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

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Message-ID: <CACGkMEtvabru_uja8chVhLC27pDoP6y_mBqTKEmN1ohWuAQFPw@mail.gmail.com>
Date: Tue, 10 Sep 2024 14:17:12 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org, 
	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 Mon, Sep 9, 2024 at 4:52 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> On Mon, 9 Sep 2024 16:47:02 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > On Mon, Sep 9, 2024 at 11:16 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > >
> > > On Sun, 8 Sep 2024 15:40:32 -0400, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> > > > On Tue, Aug 20, 2024 at 03:19:13PM +0800, Xuan Zhuo 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.
> > > > >
> > > > > 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>
> > > >
> > > >
> > > > BTW why isn't it needed if we revert f9dac92ba908?
> > >
> > >
> > > This patch fixes the bug in premapped mode.
> > >
> > > The revert operation just disables premapped mode.
> > >
> > > So I think this patch is enough to fix the bug, and we can enable
> > > premapped by default.
> > >
> > > If you worry about the premapped mode, I advice you merge this patch and do
> > > the revert[1]. Then the bug is fixed, and the premapped mode is
> > > disabled by default, we can just enable it for af-xdp.
> > >
> > > [1]: http://lore.kernel.org/all/20240906123137.108741-1-xuanzhuo@linux.alibaba.com
> >
> > Though I think this is a good balance but if we can't get more inputs
> > from Darren. It seems safer to merge what he had tested.
>
> So you mean just merge this:
>
>         http://lore.kernel.org/all/20240906123137.108741-1-xuanzhuo@linux.alibaba.com
>
> Right?

It looks to me it hasn't been tested by Darren yet.

Thanks

>
> Thanks
>
>
> >
> > Thanks
> >
> > >
> > > Thanks.
> > >
> > >
> > > >
> > > > > ---
> > > > >  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
> > > >
> > >
> >
>