Linux kernel nvme-tcp: a controller can force a host WARN by answering a write with C2HData

Impact

nvme_tcp_handle_c2h_data() never checks that the named command actually asked to read data. A controller - or anyone who can impersonate one on the storage network - that answers a write command with a C2HData PDU drives the host into _copy_to_iter() and trips WARN_ON_ONCE(i->data_source). No data is copied, so this is not memory corruption; what the controller gets is a kernel warning it can raise at will, plus a controller reset each time. On hosts booted with panic_on_warn, which is common in fleets that want crash-on-anomaly behaviour, that warning is a remote node kill. GPU nodes that mount datasets or checkpoints over NVMe/TCP can be knocked out repeatedly by a single misbehaving or hostile target.

Who can reach it

Network, unauthenticated at the NVMe layer - anyone who can present as the NVMe/TCP controller the host connects to, which in practice means a compromised storage target or a position on the storage network path. No tenant credentials required; tenants inside a GPU pod cannot reach this directly.

What to do

Apply a stable kernel that rejects a C2HData PDU whose command is not a read. Kernel-image change: drain and reboot each NVMe/TCP client node. Until then, the exposure is bounded by keeping the storage network segregated from tenant traffic, and by not running NVMe/TCP hosts with panic_on_warn, which is what turns this from noise into an outage.

References

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