/*
 * Encrypting tunnel for userv-ipif tunnels, actual core implementation
 */
/*
 * usage:
 *  udptunnel-forwarder <optchars>
 *                      <public-local-fd> <private-in-fd> <private-out-fd>
 *                      <encdec-keys-fd>
 *                      <mtu> <keepalive> <timeout> <reannounce>
 *                      <public-remote-addr> [<public-remote-port>]
 *                      |<mech1> [<mech1-params> ...]
 *                      |<mech2> [<mech2-params> ...]
 *                      ''
 *
 * Remote addr may '' to mean wait to receive a packet and reply to
 * whereever we get a good packet from first, in which case port
 * should not be specified.
 *
 * <optchars> is zero or more of
 *    w   means generate and write encdec keys, rather than reading them
 *    K   means do crypto debug (use with care!)
 *
 * encdec keys datastream has keys for packets from key datastream
 * writer to reader first, then keys for packets from reader to
 * writer.
 *
 * Every addr or port must be numeric.  There is very little argument checking.
 *
 * Exit status:
 *  SIGALARM   timed out
 *       0     terminated due to outbound packet stream EOF
 *       4     other error
 *       8     system problem
 *      12     usage error
 *      16     bad trouble
 */
/*
 * This file is part of ipif, part of userv-utils
 *
 * Copyright 1996-2013 Ian Jackson <ijackson@chiark.greenend.org.uk>
 * Copyright 1998 David Damerell <damerell@chiark.greenend.org.uk>
 * Copyright 1999,2003
 *    Chancellor Masters and Scholars of the University of Cambridge
 * Copyright 2010 Tony Finch <fanf@dotat.at>
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * 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
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with userv-utils; if not, see http://www.gnu.org/licenses/.
 */

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/utsname.h>
#include <sys/poll.h>

#include <string.h>
#include <errno.h>
#include <assert.h>
#include <stdlib.h>

#include <unistd.h>
#include <fcntl.h>

#include "forwarder.h"

#define MAXMECHS 10

static size_t buffer_size;
static struct utsname uname_result;

static const char *opt_chars;
static int public_local_fd, private_in_fd, private_out_fd;
static int mtu2, keepalive, timeout, reannounce;
static int public_remote_specd;
static struct sockaddr_in public_remote;
static int encdec_keys_fd, encdec_keys_write, crypto_debug;
static int n_mechs;
static const struct mechanism *mechs[MAXMECHS];

static struct mechdata *md_in[MAXMECHS], *md_out[MAXMECHS];
static int maxprefix, maxsuffix;

static struct buffer buf_in, buf_out;
static unsigned char *accum_buf;
static size_t accum_used, accum_avail;

static time_t nextsendka;

static void cdebug(int mechno /*or -1*/, const char *msg) {
  if (!crypto_debug) return;
  printf("%-8.8s: CRYPTO: %-20s %s\n",
	 uname_result.nodename,
	 mechno >= 0 ? mechs[mechno]->name : "",
	 msg);
}

static void cdebughex(int mechno /*or -1*/, const char *msg, const void *ptr,
		      size_t sz, size_t skipbefore,
		      int spc_offset, int dot_offset) {
  const unsigned char *p;
  size_t i;
  unsigned j= dot_offset;
  
  if (!crypto_debug) return;
  printf("%-8.8s: CRYPTO: %-20s %-10s",
	 uname_result.nodename,
	 mechno >= 0 ? mechs[mechno]->name : "",
	 msg);

  for (i=0; i<spc_offset; i++, j++) fputs(j&3 ? "  " : "   ",stdout);
  for (i=0; i<skipbefore; i++, j++) fputs(j&3 ? ".." : " ..",stdout);
  for (i=0, p=ptr; i<sz; i++, j++, p++) printf(j&3 ? "%02x" : " %02x",*p);

  fputc('\n',stdout);
}

static void cdebugbuf(int mechno /*or -1*/, const char *msg,
		      const struct buffer *buf, int spc_offset, int dot_offset) {
  cdebughex(mechno, msg, buf->start, buf->size, buf->start - buf->base,
	    spc_offset, dot_offset);
}

void get_random(void *ptr, size_t sz) {
  static FILE *randfile;

  size_t r;

  if (!randfile) {
    randfile= fopen("/dev/urandom","rb");
    if (!randfile && errno==ENOENT) randfile= fopen("/dev/random","rb");
    if (!randfile) sysfail("open random number generator");
  }

  r= fread(ptr,1,sz,randfile);
  if (r != sz)
    (ferror(randfile) ? sysfail : fail)("cannot read random number generator");

  cdebughex(-1, "get_random", ptr, sz, 0,0,0);
}

void random_key(void *ptr, size_t sz) {
  if (encdec_keys_write) {
    get_random(ptr,sz);
    write_must(encdec_keys_fd,ptr,sz,"write keys datastream");
  } else {
    read_must(encdec_keys_fd,ptr,sz,"read keys datastream");
    cdebughex(-1, "random_key", ptr, sz, 0,0,0);
  }
}


