linux-kernel - Re: [PATCH] security: new security_file_ioctl

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Date: Sat, 23 Dec 2023 23:41:17 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Alfred Piccioni <alpic@...gle.com>, Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>, bpf <bpf@...r.kernel.org>
Cc: linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        stable@...r.kernel.org, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] security: new security_file_ioctl_compat() hook

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?