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introduce xcalloc() and xasprintf() failure-checked allocations functions
and use them throughout openssh

xcalloc is particularly important because malloc(nmemb * size) is a
dangerous idiom (subject to integer overflow) and it is time for it to
die

feedback and ok deraadt@

/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Versions of malloc and friends that check their results, and never return
 * failure (they call fatal if they encounter an error).
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#include "includes.h"

#include "xmalloc.h"
#include "log.h"

void *
xmalloc(size_t size)
{
	void *ptr;

	if (size == 0)
		fatal("xmalloc: zero size");
	ptr = malloc(size);
	if (ptr == NULL)
		fatal("xmalloc: out of memory (allocating %lu bytes)", (u_long) size);
	return ptr;
}

void *
xcalloc(size_t nmemb, size_t size)
{
	void *ptr;

        if (nmemb && size && SIZE_T_MAX / nmemb < size)
		fatal("xcalloc: nmemb * size > SIZE_T_MAX");
	if (size == 0 || nmemb == 0)
		fatal("xcalloc: zero size");
	ptr = calloc(nmemb, size);
	if (ptr == NULL)
		fatal("xcalloc: out of memory (allocating %lu bytes)",
		    (u_long)(size * nmemb));
	return ptr;
}

void *
xrealloc(void *ptr, size_t new_size)
{
	void *new_ptr;

	if (new_size == 0)
		fatal("xrealloc: zero size");
	if (ptr == NULL)
		new_ptr = malloc(new_size);
	else
		new_ptr = realloc(ptr, new_size);
	if (new_ptr == NULL)
		fatal("xrealloc: out of memory (new_size %lu bytes)", (u_long) new_size);
	return new_ptr;
}

void
xfree(void *ptr)
{
	if (ptr == NULL)
		fatal("xfree: NULL pointer given as argument");
	free(ptr);
}

char *
xstrdup(const char *str)
{
	size_t len;
	char *cp;

	len = strlen(str) + 1;
	cp = xmalloc(len);
	strlcpy(cp, str, len);
	return cp;
}

int
xasprintf(char **ret, const char *fmt, ...)
{
	va_list ap;
	int i;

	va_start(ap, fmt);
	i = vasprintf(ret, fmt, ap);
	va_end(ap);

	if (i < 0 || *ret == NULL)
		fatal("xasprintf: could not allocate memory");

	return (i);
}