src/basic/chase.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <linux/magic.h>
   4
   5 #include "alloc-util.h"
   6 #include "chase.h"
   7 #include "fd-util.h"
   8 #include "fileio.h"
   9 #include "fs-util.h"
  10 #include "glyph-util.h"
  11 #include "log.h"
  12 #include "path-util.h"
  13 #include "string-util.h"
  14 #include "user-util.h"
  15
  16 bool unsafe_transition(const struct stat *a, const struct stat *b) {
  17         /* Returns true if the transition from a to b is safe, i.e. that we never transition from unprivileged to
  18          * privileged files or directories. Why bother? So that unprivileged code can't symlink to privileged files
  19          * making us believe we read something safe even though it isn't safe in the specific context we open it in. */
  20
  21         if (a->st_uid == 0) /* Transitioning from privileged to unprivileged is always fine */
  22                 return false;
  23
  24         return a->st_uid != b->st_uid; /* Otherwise we need to stay within the same UID */
  25 }
  26
  27 static int log_unsafe_transition(int a, int b, const char *path, ChaseFlags flags) {
  28         _cleanup_free_ char *n1 = NULL, *n2 = NULL, *user_a = NULL, *user_b = NULL;
  29         struct stat st;
  30
  31         if (!FLAGS_SET(flags, CHASE_WARN))
  32                 return -ENOLINK;
  33
  34         (void) fd_get_path(a, &n1);
  35         (void) fd_get_path(b, &n2);
  36
  37         if (fstat(a, &st) == 0)
  38                 user_a = uid_to_name(st.st_uid);
  39         if (fstat(b, &st) == 0)
  40                 user_b = uid_to_name(st.st_uid);
  41
  42         return log_warning_errno(SYNTHETIC_ERRNO(ENOLINK),
  43                                  "Detected unsafe path transition %s (owned by %s) %s %s (owned by %s) during canonicalization of %s.",
  44                                  strna(n1), strna(user_a), special_glyph(SPECIAL_GLYPH_ARROW_RIGHT), strna(n2), strna(user_b), path);
  45 }
  46
  47 static int log_autofs_mount_point(int fd, const char *path, ChaseFlags flags) {
  48         _cleanup_free_ char *n1 = NULL;
  49
  50         if (!FLAGS_SET(flags, CHASE_WARN))
  51                 return -EREMOTE;
  52
  53         (void) fd_get_path(fd, &n1);
  54
  55         return log_warning_errno(SYNTHETIC_ERRNO(EREMOTE),
  56                                  "Detected autofs mount point %s during canonicalization of %s.",
  57                                  strna(n1), path);
  58 }
  59
  60 static int log_prohibited_symlink(int fd, ChaseFlags flags) {
  61         _cleanup_free_ char *n1 = NULL;
  62
  63         assert(fd >= 0);
  64
  65         if (!FLAGS_SET(flags, CHASE_WARN))
  66                 return -EREMCHG;
  67
  68         (void) fd_get_path(fd, &n1);
  69
  70         return log_warning_errno(SYNTHETIC_ERRNO(EREMCHG),
  71                                  "Detected symlink where not symlink is allowed at %s, refusing.",
  72                                  strna(n1));
  73 }
  74
  75 int chaseat(
  76                 int dir_fd,
  77                 const char *path,
  78                 ChaseFlags flags,
  79                 char **ret_path,
  80                 int *ret_fd) {
  81
  82         _cleanup_free_ char *buffer = NULL, *done = NULL;
  83         _cleanup_close_ int fd = -EBADF, root_fd = -EBADF;
  84         unsigned max_follow = CHASE_MAX; /* how many symlinks to follow before giving up and returning ELOOP */
  85         bool exists = true, append_trail_slash = false;
  86         struct stat previous_stat;
  87         const char *todo;
  88         int r;
  89
  90         assert(path);
  91         assert(!FLAGS_SET(flags, CHASE_PREFIX_ROOT));
  92         assert(!FLAGS_SET(flags, CHASE_STEP|CHASE_EXTRACT_FILENAME));
  93         assert(!FLAGS_SET(flags, CHASE_TRAIL_SLASH|CHASE_EXTRACT_FILENAME));
  94         assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
  95
  96         /* Either the file may be missing, or we return an fd to the final object, but both make no sense */
  97         if ((flags & CHASE_NONEXISTENT))
  98                 assert(!ret_fd);
  99
 100         if ((flags & CHASE_STEP))
 101                 assert(!ret_fd);
 102
 103         if (isempty(path))
 104                 path = ".";
 105
 106         /* This function resolves symlinks of the path relative to the given directory file descriptor. If
 107          * CHASE_AT_RESOLVE_IN_ROOT is specified and a directory file descriptor is provided, symlinks
 108          * are resolved relative to the given directory file descriptor. Otherwise, they are resolved
 109          * relative to the root directory of the host.
