Re: [PATCH] pid: Add a judgment for ns null in pid_nr_ns

[Oleg Nesterov <oleg@redhat.com>]

On 08/04, 高翔 wrote:
>
>     struct task_struct *tsk = current;
>
>     struct task_struct *parent;
>
>     ...
>
>     info->pid = task_pid_vnr(tsk);
>     rcu_read_lock();
>     parent = rcu_dereference(tsk->real_parent);
>     get_task_struct(parent);
>     rcu_read_unlock();
>     info->ppid = task_tgid_vnr(parent);
>     strncpy(info->ptask_name, parent->comm, TASK_COMM_LEN);
>     put_task_struct(parent);

So I guess the kernel crashes when you try to obtain another process's pid, not
the current process's pid. This is was I suspected.

This code is buggy. tsk->real_parent points to nowhere if tsk = current was reaped.
rcu_read_lock() alone can't help. Even get_task_struct(parent) is not safe. And it
is not needed.

You need something like

	info->pid = info->ppid = 0;

	rcu_read_lock();
	if (pid_alive(tsk)) {
		info->pid = task_pid_vnr(tsk);
		info->ppid = task_tgid_vnr(tsk->real_parent);
	}
	rcu_read_unlock();

Oleg.

> 
> 
> 
> ________________________________
> 发件人: Oleg Nesterov <oleg@redhat.com>
> 发送时间: 2025年8月2日 16:45:26
> 收件人: 高翔
> 抄送: Al Viro; Xiang Gao; brauner@kernel.org; mjguzik@gmail.com; Liam.Howlett@oracle.com; joel.granados@kernel.org; lorenzo.stoakes@oracle.com; linux-kernel@vger.kernel.org
> 主题: Re: 答复: [External Mail]Re: [PATCH] pid: Add a judgment for ns null in pid_nr_ns
> 
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> 
> On 08/02, 高翔 wrote:
> >
> > Obtain the current process pid in the ufs compl command. This scene is possible.
> 
> How exactly your module tries to obtain the current process pid?
> 
> task_pid_vnr(current) should work and return 0 if the task was reaped.
> 
> Oleg.
>