+ mmput(mm);
+ return ERR_PTR(-EPERM);
+}
+
+/*
+ * If current may access user memory in @task return a reference to the
+ * corresponding mm, otherwise ERR_PTR.
+ */
+static struct mm_struct *check_mem_permission(struct task_struct *task)
+{
+ struct mm_struct *mm;
+ int err;
+
+ /*
+ * Avoid racing if task exec's as we might get a new mm but validate
+ * against old credentials.
+ */
+ err = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ if (err)
+ return ERR_PTR(err);
+
+ mm = __check_mem_permission(task);
+ mutex_unlock(&task->signal->cred_guard_mutex);
+
+ return mm;