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

To: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)
From: James Hogan <james.hogan@imgtec.com>
Date: Wed, 26 Jun 2013 12:07:44 +0100
Cc: Oleg Nesterov <oleg@redhat.com>, David Daney <ddaney@caviumnetworks.com>, David Daney <ddaney.cavm@gmail.com>, LKML <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>, <stable@vger.kernel.org>
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On 25/06/13 23:13, James Hogan wrote:
> On 25 June 2013 22:40, Andrew Morton <akpm@linux-foundation.org> wrote:
>> 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?
> 
> The first rfc patch I sent sort of satisfies that by passing 127 if
> sig==128, or slightly better would be passing 126 if sig>=127 (so that
> SIFSIGNALED returns true). Effectively #ifdef'ing it on _NSIG>127 as
> this patch does may be preferable too.
> 
> That's probably the minimum change necessary to evade the BUG_ON
> without removing it. The wait status code will still be wrong, but it
> wasn't exactly right before so it's no worse.
> 
> IMO changing the ABI by reducing _NSIG to 127 or 126 isn't appropriate
> for stable.

How does this look for a nasty/stable fix?

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