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Subject: Re: [PATCH] lockdown,selinux: fix bogus SELinux lockdown permission
 checks
To:     Ondrej Mosnacek <omosnace@redhat.com>
Cc:     Linux Security Module list 
        <linux-security-module@vger.kernel.org>,
        James Morris <jmorris@namei.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        SElinux list <selinux@vger.kernel.org>,
        linuxppc-dev@lists.ozlabs.org,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, network dev <netdev@vger.kernel.org>,
        Linux kernel mailing list <linux-kernel@vger.kernel.org>,
        Casey Schaufler <casey@schaufler-ca.com>
References: <20210507114048.138933-1-omosnace@redhat.com>
 <a8d138a6-1d34-1457-9266-4abeddb6fdba@schaufler-ca.com>
 <CAFqZXNtr1YjzRg7fTm+j=0oZF+7C5xEu5J0mCZynP-dgEzvyUg@mail.gmail.com>
 <24a61ff1-e415-adf8-17e8-d212364d4b97@schaufler-ca.com>
 <CAFqZXNvB-EyPz1Qz3cCRTr1u1+D+xT-dp7cUxFocYM1AOYSuxw@mail.gmail.com>
From:   Casey Schaufler <casey@schaufler-ca.com>
Message-ID: <e8d60664-c7ad-61de-bece-8ab3316f77bc@schaufler-ca.com>
Date:   Wed, 12 May 2021 10:12:10 -0700
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On 5/12/2021 9:44 AM, Ondrej Mosnacek wrote:
> On Wed, May 12, 2021 at 6:18 PM Casey Schaufler <casey@schaufler-ca.com=
> wrote:
>> On 5/12/2021 6:21 AM, Ondrej Mosnacek wrote:
>>> On Sat, May 8, 2021 at 12:17 AM Casey Schaufler <casey@schaufler-ca.c=
om> wrote:
>>>> On 5/7/2021 4:40 AM, Ondrej Mosnacek wrote:
>>>>> Commit 59438b46471a ("security,lockdown,selinux: implement SELinux
>>>>> lockdown") added an implementation of the locked_down LSM hook to
>>>>> SELinux, with the aim to restrict which domains are allowed to perf=
orm
>>>>> operations that would breach lockdown.
>>>>>
>>>>> However, in several places the security_locked_down() hook is calle=
d in
>>>>> situations where the current task isn't doing any action that would=

>>>>> directly breach lockdown, leading to SELinux checks that are basica=
lly
>>>>> bogus.
>>>>>
>>>>> Since in most of these situations converting the callers such that
>>>>> security_locked_down() is called in a context where the current tas=
k
>>>>> would be meaningful for SELinux is impossible or very non-trivial (=
and
>>>>> could lead to TOCTOU issues for the classic Lockdown LSM
>>>>> implementation), fix this by adding a separate hook
>>>>> security_locked_down_globally()
>>>> This is a poor solution to the stated problem. Rather than adding
>>>> a new hook you should add the task as a parameter to the existing ho=
ok
>>>> and let the security modules do as they will based on its value.
>>>> If the caller does not have an appropriate task it should pass NULL.=

>>>> The lockdown LSM can ignore the task value and SELinux can make its
>>>> own decision based on the task value passed.
>>> The problem with that approach is that all callers would then need to=

>>> be updated and I intended to keep the patch small as I'd like it to g=
o
>>> to stable kernels as well.
>>>
>>> But it does seem to be a better long-term solution - would it work fo=
r
>>> you (and whichever maintainer would be taking the patch(es)) if I jus=
t
>>> added another patch that refactors it to use the task parameter?
>> I can't figure out what you're suggesting. Are you saying that you
>> want to add a new hook *and* add the task parameter?
> No, just to keep this patch as-is (and let it go to stable in this
> form) and post another (non-stable) patch on top of it that undoes the
> new hook and re-implements the fix using your suggestion. (Yeah, it'll
> look weird, but I'm not sure how better to handle such situation - I'm
> open to doing it whatever different way the maintainers prefer.)

James gets to make the call on this one. If it was my call I would
tell you to make the task parameter change and accept the backport
pain. I think that as a security developer community we spend way too
much time and effort trying to avoid being noticed in source trees.