On 2/21/22 9:45 PM, Dongli Zhang wrote:
> Hi David,
>
> On 2/21/22 7:28 PM, David Ahern wrote:
>> On 2/20/22 10:34 PM, Dongli Zhang wrote:
>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>> index aa27268..bf7d8cd 100644
>>> --- a/drivers/net/tun.c
>>> +++ b/drivers/net/tun.c
>>> @@ -1062,13 +1062,16 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>> struct netdev_queue *queue;
>>> struct tun_file *tfile;
>>> int len = skb->len;
>>> + enum skb_drop_reason drop_reason;
>>
>> this function is already honoring reverse xmas tree style, so this needs
>> to be moved up.
>
> I will move this up to before "int txq = skb->queue_mapping;".
>
>>
>>>
>>> rcu_read_lock();
>>> tfile = rcu_dereference(tun->tfiles[txq]);
>>>
>>> /* Drop packet if interface is not attached */
>>> - if (!tfile)
>>> + if (!tfile) {
>>> + drop_reason = SKB_DROP_REASON_DEV_READY;
>>> goto drop;
>>> + }
>>>
>>> if (!rcu_dereference(tun->steering_prog))
>>> tun_automq_xmit(tun, skb);
>>> @@ -1078,22 +1081,32 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>> /* Drop if the filter does not like it.
>>> * This is a noop if the filter is disabled.
>>> * Filter can be enabled only for the TAP devices. */
>>> - if (!check_filter(&tun->txflt, skb))
>>> + if (!check_filter(&tun->txflt, skb)) {
>>> + drop_reason = SKB_DROP_REASON_DEV_FILTER;
>>> goto drop;
>>> + }
>>>
>>> if (tfile->socket.sk->sk_filter &&
>>> - sk_filter(tfile->socket.sk, skb))
>>> + sk_filter(tfile->socket.sk, skb)) {
>>> + drop_reason = SKB_DROP_REASON_SOCKET_FILTER;
>>> goto drop;
>>> + }
>>>
>>> len = run_ebpf_filter(tun, skb, len);
>>> - if (len == 0)
>>> + if (len == 0) {
>>> + drop_reason = SKB_DROP_REASON_BPF_FILTER;
>>
>> how does this bpf filter differ from SKB_DROP_REASON_SOCKET_FILTER? I
>> think the reason code needs to be a little clearer on the distinction.
>>
>
>
> While there is a diff between BPF_FILTER (here) and SOCKET_FILTER ...
>
> ... indeed the issue is: there is NO diff between BPF_FILTER (here) and
> DEV_FILTER (introduced by the patch).
>
>
> The run_ebpf_filter() is to run the bpf filter attached to the TUN device (not
> socket). This is similar to DEV_FILTER, which is to run a device specific filter.
>
> Initially, I would use DEV_FILTER at both locations. This makes trouble to me as
> there would be two places with same reason=DEV_FILTER. I will not be able to
> tell where the skb is dropped.
>
>
> I was thinking about to introduce a SKB_DROP_REASON_DEV_BPF. While I have
> limited experience in device specific bpf, the TUN is the only device I know
> that has a device specific ebpf filter (by commit aff3d70a07ff ("tun: allow to
> attach ebpf socket filter")). The SKB_DROP_REASON_DEV_BPF is not generic enough
> to be re-used by other drivers.
>
>
> Would you mind sharing your suggestion if I would re-use (1)
> SKB_DROP_REASON_DEV_FILTER or (2) introduce a new SKB_DROP_REASON_DEV_BPF, which
> is for sk_buff dropped by ebpf attached to device (not socket).
>
>
> To answer your question, the SOCKET_FILTER is for filter attached to socket, the
> BPF_FILTER was supposed for ebpf filter attached to device (tun->filter_prog).
>
>
tun/tap does have some unique filtering options. The other sets focused
on the core networking stack is adding a drop reason of
SKB_DROP_REASON_BPF_CGROUP_EGRESS for cgroup based egress filters.
For tun unique filters, how about using a shortened version of the ioctl
name used to set the filter.
