src/chown-core.c

   1 /* chown-core.c -- core functions for changing ownership.
   2    Copyright (C) 2000-2015 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  16
  17 /* Extracted from chown.c/chgrp.c and librarified by Jim Meyering.  */
  18
  19 #include <config.h>
  20 #include <stdio.h>
  21 #include <sys/types.h>
  22 #include <pwd.h>
  23 #include <grp.h>
  24
  25 #include "system.h"
  26 #include "chown-core.h"
  27 #include "error.h"
  28 #include "ignore-value.h"
  29 #include "quote.h"
  30 #include "root-dev-ino.h"
  31 #include "xfts.h"
  32
  33 #define FTSENT_IS_DIRECTORY(E)  \
  34   ((E)->fts_info == FTS_D       \
  35    || (E)->fts_info == FTS_DC   \
  36    || (E)->fts_info == FTS_DP   \
  37    || (E)->fts_info == FTS_DNR)
  38
  39 enum RCH_status
  40   {
  41     /* we called fchown and close, and both succeeded */
  42     RC_ok = 2,
  43
  44     /* required_uid and/or required_gid are specified, but don't match */
  45     RC_excluded,
  46
  47     /* SAME_INODE check failed */
  48     RC_inode_changed,
  49
  50     /* open/fchown isn't needed, isn't safe, or doesn't work due to
  51        permissions problems; fall back on chown */
  52     RC_do_ordinary_chown,
  53
  54     /* open, fstat, fchown, or close failed */
  55     RC_error
  56   };
  57
  58 extern void
  59 chopt_init (struct Chown_option *chopt)
  60 {
  61   chopt->verbosity = V_off;
  62   chopt->root_dev_ino = NULL;
  63   chopt->affect_symlink_referent = true;
  64   chopt->recurse = false;
  65   chopt->force_silent = false;
  66   chopt->user_name = NULL;
  67   chopt->group_name = NULL;
  68 }
  69
  70 extern void
  71 chopt_free (struct Chown_option *chopt _GL_UNUSED)
  72 {
  73   /* Deliberately do not free chopt->user_name or ->group_name.
  74      They're not always allocated.  */
  75 }
  76
  77 /* Convert the numeric group-id, GID, to a string stored in xmalloc'd memory,
  78    and return it.  If there's no corresponding group name, use the decimal
  79    representation of the ID.  */
  80
  81 extern char *
  82 gid_to_name (gid_t gid)
  83 {
  84   char buf[INT_BUFSIZE_BOUND (intmax_t)];
  85   struct group *grp = getgrgid (gid);
  86   return xstrdup (grp ? grp->gr_name
  87                   : TYPE_SIGNED (gid_t) ? imaxtostr (gid, buf)
  88                   : umaxtostr (gid, buf));
  89 }
  90
  91 /* Convert the numeric user-id, UID, to a string stored in xmalloc'd memory,
  92    and return it.  If there's no corresponding user name, use the decimal
  93    representation of the ID.  */
  94
  95 extern char *
  96 uid_to_name (uid_t uid)
  97 {
  98   char buf[INT_BUFSIZE_BOUND (intmax_t)];
  99   struct passwd *pwd = getpwuid (uid);
 100   return xstrdup (pwd ? pwd->pw_name
 101                   : TYPE_SIGNED (uid_t) ? imaxtostr (uid, buf)
 102                   : umaxtostr (uid, buf));
 103 }
 104
 105 /* Allocate a string representing USER and GROUP.  */
 106
 107 static char *
 108 user_group_str (char const *user, char const *group)
 109 {
 110   char *spec = NULL;
 111
 112   if (user)
 113     {
 114       if (group)
 115         {
 116           spec = xmalloc (strlen (user) + 1 + strlen (group) + 1);
 117           stpcpy (stpcpy (stpcpy (spec, user), ":"), group);
 118         }
 119       else
 120         {
 121           spec = xstrdup (user);
 122         }
 123     }
 124   else if (group)
 125     {
 126       spec = xstrdup (group);
 127     }
 128
 129   return spec;
 130 }
 131
 132 /* Tell the user how/if the user and group of FILE have been changed.
