build.sh

#!/bin/bash

func build() {
  build_dir=/tmp/padding-bug/build
  openssl_version=$1
  install_dir=$2
  lzo_version=2.10
  openvpn_version=2.4.7

  mkdir -p ${build_dir}
  pushd ${build_dir}

  wget -qO https://www.openssl.org/source/openssl-${openssl_version}.tar.gz | tar -xzf-
  pushd openssl-*
  ./config \
    -DSSL_ALLOW_ADH \
    --shared \
    --prefix=${install_dir}/external/openssl \
    --openssldir=${install_dir}/external/openssldir
  make
  make install
  popd

  wget -qO https://www.oberhumer.com/opensource/lzo/download/lzo-${lzo_version}.tar.gz | tar -xzf-
  pushd lzo-*
  ./configure \
    --prefix=${install_dir}/external/lzo
  make
  make install
  popd

  wget -qO https://swupdate.openvpn.org/community/releases/openvpn-${openvpn_version}.tar.gz | tar -xzf-
  pushd openvpn-*
  export CFLAGS="-I${install_dir}/external/openssl/include -Wl,-rpath ${install_dir}/external/openssl/lib -L${install_dir}/external/openssl/lib"
  export LZO_CFLAGS="-I${install_dir}/external/lzo/include"
  export LZO_LIBS="-L${install_dir}/external/lzo/lib -llzo2"
  ./configure \
    --prefix=${install_dir} \
    --disable-plugin-auth-pam
  make
  make install
  popd

  popd
  rm -fr ${build_dir}
}

build 1.1.0l ~/tmp/padding-bug/with-openssl-1.1.0
~/tmp/padding-bug/with-openssl-1.1.0/sbin/openvpn --version
# OpenVPN 2.4.7 x86_64-apple-darwin18.7.0 [SSL (OpenSSL)] [LZO] [LZ4] [MH/RECVDA] [AEAD] built on Sep 20 2019
# library versions: OpenSSL 1.1.0l  10 Sep 2019, LZO 2.10
# Originally developed by James Yonan
# Copyright (C) 2002-2018 OpenVPN Inc <sales@openvpn.net>
# Compile time defines: enable_async_push=no enable_comp_stub=no enable_crypto=yes enable_crypto_ofb_cfb=yes enable_debug=yes enable_def_auth=yes enable_dlopen=unknown enable_dlopen_self=unknown enable_dlopen_self_static=unknown enable_fast_install=needless enable_fragment=yes enable_iproute2=no enable_libtool_lock=yes enable_lz4=yes enable_lzo=yes enable_management=yes enable_multihome=yes enable_pam_dlopen=no enable_pedantic=no enable_pf=yes enable_pkcs11=no enable_plugin_auth_pam=no enable_plugin_down_root=yes enable_plugins=yes enable_port_share=yes enable_selinux=no enable_server=yes enable_shared=yes enable_shared_with_static_runtimes=no enable_small=no enable_static=yes enable_strict=no enable_strict_options=no enable_systemd=no enable_werror=no enable_win32_dll=yes enable_x509_alt_username=no with_aix_soname=aix with_crypto_library=openssl with_gnu_ld=no with_mem_check=no with_sysroot=no

build 1.1.1d ~/tmp/padding-bug/with-openssl-1.1.1
~/tmp/padding-bug/with-openssl-1.1.1/sbin/openvpn --version
# OpenVPN 2.4.7 x86_64-apple-darwin18.7.0 [SSL (OpenSSL)] [LZO] [LZ4] [MH/RECVDA] [AEAD] built on Sep 20 2019
# library versions: OpenSSL 1.1.1d  10 Sep 2019, LZO 2.10
# Originally developed by James Yonan
# Copyright (C) 2002-2018 OpenVPN Inc <sales@openvpn.net>
# Compile time defines: enable_async_push=no enable_comp_stub=no enable_crypto=yes enable_crypto_ofb_cfb=yes enable_debug=yes enable_def_auth=yes enable_dlopen=unknown enable_dlopen_self=unknown enable_dlopen_self_static=unknown enable_fast_install=needless enable_fragment=yes enable_iproute2=no enable_libtool_lock=yes enable_lz4=yes enable_lzo=yes enable_management=yes enable_multihome=yes enable_pam_dlopen=no enable_pedantic=no enable_pf=yes enable_pkcs11=no enable_plugin_auth_pam=no enable_plugin_down_root=yes enable_plugins=yes enable_port_share=yes enable_selinux=no enable_server=yes enable_shared=yes enable_shared_with_static_runtimes=no enable_small=no enable_static=yes enable_strict=no enable_strict_options=no enable_systemd=no enable_werror=no enable_win32_dll=yes enable_x509_alt_username=no with_aix_soname=aix with_crypto_library=openssl with_gnu_ld=no with_mem_check=no with_sysroot=no

main.go

package main

import (
	"bufio"
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/base64"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"os"
	"strings"

