Re: [PATCH net-next 1/5] virtio_net: Fix an unsafe reference to the page chain

[Liang Chen <liangchen.linux@gmail.com>]

On Sun, May 28, 2023 at 2:16 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Fri, May 26, 2023 at 01:46:17PM +0800, Liang Chen wrote:
> > "private" of buffer page is currently used for big mode to chain pages.
> > But in mergeable mode, that offset of page could mean something else,
> > e.g. when page_pool page is used instead. So excluding mergeable mode to
> > avoid such a problem.
> >
> > Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
>
> Ugh the subject makes it looks like current code has a problem
> but I don't think so because I don't think anything besides
> big packets uses page->private.
>
> The reason patch is needed is because follow up patches
> use page_pool.
> pls adjust commit log and subject to make all this clear.
>
>
> > ---
> >  drivers/net/virtio_net.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 5a7f7a76b920..c5dca0d92e64 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -497,7 +497,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> >                       return NULL;
> >
> >               page = (struct page *)page->private;
> > -             if (page)
> > +             if (!vi->mergeable_rx_bufs && page)
>
> To be safe let's limit to big packets too:
>
>         if (!vi->mergeable_rx_bufs && vi->big_packets && page)
>
>
>

Sure, thanks!

> >                       give_pages(rq, page);
> >               goto ok;
> >       }
> > --
> > 2.31.1
>