server/tun-slip: Refactor state handling somewhat.

[tripe] / server / tun-slip.c

/* -*-c-*-
 *
 * Tunnel packets via SLIP
 *
 * (c) 2005 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Trivial IP Encryption (TrIPE).
 *
 * TrIPE 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.
 *
 * TrIPE 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 TrIPE; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#define TUN_INTERNALS

#include "tripe.h"

/*----- Data structures ---------------------------------------------------*/

typedef struct slipif {
  struct slipif *next;			/* Next one in the list */
  int ifd, ofd;				/* File descriptors to talk on */
  char *name;				/* Interface name */
  pid_t kid;				/* Child process id */
  unsigned f;				/* Various flags */
#   define F_INUSE 1u			/*   Interface is in use */
#   define F_DYNAMIC 2u			/*   Interface found dynamically */
} slipif;

struct tunnel {
  const tunnel_ops *ops;		/* Pointer to operations */
  slipif *sl;				/* My interface record */
  sel_file f;				/* Selector for SLIP tty */
  struct peer *p;			/* Pointer to my peer */
  unsigned st;				/* Current parser state */
#   define ST_ESC 1u			/*   Last saw an escape character */
#   define ST_BAD 2u			/*   This packet is malformed */
#   define ST_MASK 3u			/*   Mask for the above bits */
#   define ST_EOF 4u			/*   File descriptor reported EOF */
  size_t n;				/* Number of bytes used in buffer */
  octet buf[PKBUFSZ];			/* Buffer for incoming data */
};

/*----- Static variables --------------------------------------------------*/

static slipif *slipifs;			/* List of available interfaces */
static const char *slipcmd;		/* Script to make new interfaces */

/*----- Main code ---------------------------------------------------------*/

/* --- @t_read@ --- *
 *
 * Arguments:	@int fd@ = file descriptor to read
 *		@unsigned mode@ = what's happened
 *		@void *v@ = pointer to tunnel block
 *
 * Returns:	---
 *
 * Use:		Reads data from the tunnel.
 */

static void t_read(int fd, unsigned mode, void *v)
{
  tunnel *t = v;
  ssize_t n;
  const octet *p, *l, *ll;
  octet *q;
  unsigned st;
  octet o;
  buf b;

  /* --- Read the input data --- */

  n = read(fd, buf_t, sizeof(buf_t));
  if (n < 0) {
    if (errno == EINTR ||
#if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
	errno == EWOULDBLOCK ||
#endif
	errno == EAGAIN)
      return;
    a_warn("TUN", "%s", p_ifname(t->p), "slip",
	   "read-error", "?ERRNO", A_END);
    return;
  }
  if (!n) {
    a_warn("TUN", "%s", p_ifname(t->p), "slip", "eof", A_END);
    t->st = (t->st & ~ST_MASK) | ST_EOF;
    sel_rmfile(&t->f);
    return;
  }
  IF_TRACING(T_TUNNEL, {
    trace_block(T_PACKET, "tun-slip: SLIP-encapsulated data",
		buf_t, n);
  })

  /* --- Decapsulate the packet --- */

  for (p = buf_t, l = p + n, st = t->st,
       q = t->buf + t->n, ll = t->buf + sizeof(t->buf);
       p < l;
       p++) {
    o = *p;
    switch (o) {
      case SL_END:
	if (st & ST_BAD)
	  ;
	else if (st & ST_ESC)
	  a_warn("TUN", "%s", p_ifname(t->p), "slip", "escape-end", A_END);
	else if (q == t->buf) {
	  T( trace(T_TUNNEL, "tun-slip: empty packet"); )
	} else {
	  IF_TRACING(T_TUNNEL, {
	    trace(T_TUNNEL, "tun-slip: packet arrived");
	    trace_block(T_PACKET, "tun-slip: packet contents",
			t->buf, q - t->buf);
	  })
	  buf_init(&b, t->buf, q - t->buf);
	  p_tun(t->p, &b);
	}
	q = t->buf;
	st &= ~ST_MASK;
	break;
      case SL_ESC:
	if ((st & ST_ESC) && !(st & ST_BAD)) {
	  a_warn("TUN", "%s", p_ifname(t->p), "slip", "bad-escape", A_END);
	  st |= ST_BAD;
	} else
	  st |= ST_ESC;
	break;
      case SL_ESCEND:
	if (st & ST_ESC)
	  o = SL_END;
	goto emit;
      case SL_ESCESC:
	if (st & ST_ESC)
	  o = SL_ESC;
	goto emit;
      default:
	if ((st & ST_ESC) && !(st & ST_BAD)) {
	  a_warn("TUN", "%s", p_ifname(t->p), "slip", "bad-escape", A_END);
	  st |= ST_BAD;
	}
      emit:
	if (!(st & ST_BAD)) {
	  if (q < ll)
	    *q++ = o;
	  else {
	    a_warn("TUN", "%s", p_ifname(t->p), "slip", "overflow", A_END);
	    st |= ST_BAD;
	  }
	}
	st &= ~ST_ESC;
	break;
    }
  }

