
    // things that the caller caller needs to care about, such as "couldn't write to the file to
    // enable forwarding".
    mForwardingRequests.insert(requester);
    return setIpFwdEnabled();
}

bool TetherController::disableForwarding(const char* requester) {
    mForwardingRequests.erase(requester);
    return setIpFwdEnabled();
}

size_t TetherController::forwardingRequestCount() {
    return mForwardingRequests.size();
}

#define TETHER_START_CONST_ARG        10

int TetherController::startTethering(int num_addrs, char **dhcp_ranges) {
    if (mDaemonPid != 0) {
        ALOGE("Tethering already started");
        errno = EBUSY;
        return -1;
    }

    ALOGD("Starting tethering services");

    pid_t pid;
    int pipefd[2];

    if (pipe(pipefd) < 0) {
        ALOGE("pipe failed (%s)", strerror(errno));
        return -1;
    }

    /*
     * TODO: Create a monitoring thread to handle and restart
     * the daemon if it exits prematurely
     */
    if ((pid = fork()) < 0) {
        ALOGE("fork failed (%s)", strerror(errno));
        close(pipefd[0]);
        close(pipefd[1]);
        return -1;
    }

    if (!pid) {
        close(pipefd[1]);
        if (pipefd[0] != STDIN_FILENO) {
            if (dup2(pipefd[0], STDIN_FILENO) != STDIN_FILENO) {
                ALOGE("dup2 failed (%s)", strerror(errno));
                return -1;
            }
            close(pipefd[0]);
        }

        Fwmark fwmark;
        fwmark.netId = NetworkController::LOCAL_NET_ID;
        fwmark.explicitlySelected = true;
        fwmark.protectedFromVpn = true;
        fwmark.permission = PERMISSION_SYSTEM;
        char markStr[UINT32_HEX_STRLEN];
        snprintf(markStr, sizeof(markStr), "0x%x", fwmark.intValue);

        int num_processed_args = TETHER_START_CONST_ARG + (num_addrs/2) + 1;
        char **args = (char **)malloc(sizeof(char *) * num_processed_args);
        args[num_processed_args - 1] = NULL;
        args[0] = (char *)"/system/bin/dnsmasq";
        args[1] = (char *)"--keep-in-foreground";
        args[2] = (char *)"--no-resolv";
        args[3] = (char *)"--no-poll";
        args[4] = (char *)"--dhcp-authoritative";
        // TODO: pipe through metered status from ConnService
        args[5] = (char *)"--dhcp-option-force=43,ANDROID_METERED";
        args[6] = (char *)"--pid-file";
        args[7] = (char *)"--listen-mark";
        args[8] = (char *)markStr;
        args[9] = (char *)"";

        int nextArg = TETHER_START_CONST_ARG;
        for (int addrIndex = 0; addrIndex < num_addrs; addrIndex += 2) {
            asprintf(&(args[nextArg++]),"--dhcp-range=%s,%s,1h",
                     dhcp_ranges[addrIndex], dhcp_ranges[addrIndex+1]);
        }

        if (execv(args[0], args)) {
            ALOGE("execl failed (%s)", strerror(errno));
        }
        ALOGE("Should never get here!");
        _exit(-1);
    } else {
        close(pipefd[0]);
        mDaemonPid = pid;
        mDaemonFd = pipefd[1];
        applyDnsInterfaces();
        ALOGD("Tethering services running");
    }

    return 0;
}

int TetherController::stopTethering() {

    if (mDaemonPid == 0) {
        ALOGE("Tethering already stopped");
        return 0;
    }

    ALOGD("Stopping tethering services");

    kill(mDaemonPid, SIGTERM);
    waitpid(mDaemonPid, NULL, 0);
    mDaemonPid = 0;
    close(mDaemonFd);
    mDaemonFd = -1;
    ALOGD("Tethering services stopped");
    return 0;
}

bool TetherController::isTetheringStarted() {
    return (mDaemonPid == 0 ? false : true);
}

#define MAX_CMD_SIZE 1024

int TetherController::setDnsForwarders(unsigned netId, char **servers, int numServers) {
    int i;
    char daemonCmd[MAX_CMD_SIZE];

