[OVPN3-315] GW: add netlink support

This new component iretrieves the current default IPv4 and IPv6 GW
through netlink.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>

openvpn/netconf/linux/gwnetlink.hpp

@@ -0,0 +1,141 @@
+//    OpenVPN -- An application to securely tunnel IP networks
+//               over a single port, with support for SSL/TLS-based
+//               session authentication and key exchange,
+//               packet encryption, packet authentication, and
+//               packet compression.
+//
+//    Copyright (C) 2012-2017 OpenVPN Inc.
+//
+//    This program is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Affero General Public License Version 3
+//    as published by the Free Software Foundation.
+//
+//    This program is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Affero General Public License for more details.
+//
+//    You should have received a copy of the GNU Affero General Public License
+//    along with this program in the COPYING file.
+//    If not, see <http://www.gnu.org/licenses/>.
+
+// Find default gateways on Linux using ip route command
+
+#pragma once
+
+#include <string>
+
+#include <openvpn/common/exception.hpp>
+#include <openvpn/addr/ip.hpp>
+#include <openvpn/addr/ipv4.hpp>
+#include <openvpn/addr/ipv6.hpp>
+#include <openvpn/tun/linux/client/sitnl.hpp>
+
+namespace openvpn {
+  class LinuxGWNetlink
+  {
+  public:
+    OPENVPN_EXCEPTION(linux_gw_netlink_error);
+
+    LinuxGWNetlink(bool ipv6)
+    {
+      try
+      {
+	if (ipv6)
+	{
+	  IPv6::Addr addr6;
+
+	  if (TunNetlink::SITNL::net_route_best_gw(IP::Route6(IPv6::Addr::from_zero(), 0),
+						   addr6, dev_) < 0)
+	  {
+	    OPENVPN_THROW(linux_gw_netlink_error,
+			  "error retrieving default IPv6 GW");
+	  }
+
+	  addr_ = IP::Addr::from_ipv6(addr6);
+	}
+	else
+	{
+	  IPv4::Addr addr4;
+
+	  if (TunNetlink::SITNL::net_route_best_gw(IP::Route4(IPv4::Addr::from_zero(), 0),
+						   addr4, dev_) < 0)
+	  {
+	    OPENVPN_THROW(linux_gw_netlink_error,
+			  "error retrieving default IPv4 GW");
+	  }
+
+	  addr_ = IP::Addr::from_ipv4(addr4);
+	}
+      } catch (...)
+      {
+	/* nothing to do. just leave default GW unassigned */
+      }
+    }
+
+    const std::string& dev() const
+    {
+      return dev_;
+    }
+
+    const IP::Addr& addr() const
+    {
+      return addr_;
+    }
+
+    bool defined() const
+    {
+      return !dev_.empty() && addr_.defined();
+    }
+
+    std::string to_string() const
+    {
+      return dev_ + '/' + addr_.to_string();
+    }
+
+  private:
+    IP::Addr addr_;
+    std::string dev_;
+  };
+
+  struct LinuxGW46Netlink
+  {
+    LinuxGW46Netlink()
+      : v4(false),
+        v6(true)
+    {
+    }
+
+    std::string to_string() const
+    {
+      std::string ret = "[";
+      if (v4.defined())
+	{
+	  ret += "4:";
+	  ret += v4.to_string();
+	}
+      if (v6.defined())
+	{
+	  if (v4.defined())
+	    ret += ' ';
+	  ret += "6:";
+	  ret += v6.to_string();
+	}
+      ret += "]";
+      return ret;
+    }
+
+    std::string dev() const
+    {
+      if (v4.defined())
+	return v4.dev();
+      else if (v6.defined())
+	return v6.dev();
+      else
+	throw LinuxGWNetlink::linux_gw_netlink_error("cannot determine gateway interface");
+    }
+
+    LinuxGWNetlink v4;
+    LinuxGWNetlink v6;
+  };
+}

openvpn/tun/linux/client/tunnetlink.hpp

@@ -27,7 +27,7 @@
 #include <net/if.h>
 #include <linux/if_tun.h>
 
-#include <openvpn/netconf/linux/gw.hpp>
+#include <openvpn/netconf/linux/gwnetlink.hpp>
 #include <openvpn/common/action.hpp>
 #include <openvpn/tun/linux/client/sitnl.hpp>
 #include <openvpn/tun/client/tunbase.hpp>
@@ -606,7 +606,7 @@ namespace openvpn {
 			   ActionList& create,
 			   ActionList& destroy)
     {
-      const LinuxGW46 gw(true);
+      const LinuxGW46Netlink gw;
 
       // set local4 and local6 to point to IPv4/6 route configurations
       const TunBuilderCapture::RouteAddress* local4 = pull.vpn_ipv4();