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/*
* fdclosed.cc: Part of GNU CSSC.
*
* Copyright (C) 1998,2000, 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 2 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, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
*
*/
/* This class exists to ensure that the standard file descriptors are
* not closed. That would mean that we could open an ordinary file
* and then corrupt it since we don't realise that output to stdout or
* stderr will go to it.
*
*
* If any of the file descriptors 0, 1, 2 are not open, attach them
* to /dev/null so that we don't fopen() a file, get a low numbered
* file descriptor, and accidentally corrupt our file with a printf()
* to stdout or stderr, or trying to read from stdin (hence changing
* the file pointer on our file too).
*/
#ifdef CONFIG_SCCS_IDS
static const char rcs_id[] = "CSSC $Id: fdclosed.cc,v 1.5 2001/09/29 19:39:41 james_youngman Exp $";
#endif
#include "cssc.h"
#include "sysdep.h"
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_STDIO_H
#include <stdio.h> /* perror() */
#endif
class SafeFdCheck
{
public:
SafeFdCheck();
};
/* We want to emit an error message. If stderr has been closed, this
* is difficult. We just send the output to the closed file
* descriptor (using perror()).
*
* We do this becauase (1) there isn't really a better option, and
* (2) because the output will still show up in the strace(8) output
* if the user really needs to track down the problem.
*
* If you have an idea for a better way of implementing it, please
* feel free to do so; but remember, it needs to work when we just
* failed to open() /dev/null. So opening another file (e.g. /dev/log
* with syslog) isn't going to work.
*/
SafeFdCheck::SafeFdCheck()
{
int i, fd;
for (i=0; i<3; ++i)
{
fd = open(CONFIG_NULL_FILENAME, O_RDONLY, 0);
if (fd < 0)
{
perror(CONFIG_NULL_FILENAME);
_exit(1);
}
else if (fd > 2)
{
close(fd);
return;
}
}
}
/* Instantiate the class so that the constructor is called to do the check.
*/
static SafeFdCheck PleaseDoIt;
/* Local variables: */
/* mode: c++ */
/* End: */
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