rm_/remove.c

/* remove.c -- core functions for removing files and directories
   Copyright (C) 1988-2020 Free Software Foundation, Inc.

   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 3 of the License, 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, see <https://www.gnu.org/licenses/>.  */

/* Extracted from rm.c, librarified, then rewritten twice by Jim Meyering.  */

#include <config.h>
#include <stdio.h>
#include <sys/types.h>
#include <assert.h>

#include "system.h"
#include "error.h"
#include "file-type.h"
#include "filenamecat.h"
#include "ignore-value.h"
#include "remove.h"
#include "root-dev-ino.h"
#include "write-any-file.h"
#include "xfts.h"
#include "yesno.h"

enum Ternary
  {
    T_UNKNOWN = 2,
    T_NO,
    T_YES
  };
typedef enum Ternary Ternary;

/* The prompt function may be called twice for a given directory.
   The first time, we ask whether to descend into it, and the
   second time, we ask whether to remove it.  */
enum Prompt_action
  {
    PA_DESCEND_INTO_DIR = 2,
    PA_REMOVE_DIR
  };

/* D_TYPE(D) is the type of directory entry D if known, DT_UNKNOWN
   otherwise.  */
#if ! HAVE_STRUCT_DIRENT_D_TYPE
/* Any int values will do here, so long as they're distinct.
   Undef any existing macros out of the way.  */
# undef DT_UNKNOWN
# undef DT_DIR
# undef DT_LNK
# define DT_UNKNOWN 0
# define DT_DIR 1
# define DT_LNK 2
#endif

/* Like fstatat, but cache the result.  If ST->st_size is -1, the
   status has not been gotten yet.  If less than -1, fstatat failed
   with errno == ST->st_ino.  Otherwise, the status has already
   been gotten, so return 0.  */
static int
cache_fstatat (int fd, char const *file, struct stat *st, int flag)
{
  if (st->st_size == -1 && fstatat (fd, file, st, flag) != 0)
    {
      st->st_size = -2;
      st->st_ino = errno;
    }
  if (0 <= st->st_size)
    return 0;
  errno = (int) st->st_ino;
  return -1;
}

/* Initialize a fstatat cache *ST.  Return ST for convenience.  */
static inline struct stat *
cache_stat_init (struct stat *st)
{
  st->st_size = -1;
  return st;
}

/* Return 1 if FILE is an unwritable non-symlink,
   0 if it is writable or some other type of file,
   -1 and set errno if there is some problem in determining the answer.
   Set *BUF to the file status.  */
static int
write_protected_non_symlink (int fd_cwd,
                             char const *file,
                             struct stat *buf)
{
  if (can_write_any_file ())
    return 0;
  if (cache_fstatat (fd_cwd, file, buf, AT_SYMLINK_NOFOLLOW) != 0)
    return -1;
  if (S_ISLNK (buf->st_mode))
    return 0;
  /* Here, we know FILE is not a symbolic link.  */

  /* In order to be reentrant -- i.e., to avoid changing the working
     directory, and at the same time to be able to deal with alternate
     access control mechanisms (ACLs, xattr-style attributes) and
     arbitrarily deep trees -- we need a function like eaccessat, i.e.,
     like Solaris' eaccess, but fd-relative, in the spirit of openat.  */

  /* In the absence of a native eaccessat function, here are some of
     the implementation choices [#4 and #5 were suggested by Paul Eggert]:
     1) call openat with O_WRONLY|O_NOCTTY
        Disadvantage: may create the file and doesn't work for directory,
        may mistakenly report 'unwritable' for EROFS or ACLs even though
        perm bits say the file is writable.

     2) fake eaccessat (save_cwd, fchdir, call euidaccess, restore_cwd)
        Disadvantage: changes working directory (not reentrant) and can't
        work if save_cwd fails.

     3) if (euidaccess (full_name, W_OK) == 0)
        Disadvantage: doesn't work if full_name is too long.
        Inefficient for very deep trees (O(Depth^2)).

     4) If the full pathname is sufficiently short (say, less than
        PATH_MAX or 8192 bytes, whichever is shorter):
        use method (3) (i.e., euidaccess (full_name, W_OK));
        Otherwise: vfork, fchdir in the child, run euidaccess in the
        child, then the child exits with a status that tells the parent
        whether euidaccess succeeded.

