copyright notices

[userv-utils] / ipif / service.c

/*
 * userv service (or standalone program) for per-user IP subranges.
 *
 * When invoked appropriately, it creates a point-to-point network
 * interface with specified parameters.  It arranges for packets sent out
 * via that interface by the kernel to appear on its own stdout in SLIP or
 * CSLIP encoding, and packets injected into its own stdin to be given to
 * the kernel as if received on that interface.  Optionally, additional
 * routes can be set up to arrange for traffic for other address ranges to
 * be routed through the new interface.
 *
 * This is the service program, which is invoked as root from userv (or may
 * be invoked firectly).
 *
 * Its arguments are supposed to be, in order, as follows:
 *
 *  The first two arguments are usually supplied by the userv
 *  configuration.  See the file `ipif/ipif' in the source tree, which
 *  is installed in /etc/userv/services.d/ipif by `make install':
 *
 *  <config>
 *
 *      Specifies address ranges and gids which own them.  The default
 *      configuration supplies /etc/userv/ipif-networks, which is then read
 *      for a list of entries, one per line.
 *
 *  --
 *      Serves to separate the user-supplied and therefore untrusted
 *      arguments from the trusted first argument.
 *
 *  The remaining arguments are supplied by the (untrusted) caller:
 *
 *  <local-addr>,<peer-addr>,<mtu>,<proto>
 *
 *      As for slattach.  Supported protocols are slip, cslip, and
 *      adaptive.  Alternatively, set to `debug' to print debugging info
 *      and exit.  <local-addr> is address of the interface to be created
 *      on the local system; <peer-addr> is the address of the
 *      point-to-point peer.  They must be actual addresses (not
 *      hostnames).
 *
 *  <prefix>/<mask>,<prefix>/<mask>,...
 *
 *      List of additional routes to add for this interface.  routes will
 *      be set up on the local system arranging for packets for those
 *      networks to be sent via the created interface.  <prefix> must be an
 *      IPv4 address, and mask must be an integer (dotted-quad masks are
 *      not supported).  If no additional routes are to be set up, use `-'
 *      or supply an empty argument.
 *
 * Each <config> item - whether a line file such as
 * /etc/userv/ipif-networks, or supplied on the service program
 * command line - is one of:
 *
 *   /<config-file-name>
 *   ./<config-file-name>
 *   ../<config-file-name>
 *
 *      Reads a file which contains lines which are each <config>
 *      items.
 *
 *   <gid>,[=][-|+]<prefix>/<len>(-|+<prefix>/<len>...)[,<junk>]
 *
 *      Indicates that <gid> may allocate addresses in the relevant address
 *      range (<junk> is ignored).  <gid> must be numeric.  To specify a
 *      single host address, you must specify a mask of /32.  If `=' is
 *      specified then the specific subrange is only allowed for the local
 *      endpoint address, but not for remote addresses.
 *
 *      More than one range may be given, with each range prefixed
 *      by + or -.  In this case each address range in the rule will
 *      scanned in order, and the first range in the rule that matches
 *      any desired rule will count: if that first matching range is
 *      prefixed by `+' (or nothing) then the rule applies, if it
 *      is prefixed by `-' (or nothing matches), the rule does not.
 *
 *   *
 *      Means that anything is to be permitted.  This should not appear in
 *      /etc/userv/ipif-networks, as that would permit any user on the
 *      system to create any interfaces with any addresses and routes
 *      attached.  It is provided so that root can usefully invoke the ipif
 *      service program directly (not via userv), without needing to set up
 *      permissions in /etc/userv/ipif-networks.
 *
 *   #...
 *
 *      Comment.  Blank lines are also ignored.
 *
 *   NB: Permission is granted if _any_ config entry matches the request.
 *
 * The service program should be run from userv with no-disconnect-hup.
 */
/*
 * Copyright (C) 1999-2000,2003 Ian Jackson
 * This file is part of ipif, part of userv-utils
 *
 * 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 2 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, write to the Free Software
 * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * $Id$
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <errno.h>
#include <stdarg.h>
#include <ctype.h>
#include <limits.h>
#include <signal.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>

