Re: [PATCH] do_task_stat: don't use task_pid_nr_ns() lockless

[ebiederm@xmission.com (Eric W. Biederman)]

Oleg Nesterov <oleg@tv-sign.ru> writes:

> Without rcu/tasklist/siglock lock task_pid_nr_ns() may read the freed memory,
> move the callsite under ->siglock.
>
> Sadly, we can report pid == 0 if the task was detached.

We only get detached in release_task so it is a pretty small window
where we can return pid == 0.  Usually get_task_pid will fail first
and we will return -ESRCH.  Still the distance from open to 

There is another bug in here as well.  current->nsproxy->pid_ns is wrong.
What we want is: ns = dentry->d_sb->s_fs_info;

Otherwise we will have file descriptor passing races and the like.

We could also do: proc_pid(inode) to get the pid, which is a little
more race free, and will prevent us from returning pid == 0.

In either event it looks like we need to implement some proper
file operations for these proc files, maybe even going to seq file
status.

Eric
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