Re: [PATCH net v2 1/3] packet: do skb_probe_transport_header when we actually have data

[Jason Wang <jasowang@redhat.com>]

On 11/11/2015 06:03 AM, Daniel Borkmann wrote:
> In tpacket_fill_skb() commit c1aad275b029 ("packet: set transport
> header before doing xmit") and later on 40893fd0fd4e ("net: switch
> to use skb_probe_transport_header()") was probing for a transport
> header on the skb from a ring buffer slot, but at a time, where
> the skb has _not even_ been filled with data yet. So that call into
> the flow dissector is pretty useless. Lets do it after we've set
> up the skb frags.
>
> Fixes: c1aad275b029 ("packet: set transport header before doing xmit")
> Reported-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Jason Wang <jasowang@redhat.com>
> ---
>  net/packet/af_packet.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index af399ca..80c36c0 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2368,8 +2368,6 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
>  	skb_reserve(skb, hlen);
>  	skb_reset_network_header(skb);
>  
> -	if (!packet_use_direct_xmit(po))
> -		skb_probe_transport_header(skb, 0);
>  	if (unlikely(po->tp_tx_has_off)) {
>  		int off_min, off_max, off;
>  		off_min = po->tp_hdrlen - sizeof(struct sockaddr_ll);
> @@ -2449,6 +2447,9 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
>  		len = ((to_write > len_max) ? len_max : to_write);
>  	}
>  
> +	if (!packet_use_direct_xmit(po))
> +		skb_probe_transport_header(skb, 0);
> +
>  	return tp_len;
>  }
>  

Acked-by: Jason Wang <jasowang@redhat.com>