linux-kernel - Re: [PATCH] capabilities: Ambient capability set V2

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Date:	Thu, 5 Mar 2015 12:41:36 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
cc:	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	Jonathan Corbet <corbet@....net>,
	Aaron Jones <aaronmdjones@...il.com>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...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-api@...r.kernel.org, Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH] capabilities: Ambient capability set V2

On Thu, 5 Mar 2015, Serge E. Hallyn wrote:

> > >
> > > So I'd say drop this change ^
> >
> > Then the ambient caps get ignored for a executables that have capabilities
> > seton the file?
>
> Yes.  Those are assumed to already know what they're doing.

Do they? What if there is a LD_PRELOAD library that redirects socket calls
and that needs raw device access (there are actually a number of software
packages like that to reduce the latency of network I/O. See for example
Solarflare's software products and the current rsocket libary in OFED.
There are cap issues if the rsocket library should be made useful for
Ethernet instead of infiniband).

> Why?  Do you foresee cases where a file that has fP set needs capabilities
> that aren't in its fP?

Yes due to the library issues.

> It seems more likely that they'll risk misbehaving due to an unexpected set
> of caps.

The userspace driver code in the library wont work since it does not have
the caps to access the raw device registers.
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