netdev - Re: [Xen-devel] [PATCH 2/4] xen-netfront: drop skb when skb->len

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Date:	Mon, 18 Mar 2013 13:48:20 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"annie.li@...cle.com" <annie.li@...cle.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] [PATCH 2/4] xen-netfront: drop skb when skb->len >
 65535

On Mon, 2013-03-18 at 13:46 +0000, David Vrabel wrote:
> On 18/03/13 10:35, Wei Liu wrote:
> > The `size' field of Xen network wire format is uint16_t, anything bigger than
> > 65535 will cause overflow.
> 
> The backend needs to be able to handle these bad packets without
> disconnecting the VIF -- we can't fix all the frontend drivers.

Agreed, although that doesn't imply that we shouldn't fix the frontend
where we can -- such as upstream as Wei does here.

Ian.

> 
> David
> 
> > Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> > ---
> >  drivers/net/xen-netfront.c |   12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> > index 5527663..8c3d065 100644
> > --- a/drivers/net/xen-netfront.c
> > +++ b/drivers/net/xen-netfront.c
> > @@ -547,6 +547,18 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
> >  	unsigned int len = skb_headlen(skb);
> >  	unsigned long flags;
> >  
> > +	/*
> > +	 * wire format of xen_netif_tx_request only supports skb->len
> > +	 * < 64K, because size field in xen_netif_tx_request is
> > +	 * uint16_t.
> > +	 */
> > +	if (unlikely(skb->len > (uint16_t)(~0))) {
> > +		net_alert_ratelimited(
> > +			"xennet: skb->len = %d, too big for wire format\n",
> > +			skb->len);
> > +		goto drop;
> > +	}
> > +
> >  	slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) +
> >  		xennet_count_skb_frag_slots(skb);
> >  	if (unlikely(slots > MAX_SKB_FRAGS + 1)) {
> 


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