Date: Thu, 24 Jul 2014 20:42:26 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Andrew Vagin <avagin@parallels.com>
Cc: Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, Tejun Heo <tj@kernel.org>,
        Andrew Vagin <avagin@openvz.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Vasiliy Kulikov <segoon@openwall.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Julien Tinnes <jln@google.com>
Subject: Re: [RFC 2/2] prctl: PR_SET_MM -- Introduce PR_SET_MM_MAP operation
Message-ID: <20140724164226.GA17876@moon>
References: <20140703151102.842945837@openvz.org>
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 <20140708143830.ea078ef01e1d7d31276edbcd@linux-foundation.org>
 <20140708221336.GL17860@moon.sw.swsoft.com>
 <20140709141318.GM17860@moon.sw.swsoft.com>
 <CAGXu5jKmTSb0YmNFDtr-jymrhy_s_PXUuvj3WKYffSU98gwyqg@mail.gmail.com>
 <20140709150604.GN17860@moon.sw.swsoft.com>
 <20140711173625.GD19702@moon>
 <CAGXu5jL3exT4j+8rjMv1O54uJWQ5UHL69Z-24b61rhXROqZamQ@mail.gmail.com>
 <20140724134828.GA3553@paralelels.com>
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On Thu, Jul 24, 2014 at 05:48:28PM +0400, Andrew Vagin wrote:
> On Tue, Jul 22, 2014 at 01:07:51PM -0700, Kees Cook wrote:
> > >  - @exe_fd is referred from /proc/$pid/exe and when generating
> > >    coredump. We uses prctl_set_mm_exe_file_locked helper to update
> > >    this member, so exe-file link modification remains one-shot
> > >    action.
> > 
> > Controlling exe_fd without privileges may turn out to be dangerous. At
> > least things like tomoyo examine it for making policy decisions (see
> > tomoyo_manager()).
> >
> 
> We don't want to reduce security. How can we get a process with a
> target exe link, which executes our code?
> 
> We can execute the target file and attach to it with ptrace. ptrace
> allows to inject and execute any code.
> 
> So if we are sure that we are able to do a previous scenario, we can
> safely change exe-link, can't we?
> 
> prctl already has a check of permissions to execute the target file.
> If we execute a file. What can prevent us to attach to the process with ptrace?
> 
> The file can have a suid bit, so after executing it we may lose ability
> to attach to it. To check that we can check that uid and gid is zero
> in a current userns (local root).
> 
> What else do we need to check?

Good question. I suppose plain check for local root should be enough.
Guys, I'm about to send a new series for review. Please take a look
once time permit.
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