netdev - Re: [PATCH net] net/sched: act_ct: fix miss set mru for ovs after defrag in act

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Date:   Thu, 30 Jul 2020 16:53:24 +0800
From:   wenxu <wenxu@...oud.cn>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net/sched: act_ct: fix miss set mru for ovs after
 defrag in act_ct


On 7/30/2020 2:03 PM, Cong Wang wrote:
> On Wed, Jul 29, 2020 at 3:41 AM <wenxu@...oud.cn> wrote:
>> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
>> index c510b03..45401d5 100644
>> --- a/include/net/sch_generic.h
>> +++ b/include/net/sch_generic.h
>> @@ -384,6 +384,7 @@ struct qdisc_skb_cb {
>>         };
>>  #define QDISC_CB_PRIV_LEN 20
>>         unsigned char           data[QDISC_CB_PRIV_LEN];
>> +       u16                     mru;
>>  };
> Hmm, can you put it in the anonymous struct before 'data'?
>
> We validate this cb size and data size like blow:
>
> static inline void qdisc_cb_private_validate(const struct sk_buff *skb, int sz)
> {
>         struct qdisc_skb_cb *qcb;
>
>         BUILD_BUG_ON(sizeof(skb->cb) < offsetof(struct qdisc_skb_cb,
> data) + sz);
>         BUILD_BUG_ON(sizeof(qcb->data) < sz);
> }
>
> It _kinda_ expects ->data at the end.

It seems the data offsetof data should be align with szieof(u64)?

If I  modify it as following

@@ -383,6 +383,9 @@ struct qdisc_skb_cb {
                unsigned int            pkt_len;
                u16                     slave_dev_queue_mapping;
                u16                     tc_classid;
+               u16                     mru;
        };
 #define QDISC_CB_PRIV_LEN 20
        unsigned char           data[QDISC_CB_PRIV_LEN];

compile fail:

net/core/filter.c:7625:3: note: in expansion of macro ‘BUILD_BUG_ON’
   BUILD_BUG_ON((offsetof(struct sk_buff, cb) +

inn the file:  net/core/filter.c

case offsetof(struct __sk_buff, cb[0]) ...

             offsetofend(struct __sk_buff, cb[4]) - 1:
                BUILD_BUG_ON(sizeof_field(struct qdisc_skb_cb, data) < 20);
                BUILD_BUG_ON((offsetof(struct sk_buff, cb) +
                              offsetof(struct qdisc_skb_cb, data)) %
                             sizeof(__u64));


If I  modify it as following

@@ -383,6 +383,9 @@ struct qdisc_skb_cb {
                unsigned int            pkt_len;
                u16                     slave_dev_queue_mapping;
                u16                     tc_classid;
+               u16                     mru;
+               u16                     _pad1;
+               u32                     _pad2;
        };
 #define QDISC_CB_PRIV_LEN 20
        unsigned char           data[QDISC_CB_PRIV_LEN];


compile fail:

./include/linux/filter.h:633:2: note: in expansion of macro ‘BUILD_BUG_ON’
  BUILD_BUG_ON(sizeof(*cb) > sizeof_field(struct sk_buff, cb));


static inline void bpf_compute_data_pointers(struct sk_buff *skb)
{
        struct bpf_skb_data_end *cb = (struct bpf_skb_data_end *)skb->cb;

        BUILD_BUG_ON(sizeof(*cb) > sizeof_field(struct sk_buff, cb));
        cb->data_meta = skb->data - skb_metadata_len(skb);
        cb->data_end  = skb->data + skb_headlen(skb);
}


It seems no space for new value add before 'data'?


BR

wenxu