2 files changed, 33 insertions, 9 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1b25a37f2aee..b6467711f12e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2372,7 +2372,7 @@ static inline int thread_group_empty(struct task_struct *p)
  * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
  * subscriptions and synchronises with wait4().  Also used in procfs.  Also
  * pins the final release of task.io_context.  Also protects ->cpuset and
- * ->cgroup.subsys[].
+ * ->cgroup.subsys[]. And ->vfork_done.
  *
  * Nests both inside and outside of read_lock(&tasklist_lock).
  * It must not be nested with write_lock_irq(&tasklist_lock),
diff --git a/kernel/fork.c b/kernel/fork.c
index cf3d96379608..892c534ce6e3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -670,10 +670,34 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
 
 void complete_vfork_done(struct task_struct *tsk)
 {
-        struct completion *vfork_done = tsk->vfork_done;
+        struct completion *vfork;
 
-        tsk->vfork_done = NULL;
-        complete(vfork_done);
+        task_lock(tsk);
+        vfork = tsk->vfork_done;
+        if (likely(vfork)) {
+                tsk->vfork_done = NULL;
+                complete(vfork);
+        }
+        task_unlock(tsk);
+}
+
+static int wait_for_vfork_done(struct task_struct *child,
+                                struct completion *vfork)
+{
+        int killed;
+
+        freezer_do_not_count();
+        killed = wait_for_completion_killable(vfork);
+        freezer_count();
+
+        if (killed) {
+                task_lock(child);
+                child->vfork_done = NULL;
+                task_unlock(child);
+        }
+
+        put_task_struct(child);
+        return killed;
 }
 
 /* Please note the differences between mmput and mm_release.
@@ -717,7 +741,8 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
          * If we're exiting normally, clear a user-space tid field if
          * requested.  We leave this alone when dying by signal, to leave
          * the value intact in a core dump, and to save the unnecessary
-         * trouble otherwise.  Userland only wants this done for a sys_exit.
+         * trouble, say, a killed vfork parent shouldn't touch this mm.
+         * Userland only wants this done for a sys_exit.
          */
         if (tsk->clear_child_tid) {
                 if (!(tsk->flags & PF_SIGNALED) &&
@@ -1551,6 +1576,7 @@ long do_fork(unsigned long clone_flags,
                 if (clone_flags & CLONE_VFORK) {
                         p->vfork_done = &vfork;
                         init_completion(&vfork);
+                        get_task_struct(p);
                 }
 
                 /*
@@ -1568,10 +1594,8 @@ long do_fork(unsigned long clone_flags,
                         ptrace_event(trace, nr);
 
                 if (clone_flags & CLONE_VFORK) {
-                        freezer_do_not_count();
-                        wait_for_completion(&vfork);
-                        freezer_count();
-                        ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
+                        if (!wait_for_vfork_done(p, &vfork))
+                                ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
                 }
         } else {
                 nr = PTR_ERR(p);