mdw@git.distorted.org.uk Git - userv-utils/blob - ipif/service.c

   1 /*
   2  * userv service (or standalone program)
   3  * for per-user IP subranges.
   4  *
   5  * This is invoked as root, directly from userv.
   6  * Its arguments are supposed to be, in order:
   7  *  <config>
   8  *      Specifies address ranges and gids which own them.
   9  *  --  Indicates that the remaining arguments are user-supplied
  10  *      and therefore untrusted.
  11  *  <local-addr>,<peer-addr>,<mtu>,<proto>
  12  *      As for slattach.  Supported protocols are slip, cslip, and
  13  *      adaptive.  Alternatively, set to `debug' to print debugging
  14  *      info.  <local-addr> is address of the interface on chiark;
  15  *      <peer-addr> is the address of the point-to-point peer.
  16  *  <prefix>/<mask>,<prefix>/<mask>,...
  17  *      List of additional routes to add for this interface.
  18  *      May be the empty argument, or `-' if this is problematic.
  19  *
  20  * <config> is either
  21  *    <gid>,<prefix>/<len>[,<junk>]
  22  *      indicating that that gid may allocate addresses in
  23  *      the relevant subspace (<junk> is ignored)
  24  * or #...
  25  *      which is a comment
  26  * or /<config-file-name> or ./<config-file-name> or ../<config-file-name>
  27  *      which refers to a file which contains lines which
  28  *      are each <config>
  29  * or *
  30  *      which means that anything is permitted
  31  *
  32  * Should be run from userv with no-disconnect-hup.
  33  */
  34
  35 #include <stdio.h>
  36 #include <string.h>
  37 #include <stdlib.h>
  38 #include <assert.h>
  39 #include <errno.h>
  40 #include <stdarg.h>
  41 #include <ctype.h>
  42 #include <limits.h>
  43 #include <signal.h>
  44 #include <unistd.h>
  45
  46 #include <sys/types.h>
  47 #include <sys/wait.h>
  48 #include <sys/stat.h>
  49
  50 #define NARGS 4
  51 #define MAXEXROUTES 5
  52 #define ATXTLEN 16
  53
  54 static const unsigned long gidmaxval= (unsigned long)((gid_t)-2);
  55 static const char *const protos_ok[]= { "slip", "cslip", "adaptive", 0 };
  56 static const int signals[]= { SIGHUP, SIGINT, SIGTERM, 0 };
  57
  58 static const char *configstr, *proto;
  59 static unsigned long localaddr, peeraddr, mtu;
  60 static int localallow, peerallow, allallow;
  61 static int nexroutes;
  62 static struct exroute {
  63   unsigned long prefix, mask;
  64   int allow;
  65   char prefixtxt[ATXTLEN], masktxt[ATXTLEN];
  66 } exroutes[MAXEXROUTES];
  67
  68 static char localtxt[ATXTLEN];
  69 static char peertxt[ATXTLEN];
  70
  71 static struct pplace {
  72   struct pplace *parent;
  73   const char *filename;
  74   int lineno;
  75 } *cpplace;
  76
  77
  78 static int slpipe[2], ptmaster, undoslattach;
  79 static const char *ifname;
  80 static const char *ptyname;
  81
  82 #define NPIDS 4
  83
  84 static union {
  85   struct { pid_t sl, cout, cin, task; } byname;
  86   pid_t bynumber[NPIDS];
  87 } pids;
  88 sigset_t emptyset, fullset;
  89
  90
  91 static int cleantask(void) {
  92   pid_t pid;
  93
  94   pid= fork();
  95   if (!pid) return 1;
  96   if (pid == (pid_t)-1)
  97     perror("userv-ipif: fork for undo slattach failed - cannot clean up properly");
  98   return 0;
  99 }
 100
 101 static void terminate(int estatus) {
 102   int i, status;
 103   pid_t pid;
 104
 105   for (i=0; i<NPIDS; i++)
 106     if (pids.bynumber[i]) kill(pids.bynumber[i], SIGTERM);
 107
 108   if (undoslattach) {
 109     if (cleantask()) {
 110       execlp("slattach", "slattach", "-p", "tty", ptyname, (char*)0);
 111       perror("userv-ipif: exec slattach for undo slattach failed");
 112       exit(-1);
 113     }
 114     if (ifname && cleantask()) {
 115       execlp("ifconfig", "ifconfig", ifname, "down", (char*)0);
 116       perror("userv-ipif: exec ifconfig for undo ifconfig failed");
 117       exit(-1);
 118     }
 119   }
 120
 121   for (;;) {
 122     pid= waitpid(-1,&status,0);
 123     if (pid == (pid_t)-1) break;
 124   }
 125   exit(estatus);
 126 }
 127
 128
 129 static void fatal(const char *fmt, ...)
