linux-kernel - Re: Re: [RFC PATCH bpf-next 0/3] bpf: freeze a task cgroup from bpf

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Message-ID: <CAEiveUdCMCxp4n+gZKU_99y_xap83otQVmz+XqSaO+JAjrKM1Q@mail.gmail.com>
Date: Thu, 11 Apr 2024 10:36:27 +0200
From: Djalal Harouni <tixxdz@...il.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>, 
	Johannes Weiner <hannes@...xchg.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, bpf@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: Re: [RFC PATCH bpf-next 0/3] bpf: freeze a task cgroup from bpf

On Tue, Apr 9, 2024 at 5:32 PM Michal Koutný <mkoutny@...e.com> wrote:
>
> Hi.
>
> On Tue, Apr 02, 2024 at 07:20:45PM +0100, Djalal Harouni <tixxdz@...il.com> wrote:
> > Thanks yes, I would expect freeze to behave like signal, and if one
> > wants to block immediately there is the LSM override return. The
> > selftest attached tries to do exactly that.
>
> Are you refering to this part:
>
>         int BPF_PROG(lsm_freeze_cgroup, int cmd, union bpf_attr *attr, unsigned int size)
>                 ...
>                 ret = bpf_task_freeze_cgroup(task, 1);
>                 if (!ret) {
>                         ret = -EPERM;
>                         /* reset for next call */
> ?

Yes.

>
> > Could be security signals, reading sensitive files or related to any
> > operation management, for X reasons this user session should be freezed
> > or killed.
>
> What can be done with a frozen cgroup after anything of that happens?
> Anything besides killing anyway?

Some users would like to inspect.


> Killing of an offending process could be caught by its supervisor (like
> container runtime or systemd) and propagated accordingly to the whole
> cgroup.

Most bpf technologies do not run as a supervisor.

> > The kill is an effective defense against fork-bombs as an example.
>
> There are several ways how to prevent fork-bombs in kernel already, it
> looks like a contrived example.

I doubt if they are as effective, flexible and reflect today's workflow
as the cgroup way.

Thanks