linux-kernel - Re: [PATCH RFC] Allow introspection to already attached ptracer in __ptrace_may

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Message-ID: <20150108191813.GA30102@redhat.com>
Date:	Thu, 8 Jan 2015 20:18:13 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Stijn Volckaert <Stijn.Volckaert@...s.ugent.be>
Cc:	Kees Cook <keescook@...omium.org>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Casey Schaufler <casey@...aufler-ca.com>,
	John Johansen <john.johansen@...onical.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: [PATCH RFC] Allow introspection to already attached ptracer in
	__ptrace_may_access

On 01/08, Stijn Volckaert wrote:
>
> From that point onwards, the debugger can no longer perform any
> operations that go through __ptrace_may_access. These include
> process_vm_{read,write}v but also PTRACE_{POKE,PEEK}{TEXT,DATA}.

PTRACE_POKE/PEEK should work? not that this really matters...

> I don't see
> how Yama can possibly tell that tracee B and the debugger are still related
> at this point so I see no easy fix for this.

Well, perhaps yama can also have PR_SET_PTRACEE, I dunno.

> Patching __ptrace_may_access
> might indeed not be a good idea as it is used to check for credentials to
> perform a bunch of other non-ptrace operations throughout the kernel.

Just add the "ptrace_parent(task) == current" check into
ptracer_exception_found() ?

> The possible solutions that I can see right now are:
> 1) Adding some sort of original_parent field to task_struct, just for the
> sake of relationship tracking

And what should we do with this pointer if original_parent exits?

> 2) Changing the credentials check in process_vm_{read,write}v only so that
> you don't go all the way into __ptrace_may_access if you're already attached
> as a ptracer

This really doesn't look good, imo.

Oleg.

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