Unverified Commit 3b5bbe79 authored by Christian Brauner's avatar Christian Brauner
Browse files

pidfd: prevent creation of pidfds for kthreads 

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.

Link: https://lore.kernel.org/r/20240731-gleis-mehreinnahmen-6bbadd128383@brauner


Fixes: 32fcb426 ("pid: add pidfd_open()")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 889ced4c

kernel/fork.c

+22 −3
Original line number Diff line number Diff line
@@ -2053,11 +2053,24 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re 
 */

int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)

{

	bool thread = flags & PIDFD_THREAD;

	if (!pid)

		return -EINVAL;



	scoped_guard(rcu) {

		struct task_struct *tsk;



	if (!pid || !pid_has_task(pid, thread ? PIDTYPE_PID : PIDTYPE_TGID))

		if (flags & PIDFD_THREAD)

			tsk = pid_task(pid, PIDTYPE_PID);

		else

			tsk = pid_task(pid, PIDTYPE_TGID);

		if (!tsk)

			return -EINVAL;



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

		if (tsk->flags & PF_KTHREAD)

			return -EINVAL;

	}



	return __pidfd_prepare(pid, flags, ret);

}
@@ -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;

		}



		/* Note that no task has been attached to @pid yet. */

		retval = __pidfd_prepare(pid, flags, &pidfile);

		if (retval < 0)