  t->n = q - t->buf;
  t->st = st;
}

/* --- @t_init@ --- *
 *
 * Arguments:	---
 *
 * Returns:	---
 *
 * Use:		Initializes the tunneling system.  Maybe this will require
 *		opening file descriptors or something.
 */

static void t_init(void)
{
  char *p, *q;
  dstr d = DSTR_INIT;
  slipif *sl, **tail = &slipifs;
  unsigned long uli, ulo;
  size_t n;

  if ((p = getenv("TRIPE_SLIPIF")) == 0)
    return;

  /* --- Build the list of available interfaces --- */

  dstr_puts(&d, p);

  p = d.buf;
  for (;;) {
    if (*p == '/' || *p == '.') {
      slipcmd = p;
      T( trace(T_TUNNEL, "tun-slip: declared slip command `%s'", slipcmd); )
      break;
    }
    uli = strtoul(p, &q, 0);
    if (uli > INT_MAX || q == p)
      goto whine;
    if (*q != ',')
      ulo = uli;
    else {
      p = q + 1;
      ulo = strtoul(p, &q, 0);
      if (ulo > INT_MAX || q == p)
	goto whine;
    }
    if (*q != '=' || (n = strcspn(q + 1, ":")) == 0)
      goto whine;
    sl = CREATE(slipif);
    sl->next = 0;
    sl->ifd = uli;
    fdflags(sl->ifd, O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
    fdflags(sl->ofd, O_NONBLOCK, 0, FD_CLOEXEC, FD_CLOEXEC);
    sl->ofd = ulo;
    sl->name = xmalloc(n + 1);
    sl->kid = -1;
    sl->f = 0;
    memcpy(sl->name, q + 1, n);
    sl->name[n] = 0;
    *tail = sl;
    tail = &sl->next;
    T( trace(T_TUNNEL, "tun-slip: declared slipif %d,%d=%s",
	     sl->ifd, sl->ofd, sl->name); )
    p = q + n + 1;
    if (!*p)
      break;
    p++;
  }
  return;

whine:
  moan("bad slip interface list");
}

/* --- @t_create@ --- *
 *
 * Arguments:	@peer *p@ = pointer to peer block
 *		@int fd@ = file descriptor of tunnel device (unused)
 *		@char **ifn@ = where to put the interface name
 *
 * Returns:	A tunnel block if it worked, or null on failure.
 *
 * Use:		Initializes a new tunnel.
 */

static tunnel *t_create(peer *p, int fd, char **ifn)
{
  slipif *sl = 0;
  int pin[2] = { -1, -1 }, pout[2] = { -1, -1 };
  mdup_fd md[2];
  pid_t kid = -1;
  dstr d = DSTR_INIT;
  unsigned char ch;
  tunnel *t;
  static const char end[] = { SL_END, SL_END };

  /* --- Try to find a spare static interface --- */

  for (sl = slipifs; sl; sl = sl->next) {
    if (!(sl->f & F_INUSE)) {
      T( trace(T_TUNNEL, "tun-slip: %s using static slipif %s",
	       p_name(p), sl->name); )
      goto found;
    }
  }

  /* --- If no dynamic interfaces are available, give up --- */

  if (!slipcmd) {
    a_warn("TUN", "-", "slip", "no-slip-interfaces", A_END);
    goto fail;
  }

  /* --- Fork off a child process to create a dynamic SLIP interface --- */

  if (pipe(pin) || pipe(pout)) {
    a_warn("TUN", "-", "slip", "pipe-error", "?ERRNO", A_END);
    goto fail;
  }
  if ((kid = fork()) < 0) {
    a_warn("TUN", "-", "slip", "fork-error", "?ERRNO", A_END);
    goto fail;
  }
  if (!kid) {
    close(pin[1]); close(pout[0]);
    md[0].cur = pin[0];  md[0].want = STDIN_FILENO;
    md[1].cur = pout[1]; md[1].want = STDOUT_FILENO;
    mdup(md, 2);
    execlp(slipcmd, slipcmd, p_name(p), (char *)0);
    _exit(127);
  }

