path: root/src/chown-core.c

/* chown-core.c -- core functions for changing ownership.
   Copyright (C) 2000, 2002, 2003, 2004, 2005, 2006 Free Software Foundation.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/* Extracted from chown.c/chgrp.c and librarified by Jim Meyering.  */

#include <config.h>
#include <stdio.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>

#include "system.h"
#include "chown-core.h"
#include "error.h"
#include "inttostr.h"
#include "openat.h"
#include "quote.h"
#include "root-dev-ino.h"
#include "xfts.h"

enum RCH_status
  {
    /* we called fchown and close, and both succeeded */
    RC_ok = 2,

    /* required_uid and/or required_gid are specified, but don't match */
    RC_excluded,

    /* SAME_INODE check failed */
    RC_inode_changed,

    /* open/fchown isn't needed, isn't safe, or doesn't work due to
       permissions problems; fall back on chown */
    RC_do_ordinary_chown,

    /* open, fstat, fchown, or close failed */
    RC_error
  };

extern void
chopt_init (struct Chown_option *chopt)
{
  chopt->verbosity = V_off;
  chopt->root_dev_ino = NULL;
  chopt->affect_symlink_referent = true;
  chopt->recurse = false;
  chopt->force_silent = false;
  chopt->user_name = NULL;
  chopt->group_name = NULL;
}

extern void
chopt_free (struct Chown_option *chopt ATTRIBUTE_UNUSED)
{
  /* Deliberately do not free chopt->user_name or ->group_name.
     They're not always allocated.  */
}

/* Convert the numeric group-id, GID, to a string stored in xmalloc'd memory,
   and return it.  If there's no corresponding group name, use the decimal
   representation of the ID.  */

extern char *
gid_to_name (gid_t gid)
{
  char buf[INT_BUFSIZE_BOUND (intmax_t)];
  struct group *grp = getgrgid (gid);
  return xstrdup (grp ? grp->gr_name
		  : TYPE_SIGNED (gid_t) ? imaxtostr (gid, buf)
		  : umaxtostr (gid, buf));
}

/* Convert the numeric user-id, UID, to a string stored in xmalloc'd memory,
   and return it.  If there's no corresponding user name, use the decimal
   representation of the ID.  */

extern char *
uid_to_name (uid_t uid)
{
  char buf[INT_BUFSIZE_BOUND (intmax_t)];
  struct passwd *pwd = getpwuid (uid);
  return xstrdup (pwd ? pwd->pw_name
		  : TYPE_SIGNED (uid_t) ? imaxtostr (uid, buf)
		  : umaxtostr (uid, buf));
}

/* Tell the user how/if the user and group of FILE have been changed.
   If USER is NULL, give the group-oriented messages.
   CHANGED describes what (if anything) has happened. */

static void
describe_change (const char *file, enum Change_status changed,
		 char const *user, char const *group)
{
  const char *fmt;
  char const *spec;
  char *spec_allocated = NULL;

  if (changed == CH_NOT_APPLIED)
    {
      printf (_("neither symbolic link %s nor referent has been changed\n"),
	      quote (file));
      return;
    }

  if (user)
    {
      if (group)
	{
	  spec_allocated = xmalloc (strlen (user) + 1 + strlen (group) + 1);
	  stpcpy (stpcpy (stpcpy (spec_allocated, user), ":"), group);
	  spec = spec_allocated;
	}
      else
	{
	  spec = user;
	}
    }
  else
    {
      spec = group;
    }

  switch (changed)
    {
    case CH_SUCCEEDED:
      fmt = (user ? _("changed ownership of %s to %s\n")
	     : group ? _("changed group of %s to %s\n")
	     : _("no change to ownership of %s\n"));
      break;
    case CH_FAILED:
      fmt = (user ? _("failed to change ownership of %s to %s\n")
	     : group ? _("failed to change group of %s to %s\n")
	     : _("failed to change ownership of %s\n"));
      break;
    case CH_NO_CHANGE_REQUESTED:
      fmt = (user ? _("ownership of %s retained as %s\n")
	     : group ? _("group of %s retained as %s\n")
	     : _("ownership of %s retained\n"));
      break;
    default:
      abort ();
    }

  printf (fmt, quote (file), spec);

  free (spec_allocated);
}

/* Change the owner and/or group of the FILE to UID and/or GID (safely)
   only if REQUIRED_UID and REQUIRED_GID match the owner and group IDs
   of FILE.  ORIG_ST must be the result of `stat'ing FILE.

   The `safely' part above means that we can't simply use chown(2),
   since FILE might be replaced with some other file between the time
   of the preceding stat/lstat and this chown call.  So here we open
   FILE and do everything else via the resulting file descriptor.
   We first call fstat and verify that the dev/inode match those from
   the preceding stat call, and only then, if appropriate (given the
   required_uid and required_gid constraints) do we call fchown.

