Linux kernel BPF: sleepable programs could attach to kprobe_multi and sleep in atomic context

Impact

kprobe.multi programs run in atomic/RCU context, but bpf_kprobe_multi_link_attach() never checked the sleepable flag on the program being attached. A sleepable program could therefore be attached and call sleeping helpers such as bpf_copy_from_user() from a non-sleepable context, producing a "sleeping function called from invalid context" BUG with preemption disabled and RCU nested. The practical exposure on a GPU fleet is the privileged tracing and security agents that use kprobe_multi for low-overhead attachment: a bad attach destabilises the host kernel rather than just the agent. Impact is availability; the record shows a splat, not memory corruption or privilege escalation.

Who can reach it

Local and privileged. Attaching kprobe_multi links requires CAP_BPF/CAP_PERFMON (in practice root on the host); the splat in the report was reached from a root sudo process. Not reachable from an unprivileged tenant pod without those capabilities.

What to do

Take the stable kernel fix, which rejects sleepable programs early in bpf_kprobe_multi_link_attach() (commits linked from the NVD record). Rollout is a kernel upgrade, so drain and reboot each node; the record names no fixed release version. Until then, the mitigation is operational: do not load sleepable programs onto kprobe_multi attachment points in node agents.

References

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