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

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Date:	Tue, 30 Sep 2008 13:22:30 -0400
From:	Eric Paris <eparis@...hat.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	sds@...ho.nsa.gov, morgan@...nel.org, selinux@...ho.nsa.gov
Subject: Re: [PATCH] capability: WARN when invalid capability is requested
	rather than BUG/panic

On Tue, 2008-09-30 at 11:28 -0500, Serge E. Hallyn wrote:
> Quoting Eric Paris (eparis@...hat.com):

> > > Perhaps we should have CAP_TO_INDEX mask itself?
> > > 
> > > #define CAP_TO_INDEX(x)		(((x) >> 5) & _KERNEL_CAPABILITY_U32S)
> > 
> > Well, you save a branch and won't get the pagefault so it does 'fix' the
> > pagefault/panic from cap code.  It doesn't tell us when others screw up
> > and SELinux is still possibly going to BUG().  We are also going to
> > actually be returning a permission decision not on what was requested
> > but on something wholely different.
> 
> So exactly what was requested?

A capability that they cannot possibly have since it doesn't exist  :)

> > I like mine better, but I'm ok with yours and can just do my changes in
> > SELinux if this is how cap wants to handle it.  I don't really like the
> 
> Heh I don't like either one, just thought this would reduce the overhead
> a bit :)

No argument from me that patching up for buggy drivers sucks.  Yours
would be less overhead, and it would return the cap system back to
pre-2.6.25 operation (garbage in garbage out but no panic).  Since we
already have the branch in SELinux its no 'extra' overhead to EPERM
there instead of here (garbage in EPERM out).

-Eric

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