Linux Kernel: NFS Client UseAfterFree in NFSD Evaded
CVE-2026-90036 Published on September 16, 2026
NFSD: Prevent client use-after-free during blocked-lock reaping
In the Linux kernel, the following vulnerability has been resolved:
NFSD: Prevent client use-after-free during blocked-lock reaping
A bare lock owner -- its only remaining reference a blocked lock on
nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but
no reference keeping the client alive. When the per-net laundromat
reaps such a lock, freeing the nbl drops the owner reference
held through flc_owner, and the final nfs4_put_stateowner()
takes the client's cl_lock. Because the laundromat detaches the
nbl first, __destroy_client() no longer finds it, so a concurrent
force_expire_client() can free the client before nfs4_put_stateowner()
runs, dereferencing cl_lock in freed memory.
Pin the client with cl_rpc_users before dropping
nn->blocked_locks_lock, and skip clients already expiring, whose
blocked locks __destroy_client() frees while holding an owner
reference. Take nn->client_lock outside nn->blocked_locks_lock.
Every other site holds nn->blocked_locks_lock as a leaf, acquiring
no further lock, so placing nn->client_lock outside it cannot form
a lock-order cycle.
Products Associated with CVE-2026-90036
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Affected Versions
Linux:- Version 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b and below cd489b03587378645fe0d20142a33f1ed60bac98 is affected.
- Version 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b and below 6fedb2eaff77554ca7a0deffd2e8bc0d6e8b38b0 is affected.
- Version 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b and below 9026932ac8be4d0ae01db47f23619a98cc57b671 is affected.
- Version 4.9 is affected.
- Before 4.9 is unaffected.
- Version 6.18.51, <= 6.18.* is unaffected.
- Version 7.2.5, <= 7.2.* is unaffected.
- Version 7.3-rc1, <= * is unaffected.