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

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Date:   Fri, 22 Jul 2022 08:20:10 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Martin KaFai Lau <kafai@...com>,
        Frederick Lawler <fred@...udflare.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>,
        <casey@...aufler-ca.com>, <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>
Subject: Re: [PATCH v3 0/4] Introduce security_create_user_ns()

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.

--
paul-moore.com