#define NARGS 4
#define MAXEXROUTES 50
#define ATXTLEN 16

static const unsigned long gidmaxval= (unsigned long)((gid_t)-2);
static const char *const protos_ok[]= { "slip", "cslip", "adaptive", 0 };
static const int signals[]= { SIGHUP, SIGINT, SIGTERM, 0 };

static const char *configstr, *proto;
static unsigned long localaddr, peeraddr, mtu;
static int localpming, peerpming;
static int localallow, peerallow, allallow;
static int nexroutes;
static struct exroute {
  unsigned long prefix, mask;
  int allow, pming;
  char prefixtxt[ATXTLEN], masktxt[ATXTLEN];
} exroutes[MAXEXROUTES];

static char localtxt[ATXTLEN];
static char peertxt[ATXTLEN];

static struct pplace {
  struct pplace *parent;
  const char *filename;
  int lineno;
} *cpplace;


static int slpipe[2], ptmaster, undoslattach;
static const char *ifname;
static const char *ptyname;

#define NPIDS 4

static union {
  struct { pid_t sl, cout, cin, task; } byname;
  pid_t bynumber[NPIDS];
} pids;
sigset_t emptyset, fullset;


static int cleantask(void) {
  pid_t pid;

  pid= fork();
  if (!pid) return 1;
  if (pid == (pid_t)-1)
    perror("userv-ipif: fork for undo slattach failed - cannot clean up properly");
  return 0;
}

static void terminate(int estatus) {
  int i, status;
  pid_t pid;
  
  for (i=0; i<NPIDS; i++)
    if (pids.bynumber[i]) kill(pids.bynumber[i], SIGTERM);

  if (undoslattach) {
    if (cleantask()) {
      execlp("slattach", "slattach", "-p", "tty", ptyname, (char*)0);
      perror("userv-ipif: exec slattach for undo slattach failed");
      exit(-1);
    }
    if (ifname && cleantask()) {
      execlp("ifconfig", "ifconfig", ifname, "down", (char*)0);
      perror("userv-ipif: exec ifconfig for undo ifconfig failed");
      exit(-1);
    }
  }

  for (;;) {
    pid= waitpid(-1,&status,0);
    if (pid == (pid_t)-1) break;
  }
  exit(estatus);
}


static void fatal(const char *fmt, ...)
     __attribute__((format(printf,1,2)));
static void fatal(const char *fmt, ...) {
  va_list al;
  va_start(al,fmt);

  fputs("userv-ipif service: fatal error: ",stderr);
  vfprintf(stderr, fmt, al);
  putc('\n',stderr);
  terminate(8);
}
  
static void sysfatal(const char *fmt, ...)
     __attribute__((format(printf,1,2)));
static void sysfatal(const char *fmt, ...) {
  va_list al;
  int e;

  e= errno;
  va_start(al,fmt);

  fputs("userv-ipif service: fatal system error: ",stderr);
  vfprintf(stderr, fmt, al);
  fprintf(stderr,": %s\n", strerror(e));
  terminate(12);
}


static void badusage(const char *fmt, ...)
     __attribute__((format(printf,1,2)));
static void badusage(const char *fmt, ...) {
  va_list al;
  struct pplace *cpp;
  
  if (cpplace) {
    fprintf(stderr,
            "userv-ipif service: %s:%d: ",
            cpplace->filename, cpplace->lineno);
  } else {
    fputs("userv-ipif service: invalid usage: ",stderr);
  }
  va_start(al,fmt);
  vfprintf(stderr, fmt, al);
  putc('\n',stderr);

  if (cpplace) {
    for (cpp=cpplace->parent; cpp; cpp=cpp->parent) {
      fprintf(stderr,
              "userv-ipif service: %s:%d: ... in file included from here\n",
              cpp->filename, cpp->lineno);
    }
  }
  terminate(16);
}

static char *ip2txt(unsigned long addr, char *buf) {
  sprintf(buf, "%lu.%lu.%lu.%lu",
          (addr>>24) & 0x0ff,
          (addr>>16) & 0x0ff,
          (addr>>8) & 0x0ff,
          (addr) & 0x0ff);
  return buf;
}

