CVE-2026-89684: nfsd: fix cpntf publish race in nfs4_init_cp_state

CVE-2026-89684: nfsd: fix cpntf publish race in nfs4_init_cp_state

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

nfsd: fix cpntf publish race in nfs4_init_cp_state

nfs4_alloc_init_cpntf_state() published the new cpntf entry into the
s2s_cp_stateids IDR (with cs_type set) in one s2s_cp_lock section, then
took the lock again to list_add() it onto p_stid->sc_cp_list. In the gap
the entry is reachable by so_id but cp_list is still {NULL,NULL} from
kzalloc. A racing OFFLOAD_CANCEL (so_id is echoed to the client as
cnr_stateid, so any NFSv4.2 client can drive it) reaches
manage_cpntf_state() -> _free_cpntf_state_locked() and does list_del() on
the zeroed list_head, oopsing the server.

Fold the cs_type assignment and the list_add() into the same critical
section as idr_alloc_cyclic(), so a concurrent lookup either misses the
entry or sees a fully linked cp_list. INIT_LIST_HEAD() the entry after
allocation and switch _free_cpntf_state_locked() to list_del_init() so a
stale unlink is a no-op. nfs4_init_copy_state() passes NULL p_stid and
skips the list_add, preserving NFS4_COPY_STID semantics.

The Linux kernel CVE team has assigned CVE-2026-89684 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.6 with commit 624322f1adc58acd0b69f77a6ddc764207e97241 and fixed in 6.12.109 with commit 21d6c5957f5ca97d7352e60f55ea412beb9419f5
	Issue introduced in 5.6 with commit 624322f1adc58acd0b69f77a6ddc764207e97241 and fixed in 6.18.50 with commit a631a26a8777bb235eabd478bbbaf26a4db750bf
	Issue introduced in 5.6 with commit 624322f1adc58acd0b69f77a6ddc764207e97241 and fixed in 7.2.4 with commit c7270f62e7a05a2ee68aa2b74262b658a14463bd
	Issue introduced in 5.6 with commit 624322f1adc58acd0b69f77a6ddc764207e97241 and fixed in 7.3-rc1 with commit be3a5c1d857b0dcbc11796cea603ef25834f75b2

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89684
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/nfsd/nfs4state.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/21d6c5957f5ca97d7352e60f55ea412beb9419f5
	https://git.kernel.org/stable/c/a631a26a8777bb235eabd478bbbaf26a4db750bf
	https://git.kernel.org/stable/c/c7270f62e7a05a2ee68aa2b74262b658a14463bd
	https://git.kernel.org/stable/c/be3a5c1d857b0dcbc11796cea603ef25834f75b2