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Subject: Re: [PATCH 4.20 005/145] tap: call skb_probe_transport_header after
 setting skb->dev
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Cc:     stable@vger.kernel.org, Willem de Bruijn <willemb@google.com>,
        "David S. Miller" <davem@davemloft.net>
References: <20190107104437.308206189@linuxfoundation.org>
 <20190107104438.019339514@linuxfoundation.org>
From:   Christian Borntraeger <borntraeger@de.ibm.com>
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Date:   Mon, 7 Jan 2019 14:39:45 +0100
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On 07.01.2019 13:30, Greg Kroah-Hartman wrote:
> 4.20-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Willem de Bruijn <willemb@google.com>
> 
> [ Upstream commit 8c76e77f9069f10505c08e02646c3ee11ad79038 ]
> 
> The BPF flow dissector expects either skb->sk or skb->dev set on
> all skbs. Delay flow dissection until after skb->dev is set.
> 
> This requires calling from within an rcu read-side critical section.
> That is fine, see also the call from tun_xdp_one.
> 
> Fixes: d0e13a1488ad ("flow_dissector: lookup netns by skb->sk if skb->dev is NULL")
> Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Willem de Bruijn <willemb@google.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

I can confirm that this fixes my issue.

Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
>  drivers/net/tap.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -1177,8 +1177,6 @@ static int tap_get_user_xdp(struct tap_q
>  			goto err_kfree;
>  	}
>  
> -	skb_probe_transport_header(skb, ETH_HLEN);
> -
>  	/* Move network header to the right position for VLAN tagged packets */
>  	if ((skb->protocol == htons(ETH_P_8021Q) ||
>  	     skb->protocol == htons(ETH_P_8021AD)) &&
> @@ -1189,6 +1187,7 @@ static int tap_get_user_xdp(struct tap_q
>  	tap = rcu_dereference(q->tap);
>  	if (tap) {
>  		skb->dev = tap->dev;
> +		skb_probe_transport_header(skb, ETH_HLEN);
>  		dev_queue_xmit(skb);
>  	} else {
>  		kfree_skb(skb);
> 
>