CVE-2026-89686

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke

nfsd4_alloc_layout_stateid reads fp->fi_deleg_file without holding

fi_lock when the parent stateid is a delegation. A concurrent delegation

revoke via the laundromat can clear fi_deleg_file under fi_lock, causing

nfsd_file_get() to return NULL and triggering the BUG_ON.

This race is client-reachable: two NFS clients can trigger it by having

one hold a delegation while another opens the same file to force a

recall. When the first client doesn't respond to the recall, the

laundromat revokes it. A concurrent LAYOUTGET from any client using the

delegation stateid hits the race window.

Fix this by taking fi_lock around the fi_deleg_file read in the

SC_TYPE_DELEG path, matching the locking discipline of the

find_any_file() arm, and replacing the BUG_ON with a graceful error

return that cleans up the partially-initialized layout stateid.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References