        This avoids the O(N**2) algorithm of method (3), and it also avoids
        the failure-due-to-too-long-file-names of method (3), but it's fast
        in the normal shallow case.  It also avoids the lack-of-reentrancy
        and the save_cwd problems.
        Disadvantage; it uses a process slot for very-long file names,
        and would be very slow for hierarchies with many such files.

     5) If the full file name is sufficiently short (say, less than
        PATH_MAX or 8192 bytes, whichever is shorter):
        use method (3) (i.e., euidaccess (full_name, W_OK));
        Otherwise: look just at the file bits.  Perhaps issue a warning
        the first time this occurs.

        This is like (4), except for the "Otherwise" case where it isn't as
        "perfect" as (4) but is considerably faster.  It conforms to current
        POSIX, and is uniformly better than what Solaris and FreeBSD do (they
        mess up with long file names). */

  {
    if (faccessat (fd_cwd, file, W_OK, AT_EACCESS) == 0)
      return 0;

    return errno == EACCES ? 1 : -1;
  }
}

/* Prompt whether to remove FILENAME (ent->, if required via a combination of
   the options specified by X and/or file attributes.  If the file may
   be removed, return RM_OK.  If the user declines to remove the file,
   return RM_USER_DECLINED.  If not ignoring missing files and we
   cannot lstat FILENAME, then return RM_ERROR.

   IS_DIR is true if ENT designates a directory, false otherwise.

   Depending on MODE, ask whether to 'descend into' or to 'remove' the
   directory FILENAME.  MODE is ignored when FILENAME is not a directory.
   Set *IS_EMPTY_P to T_YES if FILENAME is an empty directory, and it is
   appropriate to try to remove it with rmdir (e.g. recursive mode).
   Don't even try to set *IS_EMPTY_P when MODE == PA_REMOVE_DIR.  */
static enum RM_status
prompt (FTS const *fts, FTSENT const *ent, bool is_dir,
        struct rm_options const *x, enum Prompt_action mode,
        Ternary *is_empty_p)
{
  int fd_cwd = fts->fts_cwd_fd;
  char const *full_name = ent->fts_path;
  char const *filename = ent->fts_accpath;
  if (is_empty_p)
    *is_empty_p = T_UNKNOWN;

  struct stat st;
  struct stat *sbuf = &st;
  cache_stat_init (sbuf);

  int dirent_type = is_dir ? DT_DIR : DT_UNKNOWN;
  int write_protected = 0;

  bool is_empty = false;
  if (is_empty_p)
    {
      is_empty = is_empty_dir (fd_cwd, filename);
      *is_empty_p = is_empty ? T_YES : T_NO;
    }

  /* When nonzero, this indicates that we failed to remove a child entry,
     either because the user declined an interactive prompt, or due to
     some other failure, like permissions.  */
  if (ent->fts_number)
    return RM_USER_DECLINED;

  if (x->interactive == RMI_NEVER)
    return RM_OK;

  int wp_errno = 0;
  if (!x->ignore_missing_files
      && ((x->interactive == RMI_ALWAYS) || x->stdin_tty)
      && dirent_type != DT_LNK)
    {
      write_protected = write_protected_non_symlink (fd_cwd, filename, sbuf);
      wp_errno = errno;
    }

  if (write_protected || x->interactive == RMI_ALWAYS)
    {
      if (0 <= write_protected && dirent_type == DT_UNKNOWN)
        {
          if (cache_fstatat (fd_cwd, filename, sbuf, AT_SYMLINK_NOFOLLOW) == 0)
            {
              if (S_ISLNK (sbuf->st_mode))
                dirent_type = DT_LNK;
              else if (S_ISDIR (sbuf->st_mode))
                dirent_type = DT_DIR;
              /* Otherwise it doesn't matter, so leave it DT_UNKNOWN.  */
            }
          else
            {
              /* This happens, e.g., with 'rm '''.  */
              write_protected = -1;
              wp_errno = errno;
            }
        }

      if (0 <= write_protected)
        switch (dirent_type)
          {
          case DT_LNK:
            /* Using permissions doesn't make sense for symlinks.  */
            if (x->interactive != RMI_ALWAYS)
              return RM_OK;
            break;

          case DT_DIR:
             /* Unless we're either deleting directories or deleting
                recursively, we want to raise an EISDIR error rather than
                prompting the user  */
            if ( ! (x->recursive || (x->remove_empty_directories && is_empty)))
              {
                write_protected = -1;
                wp_errno = EISDIR;
              }
            break;
          }

      char const *quoted_name = quoteaf (full_name);

      if (write_protected < 0)
        {
          error (0, wp_errno, _("cannot remove %s"), quoted_name);
          return RM_ERROR;
        }

