netdev - Re: [PATCH v3 bpf-next 0/4] Add support for cgroup bpf

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Date:   Mon, 30 Mar 2020 18:57:44 -0600
From:   David Ahern <dsahern@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrey Ignatov <rdna@...com>, Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next 0/4] Add support for cgroup bpf_link

On 3/30/20 6:32 PM, Alexei Starovoitov wrote:
>>
>> This is not a large feature, and there is no reason for CREATE/UPDATE -
>> a mere 4 patch set - to go in without something as essential as the
>> QUERY for observability.
> 
> As I said 'bpftool cgroup' covers it. Observability is not reduced in any way.

You want a feature where a process can prevent another from installing a
program on a cgroup. How do I learn which process is holding the
bpf_link reference and preventing me from installing a program? Unless I
have missed some recent change that is not currently covered by bpftool
cgroup, and there is no way reading kernel code will tell me.

###
To quote Lorenz from an earlier response:

"However, this behaviour concerns me. It's like Windows not
letting you delete a file while an application has it opened, which just
leads to randomly killing programs until you find the right one. It's
frustrating and counter productive.

You're taking power away from the operator. In your deployment scenario
this might make sense, but I think it's a really bad model in general.
If I am privileged I need to be able to exercise that privilege."
###

That is my point. You are restricting what root can do and people will
not want to resort to killing random processes trying to find the one
holding a reference. This is an essential missing piece and should go in
at the same time as this set.