cc3d85727d
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
238 lines
6.9 KiB
C
238 lines
6.9 KiB
C
/*-
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* Copyright (c) 1990, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Chris Torek.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#if defined(LIBC_SCCS) && !defined(lint)
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static char sccsid[] = "@(#)freopen.c 8.1 (Berkeley) 6/4/93";
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#endif /* LIBC_SCCS and not lint */
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "namespace.h"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <errno.h>
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#include <limits.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include "un-namespace.h"
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#include "libc_private.h"
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#include "local.h"
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/*
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* Re-direct an existing, open (probably) file to some other file.
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* ANSI is written such that the original file gets closed if at
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* all possible, no matter what.
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*/
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FILE *
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freopen(file, mode, fp)
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const char * __restrict file;
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const char * __restrict mode;
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FILE *fp;
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{
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int f;
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int dflags, flags, isopen, oflags, sverrno, wantfd;
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if ((flags = __sflags(mode, &oflags)) == 0) {
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sverrno = errno;
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(void) fclose(fp);
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errno = sverrno;
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return (NULL);
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}
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FLOCKFILE(fp);
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if (!__sdidinit)
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__sinit();
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/*
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* If the filename is a NULL pointer, the caller is asking us to
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* re-open the same file with a different mode. We allow this only
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* if the modes are compatible.
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*/
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if (file == NULL) {
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/* See comment below regarding freopen() of closed files. */
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if (fp->_flags == 0) {
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FUNLOCKFILE(fp);
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errno = EINVAL;
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return (NULL);
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}
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if ((dflags = _fcntl(fp->_file, F_GETFL)) < 0) {
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sverrno = errno;
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fclose(fp);
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FUNLOCKFILE(fp);
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errno = sverrno;
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return (NULL);
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}
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if ((dflags & O_ACCMODE) != O_RDWR && (dflags & O_ACCMODE) !=
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(oflags & O_ACCMODE)) {
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fclose(fp);
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FUNLOCKFILE(fp);
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errno = EINVAL;
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return (NULL);
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}
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if (fp->_flags & __SWR)
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(void) __sflush(fp);
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if ((oflags ^ dflags) & O_APPEND) {
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dflags &= ~O_APPEND;
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dflags |= oflags & O_APPEND;
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if (_fcntl(fp->_file, F_SETFL, dflags) < 0) {
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sverrno = errno;
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fclose(fp);
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FUNLOCKFILE(fp);
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errno = sverrno;
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return (NULL);
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}
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}
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if (oflags & O_TRUNC)
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(void) ftruncate(fp->_file, (off_t)0);
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if (!(oflags & O_APPEND))
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(void) _sseek(fp, (fpos_t)0, SEEK_SET);
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f = fp->_file;
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isopen = 0;
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wantfd = -1;
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goto finish;
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}
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/*
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* There are actually programs that depend on being able to "freopen"
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* descriptors that weren't originally open. Keep this from breaking.
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* Remember whether the stream was open to begin with, and which file
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* descriptor (if any) was associated with it. If it was attached to
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* a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
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* should work. This is unnecessary if it was not a Unix file.
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*/
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if (fp->_flags == 0) {
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fp->_flags = __SEOF; /* hold on to it */
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isopen = 0;
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wantfd = -1;
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} else {
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/* flush the stream; ANSI doesn't require this. */
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if (fp->_flags & __SWR)
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(void) __sflush(fp);
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/* if close is NULL, closing is a no-op, hence pointless */
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isopen = fp->_close != NULL;
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if ((wantfd = fp->_file) < 0 && isopen) {
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(void) (*fp->_close)(fp->_cookie);
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isopen = 0;
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}
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}
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/* Get a new descriptor to refer to the new file. */
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f = _open(file, oflags, DEFFILEMODE);
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sverrno = errno;
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finish:
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/*
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* Finish closing fp. Even if the open succeeded above, we cannot
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* keep fp->_base: it may be the wrong size. This loses the effect
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* of any setbuffer calls, but stdio has always done this before.
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*
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* Leave the existing file descriptor open until dup2() is called
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* below to avoid races where a concurrent open() in another thread
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* could claim the existing descriptor.
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*/
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if (fp->_flags & __SMBF)
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free((char *)fp->_bf._base);
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fp->_w = 0;
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fp->_r = 0;
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fp->_p = NULL;
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fp->_bf._base = NULL;
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fp->_bf._size = 0;
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fp->_lbfsize = 0;
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if (HASUB(fp))
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FREEUB(fp);
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fp->_ub._size = 0;
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if (HASLB(fp))
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FREELB(fp);
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fp->_lb._size = 0;
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fp->_orientation = 0;
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memset(&fp->_mbstate, 0, sizeof(mbstate_t));
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if (f < 0) { /* did not get it after all */
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if (isopen)
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(void) (*fp->_close)(fp->_cookie);
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fp->_flags = 0; /* set it free */
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FUNLOCKFILE(fp);
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errno = sverrno; /* restore in case _close clobbered */
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return (NULL);
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}
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/*
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* If reopening something that was open before on a real file, try
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* to maintain the descriptor. Various C library routines (perror)
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* assume stderr is always fd STDERR_FILENO, even if being freopen'd.
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*/
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if (wantfd >= 0) {
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if (_dup2(f, wantfd) >= 0) {
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(void)_close(f);
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f = wantfd;
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} else
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(void)_close(fp->_file);
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}
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/*
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* File descriptors are a full int, but _file is only a short.
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* If we get a valid file descriptor that is greater than
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* SHRT_MAX, then the fd will get sign-extended into an
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* invalid file descriptor. Handle this case by failing the
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* open.
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*/
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if (f > SHRT_MAX) {
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fp->_flags = 0; /* set it free */
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FUNLOCKFILE(fp);
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errno = EMFILE;
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return (NULL);
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}
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fp->_flags = flags;
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fp->_file = f;
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fp->_cookie = fp;
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fp->_read = __sread;
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fp->_write = __swrite;
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fp->_seek = __sseek;
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fp->_close = __sclose;
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/*
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* When opening in append mode, even though we use O_APPEND,
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* we need to seek to the end so that ftell() gets the right
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* answer. If the user then alters the seek pointer, or
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* the file extends, this will fail, but there is not much
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* we can do about this. (We could set __SAPP and check in
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* fseek and ftell.)
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*/
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if (oflags & O_APPEND)
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(void) _sseek(fp, (fpos_t)0, SEEK_END);
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FUNLOCKFILE(fp);
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return (fp);
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}
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