Linux kernel nfsd: dispatch error paths leave the status seqlock counter odd, exposing mutating compound state

Impact

nfsd_dispatch() sets rq_status_counter odd after decode and even after processing, forming a seqlock with the lockless reader in nfsd_nl_rpc_status_get_dumpit(). Only the fully successful path restored it to even; the cache-hit, drop and encode-error paths returned with the counter left odd. While stuck odd, the netlink reader believes the rqstp fields are stable and its retry check never fires, so it reads args->ops and args->opcnt while they are being mutated and can run past the 8-element inline ops array. The result is a heap over-read reported to userspace on the NFS server. This is the dispatch-side half of the same status-interface exposure; both patches are needed. Local only - remote clients can force the counter odd by triggering a drop or cache hit, but only a local process can read the leaked memory.

Who can reach it

A local user or process on the NFS server that can issue the nfsd RPC-status netlink dump; remote clients can help keep the counter odd but cannot read the result.

What to do

Update the server kernel to a build with the counter-advance helper (stable commits b08c30f08d57 and f6045886fe3f) and reboot the node. Apply it together with the opcnt-clearing fix for the same interface. Until patched, keep untrusted local workloads off the NFS server.

References

Related entries

• Flux CD (allow-webhooks NetworkPolicy, notification-controller event server): CROSS-TENANT EVENT FORGERY: theNCVD-2026-057-flux-cd-allow-webhooks-networkpo · Flux CD (allow-webhooks NetworkPolicy, notification-controller event server)High
• OpenSSH through 10.0 - mm_answer_authpassword uses an integer 'authenticated' flag that does not resist a single bitCVE-2023-51767 · OpenSSH through 10.0 - mm_answer_authpassword uses an integer 'authenticated' flag that does not resist a single bit…High
• AMD Radeon RGB tool - signature verification on files in the installation directory: The Radeon RGB tool doesCVE-2024-36334 · AMD Radeon RGB tool - signature verification on files in the installation directoryHigh
• Intel Neural Compressor (SQL injection, second instance): A second SQL-injection path in Neural Compressor reachableCVE-2024-39766 · Intel Neural Compressor (SQL injection, second instance)High
• Redis: Authenticated user triggers a stack/heap out-of-bounds write in hyperloglog opsCVE-2025-32023 · RedisHigh
• Redis (multi-bulk command protocol handling): PERMANENT, VENDOR-ACKNOWLEDGED DENIAL OF SERVICE WITH NO FIX PLANNED. AnNCVD-2025-021-redis-multi-bulk-command-protoco · Redis (multi-bulk command protocol handling)High