mdw@git.distorted.org.uk Git - tripe/blob - server/tun-slip.c

   1 /* -*-c-*-
   2  *
   3  * Tunnel packets via SLIP
   4  *
   5  * (c) 2005 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Trivial IP Encryption (TrIPE).
  11  *
  12  * TrIPE is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * TrIPE is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with TrIPE; if not, write to the Free Software Foundation,
  24  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25  */
  26
  27 /*----- Header files ------------------------------------------------------*/
  28
  29 #define TUN_INTERNALS
  30
  31 #include "tripe.h"
  32
  33 /*----- Data structures ---------------------------------------------------*/
  34
  35 typedef struct slipif {
  36   struct slipif *next;                  /* Next one in the list */
  37   int ifd, ofd;                         /* File descriptors to talk on */
  38   char *name;                           /* Interface name */
  39   pid_t kid;                            /* Child process id */
  40   unsigned f;                           /* Various flags */
  41 #   define F_INUSE 1u                   /*   Interface is in use */
  42 #   define F_DYNAMIC 2u                 /*   Interface found dynamically */
  43 } slipif;
  44
  45 struct tunnel {
  46   const tunnel_ops *ops;                /* Pointer to operations */
  47   slipif *sl;                           /* My interface record */
  48   sel_file f;                           /* Selector for SLIP tty */
  49   struct peer *p;                       /* Pointer to my peer */
  50   unsigned st;                          /* Current parser state */
  51 #   define ST_ESC 1u                    /*   Last saw an escape character */
  52 #   define ST_BAD 2u                    /*   This packet is malformed */
  53 #   define ST_EOF 4u                    /*   File descriptor reported EOF */
  54   size_t n;                             /* Number of bytes used in buffer */
  55   octet buf[PKBUFSZ];                   /* Buffer for incoming data */
  56 };
  57
  58 /*----- Static variables --------------------------------------------------*/
  59
  60 static slipif *slipifs;                 /* List of available interfaces */
  61 static const char *slipcmd;             /* Script to make new interfaces */
  62
  63 /*----- Main code ---------------------------------------------------------*/
  64
  65 #define SL_END 0xc0
  66 #define SL_ESC 0xdb
  67 #define SL_ESCEND 0xdc
  68 #define SL_ESCESC 0xdd
  69
  70 /* --- @t_read@ --- *
  71  *
  72  * Arguments:   @int fd@ = file descriptor to read
  73  *              @unsigned mode@ = what's happened
  74  *              @void *v@ = pointer to tunnel block
  75  *
  76  * Returns:     ---
  77  *
  78  * Use:         Reads data from the tunnel.
  79  */
  80
  81 static void t_read(int fd, unsigned mode, void *v)
  82 {
  83   tunnel *t = v;
  84   ssize_t n;
  85   const octet *p, *l, *ll;
  86   octet *q;
  87   unsigned st;
  88   octet o;
  89   buf b;
  90
  91   /* --- Read the input data --- */
  92
  93   n = read(fd, buf_t, sizeof(buf_t));
  94   if (n < 0) {
  95     if (errno == EINTR ||
  96 #if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
  97         errno == EWOULDBLOCK ||
  98 #endif
  99         errno == EAGAIN)
 100       return;
 101     a_warn("TUN", "%s", p_ifname(t->p), "read-error", "?ERRNO", A_END);
 102     return;
 103   }
 104   if (!n) {
 105     a_warn("TUN", "%s", p_ifname(t->p), "slip", "eof", A_END);
 106     t->st = ST_EOF;
 107     sel_rmfile(&t->f);
 108     return;
 109   }
 110   IF_TRACING(T_TUNNEL, {
 111     trace_block(T_PACKET, "tun-slip: SLIP-encapsulated data",
 112                 buf_t, n);
 113   })
 114
 115   /* --- Decapsulate the packet --- */
 116
 117   for (p = buf_t, l = p + n, st = t->st,
 118        q = t->buf + t->n, ll = t->buf + sizeof(t->buf);
 119        p < l;
 120        p++) {