 133    If USER is NULL, give the group-oriented messages.
 134    CHANGED describes what (if anything) has happened. */
 135
 136 static void
 137 describe_change (const char *file, enum Change_status changed,
 138                  char const *old_user, char const *old_group,
 139                  char const *user, char const *group)
 140 {
 141   const char *fmt;
 142   char *old_spec;
 143   char *spec;
 144
 145   if (changed == CH_NOT_APPLIED)
 146     {
 147       printf (_("neither symbolic link %s nor referent has been changed\n"),
 148               quote (file));
 149       return;
 150     }
 151
 152   spec = user_group_str (user, group);
 153   old_spec = user_group_str (user ? old_user : NULL, group ? old_group : NULL);
 154
 155   switch (changed)
 156     {
 157     case CH_SUCCEEDED:
 158       fmt = (user ? _("changed ownership of %s from %s to %s\n")
 159              : group ? _("changed group of %s from %s to %s\n")
 160              : _("no change to ownership of %s\n"));
 161       break;
 162     case CH_FAILED:
 163       if (old_spec)
 164         {
 165           fmt = (user ? _("failed to change ownership of %s from %s to %s\n")
 166                  : group ? _("failed to change group of %s from %s to %s\n")
 167                  : _("failed to change ownership of %s\n"));
 168         }
 169       else
 170         {
 171           fmt = (user ? _("failed to change ownership of %s to %s\n")
 172                  : group ? _("failed to change group of %s to %s\n")
 173                  : _("failed to change ownership of %s\n"));
 174           free (old_spec);
 175           old_spec = spec;
 176           spec = NULL;
 177         }
 178       break;
 179     case CH_NO_CHANGE_REQUESTED:
 180       fmt = (user ? _("ownership of %s retained as %s\n")
 181              : group ? _("group of %s retained as %s\n")
 182              : _("ownership of %s retained\n"));
 183       break;
 184     default:
 185       abort ();
 186     }
 187
 188   printf (fmt, quote (file), old_spec, spec);
 189
 190   free (old_spec);
 191   free (spec);
 192 }
 193
 194 /* Change the owner and/or group of the FILE to UID and/or GID (safely)
 195    only if REQUIRED_UID and REQUIRED_GID match the owner and group IDs
 196    of FILE.  ORIG_ST must be the result of 'stat'ing FILE.
 197
 198    The 'safely' part above means that we can't simply use chown(2),
 199    since FILE might be replaced with some other file between the time
 200    of the preceding stat/lstat and this chown call.  So here we open
 201    FILE and do everything else via the resulting file descriptor.
 202    We first call fstat and verify that the dev/inode match those from
 203    the preceding stat call, and only then, if appropriate (given the
 204    required_uid and required_gid constraints) do we call fchown.
 205
 206    Return RC_do_ordinary_chown if we can't open FILE, or if FILE is a
 207    special file that might have undesirable side effects when opening.