    Fwmark fwmark;
    fwmark.netId = netId;
    fwmark.explicitlySelected = true;
    fwmark.protectedFromVpn = true;
    fwmark.permission = PERMISSION_SYSTEM;

    snprintf(daemonCmd, sizeof(daemonCmd), "update_dns%s0x%x", SEPARATOR, fwmark.intValue);
    int cmdLen = strlen(daemonCmd);

    mDnsForwarders.clear();
    for (i = 0; i < numServers; i++) {
        ALOGD("setDnsForwarders(0x%x %d = '%s')", fwmark.intValue, i, servers[i]);

        addrinfo *res, hints = { .ai_flags = AI_NUMERICHOST };
        int ret = getaddrinfo(servers[i], NULL, &hints, &res);
        freeaddrinfo(res);
        if (ret) {
            ALOGE("Failed to parse DNS server '%s'", servers[i]);
            mDnsForwarders.clear();
            errno = EINVAL;
            return -1;
        }

        cmdLen += (strlen(servers[i]) + 1);
        if (cmdLen + 1 >= MAX_CMD_SIZE) {
            ALOGD("Too many DNS servers listed");
            break;
        }

        strcat(daemonCmd, SEPARATOR);
        strcat(daemonCmd, servers[i]);
        mDnsForwarders.push_back(servers[i]);
    }

    mDnsNetId = netId;
    if (mDaemonFd != -1) {
        ALOGD("Sending update msg to dnsmasq [%s]", daemonCmd);
        if (write(mDaemonFd, daemonCmd, strlen(daemonCmd) +1) < 0) {
            ALOGE("Failed to send update command to dnsmasq (%s)", strerror(errno));
            mDnsForwarders.clear();
            errno = EREMOTEIO;
            return -1;
        }
    }
    return 0;
}

unsigned TetherController::getDnsNetId() {
    return mDnsNetId;
}

const std::list<std::string> &TetherController::getDnsForwarders() const {
    return mDnsForwarders;
}

bool TetherController::applyDnsInterfaces() {
    char daemonCmd[MAX_CMD_SIZE];

    strcpy(daemonCmd, "update_ifaces");
    int cmdLen = strlen(daemonCmd);
    bool haveInterfaces = false;

    for (const auto &ifname : mInterfaces) {
        cmdLen += (ifname.size() + 1);
        if (cmdLen + 1 >= MAX_CMD_SIZE) {
            ALOGD("Too many DNS ifaces listed");
            break;
        }

        strcat(daemonCmd, SEPARATOR);
        strcat(daemonCmd, ifname.c_str());
        haveInterfaces = true;
    }

    if ((mDaemonFd != -1) && haveInterfaces) {
        ALOGD("Sending update msg to dnsmasq [%s]", daemonCmd);
        if (write(mDaemonFd, daemonCmd, strlen(daemonCmd) +1) < 0) {
            ALOGE("Failed to send update command to dnsmasq (%s)", strerror(errno));
            return false;
        }
    }
    return true;
}

int TetherController::tetherInterface(const char *interface) {
    ALOGD("tetherInterface(%s)", interface);
    if (!isIfaceName(interface)) {
        errno = ENOENT;
        return -1;
    }

    if (!configureForIPv6Router(interface)) {
        configureForIPv6Client(interface);
        return -1;
    }
    mInterfaces.push_back(interface);

    if (!applyDnsInterfaces()) {
        mInterfaces.pop_back();
        configureForIPv6Client(interface);
        return -1;
    } else {
        return 0;
    }
}

int TetherController::untetherInterface(const char *interface) {
    ALOGD("untetherInterface(%s)", interface);

    for (auto it = mInterfaces.cbegin(); it != mInterfaces.cend(); ++it) {
        if (!strcmp(interface, it->c_str())) {
            mInterfaces.erase(it);

            configureForIPv6Client(interface);
            return applyDnsInterfaces() ? 0 : -1;
        }
    }
    errno = ENOENT;
    return -1;
}

const std::list<std::string> &TetherController::getTetheredInterfaceList() const {
    return mInterfaces;
}

}  // namespace net
}  // namespace android