Linux Kernel up to 7.2.9 sched_ext cid.c scx_bpf_this_cid/scx_bpf_task_cid race condition

Summaryinfo

A vulnerability was found in Linux Kernel up to 7.2.9. It has been classified as very critical. The affected element is the function scx_bpf_this_cid/scx_bpf_task_cid of the file cid.c of the component sched_ext. The manipulation leads to race condition. This vulnerability is uniquely identified as CVE-2026-98942. Local access is required to approach this attack. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.2.9. It has been rated as very critical. This issue affects the function scx_bpf_this_cid/scx_bpf_task_cid of the file cid.c of the component sched_ext. The manipulation with an unknown input leads to a race condition vulnerability. Using CWE to declare the problem leads to CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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).

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2026-98942 since 09/25/2026. The exploitation is known to be easy. An attack has to be approached locally. Additional levels of successful authentication are required for exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 10/23/2026).

Upgrading to version 7.2.10 eliminates this vulnerability. Applying the patch 0e1a74369bdbc357d3d9713734418d914a981553/3a773220d39ba993dfe5d135f8b610be10794d5d is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.2.7
• 7.2.8
• 7.2.9

License

• open-source

Website

• Vendor: https://www.kernel.org/

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