      /* Issue the prompt.  */
      if (dirent_type == DT_DIR
          && mode == PA_DESCEND_INTO_DIR
          && !is_empty)
        fprintf (stderr,
                 (write_protected
                  ? _("%s: descend into write-protected directory %s? ")
                  : _("%s: descend into directory %s? ")),
                 program_name, quoted_name);
      else
        {
          if (cache_fstatat (fd_cwd, filename, sbuf, AT_SYMLINK_NOFOLLOW) != 0)
            {
              error (0, errno, _("cannot remove %s"), quoted_name);
              return RM_ERROR;
            }

          fprintf (stderr,
                   (write_protected
                    /* TRANSLATORS: In the next two strings the second %s is
                       replaced by the type of the file.  To avoid grammatical
                       problems, it may be more convenient to translate these
                       strings instead as: "%1$s: %3$s is write-protected and
                       is of type '%2$s' -- remove it? ".  */
                    ? _("%s: remove write-protected %s %s? ")
                    : _("%s: remove %s %s? ")),
                   program_name, file_type (sbuf), quoted_name);
        }

      if (!yesno ())
        return RM_USER_DECLINED;
    }
  return RM_OK;
}

/* When a function like unlink, rmdir, or fstatat fails with an errno
   value of ERRNUM, return true if the specified file system object
   is guaranteed not to exist;  otherwise, return false.  */
static inline bool
nonexistent_file_errno (int errnum)
{
  /* Do not include ELOOP here, since the specified file may indeed
     exist, but be (in)accessible only via too long a symlink chain.
     Likewise for ENAMETOOLONG, since rm -f ./././.../foo may fail
     if the "..." part expands to a long enough sequence of "./"s,
     even though ./foo does indeed exist.

     Another case to consider is when a particular name is invalid for
     a given file system.  In 2011, smbfs returns EINVAL, but the next
     revision of POSIX will require EILSEQ for that situation:
     http://austingroupbugs.net/view.php?id=293
  */

  switch (errnum)
    {
    case EILSEQ:
    case EINVAL:
    case ENOENT:
    case ENOTDIR:
      return true;
    default:
      return false;
    }
}

/* Encapsulate the test for whether the errno value, ERRNUM, is ignorable.  */
static inline bool
ignorable_missing (struct rm_options const *x, int errnum)
{
  return x->ignore_missing_files && nonexistent_file_errno (errnum);
}

/* Tell fts not to traverse into the hierarchy at ENT.  */
static void
fts_skip_tree (FTS *fts, FTSENT *ent)
{
  fts_set (fts, ent, FTS_SKIP);
  /* Ensure that we do not process ENT a second time.  */
  ignore_value (fts_read (fts));
}

/* Upon unlink failure, or when the user declines to remove ENT, mark
   each of its ancestor directories, so that we know not to prompt for
   its removal.  */
static void
mark_ancestor_dirs (FTSENT *ent)
{
  FTSENT *p;
  for (p = ent->fts_parent; FTS_ROOTLEVEL <= p->fts_level; p = p->fts_parent)
    {
      if (p->fts_number)
        break;
      p->fts_number = 1;
    }
}

/* Remove the file system object specified by ENT.  IS_DIR specifies
   whether it is expected to be a directory or non-directory.
   Return RM_OK upon success, else RM_ERROR.  */
static enum RM_status
excise (FTS *fts, FTSENT *ent, struct rm_options const *x, bool is_dir)
{
  int flag = is_dir ? AT_REMOVEDIR : 0;
  if (unlinkat (fts->fts_cwd_fd, ent->fts_accpath, flag) == 0)
    {
      if (x->verbose)
        {
          printf ((is_dir
                   ? _("removed directory %s\n")
                   : _("removed %s\n")), quoteaf (ent->fts_path));
        }
      return RM_OK;
    }