 208    In this case the caller can use the less-safe ordinary chown.
 209
 210    Return one of the RCH_status values.  */
 211
 212 static enum RCH_status
 213 restricted_chown (int cwd_fd, char const *file,
 214                   struct stat const *orig_st,
 215                   uid_t uid, gid_t gid,
 216                   uid_t required_uid, gid_t required_gid)
 217 {
 218   enum RCH_status status = RC_ok;
 219   struct stat st;
 220   int open_flags = O_NONBLOCK | O_NOCTTY;
 221   int fd;
 222
 223   if (required_uid == (uid_t) -1 && required_gid == (gid_t) -1)
 224     return RC_do_ordinary_chown;
 225
 226   if (! S_ISREG (orig_st->st_mode))
 227     {
 228       if (S_ISDIR (orig_st->st_mode))
 229         open_flags |= O_DIRECTORY;
 230       else
 231         return RC_do_ordinary_chown;
 232     }
 233
 234   fd = openat (cwd_fd, file, O_RDONLY | open_flags);
 235   if (! (0 <= fd
 236          || (errno == EACCES && S_ISREG (orig_st->st_mode)
 237              && 0 <= (fd = openat (cwd_fd, file, O_WRONLY | open_flags)))))
 238     return (errno == EACCES ? RC_do_ordinary_chown : RC_error);
 239
 240   if (fstat (fd, &st) != 0)
 241     status = RC_error;
 242   else if (! SAME_INODE (*orig_st, st))
 243     status = RC_inode_changed;
 244   else if ((required_uid == (uid_t) -1 || required_uid == st.st_uid)
 245            && (required_gid == (gid_t) -1 || required_gid == st.st_gid))
 246     {
 247       if (fchown (fd, uid, gid) == 0)
 248         {
 249           status = (close (fd) == 0
 250                     ? RC_ok : RC_error);
 251           return status;
 252         }
 253       else
 254         {
 255           status = RC_error;
 256         }
 257     }
 258
 259   int saved_errno = errno;
 260   close (fd);
 261   errno = saved_errno;
 262   return status;
 263 }
 264
 265 /* Change the owner and/or group of the file specified by FTS and ENT
 266    to UID and/or GID as appropriate.
 267    If REQUIRED_UID is not -1, then skip files with any other user ID.
 268    If REQUIRED_GID is not -1, then skip files with any other group ID.
 269    CHOPT specifies additional options.
 270    Return true if successful.  */
 271 static bool
 272 change_file_owner (FTS *fts, FTSENT *ent,
 273                    uid_t uid, gid_t gid,
 274                    uid_t required_uid, gid_t required_gid,
 275                    struct Chown_option const *chopt)
 276 {
 277   char const *file_full_name = ent->fts_path;
 278   char const *file = ent->fts_accpath;
 279   struct stat const *file_stats;
 280   struct stat stat_buf;
 281   bool ok = true;
 282   bool do_chown;
 283   bool symlink_changed = true;
 284
 285   switch (ent->fts_info)
 286     {
 287     case FTS_D:
 288       if (chopt->recurse)
 289         {
 290           if (ROOT_DEV_INO_CHECK (chopt->root_dev_ino, ent->fts_statp))
 291             {
 292               /* This happens e.g., with "chown -R --preserve-root 0 /"
 293                  and with "chown -RH --preserve-root 0 symlink-to-root".  */
 294               ROOT_DEV_INO_WARN (file_full_name);
 295               /* Tell fts not to traverse into this hierarchy.  */
 296               fts_set (fts, ent, FTS_SKIP);
 297               /* Ensure that we do not process "/" on the second visit.  */
 298               ignore_value (fts_read (fts));
 299               return false;
 300             }
 301           return true;
 302         }
 303       break;
 304
 305     case FTS_DP:
 306       if (! chopt->recurse)
 307         return true;
 308       break;
 309
 310     case FTS_NS:
 311       /* For a top-level file or directory, this FTS_NS (stat failed)
 312          indicator is determined at the time of the initial fts_open call.
