Expired Pointer Dereference Affecting kernel-zfcpdump-modules-extra package, versions *
Threat Intelligence
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Test your applications- Snyk IDSNYK-CENTOS10-KERNELZFCPDUMPMODULESEXTRA-19842665
- published16 Sept 2026
- disclosed11 Sept 2026
Introduced: 11 Sep 2026
NewCVE-2026-89708 (opens in a new tab)How to fix?
There is no fixed version for Centos:10 kernel-zfcpdump-modules-extra.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-zfcpdump-modules-extra package and not the kernel-zfcpdump-modules-extra package as distributed by Centos.
See How to fix? for Centos:10 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
nfsd: RCU-protect cl_cb_session to fix use-after-free on session teardown
After a DESTROY_SESSION the per-session teardown path can free a session while rpciod still holds an inflight callback rpc_task that dereferences clp->cl_cb_session. nfsd4_probe_callback_sync() flushes cl_callback_wq, but once nfsd4_run_cb_work() has called rpc_call_async() the rpc_task lives on rpciod; flushing the workqueue does not wait for it. rpc_shutdown_client() does drain rpciod tasks, but uses a 1-second wait_event_timeout — tasks stuck in rpc_delay() (e.g. 2-second NFS4ERR_DELAY retries) can outlive the drain.
destroy path rpciod
------------ ------
unhash_session(ses)
nfsd4_probe_callback_sync(clp)
flush_workqueue(cl_callback_wq)
/* returns; rpc_task still live */
nfsd4_put_session_locked(ses)
free_session(ses) -> kfree(ses)
nfsd4_cb_sequence_done()
reads cb_clp->cl_cb_session
/* freed slab */
A second window exists in nfsd4_process_cb_update(). When __nfsd4_find_backchannel() returns NULL because unhash_session() has already removed the destroyed session from cl_sessions, setup_callback_client() takes the v4.1 early return so clp->cl_cb_session = ses never fires and the field retains a pointer to the about-to-be-freed session.
Fix both by converting cl_cb_session to an RCU-protected pointer:
Move the cl_cb_session = ses assignment in setup_callback_client() to after rpc_create() succeeds, so it is only published when a working backchannel exists. Clear cl_cb_session on the error return in nfsd4_process_cb_update(). Both stores use rcu_assign_pointer().
Annotate cl_cb_session with __rcu. All rpciod-side readers use rcu_read_lock()/rcu_dereference() and check for NULL, bailing to the appropriate error or requeue path: encode_cb_sequence4args(), decode_cb_sequence4resok(), nfsd41_cb_get_slot(), nfsd41_cb_release_slot(), nfsd4_cb_prepare(), and nfsd4_cb_sequence_done().
Switch __free_session() from kfree() to kfree_rcu() so the session slab is not reclaimed until after an RCU grace period, guaranteeing that rpciod readers inside rcu_read_lock() never dereference freed memory.
Pass the session pointer to the nfsd_cb_seq_status and nfsd_cb_free_slot tracepoints instead of having them re-read cl_cb_session.
nfsd4_cb_prepare() calls rpc_exit() when the session is NULL, routing through the done/release path to requeue the callback.
References
- https://bugzilla.redhat.com/show_bug.cgi?id=2532446
- https://access.redhat.com/security/cve/CVE-2026-89708
- https://git.kernel.org/stable/c/01c5d5f58a5db9b0ee5afba2e49d3157788687b2
- https://git.kernel.org/stable/c/13bdd486c3aad4fc19e6d8b9c3556a4b4c190b25
- https://git.kernel.org/stable/c/f164eb52b6f3cbf40f07fe379f9f421f88e02f76