# CVE-2026-89663

## Summary

- **CVE ID:** CVE-2026-89663
- **Severity:** HIGH
- **CVSS Score:** 8.8 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

nfsd: revoke copy-notify stateids before dropping their reference

Copy-notify stateids live in the s2s_cp_stateids IDR and on their parent
stid's sc_cp_list, pinned by a single membership reference.
_free_cpntf_state_locked() only unlinks an entry once its refcount reaches
zero, so any revoke path that runs while a concurrent
find_cpntf_state()/manage_cpntf_state() holder has elevated cs_count drops
the reference without unlinking, leaving the entry discoverable with its
membership reference already consumed. A second revoke or a laundromat tick
then frees it while the reader still holds the pointer -- a
KASAN-detectable use-after-free at the reader's nfs4_put_cpntf_state().

This affected all three revoke paths:

  - The parent-stid drain (nfs4_free_cpntf_statelist()) repeatedly called
    _free_cpntf_state_locked() on the first list entry; a holder that had
    bumped cs_count made it return early, so the next iteration
    re-decremented and burned the holder's reference.

  - OFFLOAD_CANCEL (manage_cpntf_state()) and laundromat expiry likewise
    used _free_cpntf_state_locked() and could drop 2->1 without unlinking.

Add revoke_cpntf_state_locked(), which unhashes the entry from the IDR and
sc_cp_list first (deferring the final free to any holder), and use it from
all three revoke paths. The drain now walks with list_for_each_entry_safe()
and revokes each entry unconditionally, so it terminates in one pass per
entry regardless of cs_count. The unhash is gated on
!list_empty(&cps->cp_list); the idr_remove() gate matters because
idr_alloc_cyclic() may have recycled the so_id by then. Keep
_free_cpntf_state_locked() for the reference-holder put path only, where a
concurrent revoke may already have unlinked the entry (its list_del_init()
then a no-op).

## Affected Products

- Linux — Linux (624322f1adc58acd0b69f77a6ddc764207e97241)
- Linux — Linux (5.6)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.10.270)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/6b8149448cdcb476fba4559d1ecc247efee9971b)
- [CNA](https://git.kernel.org/stable/c/b56d2c5f01cddbeca7d11cce81d97db4ec9a464f)
- [CNA](https://git.kernel.org/stable/c/ff8a3cff02b92b2a82f1a9876038fcf953ae9c25)
- [CNA](https://git.kernel.org/stable/c/3b0c3595db99bb4bebd7c8aa8a36f3c50e411bb7)
- [CNA](https://git.kernel.org/stable/c/5f00e0ab4de45d4f9e4bd0883cf2517acf63fc0d)
- [CNA](https://git.kernel.org/stable/c/06a62f6dbc60791f4229c6950b1eec6b18df9af1)
- [CNA](https://git.kernel.org/stable/c/a1fca0f7bbb7b100a39c7ba8dd7922c87c4237a3)
- [CNA](https://git.kernel.org/stable/c/caddbeffab1eaba1d2bcf5ceda35547863466705)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.46%
- **EPSS Percentile:** 38.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._