Bug 2460687 (CVE-2026-31481)

Summary: CVE-2026-31481 kernel: tracing: Drain deferred trigger frees if kthread creation fails
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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OS: Linux   
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A flaw was found in the Linux kernel. A local user can exploit this vulnerability by providing specific kernel command line parameters during boot, which can lead to a NULL pointer dereference. This issue occurs due to improper handling of deferred trigger frees when kernel thread (kthread) creation fails. Successful exploitation can cause the system to crash, resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-04-22 15:05:31 UTC 
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.
Comment 1 Keith Grant 2026-04-22 18:38:38 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042258-CVE-2026-31481-390e@gregkh/T