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

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

[Frederic Weisbecker]

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

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

Thanks,
K.Prasad