coreutils/lib/euidaccess.c

/* euidaccess -- check if effective user id can access file
   Copyright (C) 1990, 1991, 1995, 1998 Free Software Foundation, Inc.

This file is part of the GNU C Library.

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

The GNU C Library 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
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 59 Temple Place -
Suite 330, Boston, MA 02111-1307, USA.  */

/* Written by David MacKenzie and Torbjorn Granlund.
   Adapted for GNU C library by Roland McGrath.  */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <sys/types.h>
#include <sys/stat.h>

#ifdef S_IEXEC
# ifndef S_IXUSR
#  define S_IXUSR S_IEXEC
# endif
# ifndef S_IXGRP
#  define S_IXGRP (S_IEXEC >> 3)
# endif
# ifndef S_IXOTH
#  define S_IXOTH (S_IEXEC >> 6)
# endif
#endif /* S_IEXEC */

#if defined (HAVE_UNISTD_H) || defined (_LIBC)
# include <unistd.h>
#endif

#ifdef _POSIX_VERSION
# include <limits.h>
# if !defined(NGROUPS_MAX) || NGROUPS_MAX < 1
#  undef NGROUPS_MAX
#  define NGROUPS_MAX sysconf (_SC_NGROUPS_MAX)
# endif /* NGROUPS_MAX */

#else /* not _POSIX_VERSION */
uid_t getuid ();
gid_t getgid ();
uid_t geteuid ();
gid_t getegid ();
# include <sys/param.h>
# if !defined(NGROUPS_MAX) && defined(NGROUPS)
#  define NGROUPS_MAX NGROUPS
# endif /* not NGROUPS_MAX and NGROUPS */
#endif /* not POSIX_VERSION */

#include <errno.h>
#ifndef errno
extern int errno;
#endif

#if defined(EACCES) && !defined(EACCESS)
# define EACCESS EACCES
#endif

#ifndef F_OK
# define F_OK 0
# define X_OK 1
# define W_OK 2
# define R_OK 4
#endif

#if !defined (S_IROTH) && defined (R_OK)
# define S_IROTH R_OK
#endif

#if !defined (S_IWOTH) && defined (W_OK)
# define S_IWOTH W_OK
#endif

#if !defined (S_IXOTH) && defined (X_OK)
# define S_IXOTH X_OK
#endif

#ifdef _LIBC

# define group_member __group_member

#else

/* The user's real user id. */
static uid_t uid;

/* The user's real group id. */
static gid_t gid;

/* The user's effective user id. */
static uid_t euid;

/* The user's effective group id. */
static gid_t egid;

/* Nonzero if UID, GID, EUID, and EGID have valid values. */
static int have_ids = 0;

# if HAVE_GETGROUPS
int group_member ();
# else
#  define group_member(gid)	0
# endif

#endif


/* Return 0 if the user has permission of type MODE on file PATH;
   otherwise, return -1 and set `errno' to EACCESS.
   Like access, except that it uses the effective user and group
   id's instead of the real ones, and it does not check for read-only
   filesystem, text busy, etc. */

int
euidaccess (const char *path, int mode)
{
  struct stat stats;
  int granted;

#ifdef	_LIBC
  uid_t uid = getuid (), euid = geteuid ();
  gid_t gid = getgid (), egid = getegid ();
#else
  if (have_ids == 0)
    {
      have_ids = 1;
      uid = getuid ();
      gid = getgid ();
      euid = geteuid ();
      egid = getegid ();
    }
#endif

  if (uid == euid && gid == egid)
    /* If we are not set-uid or set-gid, access does the same.  */
    return access (path, mode);

  if (stat (path, &stats))
    return -1;

  mode &= (X_OK | W_OK | R_OK);	/* Clear any bogus bits. */
#if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
  ?error Oops, portability assumptions incorrect.
#endif

  if (mode == F_OK)
    return 0;			/* The file exists. */

  /* The super-user can read and write any file, and execute any file
     that anyone can execute. */
  if (euid == 0 && ((mode & X_OK) == 0
		    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
    return 0;

  if (euid == stats.st_uid)
    granted = (unsigned) (stats.st_mode & (mode << 6)) >> 6;
  else if (egid == stats.st_gid || group_member (stats.st_gid))
    granted = (unsigned) (stats.st_mode & (mode << 3)) >> 3;
  else
    granted = (stats.st_mode & mode);
  if (granted == mode)
    return 0;
  errno = EACCESS;
  return -1;
}