arc: Move platform2/arc/network/ to platform2/patchpanel

Next step in the arc-networkd -> patchpanel rename, this patch moves the
location of the code.

BUG=b:151879931
TEST=units,flashed image to atlas
TEST=tasts arc.PlayStore, crostini.LaunchTerminal.download

Change-Id: I1b5cf8d670e1631d46f6449b725395157bf88dde
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2115863
Tested-by: Garrick Evans <garrick@chromium.org>
Commit-Queue: Garrick Evans <garrick@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-by: Hugo Benichi <hugobenichi@google.com>
diff --git a/patchpanel/datapath.cc b/patchpanel/datapath.cc
new file mode 100644
index 0000000..7670730
--- /dev/null
+++ b/patchpanel/datapath.cc
@@ -0,0 +1,587 @@
+// 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/strings/string_number_conversions.h>
+#include "base/posix/eintr_wrapper.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";
+
+}  // namespace
+
+std::string ArcVethHostName(std::string ifname) {
+  return "veth_" + ifname;
+}
+
+std::string ArcVethPeerName(std::string ifname) {
+  return "peer_" + 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::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 pid,
+                               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 inside the remote namespace.
+  {
+    ScopedNS ns(pid);
+    if (!ns.IsValid() && pid != kTestPID) {
+      LOG(ERROR)
+          << "Cannot create virtual link -- invalid container namespace?";
+      return false;
+    }
+
+    if (!AddVirtualInterfacePair(veth_ifname, peer_ifname)) {
+      LOG(ERROR) << "Failed to create veth pair " << veth_ifname << ","
+                 << peer_ifname;
+      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;
+    }
+  }
+
+  // Now pull the local end out into the local namespace.
+  if (runner().RestoreDefaultNamespace(veth_ifname, pid) != 0) {
+    LOG(ERROR) << "Failed to prepare interface " << veth_ifname;
+    {
+      ScopedNS ns(pid);
+      if (ns.IsValid()) {
+        RemoveInterface(peer_ifname);
+      } else {
+        LOG(ERROR) << "Failed to re-enter container namespace pid " << pid;
+      }
+    }
+    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& veth_ifname,
+                                       const std::string& peer_ifname) {
+  return process_runner_->ip(
+             "link", "add",
+             {veth_ifname, "type", "veth", "peer", "name", peer_ifname}) == 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::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::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