patchpanel/datapath.cc

// Copyright 2019 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "patchpanel/datapath.h"

#include <arpa/inet.h>
#include <fcntl.h>
#include <linux/if_tun.h>
#include <linux/sockios.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <netinet/in.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>

#include <base/files/scoped_file.h>
#include <base/logging.h>
#include <base/posix/eintr_wrapper.h>
#include <base/strings/string_number_conversions.h>
#include <brillo/userdb_utils.h>

#include "patchpanel/net_util.h"
#include "patchpanel/scoped_ns.h"

namespace patchpanel {

namespace {
// TODO(hugobenichi) Consolidate this constant definition in a single place.
constexpr pid_t kTestPID = -2;
constexpr char kDefaultIfname[] = "vmtap%d";
constexpr char kTunDev[] = "/dev/net/tun";

std::string PrefixIfname(const std::string& prefix, const std::string& ifname) {
  std::string n = prefix + ifname;
  if (n.length() < IFNAMSIZ)
    return n;

  // Best effort attempt to preserve the interface number, assuming it's the
  // last char in the name.
  auto c = ifname[ifname.length() - 1];
  n.resize(IFNAMSIZ - 1);
  n[n.length() - 1] = c;
  return n;
}

}  // namespace

std::string ArcVethHostName(const std::string& ifname) {
  return PrefixIfname("veth", ifname);
}

std::string ArcBridgeName(const std::string& ifname) {
  return PrefixIfname("arc_", ifname);
}

Datapath::Datapath(MinijailedProcessRunner* process_runner)
    : Datapath(process_runner, ioctl) {}

Datapath::Datapath(MinijailedProcessRunner* process_runner, ioctl_t ioctl_hook)
    : process_runner_(process_runner), ioctl_(ioctl_hook) {
  CHECK(process_runner_);
}

MinijailedProcessRunner& Datapath::runner() const {
  return *process_runner_;
}

bool Datapath::NetnsAttachName(const std::string& netns_name, pid_t netns_pid) {
  // Try first to delete any netns with name |netns_name| in case patchpanel
  // did not exit cleanly.
  if (process_runner_->ip_netns_delete(netns_name, false /*log_failures*/) == 0)
    LOG(INFO) << "Deleted left over network namespace name " << netns_name;
  return process_runner_->ip_netns_attach(netns_name, netns_pid) == 0;
}

bool Datapath::NetnsDeleteName(const std::string& netns_name) {
  return process_runner_->ip_netns_delete(netns_name) == 0;
}

bool Datapath::AddBridge(const std::string& ifname,
                         uint32_t ipv4_addr,
                         uint32_t ipv4_prefix_len) {
  // Configure the persistent Chrome OS bridge interface with static IP.
  if (process_runner_->brctl("addbr", {ifname}) != 0) {
    return false;
  }

  if (process_runner_->ip(
          "addr", "add",
          {IPv4AddressToCidrString(ipv4_addr, ipv4_prefix_len), "brd",
           IPv4AddressToString(Ipv4BroadcastAddr(ipv4_addr, ipv4_prefix_len)),
           "dev", ifname}) != 0) {
    RemoveBridge(ifname);
    return false;
  }

  if (process_runner_->ip("link", "set", {ifname, "up"}) != 0) {
    RemoveBridge(ifname);
    return false;
  }

  // See nat.conf in chromeos-nat-init for the rest of the NAT setup rules.
  if (!AddOutboundIPv4SNATMark(ifname)) {
    RemoveBridge(ifname);
    return false;
  }

  return true;
}

void Datapath::RemoveBridge(const std::string& ifname) {
  RemoveOutboundIPv4SNATMark(ifname);
  process_runner_->ip("link", "set", {ifname, "down"});
  process_runner_->brctl("delbr", {ifname});
}

bool Datapath::AddToBridge(const std::string& br_ifname,
                           const std::string& ifname) {
  return (process_runner_->brctl("addif", {br_ifname, ifname}) == 0);
}

std::string Datapath::AddTAP(const std::string& name,
                             const MacAddress* mac_addr,
                             const SubnetAddress* ipv4_addr,
                             const std::string& user) {
  base::ScopedFD dev(open(kTunDev, O_RDWR | O_NONBLOCK));
  if (!dev.is_valid()) {
    PLOG(ERROR) << "Failed to open " << kTunDev;
    return "";
  }

  struct ifreq ifr;
  memset(&ifr, 0, sizeof(ifr));
  strncpy(ifr.ifr_name, name.empty() ? kDefaultIfname : name.c_str(),
          sizeof(ifr.ifr_name));
  ifr.ifr_flags = IFF_TAP | IFF_NO_PI;

