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

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Date:	Fri, 9 Jan 2015 12:55:56 -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

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?

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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