cd.def

This file is cd.def, from which is created cd.c.  It implements the
builtins "cd" and "pwd" in Bash.

Copyright (C) 1987-2020 Free Software Foundation, Inc.

This file is part of GNU Bash, the Bourne Again SHell.

Bash 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.

Bash 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 Bash.  If not, see <http://www.gnu.org/licenses/>.

$PRODUCES cd.c
#include <config.h>

#if defined (HAVE_UNISTD_H)
#  ifdef _MINIX
#    include <sys/types.h>
#  endif
#  include <unistd.h>
#endif

#include "../bashtypes.h"
#include "posixdir.h"
#include "posixstat.h"
#if defined (HAVE_SYS_PARAM_H)
#include <sys/param.h>
#endif
#include <fcntl.h>

#include <stdio.h>

#include "../bashansi.h"
#include "../bashintl.h"

#include <errno.h>
#include <tilde/tilde.h>

#include "../shell.h"
#include "../flags.h"
#include "maxpath.h"
#include "common.h"
#include "bashgetopt.h"

#if !defined (errno)
extern int errno;
#endif /* !errno */

extern const char * const bash_getcwd_errstr;

static int bindpwd PARAMS((int));
static int setpwd PARAMS((char *));
static char *resetpwd PARAMS((char *));
static int change_to_directory PARAMS((char *, int, int));

static int cdxattr PARAMS((char *, char **));
static void resetxattr PARAMS((void));

/* Change this to 1 to get cd spelling correction by default. */
int cdspelling = 0;

int cdable_vars;

static int eflag;	/* file scope so bindpwd() can see it */
static int xattrflag;	/* O_XATTR support for openat */
static int xattrfd = -1;

$BUILTIN cd
$FUNCTION cd_builtin
$SHORT_DOC cd [-L|[-P [-e]] [-@]] [dir]
Change the shell working directory.

Change the current directory to DIR.  The default DIR is the value of the
HOME shell variable.

The variable CDPATH defines the search path for the directory containing
DIR.  Alternative directory names in CDPATH are separated by a colon (:).
A null directory name is the same as the current directory.  If DIR begins
with a slash (/), then CDPATH is not used.

If the directory is not found, and the shell option `cdable_vars' is set,
the word is assumed to be  a variable name.  If that variable has a value,
its value is used for DIR.

Options:
  -L	force symbolic links to be followed: resolve symbolic
		links in DIR after processing instances of `..'
  -P	use the physical directory structure without following
		symbolic links: resolve symbolic links in DIR before
		processing instances of `..'
  -e	if the -P option is supplied, and the current working
		directory cannot be determined successfully, exit with
		a non-zero status
#if defined (O_XATTR)
  -@	on systems that support it, present a file with extended
		attributes as a directory containing the file attributes
#endif

The default is to follow symbolic links, as if `-L' were specified.
`..' is processed by removing the immediately previous pathname component
back to a slash or the beginning of DIR.

Exit Status:
Returns 0 if the directory is changed, and if $PWD is set successfully when
-P is used; non-zero otherwise.
$END

/* Just set $PWD, don't change OLDPWD.  Used by `pwd -P' in posix mode. */
static int
setpwd (dirname)
     char *dirname;
{
  int old_anm;
  SHELL_VAR *tvar;

  old_anm = array_needs_making;
  tvar = bind_variable ("PWD", dirname ? dirname : "", 0);
  if (tvar && readonly_p (tvar))
    return EXECUTION_FAILURE;
  if (tvar && old_anm == 0 && array_needs_making && exported_p (tvar))
    {
      update_export_env_inplace ("PWD=", 4, dirname ? dirname : "");
      array_needs_making = 0;
    }
  return EXECUTION_SUCCESS;
}

static int
bindpwd (no_symlinks)
     int no_symlinks;
{
  char *dirname, *pwdvar;
  int old_anm, r, canon_failed;
  SHELL_VAR *tvar;

  r = sh_chkwrite (EXECUTION_SUCCESS);

#define tcwd the_current_working_directory
  dirname = tcwd ? (no_symlinks ? sh_physpath (tcwd, 0) : tcwd)
  		 : get_working_directory ("cd");
#undef tcwd

  /* If canonicalization fails, reset dirname to the_current_working_directory */
  canon_failed = 0;
  if (dirname == 0)
    {
      canon_failed = 1;
      dirname = the_current_working_directory;
    }

  old_anm = array_needs_making;
  pwdvar = get_string_value ("PWD");

  tvar = bind_variable ("OLDPWD", pwdvar, 0);
  if (tvar && readonly_p (tvar))
    r = EXECUTION_FAILURE;

  if (old_anm == 0 && array_needs_making && exported_p (tvar))
    {
      update_export_env_inplace ("OLDPWD=", 7, pwdvar);
      array_needs_making = 0;
    }

  if (setpwd (dirname) == EXECUTION_FAILURE)
    r = EXECUTION_FAILURE;
  if (canon_failed && eflag)
    r = EXECUTION_FAILURE;

  if (dirname && dirname != the_current_working_directory)
    free (dirname);

  return (r);
}

/* Call get_working_directory to reset the value of
   the_current_working_directory () */
static char *
resetpwd (caller)
     char *caller;
{
  char *tdir;
      