 110          *
 111          * Note that when a positive directory file descriptor is provided and CHASE_AT_RESOLVE_IN_ROOT is
 112          * specified and we find an absolute symlink, it is resolved relative to given directory file
 113          * descriptor and not the root of the host. Also, when following relative symlinks, this functions
 114          * ensures they cannot be used to "escape" the given directory file descriptor. If a positive
 115          * directory file descriptor is provided, the "path" parameter is always interpreted relative to the
 116          * given directory file descriptor, even if it is absolute. If the given directory file descriptor is
 117          * AT_FDCWD and "path" is absolute, it is interpreted relative to the root directory of the host.
 118          *
 119          * If "dir_fd" is a valid directory fd, "path" is an absolute path and "ret_path" is not NULL, this
 120          * functions returns a relative path in "ret_path" because openat() like functions generally ignore
 121          * the directory fd if they are provided with an absolute path. On the other hand, if "dir_fd" is
 122          * AT_FDCWD and "path" is an absolute path, we return an absolute path in "ret_path" because
 123          * otherwise, if the caller passes the returned relative path to another openat() like function, it
 124          * would be resolved relative to the current working directory instead of to "/".
 125          *
 126          * Algorithmically this operates on two path buffers: "done" are the components of the path we
 127          * already processed and resolved symlinks, "." and ".." of. "todo" are the components of the path we
 128          * still need to process. On each iteration, we move one component from "todo" to "done", processing
 129          * its special meaning each time. We always keep an O_PATH fd to the component we are currently
 130          * processing, thus keeping lookup races to a minimum.
 131          *
 132          * Suggested usage: whenever you want to canonicalize a path, use this function. Pass the absolute
 133          * path you got as-is: fully qualified and relative to your host's root. Optionally, specify the
 134          * "dir_fd" parameter to tell this function what to do when encountering a symlink with an absolute
 135          * path as directory: resolve it relative to the given directory file descriptor.
 136          *
 137          * There are five ways to invoke this function:
 138          *
 139          * 1. Without CHASE_STEP or ret_fd: in this case the path is resolved and the normalized path is
 140          *    returned in `ret_path`. The return value is < 0 on error. If CHASE_NONEXISTENT is also set, 0
 141          *    is returned if the file doesn't exist, > 0 otherwise. If CHASE_NONEXISTENT is not set, >= 0 is
 142          *    returned if the destination was found, -ENOENT if it wasn't.
 143          *
 144          * 2. With ret_fd: in this case the destination is opened after chasing it as O_PATH and this file
 145          *    descriptor is returned as return value. This is useful to open files relative to some root
 146          *    directory. Note that the returned O_PATH file descriptors must be converted into a regular one
 147          *    (using fd_reopen() or such) before it can be used for reading/writing. ret_fd may not be
 148          *    combined with CHASE_NONEXISTENT.
 149          *
 150          * 3. With CHASE_STEP: in this case only a single step of the normalization is executed, i.e. only
 151          *    the first symlink or ".." component of the path is resolved, and the resulting path is
 152          *    returned. This is useful if a caller wants to trace the path through the file system verbosely.
 153          *    Returns < 0 on error, > 0 if the path is fully normalized, and == 0 for each normalization
 154          *    step. This may be combined with CHASE_NONEXISTENT, in which case 1 is returned when a component
 155          *    is not found.
 156          *
 157          * 4. With CHASE_SAFE: in this case the path must not contain unsafe transitions, i.e. transitions
 158          *    from unprivileged to privileged files or directories. In such cases the return value is
 159          *    -ENOLINK. If CHASE_WARN is also set, a warning describing the unsafe transition is emitted.
 160          *    CHASE_WARN cannot be used in PID 1.
 161          *
 162          * 5. With CHASE_NO_AUTOFS: in this case if an autofs mount point is encountered, path normalization
 163          *    is aborted and -EREMOTE is returned. If CHASE_WARN is also set, a warning showing the path of
 164          *    the mount point is emitted. CHASE_WARN cannot be used in PID 1.
