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

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Message-ID: <202501271142.71C1B5EE6@keescook>
Date: Mon, 27 Jan 2025 11:43:07 -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 11:39:44AM -0800, Eyal Birger wrote:
> On Mon, Jan 27, 2025 at 11:33 AM Kees Cook <kees@...nel.org> wrote:
> >
> > 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...
> 
> I can. The main difference as far as I can tell is that it would not
> apply to strict mode. Is that OK? it means that existing binaries using
> strict mode would still crash if uretprobe is attached to them.

Ah, good point. Please also add it to mode1_syscalls for strict. :)

-- 
Kees Cook