MagickExport Image *FlipImage(const Image *image,ExceptionInfo *exception)
{
#define FlipImageTag  "Flip/Image"

  CacheView
    *flip_view,
    *image_view;

  Image
    *flip_image;

  MagickBooleanType
    status;

  MagickOffsetType
    progress;

  RectangleInfo
    page;

  ssize_t
    y;

  assert(image != (const Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  flip_image=CloneImage(image,image->columns,image->rows,MagickTrue,exception);
  if (flip_image == (Image *) NULL)
    return((Image *) NULL);
  /*
    Flip image.
  */
  status=MagickTrue;
  progress=0;
  page=image->page;
  image_view=AcquireVirtualCacheView(image,exception);
  flip_view=AcquireAuthenticCacheView(flip_image,exception);
#if defined(MAGICKCORE_OPENMP_SUPPORT)
  #pragma omp parallel for schedule(static,4) shared(status) \
    magick_threads(image,flip_image,1,1)
#endif
  for (y=0; y < (ssize_t) flip_image->rows; y++)
  {
    register const Quantum
      *restrict p;

    register Quantum
      *restrict q;

    register ssize_t
      x;

    if (status == MagickFalse)
      continue;
    p=GetCacheViewVirtualPixels(image_view,0,y,image->columns,1,exception);
    q=QueueCacheViewAuthenticPixels(flip_view,0,(ssize_t) (flip_image->rows-y-
      1),flip_image->columns,1,exception);
    if ((p == (const Quantum *) NULL) || (q == (Quantum *) NULL))
      {
        status=MagickFalse;
        continue;
      }
    for (x=0; x < (ssize_t) flip_image->columns; x++)
    {
      register ssize_t
        i;

      if (GetPixelReadMask(image,p) == 0)
        {
          SetPixelBackgoundColor(flip_image,q);
          p+=GetPixelChannels(image);
          q+=GetPixelChannels(flip_image);
          continue;
        }
      for (i=0; i < (ssize_t) GetPixelChannels(image); i++)
      {
        PixelChannel channel=GetPixelChannelChannel(image,i);
        PixelTrait traits=GetPixelChannelTraits(image,channel);
        PixelTrait flip_traits=GetPixelChannelTraits(flip_image,channel);
        if ((traits == UndefinedPixelTrait) ||
            (flip_traits == UndefinedPixelTrait))
          continue;
        SetPixelChannel(flip_image,channel,p[i],q);
      }
      p+=GetPixelChannels(image);
      q+=GetPixelChannels(flip_image);
    }
    if (SyncCacheViewAuthenticPixels(flip_view,exception) == MagickFalse)
      status=MagickFalse;
    if (image->progress_monitor != (MagickProgressMonitor) NULL)
      {
        MagickBooleanType
          proceed;

#if defined(MAGICKCORE_OPENMP_SUPPORT)
        #pragma omp critical (MagickCore_FlipImage)
#endif
        proceed=SetImageProgress(image,FlipImageTag,progress++,image->rows);
        if (proceed == MagickFalse)
          status=MagickFalse;
      }
  }
  flip_view=DestroyCacheView(flip_view);
  image_view=DestroyCacheView(image_view);
  flip_image->type=image->type;
  if (page.height != 0)
    page.y=(ssize_t) (page.height-flip_image->rows-page.y);
  flip_image->page=page;
  if (status == MagickFalse)
    flip_image=DestroyImage(flip_image);
  return(flip_image);
}

The product reads data past the end, or before the beginning, of the intended buffer.