  // If a template was given as the name, ifr_name will be updated with the
  // actual interface name.
  if ((*ioctl_)(dev.get(), TUNSETIFF, &ifr) != 0) {
    PLOG(ERROR) << "Failed to create tap interface " << name;
    return "";
  }
  const char* ifname = ifr.ifr_name;

  if ((*ioctl_)(dev.get(), TUNSETPERSIST, 1) != 0) {
    PLOG(ERROR) << "Failed to persist the interface " << ifname;
    return "";
  }

  if (!user.empty()) {
    uid_t uid = -1;
    if (!brillo::userdb::GetUserInfo(user, &uid, nullptr)) {
      PLOG(ERROR) << "Unable to look up UID for " << user;
      RemoveTAP(ifname);
      return "";
    }
    if ((*ioctl_)(dev.get(), TUNSETOWNER, uid) != 0) {
      PLOG(ERROR) << "Failed to set owner " << uid << " of tap interface "
                  << ifname;
      RemoveTAP(ifname);
      return "";
    }
  }

  // Create control socket for configuring the interface.
  base::ScopedFD sock(socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0));
  if (!sock.is_valid()) {
    PLOG(ERROR) << "Failed to create control socket for tap interface "
                << ifname;
    RemoveTAP(ifname);
    return "";
  }

  if (ipv4_addr) {
    struct sockaddr_in* addr =
        reinterpret_cast<struct sockaddr_in*>(&ifr.ifr_addr);
    addr->sin_family = AF_INET;
    addr->sin_addr.s_addr = static_cast<in_addr_t>(ipv4_addr->Address());
    if ((*ioctl_)(sock.get(), SIOCSIFADDR, &ifr) != 0) {
      PLOG(ERROR) << "Failed to set ip address for vmtap interface " << ifname
                  << " {" << ipv4_addr->ToCidrString() << "}";
      RemoveTAP(ifname);
      return "";
    }

    struct sockaddr_in* netmask =
        reinterpret_cast<struct sockaddr_in*>(&ifr.ifr_netmask);
    netmask->sin_family = AF_INET;
    netmask->sin_addr.s_addr = static_cast<in_addr_t>(ipv4_addr->Netmask());
    if ((*ioctl_)(sock.get(), SIOCSIFNETMASK, &ifr) != 0) {
      PLOG(ERROR) << "Failed to set netmask for vmtap interface " << ifname
                  << " {" << ipv4_addr->ToCidrString() << "}";
      RemoveTAP(ifname);
      return "";
    }
  }

  if (mac_addr) {
    struct sockaddr* hwaddr = &ifr.ifr_hwaddr;
    hwaddr->sa_family = ARPHRD_ETHER;
    memcpy(&hwaddr->sa_data, mac_addr, sizeof(*mac_addr));
    if ((*ioctl_)(sock.get(), SIOCSIFHWADDR, &ifr) != 0) {
      PLOG(ERROR) << "Failed to set mac address for vmtap interface " << ifname
                  << " {" << MacAddressToString(*mac_addr) << "}";
      RemoveTAP(ifname);
      return "";
    }
  }

  if ((*ioctl_)(sock.get(), SIOCGIFFLAGS, &ifr) != 0) {
    PLOG(ERROR) << "Failed to get flags for tap interface " << ifname;
    RemoveTAP(ifname);
    return "";
  }

  ifr.ifr_flags |= (IFF_UP | IFF_RUNNING);
  if ((*ioctl_)(sock.get(), SIOCSIFFLAGS, &ifr) != 0) {
    PLOG(ERROR) << "Failed to enable tap interface " << ifname;
    RemoveTAP(ifname);
    return "";
  }

  return ifname;
}

void Datapath::RemoveTAP(const std::string& ifname) {
  process_runner_->ip("tuntap", "del", {ifname, "mode", "tap"});
}

bool Datapath::ConnectVethPair(pid_t netns_pid,
                               const std::string& netns_name,
                               const std::string& veth_ifname,
                               const std::string& peer_ifname,
                               const MacAddress& remote_mac_addr,
                               uint32_t remote_ipv4_addr,
                               uint32_t remote_ipv4_prefix_len,
                               bool remote_multicast_flag) {
  // Set up the virtual pair across the current namespace and |netns_name|.
  if (!AddVirtualInterfacePair(netns_name, veth_ifname, peer_ifname)) {
    LOG(ERROR) << "Failed to create veth pair " << veth_ifname << ","
               << peer_ifname;
    return false;
  }

