CVE-2026-64036

Summary

In the Linux kernel, the following vulnerability has been resolved:

cgroup/rstat: validate cpu before css_rstat_cpu() access

css_rstat_updated() is exposed as a BPF kfunc and accepts a caller-provided cpu argument. The function uses cpu for per-cpu rstat lookups without checking whether it refers to a valid possible CPU.

A BPF iter/cgroup program with CAP_BPF and CAP_PERFMON can pass an invalid cpu value. On an unfixed UBSCAN_BOUNDS test kernel, cpu == 0x7fffffff triggers:

UBSAN: array-index-out-of-bounds in kernel/cgroup/rstat.c:31:9 index 2147483647 is out of range for type 'long unsigned int [64]' Call Trace: css_rstat_updated bpf_iter_run_prog cgroup_iter_seq_show bpf_seq_read

Add cpu validation to the BPF-facing css_rstat_updated() kfunc and move the common implementation to __css_rstat_updated() for in-kernel callers.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/6a01413a4e8fcb0263d7bef5075c5f8f4eb3a8b6
• https://git.kernel.org/stable/c/fd2bd9fa7700ddf28296486b2598cff2f80cc819
• https://git.kernel.org/stable/c/8817005efbdfdf5d4e4814cb5dc52b53d12917d7

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