linux-kernel - Re: [PATCH 3/5] powerpc, hw_breakpoints: Fix racy access to ptrace breakpoints

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Date:	Sun, 24 Apr 2011 13:34:15 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LPPC <linuxppc-dev@...ts.ozlabs.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	"v2.6.33.." <stable@...nel.org>
Subject: Re: [PATCH 3/5] powerpc, hw_breakpoints: Fix racy access to ptrace
 breakpoints

On Fri, Apr 22, 2011 at 03:16:27PM +0200, Frederic Weisbecker wrote:
> (resend with ppc list in cc)
> 
> While the tracer accesses ptrace breakpoints, the child task may
> concurrently exit due to a SIGKILL and thus release its breakpoints
> at the same time. We can then dereference some freed pointers.
> 
> To fix this, hold a reference on the child breakpoints before
> manipulating them.
> 
> Reported-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Prasad <prasad@...ux.vnet.ibm.com>
> Cc: Paul Mundt <lethal@...ux-sh.org>
> Cc: v2.6.33.. <stable@...nel.org>
> ---
>  arch/powerpc/kernel/ptrace.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index 55613e3..4edeeb3 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -1591,7 +1591,10 @@ long arch_ptrace(struct task_struct *child, long request,
>  	}
> 
>  	case PTRACE_SET_DEBUGREG:
> +		if (ptrace_get_breakpoints(child) < 0)
> +			return -ESRCH;
>  		ret = ptrace_set_debugreg(child, addr, data);
> +		ptrace_put_breakpoints(child);
>  		break;
> 
>  #ifdef CONFIG_PPC64
> -- 
> 1.7.3.2
>

Hi Frederic,
	Looks fine to me.

Acked-by: K.Prasad <prasad@...ux.vnet.ibm.com>

Thanks,
K.Prasad 
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