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>
addRouterAttribute(Request & r,int type,const void * data,size_t size)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
Router()44 Router::Router() : mSocketFd(-1) {
45 }
46
~Router()47 Router::~Router() {
48 if (mSocketFd != -1) {
49 ::close(mSocketFd);
50 mSocketFd = -1;
51 }
52 }
53
init()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
setDefaultGateway(in_addr_t gateway,unsigned int ifaceIndex)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
sendNetlinkMessage(const void * data,size_t size)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