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From:   Todd Kjos <tkjos@google.com>
Date:   Tue, 13 Nov 2018 08:10:23 -0800
Message-ID: <CAHRSSEwewShxNV61m9SN1by+yDTGUfWkHb=ek1qFg6g8249ERw@mail.gmail.com>
Subject: Re: [PATCH V4] binder: ipc namespace support for android binder
To:     chouryzhou@tencent.com
Cc:     christian@brauner.io, Martijn Coenen <maco@android.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>, akpm@linux-foundation.org,
        dave@stgolabs.net,
        "open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Nov 13, 2018 at 12:12 AM chouryzhou(=E5=91=A8=E5=A8=81) <chouryzhou=
@tencent.com> wrote:
>
> > I have not received an answer to my questions in the last version of th=
is patch
> > set. Also it would be good if I could be Cc'ed by default. I can't hunt=
 down all
> > patches.
> > I do not know of any kernel entity, specifically devices, that change n=
amespaces
> > on open().
> > This seems like an invitation for all kinds of security bugs.
> > A device node belongs to one namespace only which is attached to the
> > underlying kobject. Opening the device should never change that.
> > Please look at how mqueue or shm are doing this. They don't change
> > namespaces on open either.
> > I have to say that is one of the main reasons why I disagree with that =
design.
> >
> >
>
> If we must return the same context when every open in proc, we can only i=
solate
> binder with mnt namespace instead of ipc namespace, what do you think, To=
dd?

I don't have strong feelings on this -- it seems like a bizarre
use-case to send the fd through a backchannel as christian describes,
but I do agree it is strange behavior (though it seems safe to me
since it prevents communication between unrelated entities). I don't
know how mqueue and shm work, its worth a look since this patch is
modelling their behavior...

We'll talk about it here at LPC and then on this thread.