 130      __attribute__((format(printf,1,2)));
 131 static void fatal(const char *fmt, ...) {
 132   va_list al;
 133   va_start(al,fmt);
 134
 135   fputs("userv-ipif service: fatal error: ",stderr);
 136   vfprintf(stderr, fmt, al);
 137   putc('\n',stderr);
 138   terminate(8);
 139 }
 140
 141 static void sysfatal(const char *fmt, ...)
 142      __attribute__((format(printf,1,2)));
 143 static void sysfatal(const char *fmt, ...) {
 144   va_list al;
 145   int e;
 146
 147   e= errno;
 148   va_start(al,fmt);
 149
 150   fputs("userv-ipif service: fatal system error: ",stderr);
 151   vfprintf(stderr, fmt, al);
 152   fprintf(stderr,": %s\n", strerror(e));
 153   terminate(12);
 154 }
 155
 156
 157 static void badusage(const char *fmt, ...)
 158      __attribute__((format(printf,1,2)));
 159 static void badusage(const char *fmt, ...) {
 160   va_list al;
 161   struct pplace *cpp;
 162
 163   if (cpplace) {
 164     fprintf(stderr,
 165             "userv-ipif service: %s:%d: ",
 166             cpplace->filename, cpplace->lineno);
 167   } else {
 168     fputs("userv-ipif service: invalid usage: ",stderr);
 169   }
 170   va_start(al,fmt);
 171   vfprintf(stderr, fmt, al);
 172   putc('\n',stderr);
 173
 174   if (cpplace) {
 175     for (cpp=cpplace->parent; cpp; cpp=cpp->parent) {
 176       fprintf(stderr,
 177               "userv-ipif service: %s:%d: ... in file included from here\n",
 178               cpp->filename, cpp->lineno);
 179     }
 180   }
 181   terminate(16);
 182 }
 183
 184 static char *ip2txt(unsigned long addr, char *buf) {
 185   sprintf(buf, "%lu.%lu.%lu.%lu",
 186           (addr>>24) & 0x0ff,
 187           (addr>>16) & 0x0ff,
 188           (addr>>8) & 0x0ff,
 189           (addr) & 0x0ff);
 190   return buf;
 191 }
 192
 193 static unsigned long eat_number(const char **argp, const char *what,
 194                                 unsigned long min, unsigned long max,
 195                                 const char *endchars, int *endchar_r) {
 196   /* If !endchars then the endchar must be a nul, otherwise it may be
 197    * a nul (resulting in *argp set to 0) or something else (*argp set
 198    * to point to after delim, *endchar_r set to delim).
 199    * *endchar_r may be 0.
