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

[Willem de Bruijn <willemb@google.com>]

On Fri, Jan 9, 2015 at 3:02 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Fri, Jan 9, 2015 at 11:47 AM, Willem de Bruijn <willemb@google.com> wrote:
>> On Fri, Jan 9, 2015 at 2:43 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>> On Fri, Jan 9, 2015 at 9:31 AM, Willem de Bruijn <willemb@google.com> wrote:
>>>> From: Willem de Bruijn <willemb@google.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.