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_MASK 3u                   /*   Mask for the above bits */
  54 #   define ST_EOF 4u                    /*   File descriptor reported EOF */
  55   size_t n;                             /* Number of bytes used in buffer */
  56   octet buf[PKBUFSZ];                   /* Buffer for incoming data */
  57 };
  58
  59 /*----- Static variables --------------------------------------------------*/
  60
  61 static slipif *slipifs;                 /* List of available interfaces */
  62 static const char *slipcmd;             /* Script to make new interfaces */
  63
  64 /*----- Main code ---------------------------------------------------------*/
  65
  66 /* --- @t_read@ --- *
  67  *
  68  * Arguments:   @int fd@ = file descriptor to read
  69  *              @unsigned mode@ = what's happened
  70  *              @void *v@ = pointer to tunnel block
  71  *
  72  * Returns:     ---
  73  *
  74  * Use:         Reads data from the tunnel.
  75  */
  76
  77 static void t_read(int fd, unsigned mode, void *v)
  78 {
  79   tunnel *t = v;
  80   ssize_t n;
  81   const octet *p, *l, *ll;
  82   octet *q;
  83   unsigned st;
  84   octet o;
  85   buf b;
  86
  87   /* --- Read the input data --- */
  88
  89   n = read(fd, buf_t, sizeof(buf_t));
  90   if (n < 0) {
  91     if (errno == EINTR ||
  92 #if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
  93         errno == EWOULDBLOCK ||
  94 #endif
  95         errno == EAGAIN)
  96       return;
  97     a_warn("TUN", "%s", p_ifname(t->p), "slip",
  98            "read-error", "?ERRNO", A_END);
  99     return;
 100   }
 101   if (!n) {
 102     a_warn("TUN", "%s", p_ifname(t->p), "slip", "eof", A_END);
 103     t->st = (t->st & ~ST_MASK) | ST_EOF;
 104     sel_rmfile(&t->f);
 105     return;
 106   }
 107   IF_TRACING(T_TUNNEL, {
 108     trace_block(T_PACKET, "tun-slip: SLIP-encapsulated data",
 109                 buf_t, n);
 110   })
 111
 112   /* --- Decapsulate the packet --- */
 113
 114   for (p = buf_t, l = p + n, st = t->st,
 115        q = t->buf + t->n, ll = t->buf + sizeof(t->buf);
 116        p < l;
 117        p++) {
 118     o = *p;
 119     switch (o) {
 120       case SL_END:
 121         if (st & ST_BAD)
 122           ;
 123         else if (st & ST_ESC)
 124           a_warn("TUN", "%s", p_ifname(t->p), "slip", "escape-end", A_END);
 125         else if (q == t->buf) {
 126           T( trace(T_TUNNEL, "tun-slip: empty packet"); )
 127         } else {
 128           IF_TRACING(T_TUNNEL, {
 129             trace(T_TUNNEL, "tun-slip: packet arrived");
 130             trace_block(T_PACKET, "tun-slip: packet contents",
 131                         t->buf, q - t->buf);
 132           })
 133           buf_init(&b, t->buf, q - t->buf);
 134           p_tun(t->p, &b);
 135         }
 136         q = t->buf;
 137         st &= ~ST_MASK;
 138         break;
 139       case SL_ESC:
 140         if ((st & ST_ESC) && !(st & ST_BAD)) {
 141           a_warn("TUN", "%s", p_ifname(t->p), "slip", "bad-escape", A_END);
 142           st |= ST_BAD;
 143         } else
 144           st |= ST_ESC;
 145         break;
 146       case SL_ESCEND:
 147         if (st & ST_ESC)
 148           o = SL_END;
 149         goto emit;
 150       case SL_ESCESC:
 151         if (st & ST_ESC)
 152           o = SL_ESC;
 153         goto emit;
 154       default:
 155         if ((st & ST_ESC) && !(st & ST_BAD)) {
 156           a_warn("TUN", "%s", p_ifname(t->p), "slip", "bad-escape", A_END);
 157           st |= ST_BAD;
 158         }
 159       emit:
 160         if (!(st & ST_BAD)) {
 161           if (q < ll)
 162             *q++ = o;
 163           else {
 164             a_warn("TUN", "%s", p_ifname(t->p), "slip", "overflow", A_END);
 165             st |= ST_BAD;
 166           }
 167         }
 168         st &= ~ST_ESC;
 169         break;
 170     }
 171   }
 172
 173   t->n = q - t->buf;
 174   t->st = st;
 175 }
 176
 177 /* --- @t_init@ --- *
 178  *
 179  * Arguments:   ---
 180  *
 181  * Returns:     ---
 182  *
 183  * Use:         Initializes the tunneling system.  Maybe this will require
 184  *              opening file descriptors or something.
