Re: [PATCH] pidfd: prevent creation of pidfds for kthreads

On 07/31, Christian Brauner wrote:

It's currently possible to create pidfds for kthreads but it is unclear what that is supposed to mean. Until we have use-cases for it and we figured out what behavior we want block the creation of pidfds for kthreads.

Hmm... could you explain your concerns? Why do you think we should disallow pidfd_open(pid-of-kthread) ?

@@ -2403,6 +2416,12 @@ __latent_entropy struct task_struct *copy_process( if (clone_flags & CLONE_PIDFD) { int flags = (clone_flags & CLONE_THREAD) ? PIDFD_THREAD : 0;

• /* Don't create pidfds for kernel threads for now. */
  

• if (args->kthread) {
  

• 	retval = -EINVAL;
  

• 	goto bad_fork_free_pid;
  

Do we really need this check? Userspace can't use args->kthread != NULL, the kernel users should not use CLONE_PIDFD.

Oleg.