1 files changed, 29 insertions, 10 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 227fec36b12a..c8e0e050a36a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -456,8 +456,6 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
 
 static int ptrace_detach(struct task_struct *child, unsigned int data)
 {
-        bool dead = false;
-
         if (!valid_signal(data))
                 return -EIO;
 
@@ -467,18 +465,19 @@ static int ptrace_detach(struct task_struct *child, unsigned int data)
 
         write_lock_irq(&tasklist_lock);
         /*
-         * This child can be already killed. Make sure de_thread() or
-         * our sub-thread doing do_wait() didn't do release_task() yet.
+         * We rely on ptrace_freeze_traced(). It can't be killed and
+         * untraced by another thread, it can't be a zombie.
          */
-        if (child->ptrace) {
-                child->exit_code = data;
-                dead = __ptrace_detach(current, child);
-        }
+        WARN_ON(!child->ptrace || child->exit_state);
+        /*
+         * tasklist_lock avoids the race with wait_task_stopped(), see
+         * the comment in ptrace_resume().
+         */
+        child->exit_code = data;
+        __ptrace_detach(current, child);
         write_unlock_irq(&tasklist_lock);
 
         proc_ptrace_connector(child, PTRACE_DETACH);
-        if (unlikely(dead))
-                release_task(child);
 
         return 0;
 }
@@ -697,6 +696,8 @@ 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 +725,26 @@ 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;
 }