Re: [PATCH 03/12] pid: get ppid pid_t of task in init_pid_ns safely
On 08/20, Richard Guy Briggs wrote:
Added the functions
task_ppid()
task_ppid_nr_ns()
task_ppid_nr_init_ns()
to safely abstract the lookup of the PPID
but it is not safe.
+static inline struct pid *task_ppid(struct task_struct *task)
+{
+ return task_tgid(rcu_dereference(current->real_parent));
^^^^^^^
task?
+static inline pid_t task_ppid_nr_ns(struct task_struct *tsk,
+ struct pid_namespace *ns)
+{
+ pid_t pid;
+
+ rcu_read_lock();
+ pid = pid_nr_ns(task_ppid(current), ns);
^^^^^^^
again.
+ rcu_read_unlock();
And why this is safe?
rcu_read_lock() can't help if tsk was already dead _before_ it takes
the rcu lock. ->real_parent can point the already freed/reused/unmapped
memory.
This is safe if, for example, the caller alredy holds rcu_read_lock()
and tsk was found by find_task_by*(), or tsk is current.
Richard, just in case... I am going to vacation, I will be completely
offline till Sep 10.
Oleg.