FAILED: patch "[PATCH] sched_ext: Avoid UAF in scx_root_enable_workfn() init failure" failed to apply to 6.18-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.18-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 <stable@vger.kernel.org>.

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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 9a415cc53711f2238e0f0ca8a6bcc796c003b127
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026051526-vastness-flattop-e72e@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 9a415cc53711f2238e0f0ca8a6bcc796c003b127 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Mon, 11 May 2026 12:05:48 -1000
Subject: [PATCH] sched_ext: Avoid UAF in scx_root_enable_workfn() init failure
 path

In scx_root_enable_workfn(), put_task_struct(p) is called before scx_error()
dereferences p->comm and p->pid. If the iterator's reference is the last
drop, the task is freed synchronously and the deref becomes a UAF.

Move put_task_struct() past scx_error().

Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260511214031.AF5E9C2BCB0@smtp.kernel.org/
Fixes: f0e1a0643a59 ("sched_ext: Implement BPF extensible scheduler class")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 1efd5d82b08b..9354da79e162 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -6973,10 +6973,10 @@ static void scx_root_enable_workfn(struct kthread_work *work)
 			if (scx_get_task_state(p) != SCX_TASK_DEAD)
 				scx_set_task_state(p, SCX_TASK_NONE);
 			task_rq_unlock(rq, p, &rf);
-			put_task_struct(p);
 			scx_task_iter_stop(&sti);
 			scx_error(sch, "ops.init_task() failed (%d) for %s[%d]",
 				  ret, p->comm, p->pid);
+			put_task_struct(p);
 			goto err_disable_unlock_all;
 		}