 165          */
 166
 167         if (FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT)) {
 168                 /* If we get AT_FDCWD or dir_fd points to "/", then we always resolve symlinks relative to
 169                  * the host's root. Hence, CHASE_AT_RESOLVE_IN_ROOT is meaningless. */
 170
 171                 if (dir_fd >= 0)
 172                         r = dir_fd_is_root(dir_fd);
 173                 else
 174                         r = true;
 175                 if (r < 0)
 176                         return r;
 177                 if (r > 0)
 178                         flags &= ~CHASE_AT_RESOLVE_IN_ROOT;
 179         }
 180
 181         if (!(flags &
 182               (CHASE_AT_RESOLVE_IN_ROOT|CHASE_NONEXISTENT|CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_STEP|
 183                CHASE_PROHIBIT_SYMLINKS|CHASE_MKDIR_0755)) &&
 184             !ret_path && ret_fd) {
 185
 186                 /* Shortcut the ret_fd case if the caller isn't interested in the actual path and has no root
 187                  * set and doesn't care about any of the other special features we provide either. */
 188                 r = openat(dir_fd, buffer ?: path, O_PATH|O_CLOEXEC|((flags & CHASE_NOFOLLOW) ? O_NOFOLLOW : 0));
 189                 if (r < 0)
 190                         return -errno;
 191
 192                 *ret_fd = r;
 193                 return 0;
 194         }
 195
 196         if (!buffer) {
 197                 buffer = strdup(path);
 198                 if (!buffer)
 199                         return -ENOMEM;
 200         }
 201
 202         /* If we receive an absolute path together with AT_FDCWD, we need to return an absolute path, because
 203          * a relative path would be interpreted relative to the current working directory. */
 204         bool need_absolute = dir_fd == AT_FDCWD && path_is_absolute(path);
 205         if (need_absolute) {
 206                 done = strdup("/");
 207                 if (!done)
 208                         return -ENOMEM;
 209         }
 210
 211         /* If we get AT_FDCWD, we always resolve symlinks relative to the host's root. Only if a positive
 212          * directory file descriptor is provided will we look at CHASE_AT_RESOLVE_IN_ROOT to determine
 213          * whether to resolve symlinks in it or not. */
 214         if (dir_fd >= 0 && FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT))
 215                 root_fd = openat(dir_fd, ".", O_CLOEXEC|O_DIRECTORY|O_PATH);
 216         else
 217                 root_fd = open("/", O_CLOEXEC|O_DIRECTORY|O_PATH);
 218         if (root_fd < 0)
 219                 return -errno;
 220
 221         /* If a positive directory file descriptor is provided, always resolve the given path relative to it,
 222          * regardless of whether it is absolute or not. If we get AT_FDCWD, follow regular openat()
 223          * semantics, if the path is relative, resolve against the current working directory. Otherwise,
 224          * resolve against root. */
 225         if (dir_fd >= 0 || !path_is_absolute(path))
 226                 fd = openat(dir_fd, ".", O_CLOEXEC|O_DIRECTORY|O_PATH);
 227         else
 228                 fd = open("/", O_CLOEXEC|O_DIRECTORY|O_PATH);
 229         if (fd < 0)
 230                 return -errno;
 231
 232         if (fstat(fd, &previous_stat) < 0)
 233                 return -errno;
 234
 235         if (flags & CHASE_TRAIL_SLASH)
 236                 append_trail_slash = ENDSWITH_SET(buffer, "/", "/.");
 237
 238         for (todo = buffer;;) {
 239                 _cleanup_free_ char *first = NULL;
 240                 _cleanup_close_ int child = -EBADF;
 241                 struct stat st;
 242                 const char *e;
 243
 244                 r = path_find_first_component(&todo, /* accept_dot_dot= */ true, &e);
 245                 if (r < 0)
 246                         return r;
 247                 if (r == 0) { /* We reached the end. */
 248                         if (append_trail_slash)
 249                                 if (!strextend(&done, "/"))
 250                                         return -ENOMEM;
 251                         break;
 252                 }
 253
 254                 first = strndup(e, r);
 255                 if (!first)
 256                         return -ENOMEM;
 257
 258                 /* Two dots? Then chop off the last bit of what we already found out. */
 259                 if (path_equal(first, "..")) {
 260                         _cleanup_free_ char *parent = NULL;
 261                         _cleanup_close_ int fd_parent = -EBADF;
 262
 263                         /* If we already are at the top, then going up will not change anything. This is
 264                          * in-line with how the kernel handles this. */
 265                         if (empty_or_root(done) && FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT))
 266                                 continue;
 267
 268                         fd_parent = openat(fd, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH|O_DIRECTORY);
 269                         if (fd_parent < 0)
 270                                 return -errno;
 271
 272                         if (fstat(fd_parent, &st) < 0)
 273                                 return -errno;
 274
 275                         /* If we opened the same directory, that means we're at the host root directory, so
 276                          * going up won't change anything. */
 277                         if (st.st_dev == previous_stat.st_dev && st.st_ino == previous_stat.st_ino)
 278                                 continue;
 279
 280                         r = path_extract_directory(done, &parent);
 281                         if (r >= 0 || r == -EDESTADDRREQ)
 282                                 free_and_replace(done, parent);
 283                         else if (IN_SET(r, -EINVAL, -EADDRNOTAVAIL)) {
 284                                 /* If we're at the top of "dir_fd", start appending ".." to "done". */
 285                                 if (!path_extend(&done, ".."))
