git.distorted.org.uk Git - u/mdw/catacomb/blob - key/key-file.c

   1 /* -*-c-*-
   2  *
   3  * System-dependent key filing operations
   4  *
   5  * (c) 1999 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb 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 Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include <errno.h>
  31 #include <stdio.h>
  32 #include <stdlib.h>
  33 #include <string.h>
  34
  35 #include <sys/types.h>
  36 #include <sys/time.h>
  37 #include <sys/stat.h>
  38 #include <unistd.h>
  39 #include <fcntl.h>
  40
  41 #include <mLib/dstr.h>
  42 #include <mLib/lock.h>
  43
  44 #include "key.h"
  45
  46 /*----- Main code ---------------------------------------------------------*/
  47
  48 /* --- @fdcopy@ --- *
  49  *
  50  * Arguments:   @int source@ = source file descriptor
  51  *              @int dest@ = destination file descriptor
  52  *
  53  * Returns:     Zero if OK, nonzero otherwise.
  54  *
  55  * Use:         Copies data from one file descriptor to another.
  56  */
  57
  58 static int fdcopy(int source, int dest)
  59 {
  60   char buf[4096];
  61   char *p;
  62
  63   if (lseek(source, 0, SEEK_SET) < 0||
  64       lseek(dest, 0, SEEK_SET) < 0 ||
  65       ftruncate(dest, 0) < 0)
  66     return (-1);
  67   for (;;) {
  68     int n = read(source, buf, sizeof(buf));
  69     if (n < 0)
  70       return (-1);
  71     else if (n == 0)
  72       break;
  73     p = buf;
  74     while (n) {
  75       int nn = write(dest, p, n);
  76       if (nn < 0)
  77         return (-1);
  78       p += nn;
  79       n -= nn;
  80     }
  81   }
  82   return (0);
  83 }
  84
  85 /* --- @key_save@ --- *
  86  *
  87  * Arguments:   @key_file *f@ = pointer to key file block
  88  *
  89  * Returns:     A @KWRITE_@ code indicating how well it worked.
  90  *
  91  * Use:         Writes a key file's data back to the actual file.  This code
  92  *              is extremely careful about error handling.  It should usually
  93  *              be able to back out somewhere sensible, but it can tell when
  94  *              it's got itself into a real pickle and starts leaving well
  95  *              alone.
  96  *
  97  *              Callers, please make sure that you ring alarm bells when this
  98  *              function returns @KWRITE_BROKEN@.
  99  */
 100
 101 int key_save(key_file *f)
 102 {
 103   dstr n_older = DSTR_INIT, n_old = DSTR_INIT, n_new = DSTR_INIT;
 104   int rc = KWRITE_FAIL;
 105
 106   if (!(f->f & KF_MODIFIED))
 107     return (KWRITE_OK);
 108   if (!f->fp)
 109     return (KWRITE_FAIL);
 110
 111   /* --- Write a new key file out --- *
 112    *
 113    * Check for an error after each key line.  This ought to be enough.
 114    * Checking after each individual byte write and @fprintf@ isn't much fun.
 115    */
 116
 117   dstr_putf(&n_new, "%s.new", f->name);
 118
 119   {
 120     key *k;
 121     key_iter i;
 122     FILE *fp;
 123
 124     if ((fp = fopen(n_new.buf, "w")) == 0)
 125       goto fail_open;
 126
 127     for (key_mkiter(&i, f); (k = key_next(&i)) != 0; ) {
 128       if (key_extract(f, k, fp, 0)) {
 129         fclose(fp);
 130         goto fail_write;
 131       }
 132     }
 133
 134     if (fclose(fp))
 135       goto fail_write;
 136   }
 137
 138   /* --- Set up the other filenames --- */
 139
 140   dstr_putf(&n_older, "%s.older", f->name);
 141   dstr_putf(&n_old, "%s.old", f->name);
 142
 143   /* --- Move the current backup on one --- *
 144    *
 145    * If the `older' file exists, then we're in need of attention.
 146    */
 147
 148   {
 149     struct stat st;
 150     if (stat(n_older.buf, &st) == 0 || errno != ENOENT) {
 151       errno = EEXIST;
 152       rc = KWRITE_BROKEN;
 153       goto fail_shift;
 154     }
 155     if (rename(n_old.buf, n_older.buf) && errno != ENOENT)
 156       goto fail_shift;
 157   }
 158
 159   /* --- Copy the current file to the backup --- */
 160
 161   {
 162     int fd;
 163     if ((fd = open(n_old.buf, O_WRONLY | O_CREAT | O_EXCL, 0600)) < 0)
 164       goto fail_backup;
 165     if (fdcopy(fileno(f->fp), fd)) {
 166       close(fd);
 167       goto fail_backup;
 168     }
 169     if (close(fd))
 170       goto fail_backup;
 171   }
 172
 173   /* --- Copy the newly created file to the current one --- *
 174    *
 175    * This is the dangerous bit.
