1 files changed, 11 insertions, 12 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 3ce5ae9e3d2d..917f338a6739 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -237,20 +237,19 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
         struct mm_struct *mm = get_task_mm(task);
         if (!mm)
                 return NULL;
+        if (mm != current->mm) {
+                /*
+                 * task->mm can be changed before security check,
+                 * in that case we must notice the change after.
+                 */
+                if (!ptrace_may_access(task, PTRACE_MODE_READ) ||
+                    mm != task->mm) {
+                        mmput(mm);
+                        return NULL;
+                }
+        }
         down_read(&mm->mmap_sem);
-        task_lock(task);
-        if (task->mm != mm)
-                goto out;
-        if (task->mm != current->mm &&
-            __ptrace_may_access(task, PTRACE_MODE_READ) < 0)
-                goto out;
-        task_unlock(task);
         return mm;
-out:
-        task_unlock(task);
-        up_read(&mm->mmap_sem);
-        mmput(mm);
-        return NULL;
 }
 
 static int proc_pid_cmdline(struct task_struct *task, char * buffer)