linux-kernel - Re: [PATCH v3 0/4] Introduce security_create_user

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Message-ID: <87a68mcouk.fsf@email.froward.int.ebiederm.org>
Date:   Tue, 02 Aug 2022 16:33:39 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Martin KaFai Lau <kafai@...com>,
        Frederick Lawler <fred@...udflare.com>, <kpsingh@...nel.org>,
        <revest@...omium.org>, <jackmanb@...omium.org>, <ast@...nel.org>,
        <daniel@...earbox.net>, <andrii@...nel.org>,
        <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 v3 0/4] Introduce security_create_user_ns()

Paul Moore <paul@...l-moore.com> writes:

> On July 22, 2022 2:12:03 AM Martin KaFai Lau <kafai@...com> wrote:
>
>> On Thu, Jul 21, 2022 at 12:28:04PM -0500, Frederick Lawler wrote:
>>> While creating a LSM BPF MAC policy to block user namespace creation, we
>>> used the LSM cred_prepare hook because that is the closest hook to prevent
>>> a call to create_user_ns().
>>>
>>> The calls look something like this:
>>>
>>> cred = prepare_creds()
>>> security_prepare_creds()
>>> call_int_hook(cred_prepare, ...
>>> if (cred)
>>> create_user_ns(cred)
>>>
>>> We noticed that error codes were not propagated from this hook and
>>> introduced a patch [1] to propagate those errors.
>>>
>>> The discussion notes that security_prepare_creds()
>>> is not appropriate for MAC policies, and instead the hook is
>>> meant for LSM authors to prepare credentials for mutation. [2]
>>>
>>> Ultimately, we concluded that a better course of action is to introduce
>>> a new security hook for LSM authors. [3]
>>>
>>> This patch set first introduces a new security_create_user_ns() function
>>> and userns_create LSM hook, then marks the hook as sleepable in BPF.
>> Patch 1 and 4 still need review from the lsm/security side.
>
>
> This patchset is in my review queue and assuming everything checks
> out, I expect to merge it after the upcoming merge window closes.

It doesn't even address my issues with the last patchset.

So it has my NACK.

Eric