  FREE (the_current_working_directory);
  the_current_working_directory = (char *)NULL;
  tdir = get_working_directory (caller);
  return (tdir);
}

static int
cdxattr (dir, ndirp)
     char *dir;		/* don't assume we can always free DIR */
     char **ndirp;	/* return new constructed directory name */
{
#if defined (O_XATTR)
  int apfd, fd, r, e;
  char buf[11+40+40];	/* construct new `fake' path for pwd */

  apfd = openat (AT_FDCWD, dir, O_RDONLY|O_NONBLOCK);
  if (apfd < 0)
    return -1;
  fd = openat (apfd, ".", O_XATTR);
  e = errno;
  close (apfd);		/* ignore close error for now */
  errno = e;
  if (fd < 0)
    return -1;
  r = fchdir (fd);	/* assume fchdir exists everywhere with O_XATTR */
  if (r < 0)
    {
      close (fd);
      return -1;
    }
  /* NFSv4 and ZFS extended attribute directories do not have names which are
     visible in the standard Unix directory tree structure.  To ensure we have
     a valid name for $PWD, we synthesize one under /proc, but to keep that
     path valid, we need to keep the file descriptor open as long as we are in
     this directory.  This imposes a certain structure on /proc. */
  if (ndirp)
    {
      sprintf (buf, "/proc/%d/fd/%d", getpid(), fd);
      *ndirp = savestring (buf);
    }

  if (xattrfd >= 0)
    close (xattrfd);
  xattrfd = fd;  

  return r;
#else
  return -1;
#endif
}

/* Clean up the O_XATTR baggage.  Currently only closes xattrfd */
static void
resetxattr ()
{
#if defined (O_XATTR)
  if (xattrfd >= 0)
    {
      close (xattrfd);
      xattrfd = -1;
    }
#else
  xattrfd = -1;		/* not strictly necessary */
#endif
}

#define LCD_DOVARS	0x001
#define LCD_DOSPELL	0x002
#define LCD_PRINTPATH	0x004
#define LCD_FREEDIRNAME	0x008

/* This builtin is ultimately the way that all user-visible commands should
   change the current working directory.  It is called by cd_to_string (),
   so the programming interface is simple, and it handles errors and
   restrictions properly. */
int
cd_builtin (list)
     WORD_LIST *list;
{
  char *dirname, *cdpath, *path, *temp;
  int path_index, no_symlinks, opt, lflag, e;

#if defined (RESTRICTED_SHELL)
  if (restricted)
    {
      sh_restricted ((char *)NULL);
      return (EXECUTION_FAILURE);
    }
#endif /* RESTRICTED_SHELL */

  eflag = 0;
  no_symlinks = no_symbolic_links;
  xattrflag = 0;
  reset_internal_getopt ();
#if defined (O_XATTR)
  while ((opt = internal_getopt (list, "eLP@")) != -1)
#else
  while ((opt = internal_getopt (list, "eLP")) != -1)
#endif
    {
      switch (opt)
	{
	case 'P':
	  no_symlinks = 1;
	  break;
	case 'L':
	  no_symlinks = 0;
	  break;
	case 'e':
	  eflag = 1;
	  break;
#if defined (O_XATTR)
	case '@':
	  xattrflag = 1;
	  break;
#endif
	CASE_HELPOPT;
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

  lflag = (cdable_vars ? LCD_DOVARS : 0) |
	  ((interactive && cdspelling) ? LCD_DOSPELL : 0);
  if (eflag && no_symlinks == 0)
    eflag = 0;

  if (list == 0)
    {
      /* `cd' without arguments is equivalent to `cd $HOME' */
      dirname = get_string_value ("HOME");

      if (dirname == 0)
	{
	  builtin_error (_("HOME not set"));
	  return (EXECUTION_FAILURE);
	}
      lflag = 0;
    }
#if defined (CD_COMPLAINS)
  else if (list->next)
    {
      builtin_error (_("too many arguments"));
      return (EXECUTION_FAILURE);
    }
#endif
#if 0
  else if (list->word->word[0] == '\0')
    {
      builtin_error (_("null directory"));
      return (EXECUTION_FAILURE);
    }
#endif
  else if (list->word->word[0] == '-' && list->word->word[1] == '\0')
    {
      /* This is `cd -', equivalent to `cd $OLDPWD' */
      dirname = get_string_value ("OLDPWD");

      if (dirname == 0)
	{
	  builtin_error (_("OLDPWD not set"));
	  return (EXECUTION_FAILURE);
	}
#if 0
      lflag = interactive ? LCD_PRINTPATH : 0;
#else
      lflag = LCD_PRINTPATH;		/* According to SUSv3 */
#endif
    }
  else if (absolute_pathname (list->word->word))
    dirname = list->word->word;
  else if (privileged_mode == 0 && (cdpath = get_string_value ("CDPATH")))
    {
      dirname = list->word->word;