static unsigned long eat_number(const char **argp, const char *what,
                                unsigned long min, unsigned long max,
                                const char *endchars, int *endchar_r) {
  /* If !endchars then the endchar must be a nul, otherwise it may be
   * a nul (resulting in *argp set to 0) or something else (*argp set
   * to point to after delim, *endchar_r set to delim).
   * *endchar_r may be 0.
   */
  unsigned long rv;
  char *ep;
  int endchar;

  if (!*argp) { badusage("missing number %s",what); }
  rv= strtoul(*argp,&ep,0);
  if ((endchar= *ep)) {
    if (!endchars) badusage("junk after number %s",what);
    if (!strchr(endchars,endchar))
      badusage("invalid character or delimiter `%c' in or after number, %s:"
               " expected %s (or none?)", endchar,what,endchars);
    *argp= ep+1;
  } else {
    *argp= 0;
  }
  if (endchar_r) *endchar_r= endchar;
  if (rv < min || rv > max) badusage("number %s value %lu out of range %lu..%lu",
                                     what, rv, min, max);
  return rv;
}

static int addrnet_overlap(unsigned long p1, unsigned long m1,
                           unsigned long p2, unsigned long m2) {
  unsigned long mask;

  mask= m1&m2;
  return (p1 & mask) == (p2 & mask);
}

static void addrnet_mustdiffer(const char *w1, unsigned long p1, unsigned long m1,
                               const char *w2, unsigned long p2, unsigned long m2) {
  if (!addrnet_overlap(p1,m1,p2,m2)) return;
  badusage("%s %08lx/%08lx overlaps/clashes with %s %08lx/%08lx",
           w1,p1,m1, w2,p2,m2);
}
  
static unsigned long eat_addr(const char **argp, const char *what,
                              const char *endchars, int *endchar_r) {
  char whatbuf[100];
  unsigned long rv;
  int i;

  for (rv=0, i=0;
       i<4;
       i++) {
    rv <<= 8;
    sprintf(whatbuf,"%s byte #%d",what,i);
    rv |= eat_number(argp,whatbuf, 0,255, i<3 ? "." : endchars, endchar_r);
  }

  return rv;
}

static void eat_prefixmask(const char **argp, const char *what,
                           const char *endchars, int *endchar_r,
                           unsigned long *prefix_r, unsigned long *mask_r, int *len_r) {
  /* mask_r and len_r may be 0 */
  char whatbuf[100];
  int len;
  unsigned long prefix, mask;

  prefix= eat_addr(argp,what, "/",0);
  sprintf(whatbuf,"%s length",what);
  len= eat_number(argp,whatbuf, 0,32, endchars,endchar_r);

  mask= len ? (~0UL << (32-len)) : 0UL;
  if (prefix & ~mask) badusage("%s prefix %08lx not fully contained in mask %08lx",
                               what,prefix,mask);
  *prefix_r= prefix;
  if (mask_r) *mask_r= mask;
  if (len_r) *len_r= len;
}

static int addrnet_isin(unsigned long prefix, unsigned long mask,
                        unsigned long mprefix, unsigned long mmask) {
  return  !(~mask & mmask)  &&  (prefix & mmask) == mprefix;
}

/* Totally hideous algorithm for parsing the config file lines.
 * For each config file line, we first see if its gid applies.  If not
 * we skip it.  Otherwise, we do
 *  permit_begin
 *     which sets <foo>pming to 1
 * for each range.  <foo>pming may be 0 if we've determined that
 * this line does not apply to <foo>.
 *  permit_range
 *     which calls permit_range_thing for each <foo>
 *        which checks to see if <foo> is inside the relevant
 *        range (for +) or overlaps it (for -) and updates
 *        <foo>allow and <foo>pming.
 */

static void permit_begin(void) {
  int i;
  
