netdev - Re: [PATCH bpf-next] bpf: add read/write access to skb->tstamp from tc clsact progs

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Message-ID: <85eaa8aa-cb4d-5ae5-7e52-fc7700a5e16f@iogearbox.net>
Date:   Wed, 21 Nov 2018 23:57:52 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Vlad Dumitrescu <vlad@...itrescu.ro>, eric.dumazet@...il.com,
        alexei.starovoitov@...il.com
Cc:     Vlad Dumitrescu <vladum@...gle.com>, ast@...nel.org,
        netdev@...r.kernel.org, edumazet@...gle.com, willemb@...gle.com
Subject: Re: [PATCH bpf-next] bpf: add read/write access to skb->tstamp from
 tc clsact progs

On 11/21/2018 07:48 PM, Vlad Dumitrescu wrote:
> On Wed, Nov 21, 2018 at 5:08 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On 11/20/2018 06:40 PM, Alexei Starovoitov wrote:
>>>
>>> looks good to me.
>>>
>>> Any particular reason you decided to disable it for cg_skb ?
>>> It seems to me the same EDT approach will work from
>>> cgroup-bpf skb hooks just as well and then we can have neat
>>> way of controlling traffic per-container instead of tc-clsbpf global.
>>> If you're already on cgroup v2 it will save you a lot of classifier
>>> cycles, since you'd be able to group apps by cgroup
>>> instead of relying on ip only.
>>
>> Vlad first wrote a complete version, but we felt explaining the _why_
>> was probably harder.
>>
>> No particular reason, other than having to write more tests perhaps.
> 
> This sounds reasonable to me. I can prepare a v2.
> 
> Any concerns regarding capabilities? For example data and data_end are
> only available to CAP_SYS_ADMIN. Note that enforcement of this would
> be done by a global component later in the pipeline (e.g., FQ qdisc).

cg_skb_is_valid_access() has the CAP_SYS_ADMIN enforcement for direct
packet access since cg_skb can also run from unprivileged. Makes sense
to do the same for skb->tstamp for the STX_MEM part at least.

> Any opinions on sk_filter, lwt, and sk_skb before I send v2?

I'd probably leave that out for the time being if there is no concrete
use at this point.

Thanks,
Daniel