CVE-2026-98942sched_ext: Build the cid tables privately and publish them with RCU
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No exploitation reported and no EPSS estimate yet.
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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).
- CVSS
- Not yet scored
- Weakness (CWE)
- Not given
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Linux
- NVD analysis
- Received
- Record last updated
- Oct 26, 2026
- First seen by InfoSec Signals
- Oct 23, 2026
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