  // Configure the remote veth in namespace |netns_name|.
  {
    ScopedNS ns(netns_pid);
    if (!ns.IsValid() && netns_pid != kTestPID) {
      LOG(ERROR)
          << "Cannot create virtual link -- invalid container namespace?";
      return false;
    }

    if (!ConfigureInterface(peer_ifname, remote_mac_addr, remote_ipv4_addr,
                            remote_ipv4_prefix_len, true /* link up */,
                            remote_multicast_flag)) {
      LOG(ERROR) << "Failed to configure interface " << peer_ifname;
      RemoveInterface(peer_ifname);
      return false;
    }
  }

  if (!ToggleInterface(veth_ifname, true /*up*/)) {
    LOG(ERROR) << "Failed to bring up interface " << veth_ifname;
    RemoveInterface(veth_ifname);
    return false;
  }

  return true;
}

bool Datapath::AddVirtualInterfacePair(const std::string& netns_name,
                                       const std::string& veth_ifname,
                                       const std::string& peer_ifname) {
  return process_runner_->ip("link", "add",
                             {veth_ifname, "type", "veth", "peer", "name",
                              peer_ifname, "netns", netns_name}) == 0;
}

bool Datapath::ToggleInterface(const std::string& ifname, bool up) {
  const std::string link = up ? "up" : "down";
  return process_runner_->ip("link", "set", {ifname, link}) == 0;
}

bool Datapath::ConfigureInterface(const std::string& ifname,
                                  const MacAddress& mac_addr,
                                  uint32_t ipv4_addr,
                                  uint32_t ipv4_prefix_len,
                                  bool up,
                                  bool enable_multicast) {
  const std::string link = up ? "up" : "down";
  const std::string multicast = enable_multicast ? "on" : "off";
  return (process_runner_->ip(
              "addr", "add",
              {IPv4AddressToCidrString(ipv4_addr, ipv4_prefix_len), "brd",
               IPv4AddressToString(
                   Ipv4BroadcastAddr(ipv4_addr, ipv4_prefix_len)),
               "dev", ifname}) == 0) &&
         (process_runner_->ip("link", "set",
                              {
                                  "dev",
                                  ifname,
                                  link,
                                  "addr",
                                  MacAddressToString(mac_addr),
                                  "multicast",
                                  multicast,
                              }) == 0);
}

void Datapath::RemoveInterface(const std::string& ifname) {
  process_runner_->ip("link", "delete", {ifname}, false /*log_failures*/);
}

bool Datapath::AddLegacyIPv4DNAT(const std::string& ipv4_addr) {
  // Forward "unclaimed" packets to Android to allow inbound connections
  // from devices on the LAN.
  if (process_runner_->iptables("nat", {"-N", "dnat_arc", "-w"}) != 0)
    return false;

  if (process_runner_->iptables("nat", {"-A", "dnat_arc", "-j", "DNAT",
                                        "--to-destination", ipv4_addr, "-w"}) !=
      0) {
    RemoveLegacyIPv4DNAT();
    return false;
  }

  // This chain is dynamically updated whenever the default interface
  // changes.
  if (process_runner_->iptables("nat", {"-N", "try_arc", "-w"}) != 0) {
    RemoveLegacyIPv4DNAT();
    return false;
  }

  if (process_runner_->iptables(
          "nat", {"-A", "PREROUTING", "-m", "socket", "--nowildcard", "-j",
                  "ACCEPT", "-w"}) != 0) {
    RemoveLegacyIPv4DNAT();
    return false;
  }

  if (process_runner_->iptables("nat", {"-A", "PREROUTING", "-p", "tcp", "-j",
                                        "try_arc", "-w"}) != 0) {
    RemoveLegacyIPv4DNAT();
    return false;
  }

  if (process_runner_->iptables("nat", {"-A", "PREROUTING", "-p", "udp", "-j",
                                        "try_arc", "-w"}) != 0) {
    RemoveLegacyIPv4DNAT();
    return false;
  }

