linux-kernel - Re: [RFC] [PATCH 2/2] capabilities: implement 64-bit capabilities

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Message-ID: <20071018153023.GA12123@vino.hallyn.com>
Date:	Thu, 18 Oct 2007 10:30:23 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Andrew Morgan <morgan@...nel.org>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Serge E. Hallyn" <serue@...ibm.com>, sds@...ho.nsa.gov,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, kaigai@...gai.gr.jp,
	casey@...aufler-ca.com
Subject: Re: [RFC] [PATCH 2/2] capabilities: implement 64-bit capabilities

Quoting Andrew Morgan (morgan@...nel.org):
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Serge E. Hallyn wrote:
> > Quoting Chris Wright (chrisw@...s-sol.org):
> >> * Serge E. Hallyn (serge@...lyn.com) wrote:
> >>> I guess now that I've written this out, it seems pretty clear
> >>> that capget64() and capget64() are the way to go.  Any objections?
> >> How is capget64() different from capget() that supports 2 different
> >> header->versions (I thought that was the whole point of the versioned,
> >> rather opaque interface)?  I don't object to a new syscall, but I don't
> >> see why it's required to avoid breaking libcap.
> > 
> > Hmm, I guess it *works*, it's just harder to explain the "inconsistent"
> > behavior.  Now instead of saying "capget() will fail under certain
> > conditions while capget64() will always succeed", capget() will actually
> > fail under certain conditions only if you send in a certain header.
> > 
> > Again, once I've written it out, I guess it isn't *so* bad.
> 
> [I'm just wading back into a mass of neglected email. Long story.]
> 
> Chris is right, this is precisely why the interface is versioned, and
> there is at least one version of libcap that was written to support this
> versioning scheme

Ok - i actually didn't default to backward compatibility because I was
pretty sure you would object to it on the grounds that old userspace
might get unexpected behavior.  But I guess since all high caps should be
new ones for new features, it'll require new userspace to exploit
anyway.

> cvs -z3
> - -d:pserver:anonymous@....linux-privs.sourceforge.net:/cvsroot/linux-privs
> co -r libcap-pre2 libcap
> 
> I'll try and unwind all the threads of email I've been neglecting and
> have something useful to say over the next few days.

Thanks.  I'll try to get a backward-compatible patch out today (again
just for rfc)  If not today, at least tomorrow.

thanks,
-serge
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