nfsd: revoke copy-notify stateids before dropping their reference

Overview

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

• Linux >= 624322f1adc58acd0b69f77a6ddc764207e97241 < 5f00e0ab4de45d4f9e4bd0883cf2517acf63fc0d
• Linux >= 624322f1adc58acd0b69f77a6ddc764207e97241 < 06a62f6dbc60791f4229c6950b1eec6b18df9af1
• Linux >= 624322f1adc58acd0b69f77a6ddc764207e97241 < a1fca0f7bbb7b100a39c7ba8dd7922c87c4237a3
• Linux >= 624322f1adc58acd0b69f77a6ddc764207e97241 < caddbeffab1eaba1d2bcf5ceda35547863466705
• Linux >= 624322f1adc58acd0b69f77a6ddc764207e97241 < 6b8149448cdcb476fba4559d1ecc247efee9971b
• Linux >= 624322f1adc58acd0b69f77a6ddc764207e97241 < b56d2c5f01cddbeca7d11cce81d97db4ec9a464f
• Linux >= 624322f1adc58acd0b69f77a6ddc764207e97241 < ff8a3cff02b92b2a82f1a9876038fcf953ae9c25
• Linux >= 624322f1adc58acd0b69f77a6ddc764207e97241 < 3b0c3595db99bb4bebd7c8aa8a36f3c50e411bb7
• Linux 5.6

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-27 · vex