  return true;
}

void Datapath::RemoveLegacyIPv4DNAT() {
  process_runner_->iptables(
      "nat", {"-D", "PREROUTING", "-p", "udp", "-j", "try_arc", "-w"});
  process_runner_->iptables(
      "nat", {"-D", "PREROUTING", "-p", "tcp", "-j", "try_arc", "-w"});
  process_runner_->iptables("nat", {"-D", "PREROUTING", "-m", "socket",
                                    "--nowildcard", "-j", "ACCEPT", "-w"});
  process_runner_->iptables("nat", {"-F", "try_arc", "-w"});
  process_runner_->iptables("nat", {"-X", "try_arc", "-w"});
  process_runner_->iptables("nat", {"-F", "dnat_arc", "-w"});
  process_runner_->iptables("nat", {"-X", "dnat_arc", "-w"});
}

bool Datapath::AddLegacyIPv4InboundDNAT(const std::string& ifname) {
  return (process_runner_->iptables("nat", {"-A", "try_arc", "-i", ifname, "-j",
                                            "dnat_arc", "-w"}) != 0);
}

void Datapath::RemoveLegacyIPv4InboundDNAT() {
  process_runner_->iptables("nat", {"-F", "try_arc", "-w"});
}

bool Datapath::AddInboundIPv4DNAT(const std::string& ifname,
                                  const std::string& ipv4_addr) {
  // Direct ingress IP traffic to existing sockets.
  if (process_runner_->iptables(
          "nat", {"-A", "PREROUTING", "-i", ifname, "-m", "socket",
                  "--nowildcard", "-j", "ACCEPT", "-w"}) != 0)
    return false;

  // Direct ingress TCP & UDP traffic to ARC interface for new connections.
  if (process_runner_->iptables(
          "nat", {"-A", "PREROUTING", "-i", ifname, "-p", "tcp", "-j", "DNAT",
                  "--to-destination", ipv4_addr, "-w"}) != 0) {
    RemoveInboundIPv4DNAT(ifname, ipv4_addr);
    return false;
  }
  if (process_runner_->iptables(
          "nat", {"-A", "PREROUTING", "-i", ifname, "-p", "udp", "-j", "DNAT",
                  "--to-destination", ipv4_addr, "-w"}) != 0) {
    RemoveInboundIPv4DNAT(ifname, ipv4_addr);
    return false;
  }

  return true;
}

void Datapath::RemoveInboundIPv4DNAT(const std::string& ifname,
                                     const std::string& ipv4_addr) {
  process_runner_->iptables(
      "nat", {"-D", "PREROUTING", "-i", ifname, "-p", "udp", "-j", "DNAT",
              "--to-destination", ipv4_addr, "-w"});
  process_runner_->iptables(
      "nat", {"-D", "PREROUTING", "-i", ifname, "-p", "tcp", "-j", "DNAT",
              "--to-destination", ipv4_addr, "-w"});
  process_runner_->iptables(
      "nat", {"-D", "PREROUTING", "-i", ifname, "-m", "socket", "--nowildcard",
              "-j", "ACCEPT", "-w"});
}

bool Datapath::AddOutboundIPv4(const std::string& ifname) {
  return process_runner_->iptables("filter", {"-A", "FORWARD", "-o", ifname,
                                              "-j", "ACCEPT", "-w"}) == 0;
}

void Datapath::RemoveOutboundIPv4(const std::string& ifname) {
  process_runner_->iptables(
      "filter", {"-D", "FORWARD", "-o", ifname, "-j", "ACCEPT", "-w"});
}

bool Datapath::AddSNATMarkRules() {
  // chromium:1050579: INVALID packets cannot be tracked by conntrack therefore
  // need to be explicitly dropped.
  if (process_runner_->iptables(
          "filter", {"-A", "FORWARD", "-m", "mark", "--mark", "1", "-m",
                     "state", "--state", "INVALID", "-j", "DROP", "-w"}) != 0) {
    return false;
  }
  if (process_runner_->iptables(
          "filter", {"-A", "FORWARD", "-m", "mark", "--mark", "1", "-j",
                     "ACCEPT", "-w"}) != 0) {
    return false;
  }
  if (process_runner_->iptables(
          "nat", {"-A", "POSTROUTING", "-m", "mark", "--mark", "1", "-j",
                  "MASQUERADE", "-w"}) != 0) {
    RemoveSNATMarkRules();
    return false;
  }
  return true;
}

