linux-kernel - Re: Crash when attaching uretprobes to processes running in Docker

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Message-ID: <CAEf4BzZquQBW1DuEmfhUTicoyHOeEpT6FG7VBR-kG35f7Rb5Zw@mail.gmail.com>
Date: Tue, 14 Jan 2025 15:52:23 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Jiri Olsa <olsajiri@...il.com>, Aleksa Sarai <cyphar@...har.com>, 
	Eyal Birger <eyal.birger@...il.com>, mhiramat@...nel.org, 
	linux-kernel <linux-kernel@...r.kernel.org>, linux-trace-kernel@...r.kernel.org, 
	BPF-dev-list <bpf@...r.kernel.org>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, 
	John Fastabend <john.fastabend@...il.com>, peterz@...radead.org, tglx@...utronix.de, 
	bp@...en8.de, x86@...nel.org, linux-api@...r.kernel.org, 
	Andrii Nakryiko <andrii@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Alexei Starovoitov <ast@...nel.org>, "rostedt@...dmis.org" <rostedt@...dmis.org>, rafi@....io, 
	Shmulik Ladkani <shmulik.ladkani@...il.com>
Subject: Re: Crash when attaching uretprobes to processes running in Docker

On Tue, Jan 14, 2025 at 2:11 PM Oleg Nesterov <oleg@...hat.com> wrote:
>
> On 01/14, Andrii Nakryiko wrote:
> >
> > On Tue, Jan 14, 2025 at 12:40 PM Oleg Nesterov <oleg@...hat.com> wrote:
> > >
> > > But, unlike sys_uretprobe(), sys_rt_sigreturn() is old, so the existing
> > > setups must know that sigreturn() should be respected...
> >
> > someday sys_uretprobe will be old as well ;) FWIW, systemd allowlisted
> > sys_uretprobe, see [0]
>
> And I agree! ;)
>
> I mean, I'd personally prefer to do nothing and wait until userspace figures
> out that we have another "special" syscall.
>
> But can we do it? I simply do not know. Can we ignore this (valid) bug report?
>

Seems wrong for kernel to try to guess whether some syscall is
filtered by some policy or not (though maybe I'm misunderstanding the
details and it's kernel-originated problem?). Seems like a recipe for
more problems.

Nothing is really fundamentally broken. Some piece of software needs
an upgraded library to not disable the kernel's special syscall (just
like sys_rt_sigreturn, nothing "new" here, really). Users can't do
uprobing in such broken setups (but not in general), seems like a good
incentive for everyone to push for the right thing here: fixed up to
date software.

> Oleg.
>