1/*	$OpenBSD: freopen.c,v 1.17 2019/06/29 16:12:21 deraadt Exp $ */
2/*-
3 * Copyright (c) 1990, 1993
4 *	The Regents of the University of California.  All rights reserved.
5 *
6 * This code is derived from software contributed to Berkeley by
7 * Chris Torek.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 *    notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 *    notice, this list of conditions and the following disclaimer in the
16 *    documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34#include <sys/types.h>
35#include <sys/stat.h>
36#include <fcntl.h>
37#include <errno.h>
38#include <limits.h>
39#include <unistd.h>
40#include <stdio.h>
41#include <stdlib.h>
42#include "local.h"
43
44/*
45 * Re-direct an existing, open (probably) file to some other file.
46 * ANSI is written such that the original file gets closed if at
47 * all possible, no matter what.
48 */
49FILE *
50freopen(const char *file, const char *mode, FILE *fp)
51{
52	int f;
53	int flags, isopen, oflags, sverrno, wantfd;
54
55	if ((flags = __sflags(mode, &oflags)) == 0) {
56		(void) fclose(fp);
57		return (NULL);
58	}
59
60	if (!__sdidinit)
61		__sinit();
62
63	FLOCKFILE(fp);
64
65	/*
66	 * There are actually programs that depend on being able to "freopen"
67	 * descriptors that weren't originally open.  Keep this from breaking.
68	 * Remember whether the stream was open to begin with, and which file
69	 * descriptor (if any) was associated with it.  If it was attached to
70	 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
71	 * should work.  This is unnecessary if it was not a Unix file.
72	 */
73	if (fp->_flags == 0) {
74		fp->_flags = __SEOF;	/* hold on to it */
75		isopen = 0;
76		wantfd = -1;
77	} else {
78		/* flush the stream; ANSI doesn't require this. */
79		if (fp->_flags & __SWR)
80			(void) __sflush(fp);
81		/* if close is NULL, closing is a no-op, hence pointless */
82		isopen = fp->_close != NULL;
83		if ((wantfd = fp->_file) < 0 && isopen) {
84			(void) (*fp->_close)(fp->_cookie);
85			isopen = 0;
86		}
87	}
88
89	/* Get a new descriptor to refer to the new file. */
90	f = open(file, oflags, DEFFILEMODE);
91	if (f == -1 && isopen) {
92		/* If out of fd's close the old one and try again. */
93		if (errno == ENFILE || errno == EMFILE) {
94			(void) (*fp->_close)(fp->_cookie);
95			isopen = 0;
96			f = open(file, oflags, DEFFILEMODE);
97		}
98	}
99	sverrno = errno;
100
101	/*
102	 * Finish closing fp.  Even if the open succeeded above, we cannot
103	 * keep fp->_base: it may be the wrong size.  This loses the effect
104	 * of any setbuffer calls, but stdio has always done this before.
105	 */
106	if (isopen && f != wantfd)
107		(void) (*fp->_close)(fp->_cookie);
108	if (fp->_flags & __SMBF)
109		free((char *)fp->_bf._base);
110	fp->_w = 0;
111	fp->_r = 0;
112	fp->_p = NULL;
113	fp->_bf._base = NULL;
114	fp->_bf._size = 0;
115	fp->_lbfsize = 0;
116	if (HASUB(fp))
117		FREEUB(fp);
118	_UB(fp)._size = 0;
119	WCIO_FREE(fp);
120	if (HASLB(fp))
121		FREELB(fp);
122	fp->_lb._size = 0;
123
124	if (f == -1) {			/* did not get it after all */
125		fp->_flags = 0;		/* set it free */
126		FUNLOCKFILE(fp);
127		errno = sverrno;	/* restore in case _close clobbered */
128		return (NULL);
129	}
130
131	/*
132	 * If reopening something that was open before on a real file, try
133	 * to maintain the descriptor.  Various C library routines (perror)
134	 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
135	 */
136	if (wantfd >= 0 && f != wantfd) {
137		if (dup3(f, wantfd, oflags & O_CLOEXEC) >= 0) {
138			(void) close(f);
139			f = wantfd;
140		}
141	}
142
143	/* _file is only a short */
144	if (f > SHRT_MAX) {
145		fp->_flags = 0;		/* set it free */
146		FUNLOCKFILE(fp);
147		errno = EMFILE;
148		return (NULL);
149	}
150
151	fp->_flags = flags;
152	fp->_file = f;
153	fp->_cookie = fp;
154	fp->_read = __sread;
155	fp->_write = __swrite;
156	fp->_seek = __sseek;
157	fp->_close = __sclose;
158
159	/*
160	 * When opening in append mode, even though we use O_APPEND,
161	 * we need to seek to the end so that ftell() gets the right
162	 * answer.  If the user then alters the seek pointer, or
163	 * the file extends, this will fail, but there is not much
164	 * we can do about this.  (We could set __SAPP and check in
165	 * fseek and ftell.)
166	 */
167	if (oflags & O_APPEND)
168		(void) __sseek(fp, 0, SEEK_END);
169	FUNLOCKFILE(fp);
170	return (fp);
171}
172DEF_STRONG(freopen);
173