netdev - Re: [PATCH net] virtio-net: fix overflow inside virtnet_rq

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Message-ID: <1724843499.0572476-1-xuanzhuo@linux.alibaba.com>
Date: Wed, 28 Aug 2024 19:11:39 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org,
 "Michael S. Tsirkin" <mst@...hat.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 virtualization@...ts.linux.dev,
 "Si-Wei Liu" <si-wei.liu@...cle.com>,
 Darren Kenny <darren.kenny@...cle.com>
Subject: Re: [PATCH net] virtio-net: fix overflow inside virtnet_rq_alloc

On Tue, 27 Aug 2024 11:38:45 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Tue, Aug 20, 2024 at 3:19 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> >
> > leads to regression on VM with the sysctl value of:
> >
> > - net.core.high_order_alloc_disable=1
> >
> > which could see reliable crashes or scp failure (scp a file 100M in size
> > to VM):
> >
> > The issue is that the virtnet_rq_dma takes up 16 bytes at the beginning
> > of a new frag. When the frag size is larger than PAGE_SIZE,
> > everything is fine. However, if the frag is only one page and the
> > total size of the buffer and virtnet_rq_dma is larger than one page, an
> > overflow may occur. In this case, if an overflow is possible, I adjust
> > the buffer size. If net.core.high_order_alloc_disable=1, the maximum
> > buffer size is 4096 - 16. If net.core.high_order_alloc_disable=0, only
> > the first buffer of the frag is affected.
>
> I wonder instead of trying to make use of headroom, would it be
> simpler if we allocate dedicated arrays of virtnet_rq_dma？

Sorry for the late reply. My mailbox was full, so I missed the reply to this
thread. Thanks to Si-Wei for reminding me.

If the virtnet_rq_dma is at the headroom, we can get the virtnet_rq_dma by buf.

	struct page *page = virt_to_head_page(buf);

	head = page_address(page);

If we use a dedicated array, then we need pass the virtnet_rq_dma pointer to
virtio core, the array has the same size with the rx ring.

The virtnet_rq_dma will be:

struct virtnet_rq_dma {
	dma_addr_t addr;
	u32 ref;
	u16 len;
	u16 need_sync;
+	void *buf;
};

That will be simpler.

>
> Btw, I see it has a need_sync, I wonder if it can help for performance
> or not? If not, any reason to keep that?

I think yes, we can skip the cpu sync when we do not need it.

Thanks.


>
> >
> > Fixes: f9dac92ba908 ("virtio_ring: enable premapped mode whatever use_dma_api")
> > Reported-by: "Si-Wei Liu" <si-wei.liu@...cle.com>
> > Closes: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.com
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >  drivers/net/virtio_net.c | 12 +++++++++---
> >  1 file changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index c6af18948092..e5286a6da863 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -918,9 +918,6 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> >         void *buf, *head;
> >         dma_addr_t addr;
> >
> > -       if (unlikely(!skb_page_frag_refill(size, alloc_frag, gfp)))
> > -               return NULL;
> > -
> >         head = page_address(alloc_frag->page);
> >
> >         dma = head;
> > @@ -2421,6 +2418,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> >         len = SKB_DATA_ALIGN(len) +
> >               SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> >
> > +       if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
> > +               return -ENOMEM;
> > +
> >         buf = virtnet_rq_alloc(rq, len, gfp);
> >         if (unlikely(!buf))
> >                 return -ENOMEM;
> > @@ -2521,6 +2521,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> >          */
> >         len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
> >
> > +       if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> > +               return -ENOMEM;
> > +
> > +       if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
> > +               len -= sizeof(struct virtnet_rq_dma);
> > +
> >         buf = virtnet_rq_alloc(rq, len + room, gfp);
> >         if (unlikely(!buf))
> >                 return -ENOMEM;
> > --
> > 2.32.0.3.g01195cf9f
>
> Thanks
>
> >
>
>
>