1 /* 2 * Copyright (C) 2014 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 "FwmarkServer.h" 18 19 #include "Fwmark.h" 20 #include "FwmarkCommand.h" 21 #include "NetworkController.h" 22 #include "resolv_netid.h" 23 24 #include <sys/socket.h> 25 #include <unistd.h> 26 27 FwmarkServer::FwmarkServer(NetworkController* networkController) : 28 SocketListener("fwmarkd", true), mNetworkController(networkController) { 29 } 30 31 bool FwmarkServer::onDataAvailable(SocketClient* client) { 32 int socketFd = -1; 33 int error = processClient(client, &socketFd); 34 if (socketFd >= 0) { 35 close(socketFd); 36 } 37 38 // Always send a response even if there were connection errors or read errors, so that we don't 39 // inadvertently cause the client to hang (which always waits for a response). 40 client->sendData(&error, sizeof(error)); 41 42 // Always close the client connection (by returning false). This prevents a DoS attack where 43 // the client issues multiple commands on the same connection, never reading the responses, 44 // causing its receive buffer to fill up, and thus causing our client->sendData() to block. 45 return false; 46 } 47 48 int FwmarkServer::processClient(SocketClient* client, int* socketFd) { 49 FwmarkCommand command; 50 51 iovec iov; 52 iov.iov_base = &command; 53 iov.iov_len = sizeof(command); 54 55 msghdr message; 56 memset(&message, 0, sizeof(message)); 57 message.msg_iov = &iov; 58 message.msg_iovlen = 1; 59 60 union { 61 cmsghdr cmh; 62 char cmsg[CMSG_SPACE(sizeof(*socketFd))]; 63 } cmsgu; 64 65 memset(cmsgu.cmsg, 0, sizeof(cmsgu.cmsg)); 66 message.msg_control = cmsgu.cmsg; 67 message.msg_controllen = sizeof(cmsgu.cmsg); 68 69 int messageLength = TEMP_FAILURE_RETRY(recvmsg(client->getSocket(), &message, 0)); 70 if (messageLength <= 0) { 71 return -errno; 72 } 73 74 if (messageLength != sizeof(command)) { 75 return -EBADMSG; 76 } 77 78 cmsghdr* const cmsgh = CMSG_FIRSTHDR(&message); 79 if (cmsgh && cmsgh->cmsg_level == SOL_SOCKET && cmsgh->cmsg_type == SCM_RIGHTS && 80 cmsgh->cmsg_len == CMSG_LEN(sizeof(*socketFd))) { 81 memcpy(socketFd, CMSG_DATA(cmsgh), sizeof(*socketFd)); 82 } 83 84 if (*socketFd < 0) { 85 return -EBADF; 86 } 87 88 Fwmark fwmark; 89 socklen_t fwmarkLen = sizeof(fwmark.intValue); 90 if (getsockopt(*socketFd, SOL_SOCKET, SO_MARK, &fwmark.intValue, &fwmarkLen) == -1) { 91 return -errno; 92 } 93 94 Permission permission = mNetworkController->getPermissionForUser(client->getUid()); 95 96 switch (command.cmdId) { 97 case FwmarkCommand::ON_ACCEPT: { 98 // Called after a socket accept(). The kernel would've marked the NetId and necessary 99 // permissions bits, so we just add the rest of the user's permissions here. 100 permission = static_cast<Permission>(permission | fwmark.permission); 101 break; 102 } 103 104 case FwmarkCommand::ON_CONNECT: { 105 // Called before a socket connect() happens. Set an appropriate NetId into the fwmark so 106 // that the socket routes consistently over that network. Do this even if the socket 107 // already has a NetId, so that calling connect() multiple times still works. 108 // 109 // But if the explicit bit was set, the existing NetId was explicitly preferred (and not 110 // a case of connect() being called multiple times). Don't reset the NetId in that case. 111 // 112 // An "appropriate" NetId is the NetId of a bypassable VPN that applies to the user, or 113 // failing that, the default network. We'll never set the NetId of a secure VPN here. 114 // See the comments in the implementation of getNetworkForConnect() for more details. 