png_inflate_read(png_structrp png_ptr, png_bytep read_buffer, uInt read_size,
    png_uint_32p chunk_bytes, png_bytep next_out, png_alloc_size_t *out_size,
    int finish)
{
   if (png_ptr->zowner == png_ptr->chunk_name)
   {
      int ret;

      /* next_in and avail_in must have been initialized by the caller. */
      png_ptr->zstream.next_out = next_out;
      png_ptr->zstream.avail_out = 0; /* set in the loop */

      do
      {
         if (png_ptr->zstream.avail_in == 0)
         {
            if (read_size > *chunk_bytes)
               read_size = (uInt)*chunk_bytes;
            *chunk_bytes -= read_size;

            if (read_size > 0)
               png_crc_read(png_ptr, read_buffer, read_size);

            png_ptr->zstream.next_in = read_buffer;
            png_ptr->zstream.avail_in = read_size;
         }

         if (png_ptr->zstream.avail_out == 0)
         {
            uInt avail = ZLIB_IO_MAX;
            if (avail > *out_size)
               avail = (uInt)*out_size;
            *out_size -= avail;

            png_ptr->zstream.avail_out = avail;
         }

         /* Use Z_SYNC_FLUSH when there is no more chunk data to ensure that all
          * the available output is produced; this allows reading of truncated
          * streams.
          */
         ret = PNG_INFLATE(png_ptr, *chunk_bytes > 0 ?
             Z_NO_FLUSH : (finish ? Z_FINISH : Z_SYNC_FLUSH));
      }
      while (ret == Z_OK && (*out_size > 0 || png_ptr->zstream.avail_out > 0));

      *out_size += png_ptr->zstream.avail_out;
      png_ptr->zstream.avail_out = 0; /* Should not be required, but is safe */

      /* Ensure the error message pointer is always set: */
      png_zstream_error(png_ptr, ret);
      return ret;
   }

   else
   {
      png_ptr->zstream.msg = PNGZ_MSG_CAST("zstream unclaimed");
      return Z_STREAM_ERROR;
   }
}

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.