static void setnonblock(int fd, int nonblock) {
  int r;
  
  r= fcntl(fd,F_GETFL);
  if (r==-1) sysfail("fcntl F_GETFL");
  r= fcntl(fd,F_SETFL, nonblock ? r|O_NONBLOCK : r&~O_NONBLOCK);
  if (r==-1) sysfail("fcntl F_SETFL");
}

static const struct mechanism *find_mech(const char *name) {
  const struct mechanism *mech, *const *mechlist;

  for (mechlist= mechanismlists;
       *mechlist;
       mechlist++)
    for (mech= *mechlist; mech->name; mech++)
      if (!strcmp(mech->name,name)) return mech;

  fprintf(stderr,"%s: unknown mechanism: %s\n",programid,name);
  exit(4);
}

static void inbound(void) {
  static int any_recvd;
  static time_t nextreann;
  static unsigned long npackets, nbytes;
  
  struct sockaddr_in this_saddr;
  size_t this_saddrlen;
  int r, i, different;
  const char *emsg;

  buf_in.start= buf_in.base+1;
  buf_in.size= buffer_size-2;
  
  setnonblock(public_local_fd,1);
  this_saddrlen= sizeof(this_saddr);
  r= recvfrom(public_local_fd, buf_in.start, buf_in.size, 0,
	      &this_saddr, &this_saddrlen);
  if (!r) { diag("empty ciphertext"); return; }

  if (r<0) {
    if (errno != EAGAIN && errno != EINTR) { sysdiag("receive"); sleep(1); }
    return;
  }
  if (this_saddr.sin_family != AF_INET) {
    fprintf(stderr,"%s: received unknown AF %lu\n",
	    programid, (unsigned long)this_saddr.sin_family);
    return;
  }
  assert(this_saddrlen == sizeof(this_saddr));

  assert(r <= buf_in.size);
  buf_in.size= r;
  cdebugbuf(-1, "decode", &buf_in, 3,0);
  for (i=n_mechs-1; i>=0; i--) {
    emsg= mechs[i]->decode(md_in[i],&buf_in);
    if (emsg) {
      if (*emsg)
	fprintf(stderr, "%s: bad packet: %s: %s\n",
		programid, mechs[i]->name, emsg);
      else
	cdebug(i,"silently discarded");
      return;
    }
    cdebugbuf(i, "decode", &buf_in, 3,0);
  }

  npackets++;
  nbytes += buf_in.size;
  alarm(timeout);

  different= (!public_remote_specd ||
	      public_remote.sin_addr.s_addr != this_saddr.sin_addr.s_addr ||
	      public_remote.sin_port != this_saddr.sin_port);

  if (different) {

    if (public_remote_specd==2) {
      fprintf(stderr, "%s: packet from unexpected sender %s:%lu\n",
	      programid, inet_ntoa(this_saddr.sin_addr),
	      (unsigned long)ntohs(this_saddr.sin_port));
      return;
    }

    fprintf(stderr, "%s: tunnel open with peer %s:%lu\n",
	    programid, inet_ntoa(this_saddr.sin_addr),
	    (unsigned long)ntohs(this_saddr.sin_port));
    nextsendka= now();
    public_remote_specd= 1;
    memcpy(&public_remote,&this_saddr,sizeof(public_remote));

  } else if (!any_recvd) {

    diag("tunnel open");

  } else if (reannounce && now() >= nextreann) {

    fprintf(stderr, "%s: tunnel still open: received %lu packets, %lu bytes\n",
	    programid, npackets, nbytes);

  } else {

    goto no_set_reann; /* only reset this if we don't print a message. */

  }

  if (reannounce)
    nextreann= now() + reannounce;
  
no_set_reann:

  any_recvd= 1;

  if (!buf_in.size || *buf_in.start != 0300) {
    *--buf_in.start= 0300;
    buf_in.size++;
  }
  if (buf_in.start[buf_in.size-1] != 0300) {
    buf_in.start[buf_in.size++]= 0300;
  }

  setnonblock(private_in_fd,0);
  write_must(private_in_fd, buf_in.start, buf_in.size, "write down");
}

static void sendpacket(const unsigned char *message, size_t size) {
  int i, r;
  
  buf_out.start= buf_out.base+maxprefix;
  buf_out.size= size;
  memcpy(buf_out.start, message, size);

  nextsendka= now() + keepalive;

  cdebugbuf(-1, "encode", &buf_out, 4,0);
  for (i=0; i<n_mechs; i++) {
    mechs[i]->encode(md_out[i],&buf_out);
    cdebugbuf(i, "encode", &buf_out, 4,0);
  }
  assert(public_remote_specd);
  
