netdev - Re: [PATCH net-next RFC 1/5] net-timestamp: no-payload option

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Date:	Fri, 9 Jan 2015 14:00:17 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Willem de Bruijn <willemb@...gle.com>
Cc:	Network Development <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Richard Cochran <richardcochran@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next RFC 1/5] net-timestamp: no-payload option

OK, makes sense.

On Fri, Jan 9, 2015 at 1:18 PM, Willem de Bruijn <willemb@...gle.com> wrote:
> On Fri, Jan 9, 2015 at 3:55 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Fri, Jan 9, 2015 at 12:33 PM, Willem de Bruijn <willemb@...gle.com> wrote:
>>> On Fri, Jan 9, 2015 at 3:02 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>>> On Fri, Jan 9, 2015 at 11:47 AM, Willem de Bruijn <willemb@...gle.com> wrote:
>>>>> On Fri, Jan 9, 2015 at 2:43 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>>>>> On Fri, Jan 9, 2015 at 9:31 AM, Willem de Bruijn <willemb@...gle.com> wrote:
>>>>>>> From: Willem de Bruijn <willemb@...gle.com>
>>>>>>>
>>>>>>> Add timestamping option SOF_TIMESTAMPING_OPT_TSONLY. For transmit
>>>>>>> timestamps, this loops timestamps on top of empty packets.
>>>>>>>
>>>>>>> Doing so reduces the pressure on SO_RCVBUF. Payload inspection and
>>>>>>> cmsg reception (aside from timestamps) are no longer possible. This
>>>>>>> works together with a follow on patch that allows administrators to
>>>>>>> only allow tx timestamping if it does not loop payload or metadata.
>>>>>>
>>>>>> If this loses IP_PKTINFO, that will be a bit unfortunate.
>>>>>>
>>>>>
>>>>> If it doesn't, then we might as well loop the entire payload. For applications
>>>>> that need pktinfo or other cmsg, do not select the option.
>>>>
>>>> Right, but it loses the ability to get the ifindex if the sysctl is
>>>> set to the conservative option, which I don't think is desirable.
>>>
>>> Understood. I just find the alternative, where the no-data policy is
>>> weakened by exceptions, even less desirable. That makes it
>>> harder to explain what the sysctl/option do and what the security
>>> implications are.
>>
>> Agreed.
>>
>> If there was no-payload but not no-cmsg, then it would be a nice
>> middle ground, but I guess that's bad for some reason involving
>> accounting?
>
> Enabling all cmsg opens up quite a few holes, including the tos
> options that we previously discussed. Also, these are implemented
> by reading the relevant bits from the payload at recvmsg time, so
> at least we would have to queue the full payload (though not
> necessarily return it).
>
>> --Andy
>>
>> --
>> Andy Lutomirski
>> AMA Capital Management, LLC



-- 
Andy Lutomirski
AMA Capital Management, LLC
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