[PATCH 4/5] arm, hw_breakpoints: Fix racy access to ptrace breakpoints

From: Frederic Weisbecker
Date: Fri Apr 08 2011 - 13:35:44 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>
arch/arm/kernel/ptrace.c | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 2bf27f3..8182f45 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -767,12 +767,20 @@ long arch_ptrace(struct task_struct *child, long request,

+ if (ptrace_get_breakpoints(child) < 0)
+ return -ESRCH;
ret = ptrace_gethbpregs(child, addr,
(unsigned long __user *)data);
+ ptrace_put_breakpoints(child);
+ if (ptrace_get_breakpoints(child) < 0)
+ return -ESRCH;
ret = ptrace_sethbpregs(child, addr,
(unsigned long __user *)data);
+ ptrace_put_breakpoints(child);


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