 200    */
 201   unsigned long rv;
 202   char *ep;
 203   int endchar;
 204
 205   if (!*argp) { badusage("missing number %s",what); }
 206   rv= strtoul(*argp,&ep,0);
 207   if ((endchar= *ep)) {
 208     if (!endchars) badusage("junk after number %s",what);
 209     if (!strchr(endchars,endchar))
 210       badusage("invalid character or delimiter `%c' in or after number, %s:"
 211                " expected %s (or none?)", endchar,what,endchars);
 212     *argp= ep+1;
 213   } else {
 214     *argp= 0;
 215   }
 216   if (endchar_r) *endchar_r= endchar;
 217   if (rv < min || rv > max) badusage("number %s value %lu out of range %lu..%lu",
 218                                      what, rv, min, max);
 219   return rv;
 220 }
 221
 222 static void addrnet_mustdiffer(const char *w1, unsigned long p1, unsigned long m1,
 223                                const char *w2, unsigned long p2, unsigned long m2) {
 224   unsigned long mask;
 225
 226   mask= m1&m2;
 227   if ((p1 & mask) != (p2 & mask)) return;
 228   badusage("%s %08lx/%08lx overlaps/clashes with %s %08lx/%08lx",
 229            w1,p1,m1, w2,p2,m2);
 230 }
 231
 232 static unsigned long eat_addr(const char **argp, const char *what,
 233                               const char *endchars, int *endchar_r) {
 234   char whatbuf[100];
 235   unsigned long rv;
 236   int i;
 237
 238   for (rv=0, i=0;
 239        i<4;
 240        i++) {
 241     rv <<= 8;
 242     sprintf(whatbuf,"%s byte #%d",what,i);
 243     rv |= eat_number(argp,whatbuf, 0,255, i<3 ? "." : endchars, endchar_r);
 244   }
 245
 246   return rv;
 247 }
 248
 249 static void eat_prefixmask(const char **argp, const char *what,
 250                            const char *endchars, int *endchar_r,
 251                            unsigned long *prefix_r, unsigned long *mask_r, int *len_r) {
 252   /* mask_r and len_r may be 0 */
 253   char whatbuf[100];
 254   int len;
 255   unsigned long prefix, mask;
 256
 257   prefix= eat_addr(argp,what, "/",0);
 258   sprintf(whatbuf,"%s length",what);
 259   len= eat_number(argp,whatbuf, 0,32, endchars,endchar_r);
 260
 261   mask= (~0UL << (32-len));
 262   if (prefix & ~mask) badusage("%s prefix %08lx not fully contained in mask %08lx",
 263                                what,prefix,mask);
 264   *prefix_r= prefix;
 265   if (mask_r) *mask_r= mask;
 266   if (len_r) *len_r= len;
 267 }
 268
 269 static int addrnet_isin(unsigned long prefix, unsigned long mask,
 270                         unsigned long mprefix, unsigned long mmask) {
 271   return  !(~mask & mmask)  &&  (prefix & mmask) == mprefix;
 272 }
 273
 274
 275 static void permit(unsigned long pprefix, unsigned long pmask) {
 276   int i, any;
 277
 278   assert(!(pprefix & ~pmask));
 279   any= 0;
 280
 281   if (!proto) fputs("permits",stdout);
 282   if (addrnet_isin(localaddr,~0UL, pprefix,pmask)) {
 283     if (!proto) fputs(" local-addr",stdout);
 284     any= localallow= 1;
 285   }
 286   if (addrnet_isin(peeraddr,~0UL, pprefix,pmask)) {
 287     if (!proto) fputs(" peer-addr",stdout);
 288     any= peerallow= 1;
 289   }
 290   for (i=0; i<nexroutes; i++) {
 291     if (addrnet_isin(exroutes[i].prefix,exroutes[i].mask, pprefix,pmask)) {
 292       if (!proto) printf(" route#%d",i);
 293       any= exroutes[i].allow= 1;
 294     }
 295   }
 296   if (!proto) {
 297     if (!any) fputs(" nothing",stdout);
 298     putchar('\n');