 286                                         return -ENOMEM;
 287                         } else
 288                                 return r;
 289
 290                         if (flags & CHASE_STEP)
 291                                 goto chased_one;
 292
 293                         if (flags & CHASE_SAFE) {
 294                                 if (unsafe_transition(&previous_stat, &st))
 295                                         return log_unsafe_transition(fd, fd_parent, path, flags);
 296
 297                                 previous_stat = st;
 298                         }
 299
 300                         if (FLAGS_SET(flags, CHASE_PARENT) && isempty(todo))
 301                                 break;
 302
 303                         close_and_replace(fd, fd_parent);
 304
 305                         continue;
 306                 }
 307
 308                 /* Otherwise let's see what this is. */
 309                 child = r = RET_NERRNO(openat(fd, first, O_CLOEXEC|O_NOFOLLOW|O_PATH));
 310                 if (r < 0) {
 311                         if (r != -ENOENT)
 312                                 return r;
 313
 314                         if (!isempty(todo) && !path_is_safe(todo))
 315                                 return r;
 316
 317                         if (FLAGS_SET(flags, CHASE_MKDIR_0755) && !isempty(todo)) {
 318                                 child = xopenat(fd, first, O_DIRECTORY|O_CREAT|O_EXCL|O_NOFOLLOW|O_CLOEXEC, 0755);
 319                                 if (child < 0)
 320                                         return child;
 321                         } else if (FLAGS_SET(flags, CHASE_PARENT) && isempty(todo)) {
 322                                 if (!path_extend(&done, first))
 323                                         return -ENOMEM;
 324
 325                                 break;
 326                         } else if (flags & CHASE_NONEXISTENT) {
 327                                 if (!path_extend(&done, first, todo))
 328                                         return -ENOMEM;
 329
 330                                 exists = false;
 331                                 break;
 332                         } else
 333                                 return r;
 334                 }
 335
 336                 if (fstat(child, &st) < 0)
 337                         return -errno;
 338                 if ((flags & CHASE_SAFE) &&
 339                     unsafe_transition(&previous_stat, &st))
 340                         return log_unsafe_transition(fd, child, path, flags);
 341
 342                 previous_stat = st;
 343
 344                 if ((flags & CHASE_NO_AUTOFS) &&
 345                     fd_is_fs_type(child, AUTOFS_SUPER_MAGIC) > 0)
 346                         return log_autofs_mount_point(child, path, flags);
 347
 348                 if (S_ISLNK(st.st_mode) && !((flags & CHASE_NOFOLLOW) && isempty(todo))) {
 349                         _cleanup_free_ char *destination = NULL;
 350
 351                         if (flags & CHASE_PROHIBIT_SYMLINKS)
 352                                 return log_prohibited_symlink(child, flags);
 353
 354                         /* This is a symlink, in this case read the destination. But let's make sure we
 355                          * don't follow symlinks without bounds. */
 356                         if (--max_follow <= 0)
 357                                 return -ELOOP;
 358
 359                         r = readlinkat_malloc(fd, first, &destination);
 360                         if (r < 0)
 361                                 return r;
 362                         if (isempty(destination))
 363                                 return -EINVAL;
 364
 365                         if (path_is_absolute(destination)) {
 366
 367                                 /* An absolute destination. Start the loop from the beginning, but use the
 368                                  * root file descriptor as base. */
 369
 370                                 safe_close(fd);
 371                                 fd = fd_reopen(root_fd, O_CLOEXEC|O_PATH|O_DIRECTORY);
 372                                 if (fd < 0)
 373                                         return fd;
 374
 375                                 if (flags & CHASE_SAFE) {
 376                                         if (fstat(fd, &st) < 0)
 377                                                 return -errno;
 378
 379                                         if (unsafe_transition(&previous_stat, &st))
 380                                                 return log_unsafe_transition(child, fd, path, flags);
 381
 382                                         previous_stat = st;
 383                                 }
 384
 385                                 r = free_and_strdup(&done, need_absolute ? "/" : NULL);
 386                                 if (r < 0)
 387                                         return r;
 388                         }
 389
 390                         /* Prefix what's left to do with what we just read, and start the loop again, but
 391                          * remain in the current directory. */
 392                         if (!path_extend(&destination, todo))
 393                                 return -ENOMEM;
 394
 395                         free_and_replace(buffer, destination);
 396                         todo = buffer;
 397
 398                         if (flags & CHASE_STEP)
 399                                 goto chased_one;
 400
 401                         continue;
 402                 }
 403
 404                 /* If this is not a symlink, then let's just add the name we read to what we already verified. */
 405                 if (!path_extend(&done, first))
 406                         return -ENOMEM;
 407
 408                 if (FLAGS_SET(flags, CHASE_PARENT) && isempty(todo))