void Datapath::RemoveSNATMarkRules() {
  process_runner_->iptables("nat", {"-D", "POSTROUTING", "-m", "mark", "--mark",
                                    "1", "-j", "MASQUERADE", "-w"});
  process_runner_->iptables("filter", {"-D", "FORWARD", "-m", "mark", "--mark",
                                       "1", "-j", "ACCEPT", "-w"});
  process_runner_->iptables(
      "filter", {"-D", "FORWARD", "-m", "mark", "--mark", "1", "-m", "state",
                 "--state", "INVALID", "-j", "DROP", "-w"});
}

bool Datapath::AddInterfaceSNAT(const std::string& ifname) {
  return process_runner_->iptables("nat", {"-A", "POSTROUTING", "-o", ifname,
                                           "-j", "MASQUERADE", "-w"}) == 0;
}

void Datapath::RemoveInterfaceSNAT(const std::string& ifname) {
  process_runner_->iptables(
      "nat", {"-D", "POSTROUTING", "-o", ifname, "-j", "MASQUERADE", "-w"});
}

bool Datapath::AddOutboundIPv4SNATMark(const std::string& ifname) {
  return process_runner_->iptables(
             "mangle", {"-A", "PREROUTING", "-i", ifname, "-j", "MARK",
                        "--set-mark", "1", "-w"}) == 0;
}

void Datapath::RemoveOutboundIPv4SNATMark(const std::string& ifname) {
  process_runner_->iptables("mangle", {"-D", "PREROUTING", "-i", ifname, "-j",
                                       "MARK", "--set-mark", "1", "-w"});
}

bool Datapath::AddForwardEstablishedRule() {
  return process_runner_->iptables(
             "filter", {"-A", "FORWARD", "-m", "state", "--state",
                        "ESTABLISHED,RELATED", "-j", "ACCEPT", "-w"}) == 0;
}

void Datapath::RemoveForwardEstablishedRule() {
  process_runner_->iptables("filter",
                            {"-D", "FORWARD", "-m", "state", "--state",
                             "ESTABLISHED,RELATED", "-j", "ACCEPT", "-w"});
}

bool Datapath::MaskInterfaceFlags(const std::string& ifname,
                                  uint16_t on,
                                  uint16_t off) {
  base::ScopedFD sock(socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0));
  if (!sock.is_valid()) {
    PLOG(ERROR) << "Failed to create control socket";
    return false;
  }
  ifreq ifr;
  snprintf(ifr.ifr_name, IFNAMSIZ, "%s", ifname.c_str());
  if ((*ioctl_)(sock.get(), SIOCGIFFLAGS, &ifr) < 0) {
    PLOG(WARNING) << "ioctl() failed to get interface flag on " << ifname;
    return false;
  }
  ifr.ifr_flags |= on;
  ifr.ifr_flags &= ~off;
  if ((*ioctl_)(sock.get(), SIOCSIFFLAGS, &ifr) < 0) {
    PLOG(WARNING) << "ioctl() failed to set flag 0x" << std::hex << on
                  << " unset flag 0x" << std::hex << off << " on " << ifname;
    return false;
  }
  return true;
}

bool Datapath::AddIPv6HostRoute(const std::string& ifname,
                                const std::string& ipv6_addr,
                                int ipv6_prefix_len) {
  std::string ipv6_addr_cidr =
      ipv6_addr + "/" + std::to_string(ipv6_prefix_len);

  return process_runner_->ip6("route", "replace",
                              {ipv6_addr_cidr, "dev", ifname}) == 0;
}

void Datapath::RemoveIPv6HostRoute(const std::string& ifname,
                                   const std::string& ipv6_addr,
                                   int ipv6_prefix_len) {
  std::string ipv6_addr_cidr =
      ipv6_addr + "/" + std::to_string(ipv6_prefix_len);

  process_runner_->ip6("route", "del", {ipv6_addr_cidr, "dev", ifname});
}

bool Datapath::AddIPv6Neighbor(const std::string& ifname,
                               const std::string& ipv6_addr) {
  return process_runner_->ip6("neigh", "add",
                              {"proxy", ipv6_addr, "dev", ifname}) == 0;
}

void Datapath::RemoveIPv6Neighbor(const std::string& ifname,
                                  const std::string& ipv6_addr) {
  process_runner_->ip6("neigh", "del", {"proxy", ipv6_addr, "dev", ifname});
}

bool Datapath::AddIPv6Forwarding(const std::string& ifname1,
                                 const std::string& ifname2) {
  if (process_runner_->ip6tables(
          "filter",
          {"-C", "FORWARD", "-i", ifname1, "-o", ifname2, "-j", "ACCEPT", "-w"},
          false /*log_failures*/) != 0 &&
      process_runner_->ip6tables(
          "filter", {"-A", "FORWARD", "-i", ifname1, "-o", ifname2, "-j",
                     "ACCEPT", "-w"}) != 0) {
    return false;
  }

