linux-kernel - Re: [PATCH] capability: WARN when invalid capability is requested rather than BUG/panic

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Date:	Wed, 01 Oct 2008 21:36:39 +0200
From:	Bodo Eggert <7eggert@....de>
To:	Eric Paris <eparis@...hat.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	sds@...ho.nsa.gov, morgan@...nel.org, selinux@...ho.nsa.gov,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] capability: WARN when invalid capability is requested 	rather than BUG/panic

Eric Paris <eparis@...hat.com> wrote:

> Do we have any concern of a module being compiled against a new kernel
> say with cap number 35 defined and then loaded into a kernel with only
> 34 capabilities?  Do we care about that forward compatibility?  If we
> care BUG is scary.  EPERM would be the right thing since clearly on this
> kernel the process can't possibly have cap #35.
> 
> We really have 4 options (in the order I like them).
> 
> 1) do nothing (garbage in garbage out, sometimes panic sometimes not)
> 2) mask CAP_TO_INDEX (garbage in garbage out, no panic)
> 3) BUG_ON(!cap_valid(flag)) (garbage in BUG out, no panic)
> 4) WARN_ON/EPERM (garbage in EPERM out, no panic)

5) Use a macro or inline function to test for $cap <= $max_cap, eliminating
   the test in the final code.

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