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 1efd5d82b08bba16d2993fc83f10a5e7a9703022..9354da79e162a73e15d60bbac4a6d28235b34fd5 100644 (file)
--- 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;
                }