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Date: Sat, 23 Dec 2023 23:41:17 +0900
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Subject: Re: [PATCH] security: new security_file_ioctl_compat() hook
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To: Alfred Piccioni <alpic@google.com>, Paul Moore <paul@paul-moore.com>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        Eric Paris <eparis@parisplace.org>, bpf <bpf@vger.kernel.org>
Cc: linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        stable@vger.kernel.org, selinux@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20230906102557.3432236-1-alpic@google.com>
 <20231219090909.2827497-1-alpic@google.com>
 <CALcwBGC9LzzdJeq3SWy9F3g5A32s5uSvJZae4j+rwNQqqLHCKg@mail.gmail.com>
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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Adding BPF.

On 2023/12/19 18:10, Alfred Piccioni wrote:
>> I didn't do an audit but does anything need to be updated for the BPF
>> LSM or does it auto-magically pick up new hooks?
> 
> I'm unsure. I looked through the BPF LSM and I can't see any way it's
> picking up the file_ioctl hook to begin with. It appears to me
> skimming through the code that it automagically picks it up, but I'm
> not willing to bet the kernel on it.

If BPF LSM silently picks up security_file_ioctl_compat() hook, I worry
that some existing BPF programs which check ioctl() using BPF LSM fail to
understand that such BPF programs need to be updated.

We basically don't care about out-of-tree kernel code. But does that rule
apply to BPF programs? Since BPF programs are out-of-tree, are BPF programs
which depend on BPF LSM considered as "we don't care about" rule?
Or is breakage of existing BPF programs considered as a regression?
(Note that this patch is CC:ed for stable kernels.)

Maybe BPF LSM should at least emit warning if the loaded BPF program defined
security_file_ioctl() hook and did not define security_file_ioctl_compat() hook?

We could use a struct where undefined hooks needs to be manually filled with
a dummy pointer, so that we can catch erroneously undefined hooks (detected by
being automatically filled with a NULL pointer) at load time?