CVE-2026-31481tracing: Drain deferred trigger frees if kthread creation fails

Official description

In the Linux kernel, the following vulnerability has been resolved: tracing: Drain deferred trigger frees if kthread creation fails Boot-time trigger registration can fail before the trigger-data cleanup kthread exists. Deferring those frees until late init is fine, but the post-boot fallback must still drain the deferred list if kthread creation never succeeds. Otherwise, boot-deferred nodes can accumulate on trigger_data_free_list, later frees fall back to synchronously freeing only the current object, and the older queued entries are leaked forever. To trigger this, add the following to the kernel command line: trace_event=sched_switch trace_trigger=sched_switch.traceon,sched_switch.traceon The second traceon trigger will fail and be freed. This triggers a NULL pointer dereference and crashes the kernel. Keep the deferred boot-time behavior, but when kthread creation fails, drain the whole queued list synchronously. Do the same in the late-init drain path so queued entries are not stranded there either.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/771624b7884a83bb9f922ae64ee41a5f8b7576c9
• https://git.kernel.org/stable/c/250ab25391edeeab8462b68be42e4904506c409c