 121     o = *p;
 122     switch (o) {
 123       case SL_END:
 124         if (st & ST_BAD)
 125           ;
 126         else if (st & ST_ESC)
 127           a_warn("TUN", "%s", p_ifname(t->p), "slip", "escape-end", A_END);
 128         else if (q == t->buf) {
 129           T( trace(T_TUNNEL, "tun-slip: empty packet"); )
 130         } else {
 131           IF_TRACING(T_TUNNEL, {
 132             trace(T_TUNNEL, "tun-slip: packet arrived");
 133             trace_block(T_PACKET, "tun-slip: packet contents",
 134                         t->buf, q - t->buf);
 135           })
 136           buf_init(&b, t->buf, q - t->buf);
 137           p_tun(t->p, &b);
 138         }
 139         q = t->buf;
 140         st &= ~(ST_ESC | ST_BAD);
 141         break;
 142       case SL_ESC:
 143         if ((st & ST_ESC) && !(st & ST_BAD)) {
 144           a_warn("TUN", "%s", p_ifname(t->p), "slip", "bad-escape", A_END);
 145           st |= ST_BAD;
 146         } else
 147           st |= ST_ESC;
 148         break;
 149       case SL_ESCEND:
 150         if (st & ST_ESC)
 151           o = SL_END;
 152         goto emit;
 153       case SL_ESCESC:
 154         if (st & ST_ESC)
 155           o = SL_ESC;
 156         goto emit;
 157       default:
 158         if ((st & ST_ESC) && !(st & ST_BAD)) {
 159           a_warn("TUN", "%s", p_ifname(t->p), "slip", "bad-escape", A_END);
 160           st |= ST_BAD;
 161         }
 162       emit:
 163         if (!(st & ST_BAD)) {
 164           if (q < ll)
 165             *q++ = o;
 166           else {
 167             a_warn("TUN", "%s", p_ifname(t->p), "slip", "overflow", A_END);
 168             st |= ST_BAD;
 169           }
 170         }
 171         st &= ~ST_ESC;
 172         break;
 173     }
 174   }
 175
 176   t->n = q - t->buf;
 177   t->st = st;
 178 }
 179
 180 /* --- @t_init@ --- *
 181  *
 182  * Arguments:   ---
 183  *
 184  * Returns:     ---
 185  *
 186  * Use:         Initializes the tunneling system.  Maybe this will require
 187  *              opening file descriptors or something.
 188  */
 189
 190 static void t_init(void)
 191 {
 192   char *p, *q;
 193   dstr d = DSTR_INIT;
 194   slipif *sl, **tail = &slipifs;
 195   unsigned long uli, ulo;
 196   size_t n;
 197
 198   if ((p = getenv("TRIPE_SLIPIF")) == 0)
 199     return;
 200
 201   /* --- Build the list of available interfaces --- */
 202
 203   dstr_puts(&d, p);
 204
 205   p = d.buf;
 206   for (;;) {
 207     if (*p == '/' || *p == '.') {
 208       slipcmd = p;
 209       T( trace(T_TUNNEL, "tun-slip: declared slip command `%s'", slipcmd); )
 210       break;
 211     }
 212     uli = strtoul(p, &q, 0);
 213     if (uli > INT_MAX || q == p)
 214       goto whine;
 215     if (*q != ',')
 216       ulo = uli;
 217     else {
 218       p = q + 1;
 219       ulo = strtoul(p, &q, 0);
 220       if (ulo > INT_MAX || q == p)
 221         goto whine;
 222     }
 223     if (*q != '=' || (n = strcspn(q + 1, ":")) == 0)
 224       goto whine;
 225     sl = CREATE(slipif);
 226     sl->next = 0;
 227     sl->ifd = uli;
 228     fdflags(sl->ifd, O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
 229     fdflags(sl->ofd, O_NONBLOCK, 0, FD_CLOEXEC, FD_CLOEXEC);
 230     sl->ofd = ulo;
 231     sl->name = xmalloc(n + 1);
 232     sl->kid = -1;
 233     sl->f = 0;
 234     memcpy(sl->name, q + 1, n);
 235     sl->name[n] = 0;
 236     *tail = sl;
 237     tail = &sl->next;
 238     T( trace(T_TUNNEL, "tun-slip: declared slipif %d,%d=%s",
 239              sl->ifd, sl->ofd, sl->name); )
 240     p = q + n + 1;
 241     if (!*p)
 242       break;
 243     p++;
 244   }
 245   return;
 246
 247 whine:
 248   moan("bad slip interface list");
 249 }
 250
 251 /* --- @t_create@ --- *
 252  *
 253  * Arguments:   @peer *p@ = pointer to peer block
 254  *              @char **ifn@ = where to put the interface name
 255  *
 256  * Returns:     A tunnel block if it worked, or null on failure.