  localpming= peerpming= 1;
  for (i=0; i<nexroutes; i++) exroutes[i].pming= 1;
}

static void permit_range_thing(unsigned long tprefix, unsigned long tmask,
                               const char *what, int *tallow, int *tpming,
                               unsigned long pprefix, unsigned long pmask,
                               int plus, int *any) {
  if (plus) {
    if (!addrnet_isin(tprefix,tmask, pprefix,pmask)) return;
    if (*tpming) *tallow= 1;
  } else {
    if (!addrnet_overlap(tprefix,tmask, pprefix,pmask)) return;
    *tpming= 0;
  }
  if (!proto) printf(" %c%s", plus?'+':'-', what);
  *any= 1;
}

static void permit_range(unsigned long prefix, unsigned long mask,
                         int plus, int localonly) {
  int i, any;
  char idbuf[40];
  
  assert(!(prefix & ~mask));
  any= 0;

  permit_range_thing(localaddr,~0UL,"local", &localallow,&localpming,
                     prefix,mask, plus,&any);

  if (!localonly) {
    permit_range_thing(peeraddr,~0UL, "peer-addr", &peerallow,&peerpming,
                       prefix,mask, plus,&any);
    for (i=0; i<nexroutes; i++) {
      sprintf(idbuf,"route#%d",i);
      permit_range_thing(exroutes[i].prefix,exroutes[i].mask, idbuf,
                         &exroutes[i].allow,&exroutes[i].pming,
                         prefix,mask, plus,&any);
    }
  }
  if (!proto)
    if (!any) fputs(" nothing",stdout);
}

static void pconfig(const char *configstr, int truncated);

static void pfile(const char *filename) {
  FILE *file;
  char buf[PATH_MAX];
  int l, truncated, c;
  struct pplace npp, *cpp;

  for (cpp=cpplace; cpp; cpp=cpp->parent) {
    if (!strcmp(cpp->filename,filename))
      badusage("recursive configuration file `%s'",filename);
  }

  file= fopen(filename,"r");
  if (!file)
    badusage("cannot open configuration file `%s': %s", filename, strerror(errno));

  if (!proto) printf("config file `%s':\n",filename);

  npp.parent= cpplace;
  npp.filename= filename;
  npp.lineno= 0;
  cpplace= &npp;

  while (fgets(buf, sizeof(buf), file)) {
    npp.lineno++;
    l= strlen(buf);
    if (!l) continue;

    truncated= (buf[l-1] != '\n');
    while (l>0 && isspace((unsigned char) buf[l-1])) l--;
    if (!l) continue;
    buf[l]= 0;

    if (truncated) {
      while ((c= getc(file)) != EOF && c != '\n');
      if (c == EOF) break;
    }

    pconfig(buf,truncated);
  }
  if (ferror(file))
    badusage("failed while reading configuration file: %s", strerror(errno));

  cpplace= npp.parent;
}

static void pconfig(const char *configstr, int truncated) {
  unsigned long fgid, tgid, pprefix, pmask;
  int plen, localonly, plus, rangeix, delim;
  char ptxt[ATXTLEN];
  char whattxt[100];
  const char *gidlist;
  
  switch (configstr[0]) {
  case '*':
    permit_begin();
    permit_range(0UL,0UL,1,0);
    return;
    
  case '#':
    return;
    
  case '/': case '.':
    if (truncated) badusage("filename too long (`%.100s...')",configstr);
    pfile(configstr);
    return;
    
  default:
    if (!isdigit((unsigned char)configstr[0]))
      badusage("unknown configuration directive");
    
    fgid= eat_number(&configstr,"gid", 0,gidmaxval, ",",0);

    if (!proto) printf(" %5lu", fgid);

    gidlist= getenv("USERV_GID");
    if (!gidlist) fatal("USERV_GID not set");
    for (;;) {
      if (!gidlist) {
        if (!proto) printf(" no matching gid\n");
        return;
      }
      tgid= eat_number(&gidlist,"userv-gid", 0,gidmaxval, " ",0);
      if (tgid == fgid) break;
    }

    if (configstr[0] == '=') {
      localonly= 1;
      configstr++;
    } else {
      localonly= 0;
    }

    permit_begin();

    rangeix= 0;
    plus= 1;
    switch (configstr[0]) {
    case '-': plus= 0;     /* fall through */
    case '+': configstr++;
    default:;
    }