 299   }
 300 }
 301
 302 static void pconfig(const char *configstr, int truncated);
 303
 304 static void pfile(const char *filename) {
 305   FILE *file;
 306   char buf[PATH_MAX];
 307   int l, truncated, c;
 308   struct pplace npp, *cpp;
 309
 310   for (cpp=cpplace; cpp; cpp=cpp->parent) {
 311     if (!strcmp(cpp->filename,filename))
 312       badusage("recursive configuration file `%s'",filename);
 313   }
 314
 315   file= fopen(filename,"r");
 316   if (!file)
 317     badusage("cannot open configuration file `%s': %s", filename, strerror(errno));
 318
 319   if (!proto) printf("config file `%s':\n",filename);
 320
 321   npp.parent= cpplace;
 322   npp.filename= filename;
 323   npp.lineno= 0;
 324   cpplace= &npp;
 325
 326   while (fgets(buf, sizeof(buf), file)) {
 327     npp.lineno++;
 328     l= strlen(buf);
 329     if (!l) continue;
 330
 331     truncated= (buf[l-1] != '\n');
 332     while (l>0 && isspace((unsigned char) buf[l-1])) l--;
 333     if (!l) continue;
 334     buf[l]= 0;
 335
 336     if (truncated) {
 337       while ((c= getc(file)) != EOF && c != '\n');
 338       if (c == EOF) break;
 339     }
 340
 341     pconfig(buf,truncated);
 342   }
 343   if (ferror(file))
 344     badusage("failed while reading configuration file: %s", strerror(errno));
 345
 346   cpplace= npp.parent;
 347 }
 348
 349 static void pconfig(const char *configstr, int truncated) {
 350   unsigned long fgid, tgid, pprefix, pmask;
 351   int plen;
 352   char ptxt[ATXTLEN];
 353   const char *gidlist;
 354
 355   switch (configstr[0]) {
 356   case '*':
 357     if (strcmp(configstr,"*")) badusage("`*' directive must be only thing on line");
 358     permit(0UL,0UL);
 359     return;
 360
 361   case '#':
 362     return;
 363
 364   case '/': case '.':
 365     if (truncated) badusage("filename too long (`%.100s...')",configstr);
 366     pfile(configstr);
 367     return;
 368
 369   default:
 370     if (!isdigit((unsigned char)configstr[0]))
 371       badusage("unknown configuration directive");
 372
 373     fgid= eat_number(&configstr,"gid", 0,gidmaxval, ",",0);
 374     eat_prefixmask(&configstr,"permitted-prefix", ",",0, &pprefix,&pmask,&plen);
 375     if (!configstr && truncated) badusage("gid,prefix/len,... spec too long");
 376
 377     if (!proto) printf(" %5lu,%s/%d: ", fgid, ip2txt(pprefix,ptxt), plen);
 378
 379     gidlist= getenv("USERV_GID");
 380     if (!gidlist) fatal("USERV_GID not set");
 381     for (;;) {
 382       if (!gidlist) {
 383         if (!proto) printf("no matching gid\n");
 384         return;
 385       }
 386       tgid= eat_number(&gidlist,"userv-gid", 0,gidmaxval, " ",0);
 387       if (tgid == fgid) break;
 388     }
 389     permit(pprefix,pmask);
 390     return;
 391   }
 392 }
 393
 394 static void checkallow(int allow, const char *what,
 395                        const char *prefixtxt, const char *masktxt) {
 396   if (allow) return;
 397   fprintf(stderr,"userv-ipif service: access denied for %s, %s/%s\n",
 398           what, prefixtxt, masktxt);
 399   allallow= 0;
 400 }
 401
 402 static void parseargs(int argc, const char *const *argv) {
 403   unsigned long routeaddr, routemask;
 404   const char *carg;
 405   const char *const *cprotop;
 406   int i;
 407   char erwhatbuf[100], erwhatbuf2[100];
 408
 409   if (argc < NARGS+1) { badusage("too few arguments"); }
 410   if (argc > NARGS+1) { badusage("too many arguments"); }