   Return RC_do_ordinary_chown if we can't open FILE, or if FILE is a
   special file that might have undesirable side effects when opening.
   In this case the caller can use the less-safe ordinary chown.

   Return one of the RCH_status values.  */

static enum RCH_status
restricted_chown (int cwd_fd, char const *file,
		  struct stat const *orig_st,
		  uid_t uid, gid_t gid,
		  uid_t required_uid, gid_t required_gid)
{
  enum RCH_status status = RC_ok;
  struct stat st;
  int open_flags = O_NONBLOCK | O_NOCTTY;
  int fd;

  if (required_uid == (uid_t) -1 && required_gid == (gid_t) -1)
    return RC_do_ordinary_chown;

  if (! S_ISREG (orig_st->st_mode))
    {
      if (S_ISDIR (orig_st->st_mode))
	open_flags |= O_DIRECTORY;
      else
	return RC_do_ordinary_chown;
    }

  fd = openat (cwd_fd, file, O_RDONLY | open_flags);
  if (! (0 <= fd
	 || (errno == EACCES && S_ISREG (orig_st->st_mode)
	     && 0 <= (fd = openat (cwd_fd, file, O_WRONLY | open_flags)))))
    return (errno == EACCES ? RC_do_ordinary_chown : RC_error);

  if (fstat (fd, &st) != 0)
    status = RC_error;
  else if (! SAME_INODE (*orig_st, st))
    status = RC_inode_changed;
  else if ((required_uid == (uid_t) -1 || required_uid == st.st_uid)
	   && (required_gid == (gid_t) -1 || required_gid == st.st_gid))
    {
      if (fchown (fd, uid, gid) == 0)
	{
	  status = (close (fd) == 0
		    ? RC_ok : RC_error);
	  return status;
	}
      else
	{
	  status = RC_error;
	}
    }

  { /* FIXME: remove these curly braces when we assume C99.  */
    int saved_errno = errno;
    close (fd);
    errno = saved_errno;
    return status;
  }
}

/* Change the owner and/or group of the file specified by FTS and ENT
   to UID and/or GID as appropriate.
   If REQUIRED_UID is not -1, then skip files with any other user ID.
   If REQUIRED_GID is not -1, then skip files with any other group ID.
   CHOPT specifies additional options.
   Return true if successful.  */
static bool
change_file_owner (FTS *fts, FTSENT *ent,
		   uid_t uid, gid_t gid,
		   uid_t required_uid, gid_t required_gid,
		   struct Chown_option const *chopt)
{
  char const *file_full_name = ent->fts_path;
  char const *file = ent->fts_accpath;
  struct stat const *file_stats;
  struct stat stat_buf;
  bool ok = true;
  bool do_chown;
  bool symlink_changed = true;

  switch (ent->fts_info)
    {
    case FTS_D:
      if (chopt->recurse)
	return true;
      break;

    case FTS_DP:
      if (! chopt->recurse)
	return true;
      break;

    case FTS_NS:
      error (0, ent->fts_errno, _("cannot access %s"), quote (file_full_name));
      ok = false;
      break;

    case FTS_ERR:
      error (0, ent->fts_errno, _("%s"), quote (file_full_name));
      ok = false;
      break;

    case FTS_DNR:
      error (0, ent->fts_errno, _("cannot read directory %s"),
	     quote (file_full_name));
      ok = false;
      break;

    default:
      break;
    }

  if (!ok)
    {
      do_chown = false;
      file_stats = NULL;
    }
  else if (required_uid == (uid_t) -1 && required_gid == (gid_t) -1
	   && chopt->verbosity == V_off && ! chopt->root_dev_ino)
    {
      do_chown = true;
      file_stats = ent->fts_statp;
    }
  else
    {
      file_stats = ent->fts_statp;

      /* If this is a symlink and we're dereferencing them,
	 stat it to get info on the referent.  */
      if (S_ISLNK (file_stats->st_mode) && chopt->affect_symlink_referent)
	{
	  if (stat (file, &stat_buf) != 0)
	    {
	      error (0, errno, _("cannot dereference %s"),
		     quote (file_full_name));
	      ok = false;
	    }

	  file_stats = &stat_buf;
	}

      do_chown = (ok
		  && (required_uid == (uid_t) -1
		      || required_uid == file_stats->st_uid)
		  && (required_gid == (gid_t) -1
		      || required_gid == file_stats->st_gid));
    }

  if (do_chown && ROOT_DEV_INO_CHECK (chopt->root_dev_ino, file_stats))
    {
      ROOT_DEV_INO_WARN (file_full_name);
      ok = do_chown = false;
    }

  if (do_chown)
    {
      if ( ! chopt->affect_symlink_referent)
	{
	  ok = (lchownat (fts->fts_cwd_fd, file, uid, gid) == 0);

