netdev - Re: [PATCH v4 0/4] Introduce security_create_user

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Date:   Mon, 08 Aug 2022 14:43:41 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Frederick Lawler <fred@...udflare.com>, kpsingh@...nel.org,
        revest@...omium.org, jackmanb@...omium.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, john.fastabend@...il.com,
        jmorris@...ei.org, serge@...lyn.com,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        shuah@...nel.org, brauner@...nel.org, casey@...aufler-ca.com,
        bpf@...r.kernel.org, linux-security-module@...r.kernel.org,
        selinux@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        kernel-team@...udflare.com, cgzones@...glemail.com,
        karl@...badwolfsecurity.com
Subject: Re: [PATCH v4 0/4] Introduce security_create_user_ns()

"Eric W. Biederman" <ebiederm@...ssion.com> writes:

> Paul Moore <paul@...l-moore.com> writes:
>
>>> I did provide constructive feedback.  My feedback to his problem
>>> was to address the real problem of bugs in the kernel.
>>
>> We've heard from several people who have use cases which require
>> adding LSM-level access controls and observability to user namespace
>> creation.  This is the problem we are trying to solve here; if you do
>> not like the approach proposed in this patchset please suggest another
>> implementation that allows LSMs visibility into user namespace
>> creation.
>
> Please stop, ignoring my feedback, not detailing what problem or
> problems you are actually trying to be solved, and threatening to merge
> code into files that I maintain that has the express purpose of breaking
> my users.
>
> You just artificially constrained the problems, so that no other
> solution is acceptable.  On that basis alone I am object to this whole
> approach to steam roll over me and my code.

If you want an example of what kind of harm it can cause to introduce a
failure where no failure was before I invite you to look at what
happened with sendmail when setuid was modified to fail, when changing
the user of a process would cause RLIMIT_NPROC to be exceeded.

I am not arguing that what you are proposing is that bad but unexpected
failures cause real problems, and at a minimum that needs a better
response than: "There is at least one user that wants a failure here".

Frankly I would love to see an argument that semantically it ever makes
sense for creating a user namespace to fail.  If that argument has
already been made, my apologies to the person who made as I missed it,
in being sick and tired, and frustrated at being blown off, when
I asked for a proper discuss of the problem at hand.

Eric