/*

 * SPDX-FileCopyrightText: Copyright (C) 2008 Otto Moerbeek <otto@drijf.net>

 * SPDX-License-Identifier: MIT

 */

#include <errno.h>

#include <stdint.h>

#include <stdlib.h>

#include <sys/types.h>

#ifndef SIZE_MAX

#define SIZE_MAX UINTPTR_MAX

#endif

/*

 * This is sqrt(SIZE_MAX+1), as s1*s2 <= SIZE_MAX

 * if both s1 < MUL_NO_OVERFLOW and s2 < MUL_NO_OVERFLOW

 */

#define MUL_NO_OVERFLOW ((size_t)1 << (sizeof(size_t) * 4))

void *openbsd_reallocarray(void *optr, size_t nmemb, size_t size) {

  if ((nmemb >= MUL_NO_OVERFLOW || size >= MUL_NO_OVERFLOW) &&

      nmemb > 0 && SIZE_MAX / nmemb < size) {

    errno = ENOMEM;

    return NULL;

  }

  /*

   * Head off variations in realloc behavior on different

   * platforms (reported by MarkR <mrogers6@users.sf.net>)

   *

   * The behaviour of reallocarray is implementation-defined if

   * nmemb or size is zero. It can return NULL or non-NULL

   * depending on the platform.

   * https://www.securecoding.cert.org/confluence/display/c/MEM04-C.Beware+of+zero-lengthallocations

   *

   * Here are some extracts from realloc man pages on different platforms.

   *

   * void realloc( void memblock, size_t size );

   *

   * Windows:

   *

   * If there is not enough available memory to expand the block

   * to the given size, the original block is left unchanged,

   * and NULL is returned.  If size is zero, then the block

   * pointed to by memblock is freed; the return value is NULL,

   * and memblock is left pointing at a freed block.

   *

   * OpenBSD:

   *

   * If size or nmemb is equal to 0, a unique pointer to an

   * access protected, zero sized object is returned. Access via

   * this pointer will generate a SIGSEGV exception.

   *

   * Linux:

   *

   * If size was equal to 0, either NULL or a pointer suitable

   * to be passed to free() is returned.

   *

   * OS X:

   *

   * If size is zero and ptr is not NULL, a new, minimum sized

   * object is allocated and the original object is freed.

   *

   * It looks like images with zero width or height can trigger

   * this, and fuzzing behaviour will differ by platform, so

   * fuzzing on one platform may not detect zero-size allocation

   * problems on other platforms.

   */

  if (size == 0 || nmemb == 0) {

    return NULL;

  }

  return realloc(optr, size * nmemb);

}