freebsd-dev/lib/libc/stdio/freopen.c
John Baldwin cc3d85727d When reopening a stream backed by an open file descriptor, do not close
the existing file descriptor.  Instead, let dup2() atomically close the
old file descriptor when assigning the newly opened file to the same
descriptor.  This closes a race in a multithreaded application where a
concurrent open() could allocate the existing file descriptor in between
the calls to close() and dup2().

PR:		threads/79887
Submitted by:	Dmitrij Tejblum  tejblum of yandex-team.ru
Reviewed by:	davidxu
MFC after:	1 week
2010-12-09 20:28:30 +00:00

238 lines
6.9 KiB
C

/*-
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Chris Torek.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)freopen.c 8.1 (Berkeley) 6/4/93";
#endif /* LIBC_SCCS and not lint */
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "namespace.h"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <limits.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include "un-namespace.h"
#include "libc_private.h"
#include "local.h"
/*
* Re-direct an existing, open (probably) file to some other file.
* ANSI is written such that the original file gets closed if at
* all possible, no matter what.
*/
FILE *
freopen(file, mode, fp)
const char * __restrict file;
const char * __restrict mode;
FILE *fp;
{
int f;
int dflags, flags, isopen, oflags, sverrno, wantfd;
if ((flags = __sflags(mode, &oflags)) == 0) {
sverrno = errno;
(void) fclose(fp);
errno = sverrno;
return (NULL);
}
FLOCKFILE(fp);
if (!__sdidinit)
__sinit();
/*
* If the filename is a NULL pointer, the caller is asking us to
* re-open the same file with a different mode. We allow this only
* if the modes are compatible.
*/
if (file == NULL) {
/* See comment below regarding freopen() of closed files. */
if (fp->_flags == 0) {
FUNLOCKFILE(fp);
errno = EINVAL;
return (NULL);
}
if ((dflags = _fcntl(fp->_file, F_GETFL)) < 0) {
sverrno = errno;
fclose(fp);
FUNLOCKFILE(fp);
errno = sverrno;
return (NULL);
}
if ((dflags & O_ACCMODE) != O_RDWR && (dflags & O_ACCMODE) !=
(oflags & O_ACCMODE)) {
fclose(fp);
FUNLOCKFILE(fp);
errno = EINVAL;
return (NULL);
}
if (fp->_flags & __SWR)
(void) __sflush(fp);
if ((oflags ^ dflags) & O_APPEND) {
dflags &= ~O_APPEND;
dflags |= oflags & O_APPEND;
if (_fcntl(fp->_file, F_SETFL, dflags) < 0) {
sverrno = errno;
fclose(fp);
FUNLOCKFILE(fp);
errno = sverrno;
return (NULL);
}
}
if (oflags & O_TRUNC)
(void) ftruncate(fp->_file, (off_t)0);
if (!(oflags & O_APPEND))
(void) _sseek(fp, (fpos_t)0, SEEK_SET);
f = fp->_file;
isopen = 0;
wantfd = -1;
goto finish;
}
/*
* There are actually programs that depend on being able to "freopen"
* descriptors that weren't originally open. Keep this from breaking.
* Remember whether the stream was open to begin with, and which file
* descriptor (if any) was associated with it. If it was attached to
* a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
* should work. This is unnecessary if it was not a Unix file.
*/
if (fp->_flags == 0) {
fp->_flags = __SEOF; /* hold on to it */
isopen = 0;
wantfd = -1;
} else {
/* flush the stream; ANSI doesn't require this. */
if (fp->_flags & __SWR)
(void) __sflush(fp);
/* if close is NULL, closing is a no-op, hence pointless */
isopen = fp->_close != NULL;
if ((wantfd = fp->_file) < 0 && isopen) {
(void) (*fp->_close)(fp->_cookie);
isopen = 0;
}
}
/* Get a new descriptor to refer to the new file. */
f = _open(file, oflags, DEFFILEMODE);
sverrno = errno;
finish:
/*
* Finish closing fp. Even if the open succeeded above, we cannot
* keep fp->_base: it may be the wrong size. This loses the effect
* of any setbuffer calls, but stdio has always done this before.
*
* Leave the existing file descriptor open until dup2() is called
* below to avoid races where a concurrent open() in another thread
* could claim the existing descriptor.
*/
if (fp->_flags & __SMBF)
free((char *)fp->_bf._base);
fp->_w = 0;
fp->_r = 0;
fp->_p = NULL;
fp->_bf._base = NULL;
fp->_bf._size = 0;
fp->_lbfsize = 0;
if (HASUB(fp))
FREEUB(fp);
fp->_ub._size = 0;
if (HASLB(fp))
FREELB(fp);
fp->_lb._size = 0;
fp->_orientation = 0;
memset(&fp->_mbstate, 0, sizeof(mbstate_t));
if (f < 0) { /* did not get it after all */
if (isopen)
(void) (*fp->_close)(fp->_cookie);
fp->_flags = 0; /* set it free */
FUNLOCKFILE(fp);
errno = sverrno; /* restore in case _close clobbered */
return (NULL);
}
/*
* If reopening something that was open before on a real file, try
* to maintain the descriptor. Various C library routines (perror)
* assume stderr is always fd STDERR_FILENO, even if being freopen'd.
*/
if (wantfd >= 0) {
if (_dup2(f, wantfd) >= 0) {
(void)_close(f);
f = wantfd;
} else
(void)_close(fp->_file);
}
/*
* File descriptors are a full int, but _file is only a short.
* If we get a valid file descriptor that is greater than
* SHRT_MAX, then the fd will get sign-extended into an
* invalid file descriptor. Handle this case by failing the
* open.
*/
if (f > SHRT_MAX) {
fp->_flags = 0; /* set it free */
FUNLOCKFILE(fp);
errno = EMFILE;
return (NULL);
}
fp->_flags = flags;
fp->_file = f;
fp->_cookie = fp;
fp->_read = __sread;
fp->_write = __swrite;
fp->_seek = __sseek;
fp->_close = __sclose;
/*
* When opening in append mode, even though we use O_APPEND,
* we need to seek to the end so that ftell() gets the right
* answer. If the user then alters the seek pointer, or
* the file extends, this will fail, but there is not much
* we can do about this. (We could set __SAPP and check in
* fseek and ftell.)
*/
if (oflags & O_APPEND)
(void) _sseek(fp, (fpos_t)0, SEEK_END);
FUNLOCKFILE(fp);
return (fp);
}