 313          With programs like chmod, chown, and chgrp, that modify
 314          permissions, it is possible that the file in question is
 315          accessible when control reaches this point.  So, if this is
 316          the first time we've seen the FTS_NS for this file, tell
 317          fts_read to stat it "again".  */
 318       if (ent->fts_level == 0 && ent->fts_number == 0)
 319         {
 320           ent->fts_number = 1;
 321           fts_set (fts, ent, FTS_AGAIN);
 322           return true;
 323         }
 324       if (! chopt->force_silent)
 325         error (0, ent->fts_errno, _("cannot access %s"),
 326                quote (file_full_name));
 327       ok = false;
 328       break;
 329
 330     case FTS_ERR:
 331       if (! chopt->force_silent)
 332         error (0, ent->fts_errno, "%s", quote (file_full_name));
 333       ok = false;
 334       break;
 335
 336     case FTS_DNR:
 337       if (! chopt->force_silent)
 338         error (0, ent->fts_errno, _("cannot read directory %s"),
 339                quote (file_full_name));
 340       ok = false;
 341       break;
 342
 343     case FTS_DC:                /* directory that causes cycles */
 344       if (cycle_warning_required (fts, ent))
 345         {
 346           emit_cycle_warning (file_full_name);
 347           return false;
 348         }
 349       break;
 350
 351     default:
 352       break;
 353     }
 354
 355   if (!ok)
 356     {
 357       do_chown = false;
 358       file_stats = NULL;
 359     }
 360   else if (required_uid == (uid_t) -1 && required_gid == (gid_t) -1
 361            && chopt->verbosity == V_off
 362            && ! chopt->root_dev_ino
 363            && ! chopt->affect_symlink_referent)
 364     {
 365       do_chown = true;
 366       file_stats = ent->fts_statp;
 367     }
 368   else
 369     {
 370       file_stats = ent->fts_statp;
 371
 372       /* If this is a symlink and we're dereferencing them,
 373          stat it to get info on the referent.  */
 374       if (chopt->affect_symlink_referent && S_ISLNK (file_stats->st_mode))
 375         {
 376           if (fstatat (fts->fts_cwd_fd, file, &stat_buf, 0) != 0)
 377             {
 378               if (! chopt->force_silent)
 379                 error (0, errno, _("cannot dereference %s"),
 380                        quote (file_full_name));
 381               ok = false;
 382             }
 383
 384           file_stats = &stat_buf;
 385         }
 386
 387       do_chown = (ok
 388                   && (required_uid == (uid_t) -1
 389                       || required_uid == file_stats->st_uid)
 390                   && (required_gid == (gid_t) -1
 391                       || required_gid == file_stats->st_gid));
 392     }
 393
 394   /* This happens when chown -LR --preserve-root encounters a symlink-to-/.  */
 395   if (ok
 396       && FTSENT_IS_DIRECTORY (ent)
 397       && ROOT_DEV_INO_CHECK (chopt->root_dev_ino, file_stats))
 398     {
 399       ROOT_DEV_INO_WARN (file_full_name);
 400       return false;
 401     }
 402
 403   if (do_chown)
 404     {
 405       if ( ! chopt->affect_symlink_referent)
 406         {
 407           ok = (lchownat (fts->fts_cwd_fd, file, uid, gid) == 0);
 408
 409           /* Ignore any error due to lack of support; POSIX requires
 410              this behavior for top-level symbolic links with -h, and
 411              implies that it's required for all symbolic links.  */
 412           if (!ok && errno == EOPNOTSUPP)
 413             {
 414               ok = true;
 415               symlink_changed = false;
 416             }
 417         }
 418       else
 419         {
 420           /* If possible, avoid a race condition with --from=O:G and without the
 421              (-h) --no-dereference option.  If fts's stat call determined
 422              that the uid/gid of FILE matched the --from=O:G-selected
 423              owner and group IDs, blindly using chown(2) here could lead
 424              chown(1) or chgrp(1) mistakenly to dereference a *symlink*
 425              to an arbitrary file that an attacker had moved into the
 426              place of FILE during the window between the stat and
 427              chown(2) calls.  If FILE is a regular file or a directory
 428              that can be opened, this race condition can be avoided safely.  */
 429
 430           enum RCH_status err
 431             = restricted_chown (fts->fts_cwd_fd, file, file_stats, uid, gid,
 432                                 required_uid, required_gid);
 433           switch (err)
 434             {
 435             case RC_ok:
 436               break;
 437
 438             case RC_do_ordinary_chown:
 439               ok = (chownat (fts->fts_cwd_fd, file, uid, gid) == 0);
 440               break;
 441
 442             case RC_error:
 443               ok = false;
 444               break;
 445
 446             case RC_inode_changed:
 447               /* FIXME: give a diagnostic in this case?  */
 448             case RC_excluded:
 449               do_chown = false;
 450               ok = false;
 451               break;
 452
 453             default:
 454               abort ();
 455             }
 456         }
 457
 458       /* On some systems (e.g., GNU/Linux 2.4.x),
 459          the chown function resets the 'special' permission bits.
