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      1 /*
      2  * Copyright (C) 2017 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include "router.h"
     18 
     19 #include <linux/rtnetlink.h>
     20 
     21 #include <errno.h>
     22 #include <string.h>
     23 #include <unistd.h>
     24 
     25 template<class Request>
     26 static void addRouterAttribute(Request& r,
     27                                int type,
     28                                const void* data,
     29                                size_t size) {
     30     // Calculate the offset into the character buffer where the RTA data lives
     31     // We use offsetof on the buffer to get it. This avoids undefined behavior
     32     // by casting the buffer (which is safe because it's char) instead of the
     33     // Request struct.(which is undefined because of aliasing)
     34     size_t offset = NLMSG_ALIGN(r.hdr.nlmsg_len) - offsetof(Request, buf);
     35     auto attr = reinterpret_cast<struct rtattr*>(r.buf + offset);
     36     attr->rta_type = type;
     37     attr->rta_len = RTA_LENGTH(size);
     38     memcpy(RTA_DATA(attr), data, size);
     39 
     40     // Update the message length to include the router attribute.
     41     r.hdr.nlmsg_len = NLMSG_ALIGN(r.hdr.nlmsg_len) + RTA_ALIGN(attr->rta_len);
     42 }
     43 
     44 Router::Router() : mSocketFd(-1) {
     45 }
     46 
     47 Router::~Router() {
     48     if (mSocketFd != -1) {
     49         ::close(mSocketFd);
     50         mSocketFd = -1;
     51     }
     52 }
     53 
     54 Result Router::init() {
     55     // Create a netlink socket to the router
     56     mSocketFd = ::socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
     57     if (mSocketFd == -1) {
     58         return Result::error(strerror(errno));
     59     }
     60     return Result::success();
     61 }
     62 
     63 Result Router::setDefaultGateway(in_addr_t gateway, unsigned int ifaceIndex) {
     64     struct Request {
     65         struct nlmsghdr hdr;
     66         struct rtmsg msg;
     67         char buf[256];
     68     } request;
     69 
     70     memset(&request, 0, sizeof(request));
     71 
     72     // Set up a request to create a new route
     73     request.hdr.nlmsg_len = NLMSG_LENGTH(sizeof(request.msg));
     74     request.hdr.nlmsg_type = RTM_NEWROUTE;
     75     request.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE;
     76 
     77     request.msg.rtm_family = AF_INET;
     78     request.msg.rtm_dst_len = 0;
     79     request.msg.rtm_table = RT_TABLE_MAIN;
     80     request.msg.rtm_protocol = RTPROT_BOOT;
     81     request.msg.rtm_scope = RT_SCOPE_UNIVERSE;
     82     request.msg.rtm_type = RTN_UNICAST;
     83 
     84     addRouterAttribute(request, RTA_GATEWAY, &gateway, sizeof(gateway));
     85     addRouterAttribute(request, RTA_OIF, &ifaceIndex, sizeof(ifaceIndex));
     86 
     87     return sendNetlinkMessage(&request, request.hdr.nlmsg_len);
     88 }
     89 
     90 Result Router::sendNetlinkMessage(const void* data, size_t size) {
     91     struct sockaddr_nl nlAddress;
     92     memset(&nlAddress, 0, sizeof(nlAddress));
     93     nlAddress.nl_family = AF_NETLINK;
     94 
     95     int res = ::sendto(mSocketFd, data, size, 0,
     96                        reinterpret_cast<sockaddr*>(&nlAddress),
     97                        sizeof(nlAddress));
     98     if (res == -1) {
     99         return Result::error("Unable to send on netlink socket: %s",
    100                              strerror(errno));
    101     }
    102     return Result::success();
    103 }
    104 
    105