FAILED: patch "[PATCH] pidfd: prevent creation of pidfds for kthreads" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 3b5bbe798b2451820e74243b738268f51901e7d0
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024081910-grid-bobsled-6cb3@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

3b5bbe798b24 ("pidfd: prevent creation of pidfds for kthreads")
83b290c9e3b5 ("pidfd: clone: allow CLONE_THREAD | CLONE_PIDFD together")
64bef697d33b ("pidfd: implement PIDFD_THREAD flag for pidfd_open()")
21e25205d7f9 ("pidfd: don't do_notify_pidfd() if !thread_group_empty()")
cdefbf2324ce ("pidfd: cleanup the usage of __pidfd_prepare's flags")
932562a6045e ("rseq: Split out rseq.h from sched.h")
cba6167f0adb ("restart_block: Trim includes")
f038cc1379c0 ("locking/seqlock: Split out seqlock_types.h")
53d31ba842d9 ("posix-cpu-timers: Split out posix-timers_types.h")
f995443f01b4 ("locking/seqlock: Simplify SEQCOUNT_LOCKNAME()")
58390c8ce1bd ("Merge tag 'iommu-updates-v6.4' of git://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3b5bbe798b2451820e74243b738268f51901e7d0 Mon Sep 17 00:00:00 2001
From: Christian Brauner <[email protected]>
Date: Wed, 31 Jul 2024 12:01:12 +0200
Subject: [PATCH] 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.

index cc760491f201..18bdc87209d0 100644
@@ -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 || !pid_has_task(pid, thread ? PIDTYPE_PID : PIDTYPE_TGID))
+	if (!pid)
 		return -EINVAL;
 
+	scoped_guard(rcu) {
+		struct task_struct *tsk;
+
+		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)