Bug 2532092 (CVE-2026-89660)

Summary: CVE-2026-89660 kernel: NFSD: Prevent client use-after-free during admin state revocation
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). This vulnerability, a use-after-free, occurs during the revocation of client administrative states. A race condition can allow a client's memory to be freed prematurely while still being referenced, potentially leading to system instability or a denial of service. In some scenarios, this type of memory corruption could be exploited by a remote attacker to achieve arbitrary code execution.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-09-11 20:29:10 UTC 
In the Linux kernel, the following vulnerability has been resolved:

NFSD: Prevent client use-after-free during admin state revocation

A stateid holds only a bare pointer to its nfs4_client; a stateid
reference does not pin it.  The client survives only because
__destroy_client() drains its stateids before free_client() runs.

nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(),
which dereferences the client to revoke a stateid and read
clp->cl_minorversion.  A teardown racing the dropped lock can free
the client first.

Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and
EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero.
force_expire_client() ignores it: once its wait for cl_rpc_users to
reach zero has passed, a later pin goes unnoticed.

Under client_lock, skip a client whose cl_time is already zero --
force_expire_client() clears it there before waiting -- otherwise pin
cl_rpc_users before dropping the lock.  The walk then either sees the
expiry and skips, or pins in time for that wait to cover the revoke.
Comment 1 Mauro Matteo Cascella 2026-09-18 18:11:08 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89660.mbox