arm, 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: Will Deacon <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Prasad <[email protected]>
Cc: Paul Mundt <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 2bf27f364d098c210ed7cca9ece5edca613a9f2b..8182f45ca493724f732f59cfe38e69a7c45afe44 100644 (file)
--- 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,
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
                case PTRACE_GETHBPREGS:
+                       if (ptrace_get_breakpoints(child) < 0)
+                               return -ESRCH;
+
                        ret = ptrace_gethbpregs(child, addr,
                                                (unsigned long __user *)data);
+                       ptrace_put_breakpoints(child);
                        break;
                case PTRACE_SETHBPREGS:
+                       if (ptrace_get_breakpoints(child) < 0)
+                               return -ESRCH;
+
                        ret = ptrace_sethbpregs(child, addr,
                                                (unsigned long __user *)data);
+                       ptrace_put_breakpoints(child);
                        break;
 #endif