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For open/openat, if the flags parameter does not contain O_CREAT, the
3rd (variadic) mode_t parameter is irrelevant.  Many developers in the past
have passed mode_t (0, 044, 0644, or such), which might lead future people
to copy this broken idiom, and perhaps even believe this parameter has some
meaning or implication or application. Delete them all.
This comes out of a conversation where tb@ noticed that a strange (but
intentional) pledge behaviour is to always knock-out high-bits from
mode_t on a number of system calls as a safety factor, and his bewilderment
that this appeared to be happening against valid modes (at least visually),
but no sorry, they are all irrelevant junk.  They could all be 0xdeafbeef.
ok millert

/*	$OpenBSD: buf.c,v 1.86 2021/10/24 21:24:16 deraadt Exp $	*/
/*
 * Copyright (c) 2003 Jean-Francois Brousseau <jfb@openbsd.org>
 * All rights reserved.
 *
 * 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. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``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 AUTHOR 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.
 */

#include <sys/stat.h>
#include <sys/time.h>

#include <errno.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "atomicio.h"
#include "cvs.h"
#include "buf.h"

#define BUF_INCR	128

struct buf {
	/* buffer handle, buffer size, and data length */
	u_char	*cb_buf;
	size_t	 cb_size;
	size_t	 cb_len;
};

#define SIZE_LEFT(b)	(b->cb_size - b->cb_len)

static void	buf_grow(BUF *, size_t);

/*
 * Create a new buffer structure and return a pointer to it.  This structure
 * uses dynamically-allocated memory and must be freed with buf_free(), once
 * the buffer is no longer needed.
 */
BUF *
buf_alloc(size_t len)
{
	BUF *b;

	b = xmalloc(sizeof(*b));
	/* Postpone creation of zero-sized buffers */
	if (len > 0)
		b->cb_buf = xcalloc(1, len);
	else
		b->cb_buf = NULL;

	b->cb_size = len;
	b->cb_len = 0;

	return (b);
}

/*
 * Open the file specified by <path> and load all of its contents into a
 * buffer.
 * Returns the loaded buffer.
 */
BUF *
buf_load(const char *path)
{
	int fd;
	BUF *bp;

	if ((fd = open(path, O_RDONLY)) == -1)
		fatal("buf_load: failed to load '%s' : %s", path,
		    strerror(errno));

	bp = buf_load_fd(fd);
	(void)close(fd);
	return (bp);
}

BUF *
buf_load_fd(int fd)
{
	struct stat st;
	BUF *buf;

	if (fstat(fd, &st) == -1)
		fatal("buf_load_fd: fstat: %s", strerror(errno));

	if (lseek(fd, 0, SEEK_SET) == -1)
		fatal("buf_load_fd: lseek: %s", strerror(errno));

	if ((uintmax_t)st.st_size > SIZE_MAX)
		fatal("buf_load_fd: file size too big");
	buf = buf_alloc(st.st_size);
	if (atomicio(read, fd, buf->cb_buf, buf->cb_size) != buf->cb_size)
		fatal("buf_load_fd: read: %s", strerror(errno));
	buf->cb_len = buf->cb_size;

	return (buf);
}

void
buf_free(BUF *b)
{
	if (b == NULL)
		return;
	free(b->cb_buf);
	free(b);
}

/*
 * Free the buffer <b>'s structural information but do not free the contents
 * of the buffer.  Instead, they are returned and should be freed later.
 */
void *
buf_release(BUF *b)
{
	void *tmp;

	tmp = b->cb_buf;
	free(b);
	return (tmp);
}

/*
 * Append a single character <c> to the end of the buffer <b>.
 */
void
buf_putc(BUF *b, int c)
{
	u_char *bp;

	if (SIZE_LEFT(b) == 0)
		buf_grow(b, BUF_INCR);
	bp = b->cb_buf + b->cb_len;
	*bp = (u_char)c;
	b->cb_len++;
}

/*
 * Append a C-string <str> to the end of the buffer <b>.
 */
void
buf_puts(BUF *b, const char *str)
{
	buf_append(b, str, strlen(str));
}

/*
 * Append <len> bytes of data pointed to by <data> to the buffer <b>.  If the
 * buffer is too small to accept all data, it will get resized to an
 * appropriate size to accept all data.
 */
void
buf_append(BUF *b, const void *data, size_t len)
{
	size_t left;
	u_char *bp;

	left = SIZE_LEFT(b);

	if (left < len)
		buf_grow(b, len - left);

	bp = b->cb_buf + b->cb_len;
	memcpy(bp, data, len);
	b->cb_len += len;
}

/*
 * Returns the size of the buffer that is being used.
 */
size_t
buf_len(BUF *b)
{
	return (b->cb_len);
}

/*
 * Write the contents of the buffer <b> to the specified <fd>
 */
int
buf_write_fd(BUF *b, int fd)
{
	if (atomicio(vwrite, fd, b->cb_buf, b->cb_len) != b->cb_len)
		return (-1);
	return (0);
}

/*
 * Write the contents of the buffer <b> to the file whose path is given in
 * <path>.  If the file does not exist, it is created with mode <mode>.
 */
int
buf_write(BUF *b, const char *path, mode_t mode)
{
	int fd;
open:
	if ((fd = open(path, O_WRONLY|O_CREAT|O_TRUNC, mode)) == -1) {
		if (errno == EACCES && unlink(path) != -1)
			goto open;
		else
			fatal("open: `%s': %s", path, strerror(errno));
	}

	if (buf_write_fd(b, fd) == -1) {
		(void)unlink(path);
		fatal("buf_write: buf_write_fd: `%s'", path);
	}

	if (fchmod(fd, mode) == -1)
		cvs_log(LP_ERR, "permissions not set on file %s", path);

	(void)close(fd);

	return (0);
}

/*
 * Write the contents of the buffer <b> to a temporary file whose path is
 * specified using <template> (see mkstemp.3). If <tv> is specified file
 * access and modification time is set to <tv>.
 * NB. This function will modify <template>, as per mkstemp
 */
int
buf_write_stmp(BUF *b, char *template, struct timeval *tv)
{
	int fd;

	if ((fd = mkstemp(template)) == -1)
		fatal("mkstemp: `%s': %s", template, strerror(errno));

	if (buf_write_fd(b, fd) == -1) {
		(void)unlink(template);
		fatal("buf_write_stmp: buf_write_fd: `%s'", template);
	}

	if (tv != NULL) {
		if (futimes(fd, tv) == -1)
			fatal("buf_write_stmp: futimes failed");
	}

	worklist_add(template, &temp_files);

	if (lseek(fd, 0, SEEK_SET) == -1)
		fatal("buf_write_stmp: lseek: %s", strerror(errno));

	return (fd);
}

u_char *
buf_get(BUF *bp)
{
	return (bp->cb_buf);
}

int
buf_differ(const BUF *b1, const BUF *b2)
{
	if (b1->cb_len != b2->cb_len)
		return (1);

	return (memcmp(b1->cb_buf, b2->cb_buf, b1->cb_len));
}

/*
 * Grow the buffer <b> by <len> bytes.  The contents are unchanged by this
 * operation regardless of the result.
 */
static void
buf_grow(BUF *b, size_t len)
{
	b->cb_buf = xreallocarray(b->cb_buf, 1, b->cb_size + len);
	b->cb_size += len;
}