 409                         break;
 410
 411                 /* And iterate again, but go one directory further down. */
 412                 close_and_replace(fd, child);
 413         }
 414
 415         if (flags & CHASE_PARENT) {
 416                 r = fd_verify_directory(fd);
 417                 if (r < 0)
 418                         return r;
 419         }
 420
 421         if (ret_path) {
 422                 if (FLAGS_SET(flags, CHASE_EXTRACT_FILENAME) && done) {
 423                         _cleanup_free_ char *f = NULL;
 424
 425                         r = path_extract_filename(done, &f);
 426                         if (r < 0 && r != -EDESTADDRREQ)
 427                                 return r;
 428
 429                         /* If we get EDESTADDRREQ we clear done and it will get reinitialized by the next block. */
 430                         free_and_replace(done, f);
 431                 }
 432
 433                 if (!done) {
 434                         done = strdup(append_trail_slash ? "./" : ".");
 435                         if (!done)
 436                                 return -ENOMEM;
 437                 }
 438
 439                 *ret_path = TAKE_PTR(done);
 440         }
 441
 442         if (ret_fd) {
 443                 /* Return the O_PATH fd we currently are looking to the caller. It can translate it to a
 444                  * proper fd by opening /proc/self/fd/xyz. */
 445
 446                 assert(fd >= 0);
 447                 *ret_fd = TAKE_FD(fd);
 448         }
 449
 450         if (flags & CHASE_STEP)
 451                 return 1;
 452
 453         return exists;
 454
 455 chased_one:
 456         if (ret_path) {
 457                 const char *e;
 458
 459                 if (!done) {
 460                         done = strdup(append_trail_slash ? "./" : ".");
 461                         if (!done)
 462                                 return -ENOMEM;
 463                 }
 464
 465                 /* todo may contain slashes at the beginning. */
 466                 r = path_find_first_component(&todo, /* accept_dot_dot= */ true, &e);
 467                 if (r < 0)
 468                         return r;
 469                 if (r == 0)
 470                         *ret_path = TAKE_PTR(done);
 471                 else {
 472                         char *c;
 473
 474                         c = path_join(done, e);
 475                         if (!c)
 476                                 return -ENOMEM;
 477
 478                         *ret_path = c;
 479                 }
 480         }
 481
 482         return 0;
 483 }
 484
 485 int chase(
 486                 const char *path,
 487                 const char *original_root,
 488                 ChaseFlags flags,
 489                 char **ret_path,
 490                 int *ret_fd) {
 491
 492         _cleanup_free_ char *root = NULL, *absolute = NULL, *p = NULL;
 493         _cleanup_close_ int fd = -EBADF, pfd = -EBADF;
 494         int r;
 495
 496         assert(path);
 497
 498         if (isempty(path))
 499                 return -EINVAL;
 500
 501         /* A root directory of "/" or "" is identical to none */
 502         if (empty_or_root(original_root))
 503                 original_root = NULL;
 504
 505         if (original_root) {
 506                 r = path_make_absolute_cwd(original_root, &root);
 507                 if (r < 0)
 508                         return r;
 509
 510                 /* Simplify the root directory, so that it has no duplicate slashes and nothing at the
 511                  * end. While we won't resolve the root path we still simplify it. Note that dropping the
 512                  * trailing slash should not change behaviour, since when opening it we specify O_DIRECTORY
 513                  * anyway. Moreover at the end of this function after processing everything we'll always turn
 514                  * the empty string back to "/". */
 515                 delete_trailing_chars(root, "/");
 516                 path_simplify(root);
 517
 518                 if (flags & CHASE_PREFIX_ROOT) {
 519                         absolute = path_join(root, path);
 520                         if (!absolute)
 521                                 return -ENOMEM;
 522                 }
 523         }
 524
 525         if (!absolute) {
 526                 r = path_make_absolute_cwd(path, &absolute);
 527                 if (r < 0)
 528                         return r;
 529         }
 530
 531         path = path_startswith(absolute, empty_to_root(root));
 532         if (!path)
 533                 return log_full_errno(flags & CHASE_WARN ? LOG_WARNING : LOG_DEBUG,
 534                                         SYNTHETIC_ERRNO(ECHRNG),
 535                                         "Specified path '%s' is outside of specified root directory '%s', refusing to resolve.",
 536                                         absolute, empty_to_root(root));
 537
 538         fd = open(empty_to_root(root), O_CLOEXEC|O_DIRECTORY|O_PATH);
 539         if (fd < 0)
 540                 return -errno;
 541
 542         if (!empty_or_root(root))
 543                 flags |= CHASE_AT_RESOLVE_IN_ROOT;
 544
 545         r = chaseat(fd, path, flags & ~CHASE_PREFIX_ROOT, ret_path ? &p : NULL, ret_fd ? &pfd : NULL);
 546         if (r < 0)
 547                 return r;
 548
 549         if (ret_path) {
 550                 if (!FLAGS_SET(flags, CHASE_EXTRACT_FILENAME)) {
 551                         _cleanup_free_ char *q = NULL;
 552
 553                         q = path_join(empty_to_root(root), p);
 554                         if (!q)
 555                                 return -ENOMEM;
 556
 557                         path_simplify(q);
 558
 559                         if (FLAGS_SET(flags, CHASE_TRAIL_SLASH) && ENDSWITH_SET(path, "/", "/."))
