Pollard's rho algorithm for computing discrete logs.

[u/mdw/catacomb] / key-file.c

/* -*-c-*-
 *
 * $Id: key-file.c,v 1.1 1999/12/22 15:47:48 mdw Exp $
 *
 * System-dependent key filing operations
 *
 * (c) 1999 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 * 
 * Catacomb 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 Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------* 
 *
 * $Log: key-file.c,v $
 * Revision 1.1  1999/12/22 15:47:48  mdw
 * Major key-management revision.
 *
 */

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

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <sys/types.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

#include <mLib/dstr.h>
#include <mLib/lock.h>

#include "key.h"

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

/* --- @fdcopy@ --- *
 *
 * Arguments:	@int source@ = source file descriptor
 *		@int dest@ = destination file descriptor
 *
 * Returns:	Zero if OK, nonzero otherwise.
 *
 * Use:		Copies data from one file descriptor to another.
 */

static int fdcopy(int source, int dest)
{
  char buf[4096];

  if (lseek(source, 0, SEEK_SET) < 0||
      lseek(dest, 0, SEEK_SET) < 0 ||
      ftruncate(dest, 0) < 0)
    return (-1);
  for (;;) {
    int n = read(source, buf, sizeof(buf));
    if (n < 0)
      return (-1);
    else if (n == 0)
      break;
    else if (write(dest, buf, n) < 0)
      return (-1);
  }
  return (0);
}

/* --- @key_save@ --- *
 *
 * Arguments:	@key_file *f@ = pointer to key file block
 *
 * Returns:	A @KWRITE_@ code indicating how well it worked.
 *
 * Use:		Writes a key file's data back to the actual file.  This code
 *		is extremely careful about error handling.  It should usually
 *		be able to back out somewhere sensible, but it can tell when
 *		it's got itself into a real pickle and starts leaving well
 *		alone.
 *
 *		Callers, please make sure that you ring alarm bells when this
 *		function returns @KWRITE_BROKEN@.
 */

int key_save(key_file *f)
{
  dstr n_older = DSTR_INIT, n_old = DSTR_INIT, n_new = DSTR_INIT;
  int rc = KWRITE_FAIL;

  if (!(f->f & KF_MODIFIED))
    return (KWRITE_OK);

  /* --- Write a new key file out --- *
   *
   * Check for an error after each key line.  This ought to be enough.
   * Checking after each individual byte write and @fprintf@ isn't much fun.
   */

  dstr_putf(&n_new, "%s.new", f->name);

  {
    key *k;
    key_iter i;
    FILE *fp;

    if ((fp = fopen(n_new.buf, "w")) == 0)
      goto fail_open;

    for (key_mkiter(&i, f); (k = key_next(&i)) != 0; ) {
      if (key_extract(f, k, fp, 0)) {
	fclose(fp);
	goto fail_write;
      }
    }

    if (fclose(fp))
      goto fail_write;
  }

  /* --- Set up the other filenames --- */

  dstr_putf(&n_older, "%s.older", f->name);
  dstr_putf(&n_old, "%s.old", f->name);

  /* --- Move the current backup on one --- *
   *
   * If the `older' file exists, then we're in need of attention.
   */

  {
    struct stat st;
    if (stat(n_older.buf, &st) == 0 || errno != ENOENT) {
      errno = EEXIST;
      rc = KWRITE_BROKEN;
      goto fail_shift;
    }
    if (rename(n_old.buf, n_older.buf) && errno != ENOENT)
      goto fail_shift;
  }

  /* --- Copy the current file to the backup --- */

  {
    int fd;
    if ((fd = open(n_old.buf, O_WRONLY | O_CREAT | O_EXCL, 0600)) < 0)
      goto fail_backup;
    if (fdcopy(fileno(f->fp), fd)) {
      close(fd);
      goto fail_backup;
    }
    if (close(fd))
      goto fail_backup;
  }

