linux-kernel - Re: [RFC PATCH] piped/ptraced coredump (was: Dump smaller VMAs first in ELF cores)

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Message-ID: <20240804200153.GC27866@redhat.com>
Date: Sun, 4 Aug 2024 22:01:53 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Brian Mak <makb@...iper.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Kees Cook <kees@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] piped/ptraced coredump (was: Dump smaller VMAs first
 in ELF cores)

On 08/04, Linus Torvalds wrote:
>
> On Sun, 4 Aug 2024 at 11:53, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > Apart from SIGKILL, the dumper already has the full control.
>
> What do you mean? It's a regular usermodehelper. It gets the dump data
> as input. That's all the control it has.

I meant, the dumping thread can't exit until the dumper reads the data
from stdin or closes the pipe. Until then the damper can read /proc/pid/mem
and do other things.

> > And note that the dumper can already use ptrace.
>
> .. with the normal ptrace() rules, yes.
>
> You realize that some setups literally disable ptrace() system calls,
> right? Which your patch now effectively sidesteps.

Well. If, say, selinux disables ptrace, then ptrace_attach() in this
patch should also fail.

But if some setups disable sys_ptrace() as a system call... then yes,
I didn't know that.

> THAT is why I don't like it. ptrace() is *dangerous*.

And horrible ;)

> Just adding some implicit tracing willy-nilly needs to be something
> people really worry about.

Ok, as I said I won't insist.

Oleg.