linux-kernel - Re: [PATCH v1 2/2] run-init: Add drop

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Message-ID: <CAGTjWtAyCZ9fyBeEcsrSmpzK4Lgae5uyHCfO2LExeYLSrx+4jg@mail.gmail.com>
Date:	Tue, 2 Aug 2011 14:42:11 -0700
From:	Mike Waychison <mikew@...gle.com>
To:	Maximilian Attems <max@...o.at>
Cc:	"Andrew G. Morgan" <agm@...gle.com>,
	Eric Northup <digitaleric@...gle.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	Eric Paris <eparis@...isplace.org>, klibc@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] run-init: Add drop_capabilities support.

On Tue, Aug 2, 2011 at 2:09 PM, Maximilian Attems <max@...o.at> wrote:
> On Fri, 29 Jul 2011, Mike Waychison wrote:
>
>> On Fri, Jul 29, 2011 at 1:45 PM, Maximilian Attems <max@...o.at> wrote:
>> > On Tue, 19 Jul 2011, Mike Waychison wrote:
>> >
>> >> This patch adds the ability to run-init to allow the dropping of
>> >> POSIX capabilities.
>> >>
>> >> This works by adding a "-d" flag to run-init, which takes a comma
>> >> separated list of capability names that should be dropped right before
>> >> exec'ing the real init binary.
>> >>
>> >> kinit is also modified by this change, such that it understands the same
>> >> argument when prepended with "drop_capabilities=" on the kernel command
>> >> line.
>> >>
>> >> When processing capabilities to drop, CAP_SETPCAP is special cased to be
>> >> dropped last, so that the order that capabilities are given does not
>> >> cause dropping of later enumerated capabilities to fail if it is listed
>> >> early on.
>> >>
>> >> Dropping of capabilities happens in three parts.  We explicitly drop the
>> >> capability from init's inherited, permitted and effective masks.  We
>> >> also drop the capability from the bounding set using PR_CAPBSET_DROP.
>> >> Lastly, if available, we drop the capabilities from the bset and
>> >> inheritted masks exposed at /proc/sys/kernel/usermodehelper if available
>> >> (introduced in v3.0.0).
>> >
>> > hmm as 3.0 is out, I don't think we need more backward compatibility.
>> > do you have a strong arg for it?
>> > especially since this is an *optional* calling arg I really don't see
>> > the need of that backward crap.
>>
>> I'd like to keep it for the time being. I'm still building both 2.6.34
>> and 2.6.39 kernels at the moment, though I can maintain these last few
>> compatibility bits in-house if that makes it easier for you.
>
> you include anyway linux/version.h, would build disabling help you?
> that way that macro doesn't need duplicating.
>

For correctness sake, I think it's still a runtime check thing
(consider the case of an image that is reused between kernel builds).

Reflecting on it a bit more though, I'd be okay if we removed the
version check altogether and just made it warn if the file isn't
present.
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