Linux kernel BPF uprobe_multi: unchecked __get_user on user-supplied data allows local memory disclosure or corruption

Impact

The uprobe_multi BPF link copied user-supplied data with __get_user without first validating the bounds with access_ok. A local process able to create a uprobe_multi link can hand the kernel an address it does not own, reading or writing memory outside the user range; on affected architectures this is a path from unprivileged-ish BPF access to kernel memory disclosure or corruption, and NVD rates it 7.8 local with high confidentiality, integrity and availability impact. On a GPU node this matters where BPF is reachable beyond root: eBPF-based observability agents, CNI dataplanes such as Cilium, and profiling sidecars are commonly granted CAP_BPF or CAP_SYS_ADMIN, so a compromised agent or a tenant workload holding those capabilities gets a kernel-level primitive on a host that also runs other tenants' GPU pods. It is local-only - there is no remote path - but a single node compromise on a shared GPU host means every pod resident on that node, and the node cannot be drained for free.

Who can reach it

Local authenticated user or container that can attach a uprobe_multi BPF link - in practice a process with CAP_BPF/CAP_SYS_ADMIN, or an unprivileged user on a kernel configured to permit BPF. No remote access.

What to do

Pick up the fixed stable kernel (the fix adds the missing access_ok check before __get_user); commits are in the kernel.org stable tree per the references. Applying it means a reboot of each node, so drain GPU workloads first - or defer by restricting BPF: tighten kernel.unprivileged_bpf_disabled and remove CAP_BPF/CAP_SYS_ADMIN from workloads that do not need tracing. No fixed release number is stated in the record beyond the listed stable commits.

References

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