[PATCH net] net/sched: act_ct: fix restore the qdisc_skb_cb after defrag

[PATCH net] net/sched: act_ct: fix restore the qdisc_skb_cb after defrag

[wenxu]

From: wenxu <wenxu@ucloud.cn>

The fragment packets do defrag in tcf_ct_handle_fragments
will clear the skb->cb which make the qdisc_skb_cb clear
too. So the qdsic_skb_cb should be store before defrag and
restore after that.
It also update the pkt_len after all the
fragments finish the defrag to one packet and make the
following actions counter correct.

Fixes: b57dc7c13ea9 ("net/sched: Introduce action ct")
Signed-off-by: wenxu <wenxu@ucloud.cn>
---

This patch resend followup with
"http://patchwork.ozlabs.org/project/netdev/cover/1594097711-9365-1-git-send-email-wenxu@ucloud.cn/"

 net/sched/act_ct.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
index 67504ae..e675e2d 100644
--- a/net/sched/act_ct.c
+++ b/net/sched/act_ct.c
@@ -676,6 +676,7 @@ static int tcf_ct_handle_fragments(struct net *net, struct sk_buff *skb,
 				   u8 family, u16 zone)
 {
 	enum ip_conntrack_info ctinfo;
+	struct qdisc_skb_cb cb;
 	struct nf_conn *ct;
 	int err = 0;
 	bool frag;
@@ -693,6 +694,7 @@ static int tcf_ct_handle_fragments(struct net *net, struct sk_buff *skb,
 		return err;
 
 	skb_get(skb);
+	cb = *qdisc_skb_cb(skb);
 
 	if (family == NFPROTO_IPV4) {
 		enum ip_defrag_users user = IP_DEFRAG_CONNTRACK_IN + zone;
@@ -717,6 +719,7 @@ static int tcf_ct_handle_fragments(struct net *net, struct sk_buff *skb,
 #endif
 	}
 
+	*qdisc_skb_cb(skb) = cb;
 	skb_clear_hash(skb);
 	skb->ignore_df = 1;
 	return err;
@@ -1014,6 +1017,7 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
 
 out:
 	tcf_action_update_bstats(&c->common, skb);
+	qdisc_skb_cb(skb)->pkt_len = skb->len;
 	return retval;
 
 drop:
-- 
1.8.3.1

Re: [PATCH net] net/sched: act_ct: fix restore the qdisc_skb_cb after defrag

[Florian Westphal]

wenxu@ucloud.cn <wenxu@ucloud.cn> wrote:
> From: wenxu <wenxu@ucloud.cn>
> 
> The fragment packets do defrag in tcf_ct_handle_fragments
> will clear the skb->cb which make the qdisc_skb_cb clear
> too. So the qdsic_skb_cb should be store before defrag and
> restore after that.
> It also update the pkt_len after all the
> fragments finish the defrag to one packet and make the
> following actions counter correct.
> 
> Fixes: b57dc7c13ea9 ("net/sched: Introduce action ct")
> Signed-off-by: wenxu <wenxu@ucloud.cn>

Looks ok to me.  One question:

> @@ -1014,6 +1017,7 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
>  
>  out:
>  	tcf_action_update_bstats(&c->common, skb);
> +	qdisc_skb_cb(skb)->pkt_len = skb->len;
>  	return retval;

This appears to be unconditional, I would have expected that
this only done for reassembled skbs?

Otherwise we will lose the value calculated by core via
qdisc_calculate_pkt_len().

Re: [PATCH net] net/sched: act_ct: fix restore the qdisc_skb_cb after defrag

[wenxu]

在 2020/7/18 20:30, Florian Westphal 写道:
> wenxu@ucloud.cn <wenxu@ucloud.cn> wrote:
>> From: wenxu <wenxu@ucloud.cn>
>>
>> The fragment packets do defrag in tcf_ct_handle_fragments
>> will clear the skb->cb which make the qdisc_skb_cb clear
>> too. So the qdsic_skb_cb should be store before defrag and
>> restore after that.
>> It also update the pkt_len after all the
>> fragments finish the defrag to one packet and make the
>> following actions counter correct.
>>
>> Fixes: b57dc7c13ea9 ("net/sched: Introduce action ct")
>> Signed-off-by: wenxu <wenxu@ucloud.cn>
> Looks ok to me.  One question:
>
>> @@ -1014,6 +1017,7 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
>>  
>>  out:
>>  	tcf_action_update_bstats(&c->common, skb);
>> +	qdisc_skb_cb(skb)->pkt_len = skb->len;
>>  	return retval;
> This appears to be unconditional, I would have expected that
> this only done for reassembled skbs?
Yes.
>
> Otherwise we will lose the value calculated by core via
> qdisc_calculate_pkt_len().

qdisc_calculate_pkt_len only be cablled in dev_xmit_skb and qdisc_enqueue. If all the fragment will

pass those before defrag, it will caculate correctly. If the reassembled packets pass those, it also caculate correctly after we recaculate the pkt_len of qdisc_skb_cb