linux-kernel - Re: [PATCH] capabilities: Ambient capability set V1

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Date:	Tue, 24 Feb 2015 11:28:48 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Serge Hallyn <serge.hallyn@...ntu.com>
cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	Aaron Jones <aaronmdjones@...il.com>, Ted Ts'o <tytso@....edu>,
	linux-security-module@...r.kernel.org, akpm@...uxfoundation.org,
	"Andrew G. Morgan" <morgan@...nel.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Markku Savela <msa@...h.iki.fi>,
	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] capabilities: Ambient capability set V1

On Tue, 24 Feb 2015, Serge Hallyn wrote:

> Unless I'm misunderstanding what you are saying, apps do have surprises.
> They drop capabilities, execute a file, and the result has capabilities
> which the app couldn't have expected.  At least if the bits have to be
> in fI to become part of pP', the app has a clue.

Well yes but the surprises do not occur in the cap bits they are
manipulating or inspecting via prctl.

> To be clear, I'm suggesting that the rules at exec become:
>
> pI' = pI

Ok that is new and on its own may solve the issue?

> pA' = pA  (pA is ambient)

Thats what this patch does

> pP' = (X & fP) | (pI & (fI | pA))

Hmmm... fP is empty for the file not having caps. so

pP' = pI & pA

> pE' = pP' & fE

fE? So the inherited caps are not effective? fE would be empty for a file
not having caps thus the ambient caps would not be available in the child.


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