netdev - Re: [PATCH v2 1/2] virtio-net: Verify page list size before fitting into skb

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Message-ID: <1317822654.3676.1.camel@lappy>
Date:	Wed, 05 Oct 2011 15:50:54 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH v2 1/2] virtio-net: Verify page list size before
 fitting into  skb

On Mon, 2011-10-03 at 21:04 +0200, Michael S. Tsirkin wrote:
> On Wed, Sep 28, 2011 at 05:40:54PM +0300, Sasha Levin wrote:
> > This patch verifies that the length of a buffer stored in a linked list
> > of pages is small enough to fit into a skb.
> > 
> > If the size is larger than a max size of a skb, it means that we shouldn't
> > go ahead building skbs anyway since we won't be able to send the buffer as
> > the user requested.
> > 
> > Cc: Rusty Russell <rusty@...tcorp.com.au>
> > Cc: "Michael S. Tsirkin" <mst@...hat.com>
> > Cc: virtualization@...ts.linux-foundation.org
> > Cc: netdev@...r.kernel.org
> > Cc: kvm@...r.kernel.org
> > Signed-off-by: Sasha Levin <levinsasha928@...il.com>
> > ---
> >  drivers/net/virtio_net.c |   13 +++++++++++++
> >  1 files changed, 13 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 0c7321c..bde0dec 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -195,6 +195,19 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> >  	len -= copy;
> >  	offset += copy;
> >  
> > +	/*
> > +	 * Verify that we can indeed put this data into a skb.
> > +	 * This is here to handle cases when the device erroneously
> > +	 * tries to receive more than is possible. This is usually
> > +	 * the case of a broken device.
> > +	 */
> > +	if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) {
> > +		if (net_ratelimit())
> > +			pr_debug("%s: too much data\n", skb->dev->name);
> > +		dev_kfree_skb(skb);
> > +		return NULL;
> > +	}
> > +
> 
> BTW, receive_mergeable does
>                         pr_debug("%s: packet too long\n", skb->dev->name);
>                         skb->dev->stats.rx_length_errors++;
> 
> which makes sense.

Do you think we should increase rx_length_errors here as well?

-- 

Sasha.

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