 257  *
 258  * Use:         Initializes a new tunnel.
 259  */
 260
 261 static tunnel *t_create(peer *p, char **ifn)
 262 {
 263   slipif *sl = 0;
 264   int pin[2] = { -1, -1 }, pout[2] = { -1, -1 };
 265   pid_t kid = -1;
 266   dstr d = DSTR_INIT;
 267   unsigned char ch;
 268   tunnel *t;
 269   static const char end[] = { SL_END, SL_END };
 270
 271   /* --- Try to find a spare static interface --- */
 272
 273   for (sl = slipifs; sl; sl = sl->next) {
 274     if (!(sl->f & F_INUSE)) {
 275       T( trace(T_TUNNEL, "tun-slip: %s using static slipif %s",
 276                p_name(p), sl->name); )
 277       goto found;
 278     }
 279   }
 280
 281   /* --- If no dynamic interfaces are available, give up --- */
 282
 283   if (!slipcmd) {
 284     a_warn("TUN", "-", "slip", "no-slip-interfaces", A_END);
 285     goto fail;
 286   }
 287
 288   /* --- Fork off a child process to create a dynamic SLIP interface --- */
 289
 290   if (pipe(pin) || pipe(pout)) {
 291     a_warn("TUN", "-", "slip", "pipe-error", "?ERRNO", A_END);
 292     goto fail;
 293   }
 294   if ((kid = fork()) < 0) {
 295     a_warn("TUN", "-", "slip", "fork-error", "?ERRNO", A_END);
 296     goto fail;
 297   }
 298   if (!kid) {
 299     close(pin[1]);
 300     close(pout[0]);
 301     dup2(pin[0], STDIN_FILENO);
 302     dup2(pout[1], STDOUT_FILENO);
 303     execlp(slipcmd, slipcmd, p_name(p), (char *)0);
 304     _exit(127);
 305   }
 306
 307   /* --- Read the interface name --- */
 308
 309   sl = CREATE(slipif);
 310   close(pin[0]); pin[0] = -1;
 311   close(pout[1]); pout[1] = -1;
 312   for (;;) {
 313     errno = EIO;
 314     if (read(pout[0], &ch, 1) != 1 || ch == SL_END) {
 315       a_warn("TUN", "-", "slip", "read-ifname-failed", "?ERRNO", A_END);
 316       goto fail;
 317     }
 318     if (ch == '\n')
 319       break;
 320     DPUTC(&d, (char)ch);
 321   }
 322   DPUTZ(&d);
 323   sl->name = xstrdup(d.buf);
 324   sl->ifd = pout[0];
 325   sl->ofd = pin[1];
 326   sl->kid = kid;
 327   sl->next = 0;
 328   sl->f = F_DYNAMIC;
 329   T( trace(T_TUNNEL, "tun-slip: %s using dynamic slipif %s",
 330            p_name(p), sl->name); )
 331   fdflags(pout[0], O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
 332   fdflags(pin[1], O_NONBLOCK, 0, FD_CLOEXEC, FD_CLOEXEC);
 333
 334   /* --- Set up the new tunnel --- */
 335
 336 found:
 337   t = CREATE(tunnel);
 338   t->ops = &tun_slip;
 339   t->p = p;
 340   t->sl = sl;
 341   t->st = 0;
 342   t->n = 0;
 343   sl->f |= F_INUSE;
 344   sel_initfile(&sel, &t->f, sl->ifd, SEL_READ, t_read, t);
 345   sel_addfile(&t->f);
 346   write(sl->ofd, end, sizeof(end));
 347   *ifn = xstrdup(sl->name);
 348   dstr_destroy(&d);
 349   return (t);
 350
 351   /* --- Tidy up after a failure --- */
 352
 353 fail:
 354 #define CLOSE(fd) do if (fd != -1) close(fd); while (0)
 355   CLOSE(pin[0]); CLOSE(pout[0]);
 356   CLOSE(pin[1]); CLOSE(pout[1]);
 357 #undef CLOSE
 358   if (kid != -1) kill(kid, SIGTERM);
 359   if (sl && (sl->f & F_DYNAMIC)) DESTROY(sl);
 360   dstr_destroy(&d);
 361   return (0);
 362 }
 363
 364 /* --- @t_setifname@ --- *
 365  *
 366  * Arguments:   @tunnel *t@ = pointer to tunnel block
 367  *              @const char *ifn@ = new interface name
 368  *
 369  * Returns:     ---
 370  *
 371  * Use:         Updates the interface name of a slip interface.
