static void user_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
    struct rwpng_read_data *read_data = (struct rwpng_read_data *)png_get_io_ptr(png_ptr);

    png_size_t read = fread(data, 1, length, read_data->fp);
    if (!read) {
        png_error(png_ptr, "Read error");
    }
    read_data->bytes_read += read;
}

The product 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 occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.