CVE-2026-89688nfsd: drop the stateid, not the stateowner, on seqid_op replay retry

Official description

In the Linux kernel, the following vulnerability has been resolved: nfsd: drop the stateid, not the stateowner, on seqid_op replay retry In nfs4_preprocess_seqid_op() the stateid is obtained from nfsd4_lookup_stateid(), which holds a reference on the nfs4_stid (sc_count) but takes no reference on the stateowner. openlockstateid() merely casts that stid and likewise takes no reference. When nfsd4_cstate_assign_replay() returns -EAGAIN (the replay owner is being torn down, RP_UNHASHED) it has not taken a stateowner reference on that path. The error handling nevertheless called nfs4_put_stateowner(stp->st_stateowner), dropping an so_count reference the function never acquired -- risking a stateowner refcount underflow and use-after-free -- while leaking the sc_count reference held on the stid. The leaked stid reference can also stall a concurrent nfsd4_close_open_stateid() waiting for sc_count to drop. Drop the reference actually held -- the stid -- before retrying. The stateowner stays alive through the reference held by the stid. This mirrors the open path in nfsd4_process_open1(), where the put balances a reference that path explicitly holds on the stateowner.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/69ed78b6b947c9257213164678b4edf17533093b
• https://git.kernel.org/stable/c/00843074d9b84824552c9679d423d29500ca5de0
• https://git.kernel.org/stable/c/f7cb90ddc021747fc9abfd4cf5252d425fd34eec
• https://git.kernel.org/stable/c/5e4627d3513e60accfce9d5f4c7fa95251ef93d6