CVE-2026-89659NFSD: Prevent client use-after-free during delegation revoke

Official description

In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent client use-after-free during delegation revoke A delegation stateid holds only a bare pointer to its owning nfs4_client and does not keep it alive. The client survives its stateids only because __destroy_client() drains cl_delegations and cl_revoked before free_client() runs. nfs4_laundromat() breaks that invariant: it unhashes an expired delegation from cl_delegations, drops deleg_lock, then revoke_delegation() relinks it onto cl_revoked under cl_lock. In that window the delegation is on neither list, so client_has_state() can report no remaining state. Every teardown path first requires cl_rpc_users to be zero, but the laundromat holds no such reference. A client whose recalled delegation has just timed out can therefore reach free_client() while revoke_delegation() is still about to dereference cl_lock, a use-after-free. Pin the client with cl_rpc_users across the revoke so teardown blocks until it completes, then reap the delegation from cl_revoked. A client already expiring reaps its own, so skip it and leave the delegation on del_recall_lru.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2f9a200c0ea5b214609b8cea2b6666458bcb54cd
• https://git.kernel.org/stable/c/94f0c73797c30a35812ffb32d11b8737d245c405
• https://git.kernel.org/stable/c/0dd276b1324a5e08e83c6f675919946c9f0d61c9
• https://git.kernel.org/stable/c/3c0a53ee0b442348d8d2286d6960d3f07bb3a3d3
• https://git.kernel.org/stable/c/2a9d637c2a8fd8ac29ad9b29f28d122ef75c1a56
• https://git.kernel.org/stable/c/4683ca76b3b7e5808338491c6eb3c20e6b4894d5