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

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Date:	Tue, 2 Jun 2015 07:05:06 -0600
From:	Tycho Andersen <tycho.andersen@...onical.com>
To:	Andrey Wagin <avagin@...il.com>
Cc:	LKML <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>,
	Oleg Nesterov <oleg@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>
Subject: Re: [PATCH] seccomp: add ptrace commands for suspend/resume

On Tue, Jun 02, 2015 at 12:36:16PM +0300, Andrey Wagin wrote:
> 2015-06-01 22:28 GMT+03:00 Tycho Andersen <tycho.andersen@...onical.com>:
> > This patch is the first step in enabling checkpoint/restore of processes
> > with seccomp enabled.
> >
> > One of the things CRIU does while dumping tasks is inject code into them
> > via ptrace to collect information that is only available to the process
> > itself. However, if we are in a seccomp mode where these processes are
> > prohibited from making these syscalls, then what CRIU does kills the task.
> >
> > This patch adds a new ptrace command, PTRACE_SUSPEND_SECCOMP that enables a
> > task from the init user namespace which has CAP_SYS_ADMIN to disable (and
> > re-enable) seccomp filters for another task so that they can be
> > successfully dumped (and restored).
> 
> Do we need to re-enable seccomp if a tracer detaches unexpectedly.
> CRIU can be killed and we should try to not affect the task state even
> in this case.

Yes, I think Pavel's suggestion on the CRIU list of simply
automatically re-enabling seccomp on ptrace detach is the right way to
go here; it should cover this case. The only question is whether or
not to leave the explicit ability to re-enable seccomp before detach
or not. I don't think it's necessary for CRIU, so perhaps I'll remove
it in the next version.

Tycho
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