  /* --- Copy the newly created file to the current one --- *
   *
   * This is the dangerous bit.
   */

  {
    int fd;
    if ((fd = open(n_new.buf, O_RDONLY)) < 0)
      goto fail_update;
    if (fdcopy(fd, fileno(f->fp))) {
      close(fd);
      goto fail_update;
    }
    close(fd);
    if (fsync(fileno(f->fp)))
      goto fail_update;
  }

  /* --- Clean up --- *
   *
   * Remove the `new' file and the `older' backup.  Then we're done.
   */

  unlink(n_new.buf);
  unlink(n_older.buf);
  return (KWRITE_OK);

  /* --- Failure while writing the new key file --- *
   *
   * I need to copy the backup back.  If that fails then I'm really stuffed.
   * If not, then I might as well try to get the backups sorted back out
   * again.
   */

fail_update:
  {
    int fd;
    int e = errno;

    if ((fd = open(n_old.buf, O_RDONLY)) < 0)
      rc = KWRITE_BROKEN;
    else if (fdcopy(fd, fileno(f->fp))) {
      close(fd);
      rc = KWRITE_BROKEN;
    } else {
      close(fd);
      if (fsync(fileno(f->fp)))
	rc = KWRITE_BROKEN;
    }

    errno = e;
    if (rc == KWRITE_BROKEN)
      goto fail_shift;
  }
  /* Now drop through */

  /* --- Failure while writing the new backup --- *
   *
   * The new backup isn't any use.  Try to recover the old one.
   */

fail_backup:
  {
    int e = errno;
    unlink(n_old.buf);
    if (rename(n_older.buf, n_old.buf) && errno != ENOENT)
      rc = KWRITE_BROKEN;
    errno = e;
  }
  /* Now drop through */

  /* --- Failure while demoting the current backup --- *
   *
   * Leave the completed output file there for the operator in case he wants
   * to clean up.
   */

fail_shift:
  dstr_destroy(&n_new);
  dstr_destroy(&n_old);
  dstr_destroy(&n_older);
  return (rc);
  
/* --- Failure during write of new data --- *
 *
 * Clean up the new file and return.  These errors can never cause
 * breakage.
 */

fail_write:
  unlink(n_new.buf);
  fail_open:
  dstr_destroy(&n_new);
  return (rc);
}

/* --- @key_lockfile@ --- *
 *
 * Arguments:	@key_file *f@ = pointer to file structure to initialize
 *		@const char *file@ = pointer to the file name
 *		@int how@ = opening options (@KOPEN_*@).
 *
 * Returns:	Zero if it worked, nonzero otherwise.
 *
 * Use:		Opens a keyfile and stores the information needed for
 *		continued access in the structure.
 *
 *		If the file is opened with @KOPEN_WRITE@, it's created if
 *		necessary with read and write permissions for owner only, and
 *		locked for update while it's open.
 *
 *		This is a system-dependent routine, and only really intended
 *		for the private use of @key_open@.
 */

int key_lockfile(key_file *f, const char *file, int how)
{
  int of, lf;
  const char *ff;
  int fd;

  /* --- Lots of things depend on whether we're writing --- */

  switch (how) {
    case KOPEN_READ:
      of = O_RDONLY;
      lf = LOCK_NONEXCL;
      ff = "r";
      break;
    case KOPEN_WRITE:
      of = O_RDWR | O_CREAT;
      lf = LOCK_EXCL;
      ff = "r+";
      break;
    default:
      errno = EINVAL;
      return (-1);
  }

  /* --- Open and lock the file --- */

  if ((fd = open(file, of, 0600)) < 0)
    return (-1);
  if (fcntl(fd, F_SETFD, FD_CLOEXEC) < 0 ||
      lock_file(fd, lf) < 0 ||
      (f->fp = fdopen(fd, ff)) == 0) {
    close(fd);
    return (-1);
  }

  return (0);
}

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