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

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Date:	Tue, 2 Aug 2011 15:50:53 -0700
From:	"Andrew G. Morgan" <agm@...gle.com>
To:	Mike Waychison <mikew@...gle.com>
Cc:	Maximilian Attems <max@...o.at>,
	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.

Which part of the version check are you dropping?

Also, I'm not clear you need/want to drop the permitted/effective
bits. All that will survive the exec() are the inheritable bits.

Cheers

Andrew

On Tue, Aug 2, 2011 at 2:42 PM, Mike Waychison <mikew@...gle.com> wrote:
> 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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