linux-kernel - Re: [PATCH v3] kernel/signal.c: fix BUG

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Message-Id: <20130625144015.1e4e70a0ac888f4ccf5c6a8f@linux-foundation.org>
Date:	Tue, 25 Jun 2013 14:40:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	James Hogan <james.hogan@...tec.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	David Daney <ddaney@...iumnetworks.com>,
	David Daney <ddaney.cavm@...il.com>,
	<linux-kernel@...r.kernel.org>, Ralf Baechle <ralf@...ux-mips.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Kees Cook <keescook@...omium.org>,
	David Daney <david.daney@...ium.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>, <linux-mips@...ux-mips.org>
Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)

On Mon, 24 Jun 2013 10:10:08 +0100 James Hogan <james.hogan@...tec.com> wrote:

> On 22/06/13 20:09, Oleg Nesterov wrote:
> > On 06/21, David Daney wrote:
> >> I am proposing that we just reduce the number of usable signals such
> >> that existing libc status checking macros/functions don't change in any
> >> way.
> > 
> > And I fully agree! Absolutely, sorry for confusion.
> > 
> > 
> > What I tried to say, _if_ we change the ABI instead, lets make this
> > change sane.
> 
> I agree that this approach isn't very nice (I was really just trying to
> explore the options) and reducing the number of signals is nicer. But is
> anybody here confident enough that the number of signals changing under
> the feet of existing binaries/libc won't actually break anything real?
> I.e. anything trying to use SIGRTMAX() to get a lower priority signal.

Meanwhile, unprivileged users can make a MIPS kernel go BUG.

How much of a problem is this?  Obviously less of a problem with MIPS
than it would be with some other CPU types, but I'd imagine it's still
awkward in some environments.

If this _is_ considered a problem, can we think of some nasty little
hack which at least makes the effects less damaging, which we can also
put into -stable kernels?

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