115 // 116 // If the protect bit is set, this could be either a system proxy (e.g.: the dns proxy 117 // or the download manager) acting on behalf of another user, or a VPN provider. If it's 118 // a proxy, we shouldn't reset the NetId. If it's a VPN provider, we should set the 119 // default network's NetId. 120 // 121 // There's no easy way to tell the difference between a proxy and a VPN app. We can't 122 // use PERMISSION_SYSTEM to identify the proxy because a VPN app may also have those 123 // permissions. So we use the following heuristic: 124 // 125 // If it's a proxy, but the existing NetId is not a VPN, that means the user (that the 126 // proxy is acting on behalf of) is not subject to a VPN, so the proxy must have picked 127 // the default network's NetId. So, it's okay to replace that with the current default 128 // network's NetId (which in all likelihood is the same). 129 // 130 // Conversely, if it's a VPN provider, the existing NetId cannot be a VPN. The only time 131 // we set a VPN's NetId into a socket without setting the explicit bit is here, in 132 // ON_CONNECT, but we won't do that if the socket has the protect bit set. If the VPN 133 // provider connect()ed (and got the VPN NetId set) and then called protect(), we 134 // would've unset the NetId in PROTECT_FROM_VPN below. 135 // 136 // So, overall (when the explicit bit is not set but the protect bit is set), if the 137 // existing NetId is a VPN, don't reset it. Else, set the default network's NetId. 138 if (!fwmark.explicitlySelected) { 139 if (!fwmark.protectedFromVpn) { 140 fwmark.netId = mNetworkController->getNetworkForConnect(client->getUid()); 141 } else if (!mNetworkController->isVirtualNetwork(fwmark.netId)) { 142 fwmark.netId = mNetworkController->getDefaultNetwork(); 143 } 144 } 145 break; 146 } 147 148 case FwmarkCommand::SELECT_NETWORK: { 149 fwmark.netId = command.netId; 150 if (command.netId == NETID_UNSET) { 151 fwmark.explicitlySelected = false; 152 fwmark.protectedFromVpn = false; 153 permission = PERMISSION_NONE; 154 } else { 155 if (int ret = mNetworkController->checkUserNetworkAccess(client->getUid(), 156 command.netId)) { 157 return ret; 158 } 159 fwmark.explicitlySelected = true; 160 fwmark.protectedFromVpn = mNetworkController->canProtect(client->getUid()); 161 } 162 break; 163 } 164 165 case FwmarkCommand::PROTECT_FROM_VPN: { 166 if (!mNetworkController->canProtect(client->getUid())) { 167 return -EPERM; 168 } 169 // If a bypassable VPN's provider app calls connect() and then protect(), it will end up 170 // with a socket that looks like that of a system proxy but is not (see comments for 171 // ON_CONNECT above). So, reset the NetId. 172 // 173 // In any case, it's appropriate that if the socket has an implicit VPN NetId mark, the 174 // PROTECT_FROM_VPN command should unset it. 175 if (!fwmark.explicitlySelected && mNetworkController->isVirtualNetwork(fwmark.netId)) { 176 fwmark.netId = mNetworkController->getDefaultNetwork(); 177 } 178 fwmark.protectedFromVpn = true; 179 permission = static_cast<Permission>(permission | fwmark.permission); 180 break; 181 } 182 183 case FwmarkCommand::SELECT_FOR_USER: { 184 if ((permission & PERMISSION_SYSTEM) != PERMISSION_SYSTEM) { 185 return -EPERM; 186 } 187 fwmark.netId = mNetworkController->getNetworkForUser(command.uid); 188 fwmark.protectedFromVpn = true; 189 break; 190 } 191 192 default: { 193 // unknown command 194 return -EPROTO; 195 } 196 } 197 198 fwmark.permission = permission; 199 200 if (setsockopt(*socketFd, SOL_SOCKET, SO_MARK, &fwmark.intValue, 201 sizeof(fwmark.intValue)) == -1) { 202 return -errno; 203 } 204 205 return 0; 206 } 207
