/* * 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 "router.h" #include <linux/rtnetlink.h> #include <errno.h> #include <string.h> #include <unistd.h> template<class Request> static void addRouterAttribute(Request& r, int type, const void* data, size_t size) { // Calculate the offset into the character buffer where the RTA data lives // We use offsetof on the buffer to get it. This avoids undefined behavior // by casting the buffer (which is safe because it's char) instead of the // Request struct.(which is undefined because of aliasing) size_t offset = NLMSG_ALIGN(r.hdr.nlmsg_len) - offsetof(Request, buf); auto attr = reinterpret_cast<struct rtattr*>(r.buf + offset); attr->rta_type = type; attr->rta_len = RTA_LENGTH(size); memcpy(RTA_DATA(attr), data, size); // Update the message length to include the router attribute. r.hdr.nlmsg_len = NLMSG_ALIGN(r.hdr.nlmsg_len) + RTA_ALIGN(attr->rta_len); } Router::Router() : mSocketFd(-1) { } Router::~Router() { if (mSocketFd != -1) { ::close(mSocketFd); mSocketFd = -1; } } Result Router::init() { // Create a netlink socket to the router mSocketFd = ::socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE); if (mSocketFd == -1) { return Result::error(strerror(errno)); } return Result::success(); } Result Router::setDefaultGateway(in_addr_t gateway, unsigned int ifaceIndex) { struct Request { struct nlmsghdr hdr; struct rtmsg msg; char buf[256]; } request; memset(&request, 0, sizeof(request)); // Set up a request to create a new route request.hdr.nlmsg_len = NLMSG_LENGTH(sizeof(request.msg)); request.hdr.nlmsg_type = RTM_NEWROUTE; request.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE; request.msg.rtm_family = AF_INET; request.msg.rtm_dst_len = 0; request.msg.rtm_table = RT_TABLE_MAIN; request.msg.rtm_protocol = RTPROT_BOOT; request.msg.rtm_scope = RT_SCOPE_UNIVERSE; request.msg.rtm_type = RTN_UNICAST; addRouterAttribute(request, RTA_GATEWAY, &gateway, sizeof(gateway)); addRouterAttribute(request, RTA_OIF, &ifaceIndex, sizeof(ifaceIndex)); return sendNetlinkMessage(&request, request.hdr.nlmsg_len); } Result Router::sendNetlinkMessage(const void* data, size_t size) { struct sockaddr_nl nlAddress; memset(&nlAddress, 0, sizeof(nlAddress)); nlAddress.nl_family = AF_NETLINK; int res = ::sendto(mSocketFd, data, size, 0, reinterpret_cast<sockaddr*>(&nlAddress), sizeof(nlAddress)); if (res == -1) { return Result::error("Unable to send on netlink socket: %s", strerror(errno)); } return Result::success(); }