linux-kernel - Re: [PATCH] seccomp: add ptrace commands for suspend/resume

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Message-ID: <20150602212722.GA32356@redhat.com>
Date:	Tue, 2 Jun 2015 23:27:22 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	Tycho Andersen <tycho.andersen@...onical.com>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Kees Cook <keescook@...omium.org>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>,
	Roland McGrath <roland@...k.frob.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>
Subject: Re: [PATCH] seccomp: add ptrace commands for suspend/resume

On 06/02, Pavel Emelyanov wrote:
>
> > And I am not sure I understand why do we need the additional security
> > check, but I leave this to you and Andy.
> >
> > If you have the rights to trace this task, then you can do anything
> > the tracee could do without the filtering.
>
> I think _this_ check is required, otherwise the seccomp-ed task (in
> filtered mode) fork-s a child, then this child ptrace-attach to parent
> (allowed) then suspend its seccomd.

If you force (hack) that task to do this. And if the seccomp-ed task
does this by its own we do not care.

> And -- we have unpriviledged process
> de-seccomped.

Heh. The case when the priviledged CAP_SYS_ADMIN process escapes the
filtering is much worse I think ;)

But as I said I will nott argue, just I think this needs a bit of
documentantion. And I agree in advance with something like "better
be safe than sorry, we can always remove this later" comment or a
note in the changelog.

Oleg.

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