sh, hw_breakpoints: Fix racy access to ptrace breakpoints

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 <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Acked-by: Paul Mundt <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Prasad <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]

diff --git a/arch/sh/kernel/ptrace_32.c b/arch/sh/kernel/ptrace_32.c
index 2130ca674e9bdd1674a22d339011a7f364bf0ec5..3d7b209b2178cc63c520975a35d4146c99042ba4 100644 (file)
--- a/arch/sh/kernel/ptrace_32.c
+++ b/arch/sh/kernel/ptrace_32.c
@@ -117,7 +117,11 @@ void user_enable_single_step(struct task_struct *child)
 
        set_tsk_thread_flag(child, TIF_SINGLESTEP);
 
+       if (ptrace_get_breakpoints(child) < 0)
+               return;
+
        set_single_step(child, pc);
+       ptrace_put_breakpoints(child);
 }
 
 void user_disable_single_step(struct task_struct *child)