linux-kernel - Re: [PATCH] seccomp: passthrough uretprobe systemcall without filtering

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Message-ID: <202501271131.7B5C22D@keescook>
Date: Mon, 27 Jan 2025 11:33:37 -0800
From: Kees Cook <kees@...nel.org>
To: Eyal Birger <eyal.birger@...il.com>
Cc: luto@...capital.net, wad@...omium.org, oleg@...hat.com, ldv@...ace.io,
	mhiramat@...nel.org, andrii@...nel.org, jolsa@...nel.org,
	alexei.starovoitov@...il.com, olsajiri@...il.com, cyphar@...har.com,
	songliubraving@...com, yhs@...com, john.fastabend@...il.com,
	peterz@...radead.org, tglx@...utronix.de, bp@...en8.de,
	daniel@...earbox.net, ast@...nel.org, andrii.nakryiko@...il.com,
	rostedt@...dmis.org, rafi@....io, shmulik.ladkani@...il.com,
	bpf@...r.kernel.org, linux-api@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] seccomp: passthrough uretprobe systemcall without
 filtering

On Mon, Jan 27, 2025 at 11:24:02AM -0800, Eyal Birger wrote:
> Hi Kees,
> 
> On Mon, Jan 20, 2025 at 1:34 PM Kees Cook <kees@...nel.org> wrote:
> >
> > On Sat, Jan 18, 2025 at 07:39:25PM -0800, Eyal Birger wrote:
> > > Alternatively, maybe this syscall implementation should be reverted?
> >
> > Honestly, that seems the best choice. I don't think any thought was
> > given to how it would interact with syscall interposers (including
> > ptrace, strict mode seccomp, etc).
> 
> I don't know if you noticed Andrii's and others' comments on this [1].
> 
> Given that:
> - this issue requires immediate remediation
> - there seems to be pushback for reverting the syscall implementation
> - filtering uretprobe is not within the capabilities of seccomp without this
>   syscall (so reverting the syscall is equivalent to just passing it through
>   seccomp)
> 
> is it possible to consider applying this current fix, with the possibility of
> extending seccomp in the future to support filtering uretprobe if deemed
> necessary (for example by allowing userspace to define a stricter policy)?

I still think this is a Docker problem, but I agree that uretprobe
without syscall is just as unfilterable as seccomp ignoring the syscall.

Can you please update the patch to use the existing action_cache bitmaps
instead of adding an open-coded check? We can consider adding
syscall_restart to this as well in the future...

-- 
Kees Cook