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Date:   Mon, 1 Aug 2022 08:25:23 -0700
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Subject: Re: [PATCH v3 0/4] Introduce security_create_user_ns()
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To:     Frederick Lawler <fred@cloudflare.com>,
        Paul Moore <paul@paul-moore.com>,
        Martin KaFai Lau <kafai@fb.com>
Cc:     kpsingh@kernel.org, revest@chromium.org, jackmanb@chromium.org,
        ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com,
        jmorris@namei.org, serge@hallyn.com,
        stephen.smalley.work@gmail.com, eparis@parisplace.org,
        shuah@kernel.org, brauner@kernel.org, ebiederm@xmission.com,
        bpf@vger.kernel.org, linux-security-module@vger.kernel.org,
        selinux@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        kernel-team@cloudflare.com, cgzones@googlemail.com,
        karl@bigbadwolfsecurity.com, casey@schaufler-ca.com
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From:   Casey Schaufler <casey@schaufler-ca.com>
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On 8/1/2022 6:13 AM, Frederick Lawler wrote:
> On 7/22/22 7:20 AM, Paul Moore wrote:
>> On July 22, 2022 2:12:03 AM Martin KaFai Lau <kafai@fb.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.
>>
>> I would also need an ACK from the BPF LSM folks, but they're CC'd on
>> this patchset.
>>
>
> Based on last weeks comments, should I go ahead and put up v4 for
> 5.20-rc1 when that drops, or do I need to wait for more feedback?

As the primary consumer of this hook is BPF I would really expect their
reviewed-by before accepting this. 

>
>> -- 
>> paul-moore.com
>>
>>
>