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

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Message-ID: <20250118203102.GL3557695@frogsfrogsfrogs>
Date: Sat, 18 Jan 2025 12:31:02 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Kees Cook <kees@...nel.org>
Cc: Eyal Birger <eyal.birger@...il.com>, 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 Sat, Jan 18, 2025 at 12:21:51PM -0800, Kees Cook wrote:
> On Thu, Jan 16, 2025 at 04:55:39PM -0800, Eyal Birger wrote:
> > Since uretprobe is a "kernel implementation detail" system call which is
> > not used by userspace application code directly, it is impractical and
> > there's very little point in forcing all userspace applications to
> > explicitly allow it in order to avoid crashing tracked processes.
> 
> How is this any different from sigreturn, rt_sigreturn, or
> restart_syscall? These are all handled explicitly by userspace filters
> already, and I don't see why uretprobe should be any different. Docker
> has had plenty of experience with fixing their seccomp filters for new
> syscalls. For example, many times already a given libc will suddenly
> start using a new syscall when it sees its available, etc.
> 
> Basically, this is a Docker issue, not a kernel issue. Seccomp is
> behaving correctly. I don't want to start making syscalls invisible
> without an extremely good reason. If _anything_ should be invisible, it
> is restart_syscall (which actually IS invisible under certain
> architectures).

I was wondering that too -- if ______'s security policy is to disallow
by default, then fix the security policy.  Don't blow a hole in seccomp
for all users.  Maybe someone *wants* to block uretprobe.  Maybe doing
so will be needed some day as a crude mitigation for a zeroday.

--D

> -Kees
> 
> -- 
> Kees Cook
>