linux-kernel - Re: [PATCH v5] init: Disable defaults if init= fails

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Date:	Mon, 20 Oct 2014 13:14:54 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Rob Landley <rob@...dley.net>,
	Frank Rowand <frowand.list@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Shuah Khan <shuah.kh@...sung.com>
Subject: Re: [PATCH v5] init: Disable defaults if init= fails

On Tue, Oct 14, 2014 at 2:00 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 1 Oct 2014 11:13:14 -0700 Andy Lutomirski <luto@...capital.net> wrote:
>
>> On Wed, Oct 1, 2014 at 11:05 AM,  <josh@...htriplett.org> wrote:
>> > On Tue, Sep 30, 2014 at 09:53:56PM -0700, Andy Lutomirski wrote:
>> >> I significantly prefer default N.  Scripts that play with init= really
>> >> don't want the fallback, and I can imagine contexts in which it could
>> >> be a security problem.
>> >
>> > While I certainly would prefer the non-fallback behavior for init as
>> > well, standard kernel practice has typically been to use "default y" for
>> > previously built-in features that become configurable.  And I'd
>> > certainly prefer a compile-time configuration option like this (even
>> > with default y) over a "strictinit" kernel command-line option.
>> >
>>
>> Fair enough.
>>
>> So: "default y" for a release or two, then switch the default?  Having
>> default y will annoy virtme, though it's not the end of the world.
>> Virtme is intended to work with more-or-less-normal kernels.
>>
>
> Adding another Kconfig option is tiresome.  What was wrong with strictinit=?

Now that this thread has gotten absurdly wrong, any thoughts?

My preference order is:

1. The patch as is.
2. The patch, minus the config option (i.e. making it unconditional).
3. Something else.

I would very much prefer to get *something* merged.  The current
behavior is problematic for scripted kernel boots that don't use
initramfs.

I can be flexible on the something else.  One option would be to allow
a whole list of commands in init=, but that has compatibility issues.
Another would be adding an option like init_fallback=/bin/sh.  A third
is the original strictinit mechanism.  I don't really like any of
them, because they're all more complex.

IOW, the no-fallback behavior is easy to implement, easy to
understand, and has extremely predictable behavior.  The fallback
behavior is more user friendly if you consider having a chance of
booting to something useful if you typo your init= option (but also a
chance of booting to something actively undesirable).

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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