Tethering/jni/android_net_util_TetheringUtils.cpp

/*
 * Copyright (C) 2017 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 <errno.h>
#include <error.h>
#include <jni.h>
#include <linux/filter.h>
#include <nativehelper/JNIHelp.h>
#include <nativehelper/JNIHelpCompat.h>
#include <nativehelper/ScopedUtfChars.h>
#include <net/if.h>
#include <netinet/ether.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <sys/socket.h>
#include <stdio.h>

#define LOG_TAG "TetheringUtils"
#include <android/log.h>

namespace android {

static const uint32_t kIPv6NextHeaderOffset = offsetof(ip6_hdr, ip6_nxt);
static const uint32_t kIPv6PayloadStart = sizeof(ip6_hdr);
static const uint32_t kICMPv6TypeOffset = kIPv6PayloadStart + offsetof(icmp6_hdr, icmp6_type);

static void android_net_util_setupIcmpFilter(JNIEnv *env, jobject javaFd, uint32_t type) {
    sock_filter filter_code[] = {
        // Check header is ICMPv6.
        BPF_STMT(BPF_LD  | BPF_B   | BPF_ABS,  kIPv6NextHeaderOffset),
        BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K,    IPPROTO_ICMPV6, 0, 3),

        // Check ICMPv6 type.
        BPF_STMT(BPF_LD  | BPF_B   | BPF_ABS,  kICMPv6TypeOffset),
        BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K,    type, 0, 1),

        // Accept or reject.
        BPF_STMT(BPF_RET | BPF_K,              0xffff),
        BPF_STMT(BPF_RET | BPF_K,              0)
    };

    const sock_fprog filter = {
        sizeof(filter_code) / sizeof(filter_code[0]),
        filter_code,
    };

    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter)) != 0) {
        jniThrowExceptionFmt(env, "java/net/SocketException",
                "setsockopt(SO_ATTACH_FILTER): %s", strerror(errno));
    }
}

static void android_net_util_setupNaSocket(JNIEnv *env, jobject clazz, jobject javaFd)
{
    android_net_util_setupIcmpFilter(env, javaFd, ND_NEIGHBOR_ADVERT);
}

static void android_net_util_setupNsSocket(JNIEnv *env, jobject clazz, jobject javaFd)
{
    android_net_util_setupIcmpFilter(env, javaFd, ND_NEIGHBOR_SOLICIT);
}

static void android_net_util_setupRaSocket(JNIEnv *env, jobject clazz, jobject javaFd,
        jint ifIndex)
{
    static const int kLinkLocalHopLimit = 255;

    int fd = jniGetFDFromFileDescriptor(env, javaFd);

    // Set an ICMPv6 filter that only passes Router Solicitations.
    struct icmp6_filter rs_only;
    ICMP6_FILTER_SETBLOCKALL(&rs_only);
    ICMP6_FILTER_SETPASS(ND_ROUTER_SOLICIT, &rs_only);
    socklen_t len = sizeof(rs_only);
    if (setsockopt(fd, IPPROTO_ICMPV6, ICMP6_FILTER, &rs_only, len) != 0) {
        jniThrowExceptionFmt(env, "java/net/SocketException",
                "setsockopt(ICMP6_FILTER): %s", strerror(errno));
        return;
    }

    // Most/all of the rest of these options can be set via Java code, but
    // because we're here on account of setting an icmp6_filter go ahead
    // and do it all natively for now.

    // Set the multicast hoplimit to 255 (link-local only).
    int hops = kLinkLocalHopLimit;
    len = sizeof(hops);
    if (setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &hops, len) != 0) {
        jniThrowExceptionFmt(env, "java/net/SocketException",
                "setsockopt(IPV6_MULTICAST_HOPS): %s", strerror(errno));
        return;
    }

    // Set the unicast hoplimit to 255 (link-local only).
    hops = kLinkLocalHopLimit;
    len = sizeof(hops);
    if (setsockopt(fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &hops, len) != 0) {
        jniThrowExceptionFmt(env, "java/net/SocketException",
                "setsockopt(IPV6_UNICAST_HOPS): %s", strerror(errno));
        return;
    }

    // Explicitly disable multicast loopback.
    int off = 0;
    len = sizeof(off);
    if (setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &off, len) != 0) {
        jniThrowExceptionFmt(env, "java/net/SocketException",
                "setsockopt(IPV6_MULTICAST_LOOP): %s", strerror(errno));
        return;
    }

    // Specify the IPv6 interface to use for outbound multicast.
    len = sizeof(ifIndex);
    if (setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_IF, &ifIndex, len) != 0) {
        jniThrowExceptionFmt(env, "java/net/SocketException",
                "setsockopt(IPV6_MULTICAST_IF): %s", strerror(errno));
        return;
    }

    // Additional options to be considered:
    //     - IPV6_TCLASS
    //     - IPV6_RECVPKTINFO
    //     - IPV6_RECVHOPLIMIT

    // Bind to [::].
    const struct sockaddr_in6 sin6 = {
            .sin6_family = AF_INET6,
            .sin6_port = 0,
            .sin6_flowinfo = 0,
            .sin6_addr = IN6ADDR_ANY_INIT,
            .sin6_scope_id = 0,
    };
    auto sa = reinterpret_cast<const struct sockaddr *>(&sin6);
    len = sizeof(sin6);
    if (bind(fd, sa, len) != 0) {
        jniThrowExceptionFmt(env, "java/net/SocketException",
                "bind(IN6ADDR_ANY): %s", strerror(errno));
        return;
    }

    // Join the all-routers multicast group, ff02::2%index.
    struct ipv6_mreq all_rtrs = {
        .ipv6mr_multiaddr = {{{0xff,2,0,0,0,0,0,0,0,0,0,0,0,0,0,2}}},
        .ipv6mr_interface = ifIndex,
    };
    len = sizeof(all_rtrs);
    if (setsockopt(fd, IPPROTO_IPV6, IPV6_JOIN_GROUP, &all_rtrs, len) != 0) {
        jniThrowExceptionFmt(env, "java/net/SocketException",
                "setsockopt(IPV6_JOIN_GROUP): %s", strerror(errno));
        return;
    }
}

/*
 * JNI registration.
 */
static const JNINativeMethod gMethods[] = {
    /* name, signature, funcPtr */
    { "setupNaSocket", "(Ljava/io/FileDescriptor;)V",
        (void*) android_net_util_setupNaSocket },
    { "setupNsSocket", "(Ljava/io/FileDescriptor;)V",
        (void*) android_net_util_setupNsSocket },
    { "setupRaSocket", "(Ljava/io/FileDescriptor;I)V",
        (void*) android_net_util_setupRaSocket },
};

int register_android_net_util_TetheringUtils(JNIEnv* env) {
    return jniRegisterNativeMethods(env,
            "android/net/util/TetheringUtils",
            gMethods, NELEM(gMethods));
}

extern "C" jint JNI_OnLoad(JavaVM* vm, void*) {
    JNIEnv *env;
    if (vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6) != JNI_OK) {
        __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, "ERROR: GetEnv failed");
        return JNI_ERR;
    }

    if (register_android_net_util_TetheringUtils(env) < 0) {
        return JNI_ERR;
    }

    return JNI_VERSION_1_6;
}

}; // namespace android