 185  */
 186
 187 static void t_init(void)
 188 {
 189   char *p, *q;
 190   dstr d = DSTR_INIT;
 191   slipif *sl, **tail = &slipifs;
 192   unsigned long uli, ulo;
 193   size_t n;
 194
 195   if ((p = getenv("TRIPE_SLIPIF")) == 0)
 196     return;
 197
 198   /* --- Build the list of available interfaces --- */
 199
 200   dstr_puts(&d, p);
 201
 202   p = d.buf;
 203   for (;;) {
 204     if (*p == '/' || *p == '.') {
 205       slipcmd = p;
 206       T( trace(T_TUNNEL, "tun-slip: declared slip command `%s'", slipcmd); )
 207       break;
 208     }
 209     uli = strtoul(p, &q, 0);
 210     if (uli > INT_MAX || q == p)
 211       goto whine;
 212     if (*q != ',')
 213       ulo = uli;
 214     else {
 215       p = q + 1;
 216       ulo = strtoul(p, &q, 0);
 217       if (ulo > INT_MAX || q == p)
 218         goto whine;
 219     }
 220     if (*q != '=' || (n = strcspn(q + 1, ":")) == 0)
 221       goto whine;
 222     sl = CREATE(slipif);
 223     sl->next = 0;
 224     sl->ifd = uli;
 225     fdflags(sl->ifd, O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
 226     fdflags(sl->ofd, O_NONBLOCK, 0, FD_CLOEXEC, FD_CLOEXEC);
 227     sl->ofd = ulo;
 228     sl->name = xmalloc(n + 1);
 229     sl->kid = -1;
 230     sl->f = 0;
 231     memcpy(sl->name, q + 1, n);
 232     sl->name[n] = 0;
 233     *tail = sl;
 234     tail = &sl->next;
 235     T( trace(T_TUNNEL, "tun-slip: declared slipif %d,%d=%s",
 236              sl->ifd, sl->ofd, sl->name); )
 237     p = q + n + 1;
 238     if (!*p)
 239       break;
 240     p++;
 241   }
 242   return;
 243
 244 whine:
 245   moan("bad slip interface list");
 246 }
 247
 248 /* --- @t_create@ --- *
 249  *
 250  * Arguments:   @peer *p@ = pointer to peer block
 251  *              @int fd@ = file descriptor of tunnel device (unused)
 252  *              @char **ifn@ = where to put the interface name
 253  *
 254  * Returns:     A tunnel block if it worked, or null on failure.
 255  *
 256  * Use:         Initializes a new tunnel.
 257  */
 258
 259 static tunnel *t_create(peer *p, int fd, char **ifn)
 260 {
 261   slipif *sl = 0;
 262   int pin[2] = { -1, -1 }, pout[2] = { -1, -1 };
 263   mdup_fd md[2];
 264   pid_t kid = -1;
 265   dstr d = DSTR_INIT;
 266   unsigned char ch;
 267   tunnel *t;
 268   static const char end[] = { SL_END, SL_END };
 269
 270   /* --- Try to find a spare static interface --- */
 271
 272   for (sl = slipifs; sl; sl = sl->next) {
 273     if (!(sl->f & F_INUSE)) {
 274       T( trace(T_TUNNEL, "tun-slip: %s using static slipif %s",
 275                p_name(p), sl->name); )
 276       goto found;
 277     }
 278   }
 279
 280   /* --- If no dynamic interfaces are available, give up --- */
 281
 282   if (!slipcmd) {
 283     a_warn("TUN", "-", "slip", "no-slip-interfaces", A_END);
 284     goto fail;
 285   }
 286
 287   /* --- Fork off a child process to create a dynamic SLIP interface --- */
 288
 289   if (pipe(pin) || pipe(pout)) {
 290     a_warn("TUN", "-", "slip", "pipe-error", "?ERRNO", A_END);
 291     goto fail;
 292   }
 293   if ((kid = fork()) < 0) {
 294     a_warn("TUN", "-", "slip", "fork-error", "?ERRNO", A_END);
 295     goto fail;
 296   }
 297   if (!kid) {
 298     close(pin[1]); close(pout[0]);
 299     md[0].cur = pin[0];  md[0].want = STDIN_FILENO;
 300     md[1].cur = pout[1]; md[1].want = STDOUT_FILENO;
 301     mdup(md, 2);
 302     execlp(slipcmd, slipcmd, p_name(p), (char *)0);
 303     _exit(127);
 304   }
 305
 306   /* --- Read the interface name --- */
 307
 308   sl = CREATE(slipif);
 309   close(pin[0]); pin[0] = -1;
 310   close(pout[1]); pout[1] = -1;
 311   for (;;) {
 312     errno = EIO;
 313     if (read(pout[0], &ch, 1) != 1 || ch == SL_END) {
 314       a_warn("TUN", "-", "slip", "read-ifname-failed", "?ERRNO", A_END);
