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

From: Frederic Weisbecker
Date: Fri Apr 08 2011 - 13:35:52 EST

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@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Prasad <prasad@xxxxxxxxxxxxxxxxxx>
Cc: Paul Mundt <lethal@xxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: v2.6.33.. <stable@xxxxxxxxxx>
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 895b082..330df91 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,

+ if (ptrace_get_breakpoints(child) < 0)
+ return -ESRCH;
ret = ptrace_set_debugreg(child, addr, data);
+ ptrace_put_breakpoints(child);

#ifdef CONFIG_PPC64

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/