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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: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 26 Jun 2013 18:01:12 +0200
Cc: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, David Daney <ddaney@caviumnetworks.com>, David Daney <ddaney.cavm@gmail.com>, LKML <linux-kernel@vger.kernel.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 Wed, Jun 26, 2013 at 12:07:44PM +0100, James Hogan wrote:

> > 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?

> diff --git a/kernel/signal.c b/kernel/signal.c
> index 113411b..9ea8f4f 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2366,8 +2366,14 @@ relock:
>  
>               /*
>                * Death signals, no core dump.
> +              *
> +              * Some architectures (MIPS) have 128 signals which doesn't play
> +              * nicely with the exit code since there are only 7 bits to
> +              * store the terminating signal number. Mask out higher bits to
> +              * avoid overflowing into the core dump bit and triggering
> +              * BUG_ON in do_group_exit.
>                */
> -             do_group_exit(info->si_signo);
> +             do_group_exit(info->si_signo & 0x7f);
>               /* NOTREACHED */
>       }
>       spin_unlock_irq(&sighand->siglock);

Looks like something which I think we could live with.

Clearly it also scores in the "nasty" category, so fits the bill ;)

  Ralf

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