  /* The unlinkat from kernels like linux-2.6.32 reports EROFS even for
     nonexistent files.  When the file is indeed missing, map that to ENOENT,
     so that rm -f ignores it, as required.  Even without -f, this is useful
     because it makes rm print the more precise diagnostic.  */
  if (errno == EROFS)
    {
      struct stat st;
      if ( ! (lstatat (fts->fts_cwd_fd, ent->fts_accpath, &st)
                       && errno == ENOENT))
        errno = EROFS;
    }

  if (ignorable_missing (x, errno))
    return RM_OK;

  /* When failing to rmdir an unreadable directory, we see errno values
     like EISDIR or ENOTDIR (or, on Solaris 10, EEXIST), but they would be
     meaningless in a diagnostic.  When that happens and the errno value
     from the failed open is EPERM or EACCES, use the earlier, more
     descriptive errno value.  */
  if (ent->fts_info == FTS_DNR
      && (errno == ENOTEMPTY || errno == EISDIR || errno == ENOTDIR
          || errno == EEXIST)
      && (ent->fts_errno == EPERM || ent->fts_errno == EACCES))
    errno = ent->fts_errno;
  error (0, errno, _("cannot remove %s"), quoteaf (ent->fts_path));
  mark_ancestor_dirs (ent);
  return RM_ERROR;
}

/* This function is called once for every file system object that fts
   encounters.  fts performs a depth-first traversal.
   A directory is usually processed twice, first with fts_info == FTS_D,
   and later, after all of its entries have been processed, with FTS_DP.
   Return RM_ERROR upon error, RM_USER_DECLINED for a negative response
   to an interactive prompt, and otherwise, RM_OK.  */
static enum RM_status
rm_fts (FTS *fts, FTSENT *ent, struct rm_options const *x)
{
  switch (ent->fts_info)
    {
    case FTS_D:			/* preorder directory */
      if (! x->recursive
          && !(x->remove_empty_directories
               && is_empty_dir (fts->fts_cwd_fd, ent->fts_accpath)))
        {
          /* This is the first (pre-order) encounter with a directory
             that we cannot delete.
             Not recursive, and it's not an empty directory (if we're removing
             them) so arrange to skip contents.  */
          int err = x->remove_empty_directories ? ENOTEMPTY : EISDIR;
          error (0, err, _("cannot remove %s"), quoteaf (ent->fts_path));
          mark_ancestor_dirs (ent);
          fts_skip_tree (fts, ent);
          return RM_ERROR;
        }

      /* Perform checks that can apply only for command-line arguments.  */
      if (ent->fts_level == FTS_ROOTLEVEL)
        {
          /* POSIX says:
             If the basename of a command line argument is "." or "..",
             diagnose it and do nothing more with that argument.  */
          if (dot_or_dotdot (last_component (ent->fts_accpath)))
            {
              error (0, 0,
                     _("refusing to remove %s or %s directory: skipping %s"),
                     quoteaf_n (0, "."), quoteaf_n (1, ".."),
                     quoteaf_n (2, ent->fts_path));
              fts_skip_tree (fts, ent);
              return RM_ERROR;
            }

          /* POSIX also says:
             If a command line argument resolves to "/" (and --preserve-root
             is in effect -- default) diagnose and skip it.  */
          if (ROOT_DEV_INO_CHECK (x->root_dev_ino, ent->fts_statp))
            {
              ROOT_DEV_INO_WARN (ent->fts_path);
              fts_skip_tree (fts, ent);
              return RM_ERROR;
            }

          /* If a command line argument is a mount point and
             --preserve-root=all is in effect, diagnose and skip it.
             This doesn't handle "/", but that's handled above.  */
          if (x->preserve_all_root)
            {
              bool failed = false;
              char *parent = file_name_concat (ent->fts_accpath, "..", NULL);
              struct stat statbuf;

              if (!parent || lstat (parent, &statbuf))
                {
                  error (0, 0,
                         _("failed to stat %s: skipping %s"),
                         quoteaf_n (0, parent),
                         quoteaf_n (1, ent->fts_accpath));
                  failed = true;
                }

              free (parent);

              if (failed || fts->fts_dev != statbuf.st_dev)
                {
                  if (! failed)
                    {
                      error (0, 0,
                             _("skipping %s, since it's on a different device"),
                             quoteaf (ent->fts_path));
                      error (0, 0, _("and --preserve-root=all is in effect"));
                    }
                  fts_skip_tree (fts, ent);
                  return RM_ERROR;
                }
            }
        }

