CVE-2026-89681

In the Linux kernel, nfsd4_drop_revoked_stid(), which handles FREE_STATEID for admin-revoked delegations, did not set SC_STATUS_FREED before releasing cl_lock. Without this flag the freed delegation was added to cl_revoked, causing a use-after-free when that list is later traversed in __destroy_client().

In the Linux kernel, the BOTH_TIME_SET branch in nfsd_proc_setattr() called fh_verify() early so setattr_prepare() could inspect the dentry. This caused nfsd_setattr() to skip fh_want_write(), so notify_change() ran without a mount write reference.

A use-after-free vulnerability was found in the Linux kernel nfsd module within nfsd4_sequence(). When the session shrinker reduces se_target_maxslots below se_fchannel.maxreqs, free_session_slots() may free the slot currently being processed because it does not check seq->slotid or the NFSD4_SLOT_INUSE flag. This leads to memory corruption via writes into the freed sl_data[] buffer.

In the Linux kernel's nfsd module, nfs4_preprocess_seqid_op() on an -EAGAIN error from nfsd4_cstate_assign_replay() dropped a stateowner reference it never acquired, while leaking the stid reference. This risks a stateowner refcount underflow and use-after-free, and can stall a concurrent nfsd4_close_open_stateid(). The fix drops the stid reference before retrying.

In the Linux kernel, 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 BUG_ON. The 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.

The NFSD implementