src/basic/fs-util.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2010 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <stddef.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26 #include <linux/magic.h>
  27 #include <time.h>
  28 #include <unistd.h>
  29
  30 #include "alloc-util.h"
  31 #include "dirent-util.h"
  32 #include "fd-util.h"
  33 #include "fileio.h"
  34 #include "fs-util.h"
  35 #include "log.h"
  36 #include "macro.h"
  37 #include "missing.h"
  38 #include "mkdir.h"
  39 #include "parse-util.h"
  40 #include "path-util.h"
  41 #include "stat-util.h"
  42 #include "stdio-util.h"
  43 #include "string-util.h"
  44 #include "strv.h"
  45 #include "time-util.h"
  46 #include "user-util.h"
  47 #include "util.h"
  48
  49 int unlink_noerrno(const char *path) {
  50         PROTECT_ERRNO;
  51         int r;
  52
  53         r = unlink(path);
  54         if (r < 0)
  55                 return -errno;
  56
  57         return 0;
  58 }
  59
  60 int rmdir_parents(const char *path, const char *stop) {
  61         size_t l;
  62         int r = 0;
  63
  64         assert(path);
  65         assert(stop);
  66
  67         l = strlen(path);
  68
  69         /* Skip trailing slashes */
  70         while (l > 0 && path[l-1] == '/')
  71                 l--;
  72
  73         while (l > 0) {
  74                 char *t;
  75
  76                 /* Skip last component */
  77                 while (l > 0 && path[l-1] != '/')
  78                         l--;
  79
  80                 /* Skip trailing slashes */
  81                 while (l > 0 && path[l-1] == '/')
  82                         l--;
  83
  84                 if (l <= 0)
  85                         break;
  86
  87                 t = strndup(path, l);
  88                 if (!t)
  89                         return -ENOMEM;
  90
  91                 if (path_startswith(stop, t)) {
  92                         free(t);
  93                         return 0;
  94                 }
  95
  96                 r = rmdir(t);
  97                 free(t);
  98
  99                 if (r < 0)
 100                         if (errno != ENOENT)
 101                                 return -errno;
 102         }
 103
 104         return 0;
 105 }
 106
 107 int rename_noreplace(int olddirfd, const char *oldpath, int newdirfd, const char *newpath) {
 108         struct stat buf;
 109         int ret;
 110
 111         ret = renameat2(olddirfd, oldpath, newdirfd, newpath, RENAME_NOREPLACE);
 112         if (ret >= 0)
 113                 return 0;
 114
 115         /* renameat2() exists since Linux 3.15, btrfs added support for it later.
 116          * If it is not implemented, fallback to another method. */
 117         if (!IN_SET(errno, EINVAL, ENOSYS))
 118                 return -errno;
 119
 120         /* The link()/unlink() fallback does not work on directories. But
 121          * renameat() without RENAME_NOREPLACE gives the same semantics on
 122          * directories, except when newpath is an *empty* directory. This is
 123          * good enough. */
 124         ret = fstatat(olddirfd, oldpath, &buf, AT_SYMLINK_NOFOLLOW);
 125         if (ret >= 0 && S_ISDIR(buf.st_mode)) {
 126                 ret = renameat(olddirfd, oldpath, newdirfd, newpath);
 127                 return ret >= 0 ? 0 : -errno;
 128         }
 129
 130         /* If it is not a directory, use the link()/unlink() fallback. */
 131         ret = linkat(olddirfd, oldpath, newdirfd, newpath, 0);
 132         if (ret < 0)
 133                 return -errno;
 134
 135         ret = unlinkat(olddirfd, oldpath, 0);
 136         if (ret < 0) {
 137                 /* backup errno before the following unlinkat() alters it */
 138                 ret = errno;
 139                 (void) unlinkat(newdirfd, newpath, 0);
 140                 errno = ret;
 141                 return -errno;
 142         }
 143
 144         return 0;
 145 }
 146
 147 int readlinkat_malloc(int fd, const char *p, char **ret) {
 148         size_t l = 100;
 149         int r;
 150
 151         assert(p);
 152         assert(ret);
 153
 154         for (;;) {
 155                 char *c;
 156                 ssize_t n;
 157
 158                 c = new(char, l);
 159                 if (!c)
 160                         return -ENOMEM;
 161
 162                 n = readlinkat(fd, p, c, l-1);
 163                 if (n < 0) {
 164                         r = -errno;
 165                         free(c);
 166                         return r;
 167                 }
 168
 169                 if ((size_t) n < l-1) {
 170                         c[n] = 0;
 171                         *ret = c;
 172                         return 0;
 173                 }
 174
 175                 free(c);
 176                 l *= 2;
 177         }
 178 }
 179
 180 int readlink_malloc(const char *p, char **ret) {
 181         return readlinkat_malloc(AT_FDCWD, p, ret);
 182 }
 183
 184 int readlink_value(const char *p, char **ret) {
 185         _cleanup_free_ char *link = NULL;
 186         char *value;
 187         int r;
 188
 189         r = readlink_malloc(p, &link);
 190         if (r < 0)
 191                 return r;
 192
 193         value = basename(link);
 194         if (!value)
 195                 return -ENOENT;
 196
 197         value = strdup(value);
 198         if (!value)
 199                 return -ENOMEM;
 200
 201         *ret = value;
 202
 203         return 0;
 204 }
 205
 206 int readlink_and_make_absolute(const char *p, char **r) {
 207         _cleanup_free_ char *target = NULL;
 208         char *k;
 209         int j;
 210
 211         assert(p);
 212         assert(r);
 213
 214         j = readlink_malloc(p, &target);
 215         if (j < 0)
 216                 return j;
 217
 218         k = file_in_same_dir(p, target);
 219         if (!k)
 220                 return -ENOMEM;
 221
 222         *r = k;
 223         return 0;
 224 }
 225
 226 int readlink_and_canonicalize(const char *p, const char *root, char **ret) {
 227         char *t, *s;
 228         int r;
 229
 230         assert(p);
 231         assert(ret);
 232
 233         r = readlink_and_make_absolute(p, &t);
 234         if (r < 0)
 235                 return r;
 236
 237         r = chase_symlinks(t, root, 0, &s);
 238         if (r < 0)
 239                 /* If we can't follow up, then let's return the original string, slightly cleaned up. */
 240                 *ret = path_kill_slashes(t);
 241         else {
 242                 *ret = s;
 243                 free(t);
 244         }
 245
 246         return 0;
 247 }
 248
 249 int readlink_and_make_absolute_root(const char *root, const char *path, char **ret) {
 250         _cleanup_free_ char *target = NULL, *t = NULL;
 251         const char *full;
 252         int r;
 253
 254         full = prefix_roota(root, path);
 255         r = readlink_malloc(full, &target);
 256         if (r < 0)
 257                 return r;
 258
 259         t = file_in_same_dir(path, target);
 260         if (!t)
 261                 return -ENOMEM;
 262
 263         *ret = t;
 264         t = NULL;
 265
 266         return 0;
 267 }
 268
 269 int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid) {
 270         assert(path);
 271
 272         /* Under the assumption that we are running privileged we
 273          * first change the access mode and only then hand out
 274          * ownership to avoid a window where access is too open. */
 275
 276         if (mode != MODE_INVALID)
 277                 if (chmod(path, mode) < 0)
 278                         return -errno;
 279
 280         if (uid != UID_INVALID || gid != GID_INVALID)
 281                 if (chown(path, uid, gid) < 0)
 282                         return -errno;
 283
 284         return 0;
 285 }
 286
 287 int fchmod_umask(int fd, mode_t m) {
 288         mode_t u;
 289         int r;
 290
 291         u = umask(0777);
 292         r = fchmod(fd, m & (~u)) < 0 ? -errno : 0;
 293         umask(u);
 294
 295         return r;
 296 }
 297
 298 int fd_warn_permissions(const char *path, int fd) {
 299         struct stat st;
 300
 301         if (fstat(fd, &st) < 0)
 302                 return -errno;
 303
 304         if (st.st_mode & 0111)
 305                 log_warning("Configuration file %s is marked executable. Please remove executable permission bits. Proceeding anyway.", path);
 306
 307         if (st.st_mode & 0002)
 308                 log_warning("Configuration file %s is marked world-writable. Please remove world writability permission bits. Proceeding anyway.", path);
 309
 310         if (getpid_cached() == 1 && (st.st_mode & 0044) != 0044)
 311                 log_warning("Configuration file %s is marked world-inaccessible. This has no effect as configuration data is accessible via APIs without restrictions. Proceeding anyway.", path);
 312
 313         return 0;
 314 }
 315
 316 int touch_file(const char *path, bool parents, usec_t stamp, uid_t uid, gid_t gid, mode_t mode) {
 317         _cleanup_close_ int fd;
 318         int r;
 319
 320         assert(path);
 321
 322         if (parents)
 323                 mkdir_parents(path, 0755);
 324
 325         fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY,
 326                   IN_SET(mode, 0, MODE_INVALID) ? 0644 : mode);
 327         if (fd < 0)
 328                 return -errno;
 329
 330         if (mode != MODE_INVALID) {
 331                 r = fchmod(fd, mode);
 332                 if (r < 0)
 333                         return -errno;
 334         }
 335
 336         if (uid != UID_INVALID || gid != GID_INVALID) {
 337                 r = fchown(fd, uid, gid);
 338                 if (r < 0)
 339                         return -errno;
 340         }
 341
 342         if (stamp != USEC_INFINITY) {
 343                 struct timespec ts[2];
 344
 345                 timespec_store(&ts[0], stamp);
 346                 ts[1] = ts[0];
 347                 r = futimens(fd, ts);
 348         } else
 349                 r = futimens(fd, NULL);
 350         if (r < 0)
 351                 return -errno;
 352
 353         return 0;
 354 }
 355
 356 int touch(const char *path) {
 357         return touch_file(path, false, USEC_INFINITY, UID_INVALID, GID_INVALID, MODE_INVALID);
 358 }
 359
 360 int symlink_idempotent(const char *from, const char *to) {
 361         int r;
 362
 363         assert(from);
 364         assert(to);
 365
 366         if (symlink(from, to) < 0) {
 367                 _cleanup_free_ char *p = NULL;
 368
 369                 if (errno != EEXIST)
 370                         return -errno;
 371
 372                 r = readlink_malloc(to, &p);
 373                 if (r == -EINVAL) /* Not a symlink? In that case return the original error we encountered: -EEXIST */
 374                         return -EEXIST;
 375                 if (r < 0) /* Any other error? In that case propagate it as is */
 376                         return r;
 377
 378                 if (!streq(p, from)) /* Not the symlink we want it to be? In that case, propagate the original -EEXIST */
 379                         return -EEXIST;
 380         }
 381
 382         return 0;
 383 }
 384
 385 int symlink_atomic(const char *from, const char *to) {
 386         _cleanup_free_ char *t = NULL;
 387         int r;
 388
 389         assert(from);
 390         assert(to);
 391
 392         r = tempfn_random(to, NULL, &t);
 393         if (r < 0)
 394                 return r;
 395
 396         if (symlink(from, t) < 0)
 397                 return -errno;
 398
 399         if (rename(t, to) < 0) {
 400                 unlink_noerrno(t);
 401                 return -errno;
 402         }
 403
 404         return 0;
 405 }
 406
 407 int mknod_atomic(const char *path, mode_t mode, dev_t dev) {
 408         _cleanup_free_ char *t = NULL;
 409         int r;
 410
 411         assert(path);
 412
 413         r = tempfn_random(path, NULL, &t);
 414         if (r < 0)
 415                 return r;
 416
 417         if (mknod(t, mode, dev) < 0)
 418                 return -errno;
 419
 420         if (rename(t, path) < 0) {
 421                 unlink_noerrno(t);
 422                 return -errno;
 423         }
 424
 425         return 0;
 426 }
 427
 428 int mkfifo_atomic(const char *path, mode_t mode) {
 429         _cleanup_free_ char *t = NULL;
 430         int r;
 431
 432         assert(path);
 433
 434         r = tempfn_random(path, NULL, &t);
 435         if (r < 0)
 436                 return r;
 437
 438         if (mkfifo(t, mode) < 0)
 439                 return -errno;
 440
 441         if (rename(t, path) < 0) {
 442                 unlink_noerrno(t);
 443                 return -errno;
 444         }
 445
 446         return 0;
 447 }
 448
 449 int get_files_in_directory(const char *path, char ***list) {
 450         _cleanup_closedir_ DIR *d = NULL;
 451         struct dirent *de;
 452         size_t bufsize = 0, n = 0;
 453         _cleanup_strv_free_ char **l = NULL;
 454
 455         assert(path);
 456
 457         /* Returns all files in a directory in *list, and the number
 458          * of files as return value. If list is NULL returns only the
 459          * number. */
 460
 461         d = opendir(path);
 462         if (!d)
 463                 return -errno;
 464
 465         FOREACH_DIRENT_ALL(de, d, return -errno) {
 466                 dirent_ensure_type(d, de);
 467
 468                 if (!dirent_is_file(de))
 469                         continue;
 470
 471                 if (list) {
 472                         /* one extra slot is needed for the terminating NULL */
 473                         if (!GREEDY_REALLOC(l, bufsize, n + 2))
 474                                 return -ENOMEM;
 475
 476                         l[n] = strdup(de->d_name);
 477                         if (!l[n])
 478                                 return -ENOMEM;
 479
 480                         l[++n] = NULL;
 481                 } else
 482                         n++;
 483         }
 484
 485         if (list) {
 486                 *list = l;
 487                 l = NULL; /* avoid freeing */
 488         }
 489
 490         return n;
 491 }
 492
 493 static int getenv_tmp_dir(const char **ret_path) {
 494         const char *n;
 495         int r, ret = 0;
 496
 497         assert(ret_path);
 498
 499         /* We use the same order of environment variables python uses in tempfile.gettempdir():
 500          * https://docs.python.org/3/library/tempfile.html#tempfile.gettempdir */
 501         FOREACH_STRING(n, "TMPDIR", "TEMP", "TMP") {
 502                 const char *e;
 503
 504                 e = secure_getenv(n);
 505                 if (!e)
 506                         continue;
 507                 if (!path_is_absolute(e)) {
 508                         r = -ENOTDIR;
 509                         goto next;
 510                 }
 511                 if (!path_is_safe(e)) {
 512                         r = -EPERM;
 513                         goto next;
 514                 }
 515
 516                 r = is_dir(e, true);
 517                 if (r < 0)
 518                         goto next;
 519                 if (r == 0) {
 520                         r = -ENOTDIR;
 521                         goto next;
 522                 }
 523
 524                 *ret_path = e;
 525                 return 1;
 526
 527         next:
 528                 /* Remember first error, to make this more debuggable */
 529                 if (ret >= 0)
 530                         ret = r;
 531         }
 532
 533         if (ret < 0)
 534                 return ret;
 535
 536         *ret_path = NULL;
 537         return ret;
 538 }
 539
 540 static int tmp_dir_internal(const char *def, const char **ret) {
 541         const char *e;
 542         int r, k;
 543
 544         assert(def);
 545         assert(ret);
 546
 547         r = getenv_tmp_dir(&e);
 548         if (r > 0) {
 549                 *ret = e;
 550                 return 0;
 551         }
 552
 553         k = is_dir(def, true);
 554         if (k == 0)
 555                 k = -ENOTDIR;
 556         if (k < 0)
 557                 return r < 0 ? r : k;
 558
 559         *ret = def;
 560         return 0;
 561 }
 562
 563 int var_tmp_dir(const char **ret) {
 564
 565         /* Returns the location for "larger" temporary files, that is backed by physical storage if available, and thus
 566          * even might survive a boot: /var/tmp. If $TMPDIR (or related environment variables) are set, its value is
 567          * returned preferably however. Note that both this function and tmp_dir() below are affected by $TMPDIR,
 568          * making it a variable that overrides all temporary file storage locations. */
 569
 570         return tmp_dir_internal("/var/tmp", ret);
 571 }
 572
 573 int tmp_dir(const char **ret) {
 574
 575         /* Similar to var_tmp_dir() above, but returns the location for "smaller" temporary files, which is usually
 576          * backed by an in-memory file system: /tmp. */
 577
 578         return tmp_dir_internal("/tmp", ret);
 579 }
 580
 581 int inotify_add_watch_fd(int fd, int what, uint32_t mask) {
 582         char path[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
 583         int r;
 584
 585         /* This is like inotify_add_watch(), except that the file to watch is not referenced by a path, but by an fd */
 586         xsprintf(path, "/proc/self/fd/%i", what);
 587
 588         r = inotify_add_watch(fd, path, mask);
 589         if (r < 0)
 590                 return -errno;
 591
 592         return r;
 593 }
 594
 595 int chase_symlinks(const char *path, const char *original_root, unsigned flags, char **ret) {
 596         _cleanup_free_ char *buffer = NULL, *done = NULL, *root = NULL;
 597         _cleanup_close_ int fd = -1;
 598         unsigned max_follow = 32; /* how many symlinks to follow before giving up and returning ELOOP */
 599         bool exists = true;
 600         char *todo;
 601         int r;
 602
 603         assert(path);
 604
 605         /* This is a lot like canonicalize_file_name(), but takes an additional "root" parameter, that allows following
 606          * symlinks relative to a root directory, instead of the root of the host.