 411
 412   configstr= *++argv;
 413
 414   carg= *++argv;
 415   if (strcmp(carg,"--")) badusage("separator argument `--' not found, got `%s'",carg);
 416
 417   carg= *++argv;
 418   localaddr= eat_addr(&carg,"local-addr", ",",0);
 419   peeraddr= eat_addr(&carg,"peer-addr", ",",0);
 420   mtu= eat_number(&carg,"mtu", 576,65536, ",",0);
 421   localallow= peerallow= 0;
 422
 423   if (!strcmp(carg,"debug")) {
 424     proto= 0;
 425   } else {
 426     for (cprotop= protos_ok;
 427          (proto= *cprotop) && strcmp(proto,carg);
 428          cprotop++);
 429     if (!proto) fatal("invalid protocol");
 430   }
 431
 432   addrnet_mustdiffer("local-addr",localaddr,~0UL, "peer-addr",peeraddr,~0UL);
 433
 434   carg= *++argv;
 435   if (strcmp(carg,"-")) {
 436     for (nexroutes=0;
 437          carg && *carg;
 438          nexroutes++) {
 439       if (nexroutes == MAXEXROUTES)
 440         fatal("too many extra routes (only %d allowed)",MAXEXROUTES);
 441       sprintf(erwhatbuf,"route#%d",nexroutes);
 442
 443       eat_prefixmask(&carg,erwhatbuf, ",",0, &routeaddr,&routemask,0);
 444       if (routemask == ~0UL) {
 445         addrnet_mustdiffer(erwhatbuf,routeaddr,routemask, "local-addr",localaddr,~0UL);
 446         addrnet_mustdiffer(erwhatbuf,routeaddr,routemask, "peer-addr",peeraddr,~0UL);
 447       }
 448       for (i=0; i<nexroutes; i++) {
 449         sprintf(erwhatbuf2,"route#%d",i);
 450         addrnet_mustdiffer(erwhatbuf,routeaddr,routemask,
 451                            erwhatbuf2,exroutes[i].prefix,exroutes[i].mask);
 452       }
 453       exroutes[nexroutes].prefix= routeaddr;
 454       exroutes[nexroutes].mask= routemask;
 455       exroutes[nexroutes].allow= 0;
 456       ip2txt(routeaddr,exroutes[nexroutes].prefixtxt);
 457       ip2txt(routemask,exroutes[nexroutes].masktxt);
 458     }
 459   }
 460
 461   ip2txt(localaddr,localtxt);
 462   ip2txt(peeraddr,peertxt);
 463 }
 464
 465 static void checkpermit(void) {
 466   int i;
 467   char erwhatbuf[100];
 468
 469   allallow= 1;
 470   checkallow(localallow,"local-addr", localtxt,"32");
 471   checkallow(peerallow,"peer-addr", peertxt,"32");
 472   for (i=0; i<nexroutes; i++) {
 473     sprintf(erwhatbuf, "route#%d", i);
 474     checkallow(exroutes[i].allow, erwhatbuf, exroutes[i].prefixtxt, exroutes[i].masktxt);
 475   }
 476   if (!allallow) fatal("access denied");
 477 }
 478
 479 static void dumpdebug(void) __attribute__((noreturn));
 480 static void dumpdebug(void) {
 481   int i;
 482   char erwhatbuf[100];
 483
 484   printf("protocol: debug\n"
 485          "local:    %08lx == %s\n"
 486          "peer:     %08lx == %s\n"
 487          "mtu:      %ld\n"
 488          "routes:   %d\n",
 489          localaddr, localtxt,
 490          peeraddr, peertxt,
 491          mtu,
 492          nexroutes);
 493   for (i=0; i<nexroutes; i++) {
 494     sprintf(erwhatbuf, "route#%d:", i);
 495     printf("%-9s %08lx/%08lx == %s/%s\n",
 496            erwhatbuf,
 497            exroutes[i].prefix, exroutes[i].mask,
 498            exroutes[i].prefixtxt, exroutes[i].masktxt);
 499   }
 500   if (ferror(stdout) || fclose(stdout)) sysfatal("flush stdout");
 501   exit(0);
 502 }
 503
 504
 505 static void setsigmask(const sigset_t *ss) {
 506   int r;
 507
 508   r= sigprocmask(SIG_SETMASK, ss, 0);
 509   if (r) sysfatal("[un]block signals");
 510 }
 511
