CVE-2026-98942 sched_ext: Build the cid tables privately and publish them with RCU
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-98942?
CVE-2026-98942 is a vulnerability in Linux, published on 23 Oct 2026.
Official description
In the Linux kernel, the following vulnerability has been resolved:
sched_ext: Build the cid tables privately and publish them with RCU
The cid tables are visible to the cid kfuncs while being modified: the first enable publishes the global pointers before filling them, ops.init_cids() overrides rewrite them in place, and re-enables rebuild them in place. A racing TRACING or SYSCALL program can read unfilled entries, including uninitialized memory in the kmalloc'd tables, or torn topo updates.
Tie the tables' lifetimes to the root sched instead: each root enable builds a fresh set privately and publishes the per-table __rcu globals once the layout is final, and root disable unpublishes and RCU-frees the set. A non-NULL global is now always a fully built table which stays valid for the reader's RCU read section, and lookups stay two loads. Kfuncs treat NULL as no-mapping, also after the scheduler exits instead of reporting the stale last mapping.
The cid kfuncs are available whether the root scheduler is cid-form or cpu-form, the latter to allow gradual migration to cids. Every root therefore builds and publishes a default mapping.
Every reader must either be gated on scheduler liveness or NULL-check inside an RCU read section. Fix the two kfuncs that were neither: scx_bpf_this_cid() read the table with no RCU or preemption protection and scx_bpf_task_cid() relied on KF_RCU, which doesn't put a sleepable program in an RCU read section. The hotplug callbacks are instead serialized by retiring the tables inside the cpus_read_lock() section that clears scx_root.
v2: Document why every root builds the tables (desc + cid.c comment).
Which versions are affected by CVE-2026-98942?
How do I fix CVE-2026-98942?
Upgrade to a fixed version.
Is CVE-2026-98942 being exploited?
There is no known exploitation of CVE-2026-98942 in the wild and no public exploit code.
Sources
Also known as AZL-110735, DEBIAN-CVE-2026-98942, GHSA-rh9v-mpgh-f53x, UBUNTU-CVE-2026-98942.