 560                                 if (!strextend(&q, "/"))
 561                                         return -ENOMEM;
 562
 563                         free_and_replace(p, q);
 564                 }
 565
 566                 *ret_path = TAKE_PTR(p);
 567         }
 568
 569         if (ret_fd)
 570                 *ret_fd = TAKE_FD(pfd);
 571
 572         return r;
 573 }
 574
 575 int chase_and_open(
 576                 const char *path,
 577                 const char *root,
 578                 ChaseFlags chase_flags,
 579                 int open_flags,
 580                 char **ret_path) {
 581
 582         _cleanup_close_ int path_fd = -EBADF;
 583         _cleanup_free_ char *p = NULL, *fname = NULL;
 584         mode_t mode = open_flags & O_DIRECTORY ? 0755 : 0644;
 585         const char *q;
 586         int r;
 587
 588         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 589
 590         if (empty_or_root(root) && !ret_path &&
 591             (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
 592                 /* Shortcut this call if none of the special features of this call are requested */
 593                 return RET_NERRNO(xopenat(AT_FDCWD, path,
 594                                           open_flags | (FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? O_NOFOLLOW : 0),
 595                                           mode));
 596
 597         r = chase(path, root, CHASE_PARENT|chase_flags, &p, &path_fd);
 598         if (r < 0)
 599                 return r;
 600         assert(path_fd >= 0);
 601
 602         assert_se(q = path_startswith(p, empty_to_root(root)));
 603         if (isempty(q))
 604                 q = ".";
 605
 606         r = path_extract_filename(q, &fname);
 607         if (r < 0 && r != -EADDRNOTAVAIL)
 608                 return r;
 609
 610         if (FLAGS_SET(chase_flags, CHASE_PARENT) || r == -EADDRNOTAVAIL)
 611                 r = fd_reopen(path_fd, open_flags);
 612         else
 613                 r = xopenat(path_fd, fname, open_flags|O_NOFOLLOW, mode);
 614         if (r < 0)
 615                 return r;
 616
 617         if (ret_path)
 618                 *ret_path = TAKE_PTR(p);
 619
 620         return r;
 621 }
 622
 623 int chase_and_opendir(
 624                 const char *path,
 625                 const char *root,
 626                 ChaseFlags chase_flags,
 627                 char **ret_path,
 628                 DIR **ret_dir) {
 629
 630         _cleanup_close_ int path_fd = -EBADF;
 631         _cleanup_free_ char *p = NULL;
 632         DIR *d;
 633         int r;
 634
 635         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 636         assert(ret_dir);
 637
 638         if (empty_or_root(root) && !ret_path &&
 639             (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0) {
 640                 /* Shortcut this call if none of the special features of this call are requested */
 641                 d = opendir(path);
 642                 if (!d)
 643                         return -errno;
 644
 645                 *ret_dir = d;
 646                 return 0;
 647         }
 648
 649         r = chase(path, root, chase_flags, ret_path ? &p : NULL, &path_fd);
 650         if (r < 0)
 651                 return r;
 652         assert(path_fd >= 0);
 653
 654         d = xopendirat(path_fd, ".", O_NOFOLLOW);
 655         if (!d)
 656                 return -errno;
 657
 658         if (ret_path)
 659                 *ret_path = TAKE_PTR(p);
 660
 661         *ret_dir = d;
 662         return 0;
 663 }
 664
 665 int chase_and_stat(
 666                 const char *path,
 667                 const char *root,
 668                 ChaseFlags chase_flags,
 669                 char **ret_path,
 670                 struct stat *ret_stat) {
 671
 672         _cleanup_close_ int path_fd = -EBADF;
 673         _cleanup_free_ char *p = NULL;
 674         int r;
 675
 676         assert(path);
 677         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 678         assert(ret_stat);
 679
 680         if (empty_or_root(root) && !ret_path &&
 681             (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
 682                 /* Shortcut this call if none of the special features of this call are requested */
 683                 return RET_NERRNO(fstatat(AT_FDCWD, path, ret_stat,
 684                                           FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0));
 685
 686         r = chase(path, root, chase_flags, ret_path ? &p : NULL, &path_fd);
 687         if (r < 0)
 688                 return r;
 689         assert(path_fd >= 0);
 690
 691         if (fstat(path_fd, ret_stat) < 0)
 692                 return -errno;
 693
 694         if (ret_path)
 695                 *ret_path = TAKE_PTR(p);
 696
 697         return 0;
 698 }
 699
 700 int chase_and_access(
 701                 const char *path,
 702                 const char *root,
 703                 ChaseFlags chase_flags,
 704                 int access_mode,
 705                 char **ret_path) {
 706
 707         _cleanup_close_ int path_fd = -EBADF;
 708         _cleanup_free_ char *p = NULL;
 709         int r;
 710
 711         assert(path);
 712         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 713
 714         if (empty_or_root(root) && !ret_path &&
 715             (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
 716                 /* Shortcut this call if none of the special features of this call are requested */
 717                 return RET_NERRNO(faccessat(AT_FDCWD, path, access_mode,
