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Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)

To: James Hogan <james.hogan@imgtec.com>
Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)
From: Andrew Morton <akpm@linux-foundation.org>
Date: Tue, 25 Jun 2013 14:40:15 -0700
Cc: Oleg Nesterov <oleg@redhat.com>, David Daney <ddaney@caviumnetworks.com>, David Daney <ddaney.cavm@gmail.com>, <linux-kernel@vger.kernel.org>, Ralf Baechle <ralf@linux-mips.org>, Al Viro <viro@zeniv.linux.org.uk>, Kees Cook <keescook@chromium.org>, David Daney <david.daney@cavium.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, David Howells <dhowells@redhat.com>, Dave Jones <davej@redhat.com>, <linux-mips@linux-mips.org>
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On Mon, 24 Jun 2013 10:10:08 +0100 James Hogan <james.hogan@imgtec.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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