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

[K.Prasad]

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 at redhat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec at gmail.com>
> Cc: Ingo Molnar <mingo at elte.hu>
> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Cc: Peter Zijlstra <a.p.zijlstra at chello.nl>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: Prasad <prasad at linux.vnet.ibm.com>
> Cc: Paul Mundt <lethal at linux-sh.org>
> Cc: v2.6.33.. <stable at kernel.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 at linux.vnet.ibm.com>

Thanks,
K.Prasad