 607          *
 608          * Note that "root" primarily matters if we encounter an absolute symlink. It is also used when following
 609          * relative symlinks to ensure they cannot be used to "escape" the root directory. The path parameter passed is
 610          * assumed to be already prefixed by it, except if the CHASE_PREFIX_ROOT flag is set, in which case it is first
 611          * prefixed accordingly.
 612          *
 613          * Algorithmically this operates on two path buffers: "done" are the components of the path we already
 614          * processed and resolved symlinks, "." and ".." of. "todo" are the components of the path we still need to
 615          * process. On each iteration, we move one component from "todo" to "done", processing it's special meaning
 616          * each time. The "todo" path always starts with at least one slash, the "done" path always ends in no
 617          * slash. We always keep an O_PATH fd to the component we are currently processing, thus keeping lookup races
 618          * at a minimum.
 619          *
 620          * Suggested usage: whenever you want to canonicalize a path, use this function. Pass the absolute path you got
 621          * as-is: fully qualified and relative to your host's root. Optionally, specify the root parameter to tell this
 622          * function what to do when encountering a symlink with an absolute path as directory: prefix it by the
 623          * specified path.
 624          *
 625          * Note: there's also chase_symlinks_prefix() (see below), which as first step prefixes the passed path by the
 626          * passed root. */
 627
 628         if (original_root) {
 629                 r = path_make_absolute_cwd(original_root, &root);
 630                 if (r < 0)
 631                         return r;
 632
 633                 if (flags & CHASE_PREFIX_ROOT)
 634                         path = prefix_roota(root, path);
 635         }
 636
 637         r = path_make_absolute_cwd(path, &buffer);
 638         if (r < 0)
 639                 return r;
 640
 641         fd = open("/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
 642         if (fd < 0)
 643                 return -errno;
 644
 645         todo = buffer;
 646         for (;;) {
 647                 _cleanup_free_ char *first = NULL;
 648                 _cleanup_close_ int child = -1;
 649                 struct stat st;
 650                 size_t n, m;
 651
 652                 /* Determine length of first component in the path */
 653                 n = strspn(todo, "/");                  /* The slashes */
 654                 m = n + strcspn(todo + n, "/");         /* The entire length of the component */
 655
 656                 /* Extract the first component. */
 657                 first = strndup(todo, m);
 658                 if (!first)
 659                         return -ENOMEM;
 660
 661                 todo += m;
 662
 663                 /* Just a single slash? Then we reached the end. */
 664                 if (isempty(first) || path_equal(first, "/"))
 665                         break;
 666
 667                 /* Just a dot? Then let's eat this up. */
 668                 if (path_equal(first, "/."))