 718                                             FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0));
 719
 720         r = chase(path, root, chase_flags, ret_path ? &p : NULL, &path_fd);
 721         if (r < 0)
 722                 return r;
 723         assert(path_fd >= 0);
 724
 725         r = access_fd(path_fd, access_mode);
 726         if (r < 0)
 727                 return r;
 728
 729         if (ret_path)
 730                 *ret_path = TAKE_PTR(p);
 731
 732         return 0;
 733 }
 734
 735 int chase_and_fopen_unlocked(
 736                 const char *path,
 737                 const char *root,
 738                 ChaseFlags chase_flags,
 739                 const char *open_flags,
 740                 char **ret_path,
 741                 FILE **ret_file) {
 742
 743         _cleanup_free_ char *final_path = NULL;
 744         _cleanup_close_ int fd = -EBADF;
 745         int mode_flags, r;
 746
 747         assert(path);
 748         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP|CHASE_PARENT)));
 749         assert(open_flags);
 750         assert(ret_file);
 751
 752         mode_flags = fopen_mode_to_flags(open_flags);
 753         if (mode_flags < 0)
 754                 return mode_flags;
 755
 756         fd = chase_and_open(path, root, chase_flags, mode_flags, ret_path ? &final_path : NULL);
 757         if (fd < 0)
 758                 return fd;
 759
 760         r = take_fdopen_unlocked(&fd, open_flags, ret_file);
 761         if (r < 0)
 762                 return r;
 763
 764         if (ret_path)
 765                 *ret_path = TAKE_PTR(final_path);
 766
 767         return 0;
 768 }
 769
 770 int chase_and_unlink(
 771                 const char *path,
 772                 const char *root,
 773                 ChaseFlags chase_flags,
 774                 int unlink_flags,
 775                 char **ret_path) {
 776
 777         _cleanup_free_ char *p = NULL, *fname = NULL;
 778         _cleanup_close_ int fd = -EBADF;
 779         int r;
 780
 781         assert(path);
 782         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP|CHASE_PARENT)));
 783
 784         fd = chase_and_open(path, root, chase_flags|CHASE_PARENT|CHASE_NOFOLLOW, O_PATH|O_DIRECTORY|O_CLOEXEC, &p);
 785         if (fd < 0)
 786                 return fd;
 787
 788         r = path_extract_filename(p, &fname);
 789         if (r < 0)
 790                 return r;
 791
 792         if (unlinkat(fd, fname, unlink_flags) < 0)
 793                 return -errno;
 794
 795         if (ret_path)
 796                 *ret_path = TAKE_PTR(p);
 797
 798         return 0;
 799 }
 800
 801 int chase_and_open_parent(const char *path, const char *root, ChaseFlags chase_flags, char **ret_filename) {
 802         int pfd, r;
 803
 804         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 805
 806         r = chase(path, root, CHASE_PARENT|CHASE_EXTRACT_FILENAME|chase_flags, ret_filename, &pfd);
 807         if (r < 0)
 808                 return r;
 809
 810         return pfd;
 811 }
 812
 813 int chase_and_openat(
 814                 int dir_fd,
 815                 const char *path,
 816                 ChaseFlags chase_flags,
 817                 int open_flags,
 818                 char **ret_path) {
 819
 820         _cleanup_close_ int path_fd = -EBADF;
 821         _cleanup_free_ char *p = NULL, *fname = NULL;
 822         mode_t mode = open_flags & O_DIRECTORY ? 0755 : 0644;
 823         int r;
 824
 825         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 826
 827         if (dir_fd == AT_FDCWD && !ret_path &&
 828             (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
 829                 /* Shortcut this call if none of the special features of this call are requested */
 830                 return RET_NERRNO(xopenat(dir_fd, path,
 831                                           open_flags | (FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? O_NOFOLLOW : 0),
 832                                           mode));
 833
 834         r = chaseat(dir_fd, path, chase_flags|CHASE_PARENT, &p, &path_fd);
 835         if (r < 0)
 836                 return r;
 837
 838         r = path_extract_filename(p, &fname);
 839         if (r < 0 && r != -EDESTADDRREQ)
 840                 return r;
 841
 842         if (FLAGS_SET(chase_flags, CHASE_PARENT) || r == -EDESTADDRREQ)
 843                 r = fd_reopen(path_fd, open_flags);
 844         else
 845                 r = xopenat(path_fd, fname, open_flags|O_NOFOLLOW, mode);
 846         if (r < 0)
 847                 return r;
 848
 849         if (ret_path)
 850                 *ret_path = TAKE_PTR(p);
 851
 852         return r;
 853 }
 854
 855 int chase_and_opendirat(
 856                 int dir_fd,
 857                 const char *path,
 858                 ChaseFlags chase_flags,
 859                 char **ret_path,
 860                 DIR **ret_dir) {
 861
 862         _cleanup_close_ int path_fd = -EBADF;
 863         _cleanup_free_ char *p = NULL;
 864         DIR *d;
 865         int r;
 866
 867         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 868         assert(ret_dir);
 869
 870         if (dir_fd == AT_FDCWD && !ret_path &&
 871             (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0) {
 872                 /* Shortcut this call if none of the special features of this call are requested */
 873                 d = opendir(path);
 874                 if (!d)
 875                         return -errno;
 876
 877                 *ret_dir = d;
 878                 return 0;
 879         }
 880
