Subject: Re: [PATCH net-next] net: more accurate network taps in transmit path

From: Jamie Gloudon <[email-masked]>
Date: Wed, 19 Sep 2012 11:58:30 -0400

Just to report. This patch fixed the invalid tcp tx checksum issue via tap for me. Thanks!

On Wed, Sep 19, 2012 at 08:44:49AM +0200, Eric Dumazet wrote:
> From: Eric Dumazet <[email-masked]>
> 
> dev_queue_xmit_nit() should be called right before ndo_start_xmit()
> calls or we might give wrong packet contents to taps users :
> 
> Packet checksum can be changed, or packet can be linearized or
> segmented, and segments partially sent for the later case.
> 
> Also a memory allocation can fail and packet never really hit the
> driver entry point.
> 
> Reported-by: Jamie Gloudon <[email-masked]>
> Signed-off-by: Eric Dumazet <[email-masked]>
> ---
>  net/core/dev.c |    9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index dcc673d..52cd1d7 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2213,9 +2213,6 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
>  		if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
>  			skb_dst_drop(skb);
>  
> -		if (!list_empty(&ptype_all))
> -			dev_queue_xmit_nit(skb, dev);
> -
>  		features = netif_skb_features(skb);
>  
>  		if (vlan_tx_tag_present(skb) &&
> @@ -2250,6 +2247,9 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
>  			}
>  		}
>  
> +		if (!list_empty(&ptype_all))
> +			dev_queue_xmit_nit(skb, dev);
> +
>  		skb_len = skb->len;
>  		rc = ops->ndo_start_xmit(skb, dev);
>  		trace_net_dev_xmit(skb, rc, dev, skb_len);
> @@ -2272,6 +2272,9 @@ gso:
>  		if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
>  			skb_dst_drop(nskb);
>  
> +		if (!list_empty(&ptype_all))
> +			dev_queue_xmit_nit(nskb, dev);
> +
>  		skb_len = nskb->len;
>  		rc = ops->ndo_start_xmit(nskb, dev);
>  		trace_net_dev_xmit(nskb, rc, dev, skb_len);
> 
>