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

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Message-ID: <202501181212.4C515DA02@keescook>
Date: Sat, 18 Jan 2025 12:21:51 -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 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).

-Kees

-- 
Kees Cook