 315       goto fail;
 316     }
 317     if (ch == '\n')
 318       break;
 319     DPUTC(&d, (char)ch);
 320   }
 321   DPUTZ(&d);
 322   sl->name = xstrdup(d.buf);
 323   sl->ifd = pout[0];
 324   sl->ofd = pin[1];
 325   sl->kid = kid;
 326   sl->next = 0;
 327   sl->f = F_DYNAMIC;
 328   T( trace(T_TUNNEL, "tun-slip: %s using dynamic slipif %s",
 329            p_name(p), sl->name); )
 330   fdflags(pout[0], O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
 331   fdflags(pin[1], O_NONBLOCK, 0, FD_CLOEXEC, FD_CLOEXEC);
 332
 333   /* --- Set up the new tunnel --- */
 334
 335 found:
 336   t = CREATE(tunnel);
 337   t->ops = &tun_slip;
 338   t->p = p;
 339   t->sl = sl;
 340   t->st = 0;
 341   t->n = 0;
 342   sl->f |= F_INUSE;
 343   sel_initfile(&sel, &t->f, sl->ifd, SEL_READ, t_read, t);
 344   sel_addfile(&t->f);
 345   write(sl->ofd, end, sizeof(end));
 346   *ifn = xstrdup(sl->name);
 347   dstr_destroy(&d);
 348   return (t);
 349
 350   /* --- Tidy up after a failure --- */
 351
 352 fail:
 353 #define CLOSE(fd) do if (fd != -1) close(fd); while (0)
 354   CLOSE(pin[0]); CLOSE(pout[0]);
 355   CLOSE(pin[1]); CLOSE(pout[1]);
 356 #undef CLOSE
 357   if (kid != -1) kill(kid, SIGTERM);
 358   if (sl && (sl->f & F_DYNAMIC)) DESTROY(sl);
 359   dstr_destroy(&d);
 360   return (0);
 361 }
 362
 363 /* --- @t_setifname@ --- *
 364  *
 365  * Arguments:   @tunnel *t@ = pointer to tunnel block
 366  *              @const char *ifn@ = new interface name
 367  *
 368  * Returns:     ---
 369  *
 370  * Use:         Updates the interface name of a slip interface.
 371  */
 372
 373 static void t_setifname(tunnel *t, const char *ifn)
 374   { xfree(t->sl->name); t->sl->name = xstrdup(ifn); }
 375
 376 /* --- @t_inject@ --- *
 377  *
 378  * Arguments:   @tunnel *t@ = pointer to tunnel block
 379  *              @buf *b@ = buffer to send
 380  *
 381  * Returns:     ---
 382  *
 383  * Use:         Injects a packet into the local network stack.
 384  */
 385
 386 static void t_inject(tunnel *t, buf *b)
 387 {
 388   octet buf[PKBUFSZ * 2 + 2];
 389   const octet *p, *l;
 390   octet *q;
 391
 392   IF_TRACING(T_TUNNEL, {
 393     trace(T_TUNNEL, "tun-slip: inject decrypted packet");
 394     trace_block(T_PACKET, "tun-slip: packet contents", BBASE(b), BLEN(b));
 395   })
 396
 397   q = buf;
 398   *q++ = SL_END;
 399   for (p = BBASE(b), l = BCUR(b); p < l; p++) {
 400     switch (*p) {
 401       case SL_END: *q++ = SL_ESC; *q++ = SL_ESCEND; break;
 402       case SL_ESC: *q++ = SL_ESC; *q++ = SL_ESCESC; break;
 403       default: *q++ = *p; break;
 404     }
 405   }
 406   *q++ = SL_END;
 407   IF_TRACING(T_TUNNEL, {
 408     trace_block(T_PACKET, "tun-slip: SLIP-encapsulated contents",
 409                 buf, q - buf);
 410   })
 411   write(t->sl->ofd, buf, q - buf);
 412 }
 413
 414 /* --- @t_destroy@ --- *
 415  *
 416  * Arguments:   @tunnel *t@ = pointer to tunnel block
 417  *
 418  * Returns:     ---
 419  *
 420  * Use:         Destroys a tunnel.
 421  */
 422
 423 static void t_destroy(tunnel *t)
 424 {
 425   slipif *sl = t->sl;
 426
 427   /* --- If it reported EOF, leave it out-of-action --- */
 428
 429   if (!(t->st & ST_EOF)) {
 430     sel_rmfile(&t->f);
 431     sl->f &= ~F_INUSE;
 432   }
 433   if (sl && (sl->f & F_DYNAMIC)) {
 434     T( trace(T_TUNNEL, "tun-slip: releasing dynamic slipif %s", sl->name); )
 435     close(sl->ofd);
 436     close(sl->ifd);
 437     kill(sl->kid, SIGTERM);
 438     xfree(sl->name);
 439     DESTROY(sl);
 440   }
 441   DESTROY(t);
 442 }
 443
 444 const tunnel_ops tun_slip = {
 445   "slip",
 446   0,
 447   t_init,
 448   t_create,
 449   t_setifname,
 450   t_inject,
 451   t_destroy
 452 };
 453
 454 /*----- That's all, folks -------------------------------------------------*/