 460          Do *not* restore those bits;  doing so would open a window in
 461          which a malicious user, M, could subvert a chown command run
 462          by some other user and operating on files in a directory
 463          where M has write access.  */
 464
 465       if (do_chown && !ok && ! chopt->force_silent)
 466         error (0, errno, (uid != (uid_t) -1
 467                           ? _("changing ownership of %s")
 468                           : _("changing group of %s")),
 469                quote (file_full_name));
 470     }
 471
 472   if (chopt->verbosity != V_off)
 473     {
 474       bool changed =
 475         ((do_chown && ok && symlink_changed)
 476          && ! ((uid == (uid_t) -1 || uid == file_stats->st_uid)
 477                && (gid == (gid_t) -1 || gid == file_stats->st_gid)));
 478
 479       if (changed || chopt->verbosity == V_high)
 480         {
 481           enum Change_status ch_status =
 482             (!ok ? CH_FAILED
 483              : !symlink_changed ? CH_NOT_APPLIED
 484              : !changed ? CH_NO_CHANGE_REQUESTED
 485              : CH_SUCCEEDED);
 486           char *old_usr = file_stats ? uid_to_name (file_stats->st_uid) : NULL;
 487           char *old_grp = file_stats ? gid_to_name (file_stats->st_gid) : NULL;
 488           describe_change (file_full_name, ch_status,
 489                            old_usr, old_grp,
 490                            chopt->user_name, chopt->group_name);
 491           free (old_usr);
 492           free (old_grp);
 493         }
 494     }
 495
 496   if ( ! chopt->recurse)
 497     fts_set (fts, ent, FTS_SKIP);
 498
 499   return ok;
 500 }
 501
 502 /* Change the owner and/or group of the specified FILES.
 503    BIT_FLAGS specifies how to treat each symlink-to-directory
 504    that is encountered during a recursive traversal.
 505    CHOPT specifies additional options.
 506    If UID is not -1, then change the owner id of each file to UID.
 507    If GID is not -1, then change the group id of each file to GID.
 508    If REQUIRED_UID and/or REQUIRED_GID is not -1, then change only
 509    files with user ID and group ID that match the non-(-1) value(s).
 510    Return true if successful.  */
 511 extern bool
 512 chown_files (char **files, int bit_flags,
 513              uid_t uid, gid_t gid,
 514              uid_t required_uid, gid_t required_gid,
 515              struct Chown_option const *chopt)
 516 {
 517   bool ok = true;
 518
 519   /* Use lstat and stat only if they're needed.  */
 520   int stat_flags = ((required_uid != (uid_t) -1 || required_gid != (gid_t) -1
 521                      || chopt->affect_symlink_referent
 522                      || chopt->verbosity != V_off)
 523                     ? 0
 524                     : FTS_NOSTAT);
 525
 526   FTS *fts = xfts_open (files, bit_flags | stat_flags, NULL);
 527
 528   while (1)
 529     {
 530       FTSENT *ent;
 531
 532       ent = fts_read (fts);
 533       if (ent == NULL)
 534         {
 535           if (errno != 0)
 536             {
 537               /* FIXME: try to give a better message  */
 538               if (! chopt->force_silent)
 539                 error (0, errno, _("fts_read failed"));
 540               ok = false;
 541             }
 542           break;
 543         }
 544
 545       ok &= change_file_owner (fts, ent, uid, gid,
 546                                required_uid, required_gid, chopt);
 547     }
 548
 549   if (fts_close (fts) != 0)
 550     {
 551       error (0, errno, _("fts_close failed"));
 552       ok = false;
 553     }
 554
 555   return ok;
 556 }