 512 static void setsignals(void (*handler)(int), struct sigaction *sa, int chldflags) {
 513   const int *signalp;
 514   int r, sig;
 515
 516   sa->sa_handler= handler;
 517   sa->sa_flags= 0;
 518   for (signalp=signals; (sig=*signalp); signalp++) {
 519     r= sigaction(sig, sa, 0);  if (r) sysfatal("uncatch signal");
 520   }
 521   sa->sa_flags= chldflags;
 522   r= sigaction(SIGCHLD, sa, 0);  if (r) sysfatal("uncatch children");
 523 }
 524
 525 static void infork(void) {
 526   struct sigaction sa;
 527
 528   memset(&pids,0,sizeof(pids));
 529   sigemptyset(&sa.sa_mask);
 530   setsignals(SIG_DFL,&sa,0);
 531   setsigmask(&emptyset);
 532   undoslattach= 0;
 533 }
 534
 535 static pid_t makesubproc(void (*entry)(void)) {
 536   pid_t pid;
 537
 538   pid= fork();  if (pid == (pid_t)-1) sysfatal("fork for subprocess");
 539   if (pid) return pid;
 540
 541   infork();
 542   entry();
 543   abort();
 544 }
 545
 546 static int task(void) {
 547   pid_t pid;
 548
 549   pid= fork();
 550   if (pid == (pid_t)-1) sysfatal("fork for task");
 551   if (!pid) { infork(); return 1; }
 552
 553   pids.byname.task= pid;
 554   while (pids.byname.task) sigsuspend(&emptyset);
 555   return 0;
 556 }
 557
 558 static void mdup2(int fd1, int fd2, const char *what) {
 559   int r;
 560
 561   for (;;) {
 562     r= dup2(fd1,fd2); if (r==fd2) return;
 563     if (r!=-1) fatal("dup2 in %s gave wrong answer %d instead of %d",what,r,fd2);
 564     if (errno != EINTR) sysfatal("dup2 failed in %s",what);
 565   }
 566 }
 567
 568 static void sl_entry(void) {
 569   mdup2(slpipe[1],1,"slattach child");
 570   execlp("slattach", "slattach", "-v", "-L", "-p",proto, ptyname, (char*)0);
 571   sysfatal("cannot exec slattach");
 572 }
 573
 574 static void cin_entry(void) {
 575   mdup2(ptmaster,1,"cat input child");
 576   execlp("cat", "cat", (char*)0);
 577   sysfatal("cannot exec cat input");
 578 }
 579
 580 static void cout_entry(void) {
 581   mdup2(ptmaster,0,"cat output child");
 582   execlp("cat", "cat", (char*)0);
 583   sysfatal("cannot exec cat output");
 584 }
 585
 586 static void sighandler(int signum) {
 587   pid_t pid;
 588   int estatus, status;
 589   const char *taskfail;
 590
 591   estatus= 4;
 592
 593   if (signum == SIGCHLD) {
 594     for (;;) {
 595       pid= waitpid(-1,&status,WNOHANG);
 596       if (!pid || pid == (pid_t)-1) return;
 597
 598       if (pid == pids.byname.task) {
 599         pids.byname.task= 0;
 600         if (!status) return;
 601         taskfail= "task";
 602       } else if (pid == pids.byname.cin) {
 603         pids.byname.cin= 0;
 604         if (status) {
 605           taskfail= "input cat";
 606         } else {
 607           taskfail= 0;
 608           estatus= 0;
 609         }
 610       } else if (pid == pids.byname.cout) {
 611         pids.byname.cout= 0;
 612         taskfail= "output cat";
 613       } else if (pid == pids.byname.sl) {
 614         pids.byname.sl= 0;
 615         taskfail= "slattach";
 616       } else {
 617         continue;
 618       }
 619       break;
 620     }
 621     if (taskfail) {
 622       if (WIFEXITED(status)) {
 623         fprintf(stderr,
 624                 "userv-ipif service: %s unexpectedly exited with exit status %d\n",
 625                 taskfail, WEXITSTATUS(status));
 626       } else if (WIFSIGNALED(status)) {
 627         fprintf(stderr,