	"github.com/dpb587/go-openvpn/ovpn"
	"github.com/pkg/errors"
)

var managementAddress = "127.0.0.1:12913"

func main() {
	data, err := ioutil.ReadFile(os.Args[1])
	if err != nil {
		panic(errors.Wrap(err, "reading profile"))
	}

	profile, err := ovpn.Parse(data)
	if err != nil {
		panic(errors.Wrap(err, "parsing profile"))
	}

	switch os.Args[2] {
	case "profile":
		fmt.Printf("%s", createManagedProfile(profile, managementAddress))
	case "management":
		err = startManagementServer(managementAddress, profile)
		if err != nil {
			panic(err)
		}
	default:
		panic(fmt.Errorf("unexpected command: %s", os.Args[2]))
	}
}

func createManagedProfile(profile *ovpn.Profile, managementAddress string) []byte {
	w := &bytes.Buffer{}

	for _, e := range profile.Elements {
		switch pe := e.(type) {
		case ovpn.DirectiveProfileElement:
			fmt.Fprintf(w, "%s %s\n", pe.Directive(), strings.Join(pe.Args(), " "))
		case ovpn.EmbeddedProfileElement:
			switch pe.Embed() {
			case "cert", "key":
				// ignore; handled via management
			default:
				fmt.Fprintf(w, "<%s>\n%s</%s>\n", pe.Embed(), pe.Data(), pe.Embed())
			}
		}
	}

	fmt.Fprintf(w, "management %s\n", strings.Join(strings.Split(managementAddress, ":"), " "))
	fmt.Fprintf(w, "management-client\n")
	fmt.Fprintf(w, "management-external-cert ssoca\n")
	fmt.Fprintf(w, "management-external-key\n")

	return w.Bytes()
}

func startManagementServer(managementAddress string, profile *ovpn.Profile) error {
	listener, err := net.Listen("tcp", managementAddress)
	if err != nil {
		return errors.Wrap(err, "binding")
	}

	conn, err := listener.Accept()
	defer listener.Close()

	if err != nil {
		if opErr, ok := err.(*net.OpError); ok && opErr.Timeout() {
			return nil
		}

		return err
	}

	log.Printf("new openvpn management connection (%s)", conn.RemoteAddr().String())

	err = handleManagementConnection(conn, profile)
	if err != nil {
		panic(err)
	}

	return nil
}

func handleManagementConnection(conn net.Conn, profile *ovpn.Profile) error {
	defer conn.Close()

	certPEM := profile.GetEmbedded("cert")[0].(ovpn.EmbeddedProfileElement).Data()

	block, _ := pem.Decode([]byte(profile.GetEmbedded("key")[0].(ovpn.EmbeddedProfileElement).Data()))
	if block == nil {
		return errors.New("no private key found")
	}

	privRSA, err := x509.ParsePKCS1PrivateKey(block.Bytes)
	if err != nil {
		return errors.Wrap(err, "parsing key from profile")
	}

	reader := bufio.NewReader(conn)

	for {
		log.Print("openvpn management waiting for data")

		message, err := reader.ReadString('\n')
		if err != nil {
			return err
		}

		log.Printf("openvpn management data recv: %s", message)

		var keepGoing bool

		if strings.HasPrefix(message, ">") {
			keepGoing = func(message string) bool {
				split := strings.SplitN(message, ":", 2)
				if len(split) != 2 {
					fmt.Println(fmt.Errorf("unexpected realtime message: %s", message))

					return true
				}

				var err error

				messageSource, messageText := split[0], split[1][0:len(split[1])-1]

				switch messageSource {
				case "INFO":
					log.Print(messageText)
				case "NEED-CERTIFICATE":
					conn.Write([]byte("certificate\n"))
					conn.Write([]byte(certPEM))
					conn.Write([]byte("\n"))
					conn.Write([]byte("END\n"))
				case "RSA_SIGN":
					data64, err := base64.StdEncoding.DecodeString(messageText)
					if err != nil {
						log.Fatal(errors.Wrap(err, "decoding signing token"))
					}

					signature, err := rsa.SignPKCS1v15(rand.Reader, privRSA, 0, data64)
					if err != nil {
						log.Fatal(errors.Wrap(err, "signing token"))
					}

					signature64 := base64.StdEncoding.EncodeToString(signature)

					conn.Write([]byte("rsa-sig"))
					conn.Write([]byte("\n"))
					conn.Write([]byte(signature64))
					conn.Write([]byte("\n"))
					conn.Write([]byte("END\n"))
				default:
					log.Printf("unexpected realtime message: %s", messageSource)
				}

				if err != nil {
					log.Printf("unexpected error: %s", err)
					conn.Write([]byte("signal SIGTERM\n"))
				}

				return true
			}(message[1:])
		} else {
			keepGoing = true
			log.Print(message)
		}

		if !keepGoing {
			log.Print("openvpn management exiting loop")

			break
		}
	}

	return nil
}

management-tool.sh

#!/bin/bash

go get gist.github.com/dpb587-pivotal/d0d132c586ed4053323b4d4246664a07.git
go build -o ~/tmp/padding-bug/management-tool gist.github.com/dpb587-pivotal/d0d132c586ed4053323b4d4246664a07.git