  setnonblock(public_local_fd,1);
  for (;;) {
    r= sendto(public_local_fd, buf_out.start, buf_out.size, 0,
	      &public_remote, sizeof(public_remote));
    if (r == buf_out.size) break;
    if (r >= 0) { diag("unexpected short send"); return; }
    if (errno != EINTR) { sysdiag("send"); return; }
  }
}

static void outbound(void) {
  int r;
  unsigned char *after_eaten, *delim;
  size_t this_packet;
  
  setnonblock(private_out_fd,1);

  for (;;) {
    r= read(private_out_fd, accum_buf + accum_used, accum_avail - accum_used);
    if (!r) { diag("outbound datastream closed, quitting"); exit(0); }
    if (r<0) {
      if (errno == EAGAIN) return;
      if (errno == EINTR) continue;
    }
    accum_used += r;
    assert(accum_used<=accum_avail);

    after_eaten= accum_buf;
    while ((delim= memchr(after_eaten, 0300, accum_used))) {
      this_packet= delim - after_eaten;
      if (this_packet) sendpacket(after_eaten, this_packet);
      accum_used -= this_packet+1;
      after_eaten = delim+1;
    }
    memmove(accum_buf, after_eaten, accum_used);
    
    if (accum_used == accum_avail) {
      diag("missing interpacket delimiter in output datastream");
      accum_used= 0;
    }
  }
}

int main(int argc, const char *const *const argv_in) {
  const char *arg;
  const char *const *argv_save;
  const char *const *argv_done;
  struct pollfd pollfds[2];
  int i, polltimeout, r;
  time_t tnow;

  argv= argv_in;

  if (uname(&uname_result)) { perror(PROGRAM ": uname failed"); exit(16); }
  sprintf(programid, PROGRAM ": %.*s", SYS_NMLN, uname_result.nodename);

  opt_chars= getarg_string();
  encdec_keys_write= !!strchr(opt_chars,'w');
  crypto_debug= !!strchr(opt_chars,'K');

  public_local_fd= getarg_ulong();
  private_in_fd= getarg_ulong();
  private_out_fd= getarg_ulong();
  encdec_keys_fd= getarg_ulong();

  mtu2= getarg_ulong() * 2;
  keepalive= getarg_ulong();
  timeout= getarg_ulong();
  reannounce= getarg_ulong();
  
  arg= getarg_string();
  if (*arg) {
    public_remote_specd= 1;
    public_remote.sin_family= AF_INET;
    arg_assert(inet_aton(arg,&public_remote.sin_addr));
    public_remote.sin_port= htons(getarg_ulong());
  }

  if (crypto_debug) {
    diag("crypto debugging enabled!");
    setvbuf(stdout,0,_IOLBF,0);
  }

  maxprefix= 0;
  i= 0;
  while ((arg= *++argv)) {
    arg_assert(*arg++ == '|');
    arg_assert(i <= MAXMECHS);
    mechs[i]= find_mech(arg);

    cdebug(i,"writer->reader setup");
    argv_save= argv;

    if (encdec_keys_write)
      mechs[i]->encsetup(&md_out[i], &maxprefix, &maxsuffix);
    else
      mechs[i]->decsetup(&md_in[i]);

    argv_done= argv;
    argv= argv_save;
    cdebug(i,"reader->writer setup");

    if (encdec_keys_write)
      mechs[i]->decsetup(&md_in[i]);
    else
      mechs[i]->encsetup(&md_out[i], &maxprefix, &maxsuffix);

    assert(argv == argv_done);
    
    i++;
  }
  n_mechs= i;

  if (maxprefix<1) maxprefix= 1;
  if (maxsuffix<1) maxsuffix= 1;
  buffer_size= mtu2 + maxprefix + maxsuffix;
  buf_in.base= xmalloc(buffer_size);
  buf_out.base= xmalloc(buffer_size);
  accum_avail= mtu2 + 1;
  accum_buf= xmalloc(accum_avail);

  alarm(timeout);

  pollfds[0].fd= public_local_fd;
  pollfds[0].events= POLLIN;
  pollfds[1].fd= private_out_fd;
  for (;;) {
    pollfds[1].events= public_remote_specd ? POLLIN : 0;
    pollfds[0].revents= 0;
    pollfds[1].revents= 0;

    if (keepalive) {
      tnow= now();
      if (tnow >= nextsendka && public_remote_specd)
	sendpacket((unsigned char*)"\300",1);
      polltimeout= (nextsendka - tnow)*1000;
    } else {
      polltimeout= -1;
    }
    
    r= poll(pollfds,2,polltimeout);
    if (!r) continue;
    if (r==-1 && errno==EINTR) continue;
    if (r==-1) sysfail("poll");

    if (pollfds[0].revents & (POLLIN|POLLERR)) inbound();
    if (pollfds[1].revents & (POLLIN|POLLERR)) outbound();
  }
}