      /* Find directory in $CDPATH. */
      path_index = 0;
      while (path = extract_colon_unit (cdpath, &path_index))
	{
	  /* OPT is 1 if the path element is non-empty */
	  opt = path[0] != '\0';
	  temp = sh_makepath (path, dirname, MP_DOTILDE);
	  free (path);

	  if (change_to_directory (temp, no_symlinks, xattrflag))
	    {
	      /* POSIX.2 says that if a nonempty directory from CDPATH
		 is used to find the directory to change to, the new
		 directory name is echoed to stdout, whether or not
		 the shell is interactive. */
	      if (opt && (path = no_symlinks ? temp : the_current_working_directory))
		printf ("%s\n", path);

	      free (temp);
#if 0
	      /* Posix.2 says that after using CDPATH, the resultant
		 value of $PWD will not contain `.' or `..'. */
	      return (bindpwd (posixly_correct || no_symlinks));
#else
	      return (bindpwd (no_symlinks));
#endif
	    }
	  else
	    free (temp);
	}

#if 0
      /* changed for bash-4.2 Posix cd description steps 5-6 */
      /* POSIX.2 says that if `.' does not appear in $CDPATH, we don't
	 try the current directory, so we just punt now with an error
	 message if POSIXLY_CORRECT is non-zero.  The check for cdpath[0]
	 is so we don't mistakenly treat a CDPATH value of "" as not
	 specifying the current directory. */
      if (posixly_correct && cdpath[0])
	{
	  builtin_error ("%s: %s", dirname, strerror (ENOENT));
	  return (EXECUTION_FAILURE);
	}
#endif
    }
  else
    dirname = list->word->word;

  /* When we get here, DIRNAME is the directory to change to.  If we
     chdir successfully, just return. */
  if (change_to_directory (dirname, no_symlinks, xattrflag))
    {
      if (lflag & LCD_PRINTPATH)
	printf ("%s\n", dirname);
      return (bindpwd (no_symlinks));
    }

  /* If the user requests it, then perhaps this is the name of
     a shell variable, whose value contains the directory to
     change to. */
  if (lflag & LCD_DOVARS)
    {
      temp = get_string_value (dirname);
      if (temp && change_to_directory (temp, no_symlinks, xattrflag))
	{
	  printf ("%s\n", temp);
	  return (bindpwd (no_symlinks));
	}
    }

  /* If the user requests it, try to find a directory name similar in
     spelling to the one requested, in case the user made a simple
     typo.  This is similar to the UNIX 8th and 9th Edition shells. */
  if (lflag & LCD_DOSPELL)
    {
      temp = dirspell (dirname);
      if (temp && change_to_directory (temp, no_symlinks, xattrflag))
	{
	  printf ("%s\n", temp);
	  free (temp);
	  return (bindpwd (no_symlinks));
	}
      else
	FREE (temp);
    }

  e = errno;
  temp = printable_filename (dirname, 0);
  builtin_error ("%s: %s", temp, strerror (e));
  if (temp != dirname)
    free (temp);
  return (EXECUTION_FAILURE);
}

$BUILTIN pwd
$FUNCTION pwd_builtin
$SHORT_DOC pwd [-LP]
Print the name of the current working directory.

Options:
  -L	print the value of $PWD if it names the current working
		directory
  -P	print the physical directory, without any symbolic links

By default, `pwd' behaves as if `-L' were specified.

Exit Status:
Returns 0 unless an invalid option is given or the current directory
cannot be read.
$END

/* Non-zero means that pwd always prints the physical directory, without
   symbolic links. */
static int verbatim_pwd;

/* Print the name of the current working directory. */
int
pwd_builtin (list)
     WORD_LIST *list;
{
  char *directory;
  int opt, pflag;

  verbatim_pwd = no_symbolic_links;
  pflag = 0;
  reset_internal_getopt ();
  while ((opt = internal_getopt (list, "LP")) != -1)
    {
      switch (opt)
	{
	case 'P':
	  verbatim_pwd = pflag = 1;
	  break;
	case 'L':
	  verbatim_pwd = 0;
	  break;
	CASE_HELPOPT;
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

