1 files changed, 20 insertions, 0 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 227fec36b12a..9a34bd80a745 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -697,6 +697,8 @@ static int ptrace_peek_siginfo(struct task_struct *child,
 static int ptrace_resume(struct task_struct *child, long request,
                          unsigned long data)
 {
+        bool need_siglock;
+
         if (!valid_signal(data))
                 return -EIO;
 
@@ -724,8 +726,26 @@ static int ptrace_resume(struct task_struct *child, long request,
                 user_disable_single_step(child);
         }
 
+        /*
+         * Change ->exit_code and ->state under siglock to avoid the race
+         * with wait_task_stopped() in between; a non-zero ->exit_code will
+         * wrongly look like another report from tracee.
+         *
+         * Note that we need siglock even if ->exit_code == data and/or this
+         * status was not reported yet, the new status must not be cleared by
+         * wait_task_stopped() after resume.
+         *
+         * If data == 0 we do not care if wait_task_stopped() reports the old
+         * status and clears the code too; this can't race with the tracee, it
+         * takes siglock after resume.
+         */
+        need_siglock = data && !thread_group_empty(current);
+        if (need_siglock)
+                spin_lock_irq(&child->sighand->siglock);
         child->exit_code = data;
         wake_up_state(child, __TASK_TRACED);
+        if (need_siglock)
+                spin_unlock_irq(&child->sighand->siglock);
 
         return 0;
 }