 669                         continue;
 670
 671                 /* Two dots? Then chop off the last bit of what we already found out. */
 672                 if (path_equal(first, "/..")) {
 673                         _cleanup_free_ char *parent = NULL;
 674                         int fd_parent = -1;
 675
 676                         /* If we already are at the top, then going up will not change anything. This is in-line with
 677                          * how the kernel handles this. */
 678                         if (isempty(done) || path_equal(done, "/"))
 679                                 continue;
 680
 681                         parent = dirname_malloc(done);
 682                         if (!parent)
 683                                 return -ENOMEM;
 684
 685                         /* Don't allow this to leave the root dir.  */
 686                         if (root &&
 687                             path_startswith(done, root) &&
 688                             !path_startswith(parent, root))
 689                                 continue;
 690
 691                         free_and_replace(done, parent);
 692
 693                         fd_parent = openat(fd, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH);
 694                         if (fd_parent < 0)
 695                                 return -errno;
 696
 697                         safe_close(fd);
 698                         fd = fd_parent;
 699
 700                         continue;
 701                 }
 702
 703                 /* Otherwise let's see what this is. */
 704                 child = openat(fd, first + n, O_CLOEXEC|O_NOFOLLOW|O_PATH);
 705                 if (child < 0) {
 706
 707                         if (errno == ENOENT &&
 708                             (flags & CHASE_NONEXISTENT) &&
 709                             (isempty(todo) || path_is_safe(todo))) {
 710
 711                                 /* If CHASE_NONEXISTENT is set, and the path does not exist, then that's OK, return
 712                                  * what we got so far. But don't allow this if the remaining path contains "../ or "./"
 713                                  * or something else weird. */
 714
 715                                 if (!strextend(&done, first, todo, NULL))
 716                                         return -ENOMEM;
 717
 718                                 exists = false;
 719                                 break;
 720                         }
 721
 722                         return -errno;
 723                 }
 724
 725                 if (fstat(child, &st) < 0)
 726                         return -errno;
 727                 if ((flags & CHASE_NO_AUTOFS) &&
 728                     fd_check_fstype(child, AUTOFS_SUPER_MAGIC) > 0)
 729                         return -EREMOTE;
 730
 731                 if (S_ISLNK(st.st_mode)) {
 732                         char *joined;
 733
 734                         _cleanup_free_ char *destination = NULL;
 735
 736                         /* This is a symlink, in this case read the destination. But let's make sure we don't follow
 737                          * symlinks without bounds. */
 738                         if (--max_follow <= 0)
 739                                 return -ELOOP;
 740
 741                         r = readlinkat_malloc(fd, first + n, &destination);
 742                         if (r < 0)
 743                                 return r;
 744                         if (isempty(destination))
 745                                 return -EINVAL;
 746
 747                         if (path_is_absolute(destination)) {
 748
 749                                 /* An absolute destination. Start the loop from the beginning, but use the root
 750                                  * directory as base. */
 751
 752                                 safe_close(fd);
 753                                 fd = open(root ?: "/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
 754                                 if (fd < 0)
 755                                         return -errno;
 756
 757                                 free(done);
 758
 759                                 /* Note that we do not revalidate the root, we take it as is. */
 760                                 if (isempty(root))
 761                                         done = NULL;
 762                                 else {
 763                                         done = strdup(root);
 764                                         if (!done)
 765                                                 return -ENOMEM;
 766                                 }
 767
 768                                 /* Prefix what's left to do with what we just read, and start the loop again, but
 769                                  * remain in the current directory. */
 770                                 joined = strjoin(destination, todo);
 771                         } else
 772                                 joined = strjoin("/", destination, todo);
 773                         if (!joined)
 774                                 return -ENOMEM;
 775
 776                         free(buffer);
 777                         todo = buffer = joined;
 778
 779                         continue;
 780                 }
 781
 782                 /* If this is not a symlink, then let's just add the name we read to what we already verified. */
 783                 if (!done) {
 784                         done = first;
 785                         first = NULL;
 786                 } else {
 787                         if (!strextend(&done, first, NULL))
 788                                 return -ENOMEM;
 789                 }
 790
 791                 /* And iterate again, but go one directory further down. */
 792                 safe_close(fd);
 793                 fd = child;
 794                 child = -1;
 795         }
 796
 797         if (!done) {
 798                 /* Special case, turn the empty string into "/", to indicate the root directory. */
 799                 done = strdup("/");
 800                 if (!done)
 801                         return -ENOMEM;
 802         }
 803
 804         if (ret) {
 805                 *ret = done;
 806                 done = NULL;
 807         }
 808
 809         return exists;
 810 }
 811
 812 int access_fd(int fd, int mode) {
 813         char p[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(fd) + 1];
 814         int r;
 815
 816         /* Like access() but operates on an already open fd */
 817
 818         xsprintf(p, "/proc/self/fd/%i", fd);
 819
 820         r = access(p, mode);
 821         if (r < 0)
 822                 r = -errno;
 823
 824         return r;
 825 }