 881         r = chaseat(dir_fd, path, chase_flags, ret_path ? &p : NULL, &path_fd);
 882         if (r < 0)
 883                 return r;
 884         assert(path_fd >= 0);
 885
 886         d = xopendirat(path_fd, ".", O_NOFOLLOW);
 887         if (!d)
 888                 return -errno;
 889
 890         if (ret_path)
 891                 *ret_path = TAKE_PTR(p);
 892
 893         *ret_dir = d;
 894         return 0;
 895 }
 896
 897 int chase_and_statat(
 898                 int dir_fd,
 899                 const char *path,
 900                 ChaseFlags chase_flags,
 901                 char **ret_path,
 902                 struct stat *ret_stat) {
 903
 904         _cleanup_close_ int path_fd = -EBADF;
 905         _cleanup_free_ char *p = NULL;
 906         int r;
 907
 908         assert(path);
 909         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 910         assert(ret_stat);
 911
 912         if (dir_fd == AT_FDCWD && !ret_path &&
 913             (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
 914                 /* Shortcut this call if none of the special features of this call are requested */
 915                 return RET_NERRNO(fstatat(AT_FDCWD, path, ret_stat,
 916                                           FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0));
 917
 918         r = chaseat(dir_fd, path, chase_flags, ret_path ? &p : NULL, &path_fd);
 919         if (r < 0)
 920                 return r;
 921         assert(path_fd >= 0);
 922
 923         if (fstat(path_fd, ret_stat) < 0)
 924                 return -errno;
 925
 926         if (ret_path)
 927                 *ret_path = TAKE_PTR(p);
 928
 929         return 0;
 930 }
 931
 932 int chase_and_accessat(
 933                 int dir_fd,
 934                 const char *path,
 935                 ChaseFlags chase_flags,
 936                 int access_mode,
 937                 char **ret_path) {
 938
 939         _cleanup_close_ int path_fd = -EBADF;
 940         _cleanup_free_ char *p = NULL;
 941         int r;
 942
 943         assert(path);
 944         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
 945
 946         if (dir_fd == AT_FDCWD && !ret_path &&
 947             (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
 948                 /* Shortcut this call if none of the special features of this call are requested */
 949                 return RET_NERRNO(faccessat(AT_FDCWD, path, access_mode,
 950                                             FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0));
 951
 952         r = chaseat(dir_fd, path, chase_flags, ret_path ? &p : NULL, &path_fd);
 953         if (r < 0)
 954                 return r;
 955         assert(path_fd >= 0);
 956
 957         r = access_fd(path_fd, access_mode);
 958         if (r < 0)
 959                 return r;
 960
 961         if (ret_path)
 962                 *ret_path = TAKE_PTR(p);
 963
 964         return 0;
 965 }
 966
 967 int chase_and_fopenat_unlocked(
 968                 int dir_fd,
 969                 const char *path,
 970                 ChaseFlags chase_flags,
 971                 const char *open_flags,
 972                 char **ret_path,
 973                 FILE **ret_file) {
 974
 975         _cleanup_free_ char *final_path = NULL;
 976         _cleanup_close_ int fd = -EBADF;
 977         int mode_flags, r;
 978
 979         assert(path);
 980         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP|CHASE_PARENT)));
 981         assert(open_flags);
 982         assert(ret_file);
 983
 984         mode_flags = fopen_mode_to_flags(open_flags);
 985         if (mode_flags < 0)
 986                 return mode_flags;
 987
 988         fd = chase_and_openat(dir_fd, path, chase_flags, mode_flags, ret_path ? &final_path : NULL);
 989         if (fd < 0)
 990                 return fd;
 991
 992         r = take_fdopen_unlocked(&fd, open_flags, ret_file);
 993         if (r < 0)
 994                 return r;
 995
 996         if (ret_path)
 997                 *ret_path = TAKE_PTR(final_path);
 998
 999         return 0;
1000 }
1001
1002 int chase_and_unlinkat(
1003                 int dir_fd,
1004                 const char *path,
1005                 ChaseFlags chase_flags,
1006                 int unlink_flags,
1007                 char **ret_path) {
1008
1009         _cleanup_free_ char *p = NULL, *fname = NULL;
1010         _cleanup_close_ int fd = -EBADF;
1011         int r;
1012
1013         assert(path);
1014         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP|CHASE_PARENT)));
1015
1016         fd = chase_and_openat(dir_fd, path, chase_flags|CHASE_PARENT|CHASE_NOFOLLOW, O_PATH|O_DIRECTORY|O_CLOEXEC, &p);
1017         if (fd < 0)
1018                 return fd;
1019
1020         r = path_extract_filename(p, &fname);
1021         if (r < 0)
1022                 return r;
1023
1024         if (unlinkat(fd, fname, unlink_flags) < 0)
1025                 return -errno;
1026
1027         if (ret_path)
1028                 *ret_path = TAKE_PTR(p);
1029
1030         return 0;
1031 }
1032
1033 int chase_and_open_parent_at(
1034                 int dir_fd,
1035                 const char *path,
1036                 ChaseFlags chase_flags,
1037                 char **ret_filename) {
1038
1039         int pfd, r;
1040
1041         assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
1042
1043         r = chaseat(dir_fd, path, CHASE_PARENT|CHASE_EXTRACT_FILENAME|chase_flags, ret_filename, &pfd);
1044         if (r < 0)
1045                 return r;
1046
1047         return pfd;
1048 }