Re: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to gre_rcv()

[David Ahern <dsahern@kernel.org>]

On 3/15/22 10:53 PM, Menglong Dong wrote:
> On Wed, Mar 16, 2022 at 11:49 AM David Ahern <dsahern@kernel.org> wrote:
>>
>> On 3/15/22 9:08 PM, Jakub Kicinski wrote:
>>> On Mon, 14 Mar 2022 21:33:10 +0800 menglong8.dong@gmail.com wrote:
>>>> +    reason = SKB_DROP_REASON_NOT_SPECIFIED;
>>>>      if (!pskb_may_pull(skb, 12))
>>>>              goto drop;
>>>
>>> REASON_HDR_TRUNC ?
>>>
>>>>      ver = skb->data[1]&0x7f;
>>>> -    if (ver >= GREPROTO_MAX)
>>>> +    if (ver >= GREPROTO_MAX) {
>>>> +            reason = SKB_DROP_REASON_GRE_VERSION;
>>>
>>> TBH I'm still not sure what level of granularity we should be shooting
>>> for with the reasons. I'd throw all unexpected header values into one
>>> bucket, not go for a reason per field, per protocol. But as I'm said
>>> I'm not sure myself, so we can keep what you have..
>>
>> I have stated before I do not believe every single drop point in the
>> kernel needs a unique reason code. This is overkill. The reason augments
>> information we already have -- the IP from kfree_skb tracepoint.
> 
> Is this reason unnecessary? I'm not sure if the GRE version problem should
> be reported. With versions not supported by the kernel, it seems we
> can't get the
> drop reason from the packet data, as they are fine. And previous seems not
> suitable here, as it is a L4 problem.
> 

Generically, it is "no support for a protocol version". That kind of
reason code + the IP tells you GRE is processing a packet with an
unsupported protocol version.