 628                 "userv-ipif service: %s unexpectedly killed by signal %s%s\n",
 629                 taskfail, strsignal(WTERMSIG(status)),
 630                 WCOREDUMP(status) ? " (core dumped)" : "");
 631       } else {
 632         fprintf(stderr, "userv-ipif service: %s unexpectedly terminated"
 633                 " with unknown status code %d\n", taskfail, status);
 634       }
 635     }
 636   } else {
 637     fprintf(stderr,
 638             "userv-ipif service: received signal %d, terminating\n",
 639             signum);
 640   }
 641
 642   terminate(estatus);
 643 }
 644
 645 static void startup(void) {
 646   int r;
 647   struct sigaction sa;
 648
 649   sigfillset(&fullset);
 650   sigemptyset(&emptyset);
 651
 652   ptmaster= getpt();  if (ptmaster==-1) sysfatal("allocate pty master");
 653   r= grantpt(ptmaster);  if (r) sysfatal("grab/grant pty slave");
 654   ptyname= ptsname(ptmaster);  if (!ptyname) sysfatal("get pty slave name");
 655   r= chmod(ptyname,0600);  if (r) sysfatal("chmod pty slave");
 656   r= unlockpt(ptmaster);  if (r) sysfatal("unlock pty");
 657
 658   sigfillset(&sa.sa_mask);
 659   setsignals(sighandler,&sa,SA_NOCLDSTOP);
 660   setsigmask(&fullset);
 661 }
 662
 663 static void startslattach(void) {
 664   static char ifnbuf[200];
 665
 666   FILE *piper;
 667   int r, l, k;
 668
 669   r= pipe(slpipe);  if (r) sysfatal("create pipe");
 670   piper= fdopen(slpipe[0],"r");  if (!piper) sysfatal("fdopen pipe");
 671
 672   undoslattach= 1;
 673   pids.byname.sl= makesubproc(sl_entry);
 674
 675   close(slpipe[1]);
 676   setsigmask(&emptyset);
 677   if (!fgets(ifnbuf,sizeof(ifnbuf),piper)) {
 678     if (ferror(piper)) sysfatal("cannot read ifname from slattach");
 679     else fatal("cannot read ifname from slattach");
 680   }
 681   setsigmask(&fullset);
 682   l= strlen(ifnbuf);
 683   if (l<=0 || ifnbuf[l-1] != '\n') fatal("slattach gave strange output `%s'",ifnbuf);
 684   ifnbuf[l-1]= 0;
 685   for (k=l; k>0 && ifnbuf[k-1]!=' '; k--);
 686   ifname= ifnbuf+k;
 687 }
 688
 689 static void netconfigure(void) {
 690   char mtutxt[100];
 691   int i;
 692
 693   if (task()) {
 694     sprintf(mtutxt,"%lu",mtu);
 695
 696     execlp("ifconfig", "ifconfig", ifname, localtxt,
 697            "netmask","255.255.255.255", "-broadcast", "pointopoint",peertxt,
 698            "mtu",mtutxt, "up", (char*)0);
 699     sysfatal("cannot exec ifconfig");
 700   }
 701
 702   for (i=0; i<nexroutes; i++) {
 703     if (task()) {
 704       execlp("route","route", "add", "-net",exroutes[i].prefixtxt,
 705              "netmask",exroutes[i].masktxt,
 706              "gw",peertxt, "dev",ifname, (char*)0);
 707       sysfatal("cannot exec route (for route)");
 708     }
 709   }
 710 }
 711
 712 static void copydata(void) __attribute__((noreturn));
 713 static void copydata(void) {
 714   int r;
 715
 716   pids.byname.cin= makesubproc(cin_entry);
 717   for (;;) {
 718     r= write(1, "\300", 1); if (r==1) break;
 719     assert(r==-1);  if (errno != EINTR) sysfatal("send initial delim to confirm");
 720   }
 721   pids.byname.cout= makesubproc(cout_entry);
 722
 723   for (;;) sigsuspend(&emptyset);
 724 }
 725
 726 int main(int argc, const char *const *argv) {
 727   parseargs(argc,argv);
 728   pconfig(configstr,0);
 729   checkpermit();
 730   if (!proto) dumpdebug();
 731
 732   startup();
 733   startslattach();
 734   netconfigure();
 735   copydata();
 736 }