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ispreroot.c

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*                  Copyright (c) 1985-2005 AT&T Corp.                  *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                            by AT&T Corp.                             *
*                                                                      *
*                A copy of the License is available at                 *
*            http://www.opensource.org/licenses/cpl1.0.txt             *
*         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
*                                                                      *
*              Information and Software Systems Research               *
*                            AT&T Research                             *
*                           Florham Park NJ                            *
*                                                                      *
*                 Glenn Fowler <gsf@research.att.com>                  *
*                  David Korn <dgk@research.att.com>                   *
*                   Phong Vo <kpv@research.att.com>                    *
*                                                                      *
***********************************************************************/
#pragma prototyped
/*
 * AT&T Bell Laboratories
 * return 1 if dir [any dir] is the preroot
 */

#include <ast.h>
#include <preroot.h>

#if FS_PREROOT

#include <ls.h>

/*
 * return 1 if files a and b are the same under preroot
 *
 * NOTE: the kernel disables preroot for set-uid processes
 */

static int
same(const char* a, const char* b)
{
      int         i;
      int         euid;
      int         ruid;

      struct stat ast;
      struct stat bst;

      if ((ruid = getuid()) != (euid = geteuid())) setuid(ruid);
      i = !stat(a, &ast) && !stat(b, &bst) && ast.st_dev == bst.st_dev && ast.st_ino == bst.st_ino;
      if (ruid != euid) setuid(euid);
      return(i);
}

int
ispreroot(const char* dir)
{
      static int  prerooted = -1;

      if (dir) return(same("/", dir));
      if (prerooted < 0) prerooted = !same("/", PR_REAL);
      return(prerooted);
}

#else

NoN(ispreroot)

#endif

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