    for (;;) {
      sprintf(whattxt, "%s-prefix#%d",
              plus ? "permitted" : "notpermitted",
              rangeix);
      eat_prefixmask(&configstr,whattxt, ",+-",&delim,
                     &pprefix,&pmask,&plen);
      if (!configstr && truncated)
        badusage("gid,prefix/len,... spec too long");

      if (!proto)
        printf("  %c%s/%d:", plus?'+':'-',ip2txt(pprefix,ptxt), plen);

      permit_range(pprefix,pmask,plus,localonly);
      if (delim==',') break;

      plus= delim=='-' ? 0 : 1;
      rangeix++;
    }

    putchar('\n');
    return;
  }
}

static void checkallow(int allow, const char *what,
                       const char *prefixtxt, const char *masktxt) {
  if (allow) return;
  fprintf(stderr,"userv-ipif service: access denied for %s, %s/%s\n",
          what, prefixtxt, masktxt);
  allallow= 0;
}

static void parseargs(int argc, const char *const *argv) {
  unsigned long routeaddr, routemask;
  const char *carg;
  const char *const *cprotop;
  int i;
  char erwhatbuf[100], erwhatbuf2[100];
  
  if (argc < NARGS+1) { badusage("too few arguments"); }
  if (argc > NARGS+1) { badusage("too many arguments"); }

  configstr= *++argv;
  
  carg= *++argv;
  if (strcmp(carg,"--")) badusage("separator argument `--' not found, got `%s'",carg);

  carg= *++argv;
  localaddr= eat_addr(&carg,"local-addr", ",",0);
  peeraddr= eat_addr(&carg,"peer-addr", ",",0);
  mtu= eat_number(&carg,"mtu", 576,65536, ",",0);
  localallow= peerallow= 0;
  
  if (!strcmp(carg,"debug")) {
    proto= 0;
  } else {
    for (cprotop= protos_ok;
         (proto= *cprotop) && strcmp(proto,carg);
         cprotop++);
    if (!proto) fatal("invalid protocol");
  }
  
  addrnet_mustdiffer("local-addr",localaddr,~0UL, "peer-addr",peeraddr,~0UL);
  
  carg= *++argv;
  if (strcmp(carg,"-")) {
    for (nexroutes=0;
         carg && *carg;
         nexroutes++) {
      if (nexroutes == MAXEXROUTES)
        fatal("too many extra routes (only %d allowed)",MAXEXROUTES);
      sprintf(erwhatbuf,"route#%d",nexroutes);
    
      eat_prefixmask(&carg,erwhatbuf, ",",0, &routeaddr,&routemask,0);
      if (routemask == ~0UL) {
        addrnet_mustdiffer(erwhatbuf,routeaddr,routemask, "local-addr",localaddr,~0UL);
        addrnet_mustdiffer(erwhatbuf,routeaddr,routemask, "peer-addr",peeraddr,~0UL);
      }
      for (i=0; i<nexroutes; i++) {
        sprintf(erwhatbuf2,"route#%d",i);
        addrnet_mustdiffer(erwhatbuf,routeaddr,routemask,
                           erwhatbuf2,exroutes[i].prefix,exroutes[i].mask);
      }
      exroutes[nexroutes].prefix= routeaddr;
      exroutes[nexroutes].mask= routemask;
      exroutes[nexroutes].allow= 0;
      ip2txt(routeaddr,exroutes[nexroutes].prefixtxt);
      ip2txt(routemask,exroutes[nexroutes].masktxt);
    }
  }

  ip2txt(localaddr,localtxt);
  ip2txt(peeraddr,peertxt);
}

static void checkpermit(void) {
  int i;
  char erwhatbuf[100];
  
  allallow= 1;
  checkallow(localallow,"local-addr", localtxt,"32");
  checkallow(peerallow,"peer-addr", peertxt,"32");
  for (i=0; i<nexroutes; i++) {
    sprintf(erwhatbuf, "route#%d", i);
    checkallow(exroutes[i].allow, erwhatbuf, exroutes[i].prefixtxt, exroutes[i].masktxt);
  }
  if (!allallow) fatal("access denied");
}