 372  */
 373
 374 static void t_setifname(tunnel *t, const char *ifn)
 375   { xfree(t->sl->name); t->sl->name = xstrdup(ifn); }
 376
 377 /* --- @t_inject@ --- *
 378  *
 379  * Arguments:   @tunnel *t@ = pointer to tunnel block
 380  *              @buf *b@ = buffer to send
 381  *
 382  * Returns:     ---
 383  *
 384  * Use:         Injects a packet into the local network stack.
 385  */
 386
 387 static void t_inject(tunnel *t, buf *b)
 388 {
 389   octet buf[PKBUFSZ * 2 + 2];
 390   const octet *p, *l;
 391   octet *q;
 392
 393   IF_TRACING(T_TUNNEL, {
 394     trace(T_TUNNEL, "tun-slip: inject decrypted packet");
 395     trace_block(T_PACKET, "tun-slip: packet contents", BBASE(b), BLEN(b));
 396   })
 397
 398   q = buf;
 399   *q++ = SL_END;
 400   for (p = BBASE(b), l = BCUR(b); p < l; p++) {
 401     switch (*p) {
 402       case SL_END: *q++ = SL_ESC; *q++ = SL_ESCEND; break;
 403       case SL_ESC: *q++ = SL_ESC; *q++ = SL_ESCESC; break;
 404       default: *q++ = *p; break;
 405     }
 406   }
 407   *q++ = SL_END;
 408   IF_TRACING(T_TUNNEL, {
 409     trace_block(T_PACKET, "tun-slip: SLIP-encapsulated contents",
 410                 buf, q - buf);
 411   })
 412   write(t->sl->ofd, buf, q - buf);
 413 }
 414
 415 /* --- @t_destroy@ --- *
 416  *
 417  * Arguments:   @tunnel *t@ = pointer to tunnel block
 418  *
 419  * Returns:     ---
 420  *
 421  * Use:         Destroys a tunnel.
 422  */
 423
 424 static void t_destroy(tunnel *t)
 425 {
 426   slipif *sl = t->sl;
 427
 428   /* --- If it reported EOF, leave it out-of-action --- */
 429
 430   if (!(t->st & ST_EOF)) {
 431     sel_rmfile(&t->f);
 432     sl->f &= ~F_INUSE;
 433   }
 434   if (sl && (sl->f & F_DYNAMIC)) {
 435     T( trace(T_TUNNEL, "tun-slip: releasing dynamic slipif %s", sl->name); )
 436     close(sl->ofd);
 437     close(sl->ifd);
 438     kill(sl->kid, SIGTERM);
 439     xfree(sl->name);
 440     DESTROY(sl);
 441   }
 442   DESTROY(t);
 443 }
 444
 445 const tunnel_ops tun_slip = {
 446   "slip",
 447   t_init,
 448   t_create,
 449   t_setifname,
 450   t_inject,
 451   t_destroy
 452 };
 453
 454 /*----- That's all, folks -------------------------------------------------*/