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.
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