  /* --- Read the interface name --- */

  sl = CREATE(slipif);
  close(pin[0]); pin[0] = -1;
  close(pout[1]); pout[1] = -1;
  for (;;) {
    errno = EIO;
    if (read(pout[0], &ch, 1) != 1 || ch == SL_END) {
      a_warn("TUN", "-", "slip", "read-ifname-failed", "?ERRNO", A_END);
      goto fail;
    }
    if (ch == '\n')
      break;
    DPUTC(&d, (char)ch);
  }
  DPUTZ(&d);
  sl->name = xstrdup(d.buf);
  sl->ifd = pout[0];
  sl->ofd = pin[1];
  sl->kid = kid;
  sl->next = 0;
  sl->f = F_DYNAMIC;
  T( trace(T_TUNNEL, "tun-slip: %s using dynamic slipif %s",
	   p_name(p), sl->name); )
  fdflags(pout[0], O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC);
  fdflags(pin[1], O_NONBLOCK, 0, FD_CLOEXEC, FD_CLOEXEC);

  /* --- Set up the new tunnel --- */

found:
  t = CREATE(tunnel);
  t->ops = &tun_slip;
  t->p = p;
  t->sl = sl;
  t->st = 0;
  t->n = 0;
  sl->f |= F_INUSE;
  sel_initfile(&sel, &t->f, sl->ifd, SEL_READ, t_read, t);
  sel_addfile(&t->f);
  write(sl->ofd, end, sizeof(end));
  *ifn = xstrdup(sl->name);
  dstr_destroy(&d);
  return (t);

  /* --- Tidy up after a failure --- */

fail:
#define CLOSE(fd) do if (fd != -1) close(fd); while (0)
  CLOSE(pin[0]); CLOSE(pout[0]);
  CLOSE(pin[1]); CLOSE(pout[1]);
#undef CLOSE
  if (kid != -1) kill(kid, SIGTERM);
  if (sl && (sl->f & F_DYNAMIC)) DESTROY(sl);
  dstr_destroy(&d);
  return (0);
}

/* --- @t_setifname@ --- *
 *
 * Arguments:	@tunnel *t@ = pointer to tunnel block
 *		@const char *ifn@ = new interface name
 *
 * Returns:	---
 *
 * Use:		Updates the interface name of a slip interface.
 */

static void t_setifname(tunnel *t, const char *ifn)
  { xfree(t->sl->name); t->sl->name = xstrdup(ifn); }

/* --- @t_inject@ --- *
 *
 * Arguments:	@tunnel *t@ = pointer to tunnel block
 *		@buf *b@ = buffer to send
 *
 * Returns:	---
 *
 * Use:		Injects a packet into the local network stack.
 */

static void t_inject(tunnel *t, buf *b)
{
  octet buf[PKBUFSZ * 2 + 2];
  const octet *p, *l;
  octet *q;

  IF_TRACING(T_TUNNEL, {
    trace(T_TUNNEL, "tun-slip: inject decrypted packet");
    trace_block(T_PACKET, "tun-slip: packet contents", BBASE(b), BLEN(b));
  })

  q = buf;
  *q++ = SL_END;
  for (p = BBASE(b), l = BCUR(b); p < l; p++) {
    switch (*p) {
      case SL_END: *q++ = SL_ESC; *q++ = SL_ESCEND; break;
      case SL_ESC: *q++ = SL_ESC; *q++ = SL_ESCESC; break;
      default: *q++ = *p; break;
    }
  }
  *q++ = SL_END;
  IF_TRACING(T_TUNNEL, {
    trace_block(T_PACKET, "tun-slip: SLIP-encapsulated contents",
		buf, q - buf);
  })
  write(t->sl->ofd, buf, q - buf);
}

/* --- @t_destroy@ --- *
 *
 * Arguments:	@tunnel *t@ = pointer to tunnel block
 *
 * Returns:	---
 *
 * Use:		Destroys a tunnel.
 */

static void t_destroy(tunnel *t)
{
  slipif *sl = t->sl;

  /* --- If it reported EOF, leave it out-of-action --- */

  if (!(t->st & ST_EOF)) {
    sel_rmfile(&t->f);
    sl->f &= ~F_INUSE;
  }
  if (sl && (sl->f & F_DYNAMIC)) {
    T( trace(T_TUNNEL, "tun-slip: releasing dynamic slipif %s", sl->name); )
    close(sl->ofd);
    close(sl->ifd);
    kill(sl->kid, SIGTERM);
    xfree(sl->name);
    DESTROY(sl);
  }
  DESTROY(t);
}

const tunnel_ops tun_slip = {
  "slip",
  0,
  t_init,
  t_create,
  t_setifname,
  t_inject,
  t_destroy
};

/*----- That's all, folks -------------------------------------------------*/