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

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Message-ID: <CA+FuTSdWWv65CNQYv1d9+WG1X54eGyP_+mbh3dMHw_HmH8wzYA@mail.gmail.com>
Date:	Fri, 9 Jan 2015 15:33:50 -0500
From:	Willem de Bruijn <willemb@...gle.com>
To:	Andy Lutomirski <luto@...capital.net>
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 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.
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