#define tcwd the_current_working_directory

  directory = tcwd ? (verbatim_pwd ? sh_physpath (tcwd, 0) : tcwd)
		   : get_working_directory ("pwd");

  /* Try again using getcwd() if canonicalization fails (for instance, if
     the file system has changed state underneath bash). */
  if ((tcwd && directory == 0) ||
      (posixly_correct && same_file (".", tcwd, (struct stat *)0, (struct stat *)0) == 0))
    {
      if (directory && directory != tcwd)
        free (directory);
      directory = resetpwd ("pwd");
    }

#undef tcwd

  if (directory)
    {
      opt = EXECUTION_SUCCESS;
      printf ("%s\n", directory);
      /* This is dumb but posix-mandated. */
      if (posixly_correct && pflag)
	opt = setpwd (directory);
      if (directory != the_current_working_directory)
	free (directory);
      return (sh_chkwrite (opt));
    }
  else
    return (EXECUTION_FAILURE);
}

/* Do the work of changing to the directory NEWDIR.  Handle symbolic
   link following, etc.  This function *must* return with
   the_current_working_directory either set to NULL (in which case
   getcwd() will eventually be called), or set to a string corresponding
   to the working directory.  Return 1 on success, 0 on failure. */

static int
change_to_directory (newdir, nolinks, xattr)
     char *newdir;
     int nolinks, xattr;
{
  char *t, *tdir, *ndir;
  int err, canon_failed, r, ndlen;

  tdir = (char *)NULL;

  if (the_current_working_directory == 0)
    {
      t = get_working_directory ("chdir");
      FREE (t);
    }

  t = make_absolute (newdir, the_current_working_directory);

  /* TDIR is either the canonicalized absolute pathname of NEWDIR
     (nolinks == 0) or the absolute physical pathname of NEWDIR
     (nolinks != 0). */
  tdir = nolinks ? sh_physpath (t, 0)
		 : sh_canonpath (t, PATH_CHECKDOTDOT|PATH_CHECKEXISTS);

  ndlen = strlen (newdir);

  /* Use the canonicalized version of NEWDIR, or, if canonicalization
     failed, use the non-canonical form. */
  canon_failed = 0;
  if (tdir && *tdir)
    free (t);
  else
    {
      FREE (tdir);
      tdir = t;
      canon_failed = 1;
    }

  /* In POSIX mode, if we're resolving symlinks logically and sh_canonpath
     returns NULL (because it checks the path, it will return NULL if the
     resolved path doesn't exist), fail immediately. */
#if defined (ENAMETOOLONG)
  if (posixly_correct && nolinks == 0 && canon_failed && (errno != ENAMETOOLONG || ndlen > PATH_MAX))
#else
  if (posixly_correct && nolinks == 0 && canon_failed && ndlen > PATH_MAX)
#endif
    {
#if defined ENAMETOOLONG
      if (errno != ENOENT && errno != ENAMETOOLONG)
#else
      if (errno != ENOENT)
#endif
	errno = ENOTDIR;
      free (tdir);
      return (0);
    }

#if defined (O_XATTR)
  if (xattrflag)
    {
      r = cdxattr (nolinks ? newdir : tdir, &ndir);
      if (r >= 0)
	{
	  canon_failed = 0;
	  free (tdir);
	  tdir = ndir;
	}
      else
	{
	  err = errno;
	  free (tdir);
	  errno = err;
	  return (0);		/* no xattr */
	}
    }
  else
#endif
    {
      r = chdir (nolinks ? newdir : tdir);
      if (r >= 0)
	resetxattr ();
    }

  /* If the chdir succeeds, update the_current_working_directory. */
  if (r == 0)
    {
      /* If canonicalization failed, but the chdir succeeded, reset the
	 shell's idea of the_current_working_directory. */
      if (canon_failed)
	{
	  t = resetpwd ("cd");
	  if (t == 0)
	    set_working_directory (tdir);
	  else
	    free (t);
	}
      else
	set_working_directory (tdir);

      free (tdir);
      return (1);
    }

  /* We failed to change to the appropriate directory name.  If we tried
     what the user passed (nolinks != 0), punt now. */
  if (nolinks)
    {
      free (tdir);
      return (0);
    }

  err = errno;

  /* We're not in physical mode (nolinks == 0), but we failed to change to
     the canonicalized directory name (TDIR).  Try what the user passed
     verbatim. If we succeed, reinitialize the_current_working_directory.
     POSIX requires that we just fail here, so we do in posix mode. */
  if (posixly_correct == 0 && chdir (newdir) == 0)
    {
      t = resetpwd ("cd");
      if (t == 0)
	set_working_directory (tdir);
      else
	free (t);

      r = 1;
    }
  else
    {
      errno = err;
      r = 0;
    }

  free (tdir);
  return r;
}