Re: [PATCH] seccomp: passthrough uretprobe systemcall without filtering

Darrick J. Wong
2025-01-18T20:31:03Z

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
>