static void dumpdebug(void) __attribute__((noreturn));
static void dumpdebug(void) {
  int i;
  char erwhatbuf[100];
  
  printf("protocol: debug\n"
         "local:    %08lx == %s\n"
         "peer:     %08lx == %s\n"
         "mtu:      %ld\n"
         "routes:   %d\n",
         localaddr, localtxt,
         peeraddr, peertxt,
         mtu,
         nexroutes);
  for (i=0; i<nexroutes; i++) {
    sprintf(erwhatbuf, "route#%d:", i);
    printf("%-9s %08lx/%08lx == %s/%s\n",
           erwhatbuf,
           exroutes[i].prefix, exroutes[i].mask,
           exroutes[i].prefixtxt, exroutes[i].masktxt);
  }
  if (ferror(stdout) || fclose(stdout)) sysfatal("flush stdout");
  exit(0);
}


static void setsigmask(const sigset_t *ss) {
  int r;
  
  r= sigprocmask(SIG_SETMASK, ss, 0);
  if (r) sysfatal("[un]block signals");
}  

static void setsignals(void (*handler)(int), struct sigaction *sa, int chldflags) {
  const int *signalp;
  int r, sig;
  
  sa->sa_handler= handler;
  sa->sa_flags= 0; 
  for (signalp=signals; (sig=*signalp); signalp++) {
    r= sigaction(sig, sa, 0);  if (r) sysfatal("uncatch signal");
  }
  sa->sa_flags= chldflags;
  r= sigaction(SIGCHLD, sa, 0);  if (r) sysfatal("uncatch children");
}

static void infork(void) {
  struct sigaction sa;

  memset(&pids,0,sizeof(pids));
  sigemptyset(&sa.sa_mask);
  setsignals(SIG_DFL,&sa,0);
  setsigmask(&emptyset);
  undoslattach= 0;
}

static pid_t makesubproc(void (*entry)(void)) {
  pid_t pid;

  pid= fork();  if (pid == (pid_t)-1) sysfatal("fork for subprocess");
  if (pid) return pid;

  infork();
  entry();
  abort();
}

static int task(void) {
  pid_t pid;

  pid= fork();
  if (pid == (pid_t)-1) sysfatal("fork for task");
  if (!pid) { infork(); return 1; }

  pids.byname.task= pid;
  while (pids.byname.task) sigsuspend(&emptyset);
  return 0;
}

static void mdup2(int fd1, int fd2, const char *what) {
  int r;

  for (;;) {
    r= dup2(fd1,fd2); if (r==fd2) return;
    if (r!=-1) fatal("dup2 in %s gave wrong answer %d instead of %d",what,r,fd2);
    if (errno != EINTR) sysfatal("dup2 failed in %s",what);
  }
}

static void sl_entry(void) {
  mdup2(slpipe[1],1,"slattach child");
  execlp("slattach", "slattach", "-v", "-L", "-p",proto, ptyname, (char*)0);
  sysfatal("cannot exec slattach");
}

static void cin_entry(void) {
  mdup2(ptmaster,1,"cat input child");
  execlp("cat", "cat", (char*)0);
  sysfatal("cannot exec cat input");
}

static void cout_entry(void) {
  mdup2(ptmaster,0,"cat output child");
  execlp("cat", "cat", (char*)0);
  sysfatal("cannot exec cat output");
}

static void sighandler(int signum) {
  pid_t pid;
  int estatus, status;
  const char *taskfail;

  estatus= 4;
  
  if (signum == SIGCHLD) {
    for (;;) {
      pid= waitpid(-1,&status,WNOHANG);
      if (!pid || pid == (pid_t)-1) return;

