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

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Message-ID: <9eee1d03-3153-67d3-fe21-14fcb5fe8d27@schaufler-ca.com>
Date:   Mon, 1 Aug 2022 08:25:23 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Frederick Lawler <fred@...udflare.com>,
        Paul Moore <paul@...l-moore.com>,
        Martin KaFai Lau <kafai@...com>
Cc:     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, ebiederm@...ssion.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, casey@...aufler-ca.com
Subject: Re: [PATCH v3 0/4] Introduce security_create_user_ns()

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@...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
>>
>>
>