	  /* Ignore any error due to lack of support; POSIX requires
	     this behavior for top-level symbolic links with -h, and
	     implies that it's required for all symbolic links.  */
	  if (!ok && errno == EOPNOTSUPP)
	    {
	      ok = true;
	      symlink_changed = false;
	    }
	}
      else
	{
	  /* If possible, avoid a race condition with --from=O:G and without the
	     (-h) --no-dereference option.  If fts's stat call determined
	     that the uid/gid of FILE matched the --from=O:G-selected
	     owner and group IDs, blindly using chown(2) here could lead
	     chown(1) or chgrp(1) mistakenly to dereference a *symlink*
	     to an arbitrary file that an attacker had moved into the
	     place of FILE during the window between the stat and
	     chown(2) calls.  If FILE is a regular file or a directory
	     that can be opened, this race condition can be avoided safely.  */

	  enum RCH_status err
	    = restricted_chown (fts->fts_cwd_fd, file, file_stats, uid, gid,
				required_uid, required_gid);
	  switch (err)
	    {
	    case RC_ok:
	      break;

	    case RC_do_ordinary_chown:
	      ok = (chownat (fts->fts_cwd_fd, file, uid, gid) == 0);
	      break;

	    case RC_error:
	      ok = false;
	      break;

	    case RC_inode_changed:
	      /* FIXME: give a diagnostic in this case?  */
	    case RC_excluded:
	      do_chown = false;
	      ok = false;
	      break;

	    default:
	      abort ();
	    }
	}

      /* On some systems (e.g., Linux-2.4.x),
	 the chown function resets the `special' permission bits.
	 Do *not* restore those bits;  doing so would open a window in
	 which a malicious user, M, could subvert a chown command run
	 by some other user and operating on files in a directory
	 where M has write access.  */

      if (do_chown && !ok && ! chopt->force_silent)
	error (0, errno, (uid != (uid_t) -1
			  ? _("changing ownership of %s")
			  : _("changing group of %s")),
	       quote (file_full_name));
    }

  if (chopt->verbosity != V_off)
    {
      bool changed =
	((do_chown & ok & symlink_changed)
	 && ! ((uid == (uid_t) -1 || uid == file_stats->st_uid)
	       && (gid == (gid_t) -1 || gid == file_stats->st_gid)));

      if (changed || chopt->verbosity == V_high)
	{
	  enum Change_status ch_status =
	    (!ok ? CH_FAILED
	     : !symlink_changed ? CH_NOT_APPLIED
	     : !changed ? CH_NO_CHANGE_REQUESTED
	     : CH_SUCCEEDED);
	  describe_change (file_full_name, ch_status,
			   chopt->user_name, chopt->group_name);
	}
    }

  if ( ! chopt->recurse)
    fts_set (fts, ent, FTS_SKIP);

  return ok;
}

/* Change the owner and/or group of the specified FILES.
   BIT_FLAGS specifies how to treat each symlink-to-directory
   that is encountered during a recursive traversal.
   CHOPT specifies additional options.
   If UID is not -1, then change the owner id of each file to UID.
   If GID is not -1, then change the group id of each file to GID.
   If REQUIRED_UID and/or REQUIRED_GID is not -1, then change only
   files with user ID and group ID that match the non-(-1) value(s).
   Return true if successful.  */
extern bool
chown_files (char **files, int bit_flags,
	     uid_t uid, gid_t gid,
	     uid_t required_uid, gid_t required_gid,
	     struct Chown_option const *chopt)
{
  bool ok = true;

  /* Use lstat and stat only if they're needed.  */
  int stat_flags = ((required_uid != (uid_t) -1 || required_gid != (gid_t) -1
		     || chopt->verbosity != V_off || chopt->root_dev_ino)
		    ? 0
		    : FTS_NOSTAT);

  FTS *fts = xfts_open (files, bit_flags | stat_flags, NULL);

  while (1)
    {
      FTSENT *ent;

      ent = fts_read (fts);
      if (ent == NULL)
	{
	  if (errno != 0)
	    {
	      /* FIXME: try to give a better message  */
	      error (0, errno, _("fts_read failed"));
	      ok = false;
	    }
	  break;
	}

      ok &= change_file_owner (fts, ent, uid, gid,
			       required_uid, required_gid, chopt);
    }

  /* Ignore failure, since the only way it can do so is in failing to
     return to the original directory, and since we're about to exit,
     that doesn't matter.  */
  fts_close (fts);

  return ok;
}