png_check_chunk_length(png_const_structrp png_ptr, const png_uint_32 length)
{
   png_alloc_size_t limit = PNG_UINT_31_MAX;

# ifdef PNG_SET_USER_LIMITS_SUPPORTED
   if (png_ptr->user_chunk_malloc_max > 0 &&
       png_ptr->user_chunk_malloc_max < limit)
      limit = png_ptr->user_chunk_malloc_max;
# elif PNG_USER_CHUNK_MALLOC_MAX > 0
   if (PNG_USER_CHUNK_MALLOC_MAX < limit)
      limit = PNG_USER_CHUNK_MALLOC_MAX;
# endif
   if (png_ptr->chunk_name == png_IDAT)
   {
      png_alloc_size_t idat_limit = PNG_UINT_31_MAX;
      size_t row_factor =
         (size_t)png_ptr->width
         * (size_t)png_ptr->channels
         * (png_ptr->bit_depth > 8? 2: 1)
         + 1
         + (png_ptr->interlaced? 6: 0);
      if (png_ptr->height > PNG_UINT_32_MAX/row_factor)
         idat_limit = PNG_UINT_31_MAX;
      else
         idat_limit = png_ptr->height * row_factor;
      row_factor = row_factor > 32566? 32566 : row_factor;
      idat_limit += 6 + 5*(idat_limit/row_factor+1); /* zlib+deflate overhead */
      idat_limit=idat_limit < PNG_UINT_31_MAX? idat_limit : PNG_UINT_31_MAX;
      limit = limit < idat_limit? idat_limit : limit;
   }

   if (length > limit)
   {
      png_debug2(0," length = %lu, limit = %lu",
         (unsigned long)length,(unsigned long)limit);
      png_chunk_error(png_ptr, "chunk data is too large");
   }
}
The software performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.