      {
        Ternary is_empty_directory;
        enum RM_status s = prompt (fts, ent, true /*is_dir*/, x,
                                   PA_DESCEND_INTO_DIR, &is_empty_directory);

        if (s == RM_OK && is_empty_directory == T_YES)
          {
            /* When we know (from prompt when in interactive mode)
               that this is an empty directory, don't prompt twice.  */
            s = excise (fts, ent, x, true);
            fts_skip_tree (fts, ent);
          }

        if (s != RM_OK)
          {
            mark_ancestor_dirs (ent);
            fts_skip_tree (fts, ent);
          }

        return s;
      }

    case FTS_F:			/* regular file */
    case FTS_NS:		/* stat(2) failed */
    case FTS_SL:		/* symbolic link */
    case FTS_SLNONE:		/* symbolic link without target */
    case FTS_DP:		/* postorder directory */
    case FTS_DNR:		/* unreadable directory */
    case FTS_NSOK:		/* e.g., dangling symlink */
    case FTS_DEFAULT:		/* none of the above */
      {
        /* With --one-file-system, do not attempt to remove a mount point.
           fts' FTS_XDEV ensures that we don't process any entries under
           the mount point.  */
        if (ent->fts_info == FTS_DP
            && x->one_file_system
            && FTS_ROOTLEVEL < ent->fts_level
            && ent->fts_statp->st_dev != fts->fts_dev)
          {
            mark_ancestor_dirs (ent);
            error (0, 0, _("skipping %s, since it's on a different device"),
                   quoteaf (ent->fts_path));
            return RM_ERROR;
          }

        bool is_dir = ent->fts_info == FTS_DP || ent->fts_info == FTS_DNR;
        enum RM_status s = prompt (fts, ent, is_dir, x, PA_REMOVE_DIR, NULL);
        if (s != RM_OK)
          return s;
        return excise (fts, ent, x, is_dir);
      }

    case FTS_DC:		/* directory that causes cycles */
      emit_cycle_warning (ent->fts_path);
      fts_skip_tree (fts, ent);
      return RM_ERROR;

    case FTS_ERR:
      /* Various failures, from opendir to ENOMEM, to failure to "return"
         to preceding directory, can provoke this.  */
      error (0, ent->fts_errno, _("traversal failed: %s"),
             quotef (ent->fts_path));
      fts_skip_tree (fts, ent);
      return RM_ERROR;

    default:
      error (0, 0, _("unexpected failure: fts_info=%d: %s\n"
                     "please report to %s"),
             ent->fts_info,
             quotef (ent->fts_path),
             PACKAGE_BUGREPORT);
      abort ();
    }
}

/* Remove FILEs, honoring options specified via X.
   Return RM_OK if successful.  */
enum RM_status
rm (char *const *file, struct rm_options const *x)
{
  enum RM_status rm_status = RM_OK;

  if (*file)
    {
      int bit_flags = (FTS_CWDFD
                       | FTS_NOSTAT
                       | FTS_PHYSICAL);

      if (x->one_file_system)
        bit_flags |= FTS_XDEV;

      FTS *fts = xfts_open (file, bit_flags, NULL);

      while (1)
        {
          FTSENT *ent;

          ent = fts_read (fts);
          if (ent == NULL)
            {
              if (errno != 0)
                {
                  error (0, errno, _("fts_read failed"));
                  rm_status = RM_ERROR;
                }
              break;
            }

          enum RM_status s = rm_fts (fts, ent, x);

          assert (VALID_STATUS (s));
          UPDATE_STATUS (rm_status, s);
        }

      if (fts_close (fts) != 0)
        {
          error (0, errno, _("fts_close failed"));
          rm_status = RM_ERROR;
        }
    }

  return rm_status;
}