 176    */
 177
 178   {
 179     int fd;
 180     if ((fd = open(n_new.buf, O_RDONLY)) < 0)
 181       goto fail_update;
 182     if (fdcopy(fd, fileno(f->fp))) {
 183       close(fd);
 184       goto fail_update;
 185     }
 186     close(fd);
 187     if (fsync(fileno(f->fp)))
 188       goto fail_update;
 189   }
 190
 191   /* --- Clean up --- *
 192    *
 193    * Remove the `new' file and the `older' backup.  Then we're done.
 194    */
 195
 196   unlink(n_new.buf);
 197   unlink(n_older.buf);
 198   dstr_destroy(&n_new);
 199   dstr_destroy(&n_old);
 200   dstr_destroy(&n_older);
 201   return (KWRITE_OK);
 202
 203   /* --- Failure while writing the new key file --- *
 204    *
 205    * I need to copy the backup back.  If that fails then I'm really stuffed.
 206    * If not, then I might as well try to get the backups sorted back out
 207    * again.
 208    */
 209
 210 fail_update:
 211   {
 212     int fd;
 213     int e = errno;
 214
 215     if ((fd = open(n_old.buf, O_RDONLY)) < 0)
 216       rc = KWRITE_BROKEN;
 217     else if (fdcopy(fd, fileno(f->fp))) {
 218       close(fd);
 219       rc = KWRITE_BROKEN;
 220     } else {
 221       close(fd);
 222       if (fsync(fileno(f->fp)))
 223         rc = KWRITE_BROKEN;
 224     }
 225
 226     errno = e;
 227     if (rc == KWRITE_BROKEN)
 228       goto fail_shift;
 229   }
 230   /* Now drop through */
 231
 232   /* --- Failure while writing the new backup --- *
 233    *
 234    * The new backup isn't any use.  Try to recover the old one.
 235    */
 236
 237 fail_backup:
 238   {
 239     int e = errno;
 240     unlink(n_old.buf);
 241     if (rename(n_older.buf, n_old.buf) && errno != ENOENT)
 242       rc = KWRITE_BROKEN;
 243     errno = e;
 244   }
 245   /* Now drop through */
 246
 247   /* --- Failure while demoting the current backup --- *
 248    *
 249    * Leave the completed output file there for the operator in case he wants
 250    * to clean up.
 251    */
 252
 253 fail_shift:
 254   dstr_destroy(&n_new);
 255   dstr_destroy(&n_old);
 256   dstr_destroy(&n_older);
 257   return (rc);
 258
 259   /* --- Failure during write of new data --- *
 260    *
 261    * Clean up the new file and return.  These errors can never cause
 262    * breakage.
 263    */
 264
 265 fail_write:
 266   unlink(n_new.buf);
 267 fail_open:
 268   dstr_destroy(&n_new);
 269   return (rc);
 270 }
 271
 272 /* --- @key_lockfile@ --- *
 273  *
 274  * Arguments:   @key_file *f@ = pointer to file structure to initialize
 275  *              @const char *file@ = pointer to the file name
 276  *              @unsigned how@ = opening options (@KOPEN_*@).
 277  *
 278  * Returns:     Zero if it worked, nonzero otherwise.
 279  *
 280  * Use:         Opens a keyfile and stores the information needed for
 281  *              continued access in the structure.
 282  *
 283  *              If the file is opened with @KOPEN_WRITE@, it's created if
 284  *              necessary with read and write permissions for owner only, and
 285  *              locked for update while it's open.
 286  *
 287  *              This is a system-dependent routine, and only really intended
 288  *              for the private use of @key_open@.
 289  */
 290
 291 int key_lockfile(key_file *f, const char *file, unsigned how)
 292 {
 293   int of, lf;
 294   const char *ff;
 295   int fd;
 296
 297   /* --- Handle the magic no-file option --- */
 298
 299   if (how & KOPEN_NOFILE) {
 300     f->fp = 0;
 301     return (0);
 302   }
 303
 304   /* --- Lots of things depend on whether we're writing --- */
 305
 306   switch (how & KOPEN_MASK) {
 307     case KOPEN_READ:
 308       of = O_RDONLY;
 309       lf = LOCK_NONEXCL;
 310       ff = "r";
 311       break;
 312     case KOPEN_WRITE:
 313       of = O_RDWR | O_CREAT;
 314       lf = LOCK_EXCL;
 315       ff = "r+";
 316       break;
 317     default:
 318       errno = EINVAL;
 319       return (-1);
 320   }
 321
 322   /* --- Open and lock the file --- */
 323
 324   if ((fd = open(file, of, 0600)) < 0)
 325     return (-1);
 326   if (fcntl(fd, F_SETFD, FD_CLOEXEC) < 0 ||
 327       lock_file(fd, lf) < 0 ||
 328       (f->fp = fdopen(fd, ff)) == 0) {
 329     close(fd);
 330     return (-1);
 331   }
 332
 333   return (0);
 334 }
 335
 336 /*----- That's all, folks -------------------------------------------------*/