      if (pid == pids.byname.task) {
        pids.byname.task= 0;
        if (!status) return;
        taskfail= "task";
      } else if (pid == pids.byname.cin) {
        pids.byname.cin= 0;
        if (status) {
          taskfail= "input cat";
        } else {
          taskfail= 0;
          estatus= 0;
        }
      } else if (pid == pids.byname.cout) {
        pids.byname.cout= 0;
        taskfail= "output cat";
      } else if (pid == pids.byname.sl) {
        pids.byname.sl= 0;
        taskfail= "slattach";
      } else {
        continue;
      }
      break;
    }
    if (taskfail) {
      if (WIFEXITED(status)) {
        fprintf(stderr,
                "userv-ipif service: %s unexpectedly exited with exit status %d\n",
                taskfail, WEXITSTATUS(status));
      } else if (WIFSIGNALED(status)) {
        fprintf(stderr,
                "userv-ipif service: %s unexpectedly killed by signal %s%s\n",
                taskfail, strsignal(WTERMSIG(status)),
                WCOREDUMP(status) ? " (core dumped)" : "");
      } else {
        fprintf(stderr, "userv-ipif service: %s unexpectedly terminated"
                " with unknown status code %d\n", taskfail, status);
      }
    }
  } else {
    fprintf(stderr,
            "userv-ipif service: received signal %d, terminating\n",
            signum);
  }

  terminate(estatus);
}

static void startup(void) {
  int r;
  struct sigaction sa;
  
  sigfillset(&fullset);
  sigemptyset(&emptyset);

  ptmaster= getpt();  if (ptmaster==-1) sysfatal("allocate pty master");
  r= grantpt(ptmaster);  if (r) sysfatal("grab/grant pty slave");
  ptyname= ptsname(ptmaster);  if (!ptyname) sysfatal("get pty slave name");
  r= chmod(ptyname,0600);  if (r) sysfatal("chmod pty slave");
  r= unlockpt(ptmaster);  if (r) sysfatal("unlock pty");

  sigfillset(&sa.sa_mask);
  setsignals(sighandler,&sa,SA_NOCLDSTOP);
  setsigmask(&fullset);
}

static void startslattach(void) {
  static char ifnbuf[200];

  FILE *piper;
  int r, l, k;

  r= pipe(slpipe);  if (r) sysfatal("create pipe");
  piper= fdopen(slpipe[0],"r");  if (!piper) sysfatal("fdopen pipe");

  undoslattach= 1;
  pids.byname.sl= makesubproc(sl_entry);

  close(slpipe[1]);
  setsigmask(&emptyset);
  if (!fgets(ifnbuf,sizeof(ifnbuf),piper)) {
    if (ferror(piper)) sysfatal("cannot read ifname from slattach");
    else fatal("cannot read ifname from slattach");
  }
  setsigmask(&fullset);
  l= strlen(ifnbuf);
  if (l<=0 || ifnbuf[l-1] != '\n') fatal("slattach gave strange output `%s'",ifnbuf);
  ifnbuf[l-1]= 0;
  for (k=l; k>0 && ifnbuf[k-1]!=' '; k--);
  ifname= ifnbuf+k;
}

static void netconfigure(void) {
  char mtutxt[100];
  int i;

  if (task()) {
    sprintf(mtutxt,"%lu",mtu);
  
    execlp("ifconfig", "ifconfig", ifname, localtxt,
           "netmask","255.255.255.255", "-broadcast", "pointopoint",peertxt,
           "mtu",mtutxt, "up", (char*)0);
    sysfatal("cannot exec ifconfig");
  }

  for (i=0; i<nexroutes; i++) {
    if (task()) {
      execlp("route","route", "add", "-net",exroutes[i].prefixtxt,
             "netmask",exroutes[i].masktxt,
             "gw",peertxt, "dev",ifname, (char*)0);
      sysfatal("cannot exec route (for route)");
    }
  }
}

static void copydata(void) __attribute__((noreturn));
static void copydata(void) {
  int r;
  
  pids.byname.cin= makesubproc(cin_entry);
  for (;;) {
    r= write(1, "\300", 1); if (r==1) break;
    assert(r==-1);  if (errno != EINTR) sysfatal("send initial delim to confirm");
  }
  pids.byname.cout= makesubproc(cout_entry);

  for (;;) sigsuspend(&emptyset);
}

int main(int argc, const char *const *argv) {
  parseargs(argc,argv);
  pconfig(configstr,0);
  checkpermit();
  if (!proto) dumpdebug();

  startup();
  startslattach();
  netconfigure();
  copydata();
}