Bug 2532486 (CVE-2026-89662)

Summary: CVE-2026-89662 kernel: NFSD: Prevent lock owner use-after-free during client teardown
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Network File System Daemon (NFSD). During client teardown, a race condition can occur where a lock owner is freed while still being referenced, leading to a use-after-free vulnerability. This can result in a NULL dereference, potentially causing a system crash and a denial of service.
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Description OSIDB Bzimport 2026-09-11 23:26:02 UTC 
In the Linux kernel, the following vulnerability has been resolved:

NFSD: Prevent lock owner use-after-free during client teardown

__destroy_client() releases a client's open owners, but a lock owner
whose only reference is a blocked lock (nbl) stays on
cl_ownerstr_hashtbl.  client_has_state() does not count a bare owner,
so DESTROY_CLIENTID can reach __destroy_client() with such owners
present.

__destroy_client() then walks the table, calling remove_blocked_locks()
on each owner without a reference.  Freeing a blocked lock drops the
owner reference held via flc_owner.  The per-net laundromat reaps
blocked locks from nn->blocked_locks_lru independently of client state.
The two paths share blocked_locks_lock only for the list splice, not
the owner's lifetime.  The laundromat therefore frees the owner as
__destroy_client() dereferences it, a NULL dereference in
remove_blocked_locks().

nfsd4_release_lockowner() holds a reference across the same call;
__destroy_client() does not.  Hold cl_lock across the walk, taking a
reference and unhashing each owner, then drop it before
remove_blocked_locks() and nfs4_put_stateowner(), which take
blocked_locks_lock and cl_lock.
Comment 1 Mauro Matteo Cascella 2026-09-15 12:46:24 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89662.mbox