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      1 /*
      2  * Copyright 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  * tun_interface.cpp - creates tun interfaces for testing purposes
     17  */
     18 
     19 #include <fcntl.h>
     20 #include <netdb.h>
     21 #include <stdlib.h>
     22 #include <unistd.h>
     23 #include <linux/if.h>
     24 #include <linux/if_tun.h>
     25 #include <net/if.h>
     26 #include <netinet/in.h>
     27 #include <sys/ioctl.h>
     28 #include <sys/socket.h>
     29 #include <sys/stat.h>
     30 #include <sys/types.h>
     31 
     32 #include <android-base/stringprintf.h>
     33 #include <android-base/strings.h>
     34 #include <netutils/ifc.h>
     35 
     36 #include "tun_interface.h"
     37 
     38 #define TUN_DEV "/dev/tun"
     39 
     40 using android::base::StringPrintf;
     41 
     42 namespace android {
     43 namespace net {
     44 
     45 int TunInterface::init() {
     46     // Generate a random ULA address pair.
     47     arc4random_buf(&mSrcAddr, sizeof(mSrcAddr));
     48     mSrcAddr.s6_addr[0] = 0xfd;
     49     memcpy(&mDstAddr, &mSrcAddr, sizeof(mDstAddr));
     50     mDstAddr.s6_addr[15] ^= 1;
     51 
     52     // Convert the addresses to strings because that's what ifc_add_address takes.
     53     char srcStr[INET6_ADDRSTRLEN], dstStr[INET6_ADDRSTRLEN];
     54     sockaddr_in6 src6 = { .sin6_family = AF_INET6, .sin6_addr = mSrcAddr, };
     55     sockaddr_in6 dst6 = { .sin6_family = AF_INET6, .sin6_addr = mDstAddr, };
     56     int flags = NI_NUMERICHOST;
     57     if (getnameinfo((sockaddr *) &src6, sizeof(src6), srcStr, sizeof(srcStr), NULL, 0, flags) ||
     58         getnameinfo((sockaddr *) &dst6, sizeof(dst6), dstStr, sizeof(dstStr), NULL, 0, flags)) {
     59         return -EINVAL;
     60     }
     61 
     62     // Create a tun interface with a name based on our PID and some randomness.
     63     // iptables will only accept interfaces whose name is up to IFNAMSIZ - 1 bytes long.
     64     mIfName = StringPrintf("netd%u_%u", getpid(), arc4random());
     65     if (mIfName.size() >= IFNAMSIZ) {
     66         mIfName.resize(IFNAMSIZ - 1);
     67     }
     68     struct ifreq ifr = {
     69         .ifr_ifru = { .ifru_flags = IFF_TUN },
     70     };
     71     strlcpy(ifr.ifr_name, mIfName.c_str(), sizeof(ifr.ifr_name));
     72 
     73     mFd = open(TUN_DEV, O_RDWR | O_NONBLOCK | O_CLOEXEC);
     74     if (mFd == -1) return -errno;
     75 
     76     int ret = ioctl(mFd, TUNSETIFF, &ifr, sizeof(ifr));
     77     if (ret == -1) {
     78         ret = -errno;
     79         close(mFd);
     80         return ret;
     81     }
     82 
     83     if (ifc_add_address(ifr.ifr_name, srcStr, 64) ||
     84         ifc_add_address(ifr.ifr_name, dstStr, 64)) {
     85         ret = -errno;
     86         close(mFd);
     87         return ret;
     88     }
     89 
     90     mIfIndex = if_nametoindex(ifr.ifr_name);
     91 
     92     return 0;
     93 }
     94 
     95 void TunInterface::destroy() {
     96     if (mFd != -1) {
     97         close(mFd);
     98         mFd = -1;
     99     }
    100 }
    101 
    102 }  // namespace net
    103 }  // namespace android
    104