  if (process_runner_->ip6tables(
          "filter",
          {"-C", "FORWARD", "-i", ifname2, "-o", ifname1, "-j", "ACCEPT", "-w"},
          false /*log_failures*/) != 0 &&
      process_runner_->ip6tables(
          "filter", {"-A", "FORWARD", "-i", ifname2, "-o", ifname1, "-j",
                     "ACCEPT", "-w"}) != 0) {
    RemoveIPv6Forwarding(ifname1, ifname2);
    return false;
  }

  return true;
}

void Datapath::RemoveIPv6Forwarding(const std::string& ifname1,
                                    const std::string& ifname2) {
  process_runner_->ip6tables("filter", {"-D", "FORWARD", "-i", ifname1, "-o",
                                        ifname2, "-j", "ACCEPT", "-w"});

  process_runner_->ip6tables("filter", {"-D", "FORWARD", "-i", ifname2, "-o",
                                        ifname1, "-j", "ACCEPT", "-w"});
}

bool Datapath::AddIPv4Route(uint32_t gateway_addr,
                            uint32_t addr,
                            uint32_t netmask) {
  struct rtentry route;
  memset(&route, 0, sizeof(route));
  SetSockaddrIn(&route.rt_gateway, gateway_addr);
  SetSockaddrIn(&route.rt_dst, addr & netmask);
  SetSockaddrIn(&route.rt_genmask, netmask);
  route.rt_flags = RTF_UP | RTF_GATEWAY;
  return ModifyRtentry(SIOCADDRT, &route);
}

bool Datapath::DeleteIPv4Route(uint32_t gateway_addr,
                               uint32_t addr,
                               uint32_t netmask) {
  struct rtentry route;
  memset(&route, 0, sizeof(route));
  SetSockaddrIn(&route.rt_gateway, gateway_addr);
  SetSockaddrIn(&route.rt_dst, addr & netmask);
  SetSockaddrIn(&route.rt_genmask, netmask);
  route.rt_flags = RTF_UP | RTF_GATEWAY;
  return ModifyRtentry(SIOCDELRT, &route);
}

bool Datapath::AddIPv4Route(const std::string& ifname,
                            uint32_t addr,
                            uint32_t netmask) {
  struct rtentry route;
  memset(&route, 0, sizeof(route));
  SetSockaddrIn(&route.rt_dst, addr & netmask);
  SetSockaddrIn(&route.rt_genmask, netmask);
  char rt_dev[IFNAMSIZ];
  strncpy(rt_dev, ifname.c_str(), IFNAMSIZ);
  rt_dev[IFNAMSIZ - 1] = '\0';
  route.rt_dev = rt_dev;
  route.rt_flags = RTF_UP | RTF_GATEWAY;
  return ModifyRtentry(SIOCADDRT, &route);
}

bool Datapath::DeleteIPv4Route(const std::string& ifname,
                               uint32_t addr,
                               uint32_t netmask) {
  struct rtentry route;
  memset(&route, 0, sizeof(route));
  SetSockaddrIn(&route.rt_dst, addr & netmask);
  SetSockaddrIn(&route.rt_genmask, netmask);
  char rt_dev[IFNAMSIZ];
  strncpy(rt_dev, ifname.c_str(), IFNAMSIZ);
  rt_dev[IFNAMSIZ - 1] = '\0';
  route.rt_dev = rt_dev;
  route.rt_flags = RTF_UP | RTF_GATEWAY;
  return ModifyRtentry(SIOCDELRT, &route);
}

bool Datapath::ModifyRtentry(unsigned long op, struct rtentry* route) {
  DCHECK(route);
  if (op != SIOCADDRT && op != SIOCDELRT) {
    LOG(ERROR) << "Invalid operation " << op << " for rtentry " << route;
    return false;
  }
  base::ScopedFD fd(socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0));
  if (!fd.is_valid()) {
    PLOG(ERROR) << "Failed to create socket for adding rtentry " << route;
    return false;
  }
  if (HANDLE_EINTR(ioctl_(fd.get(), op, route)) != 0) {
    std::string opname = op == SIOCADDRT ? "add" : "delete";
    PLOG(ERROR) << "Failed to " << opname << " rtentry " << route;
    return false;
  }
  return true;
}

}  // namespace patchpanel