linux-kernel - Re: [PATCH] prctl: remove one-shot limitation for changing exe link

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Date:	Mon, 25 Jul 2016 13:21:51 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>
Cc:	<peterz@...radead.org>, <mingo@...hat.com>, <mhocko@...e.com>,
	<keescook@...omium.org>, <linux-kernel@...r.kernel.org>,
	<mguzik@...hat.com>, <bsegall@...gle.com>,
	<john.stultz@...aro.org>, <oleg@...hat.com>, <gorcunov@...nvz.org>,
	<matthltc@...ibm.com>, <akpm@...ux-foundation.org>,
	<luto@...capital.net>, <vbabka@...e.cz>, <xemul@...tuozzo.com>
Subject: Re: [PATCH] prctl: remove one-shot limitation for changing exe link

Stanislav Kinsburskiy <skinsbursky@...tuozzo.com> writes:

> Gentlemen,
>
> Looks like there are no objections to this patch.

There has been objection.

The only justification for the change that has been put forward is
someone doing a restore lazily.  I don't see a reason why you can't call
prctl_set_mm_exe_file until you have the file in place instead of a
place holder that sounds like a trivial solution to any restore issues.

The truth is an unlimited settable exe link is essentially meaningless,
as you can't depend on it for anything.  One shot seems the best
compromise I have seen put forward between the definite
checkpoint/restart requirement to set the this value and the general
need to have something that makes sense and people can depend on for
system management.

Also there is a big fat bug in prctl_set_mm_exe_file.  It doesn't
validate that the new file is a actually mmaped executable.  We would
definitely need that to be fixed before even considering removing the
limit.

Right now all I see is people involved in the implementation details of
their own little feature

So for the patch I am responding to:
Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Plus the merge window is open so no one is taking any patches right now.
It is the time to take what has already been staged and get that code
merged.

Eric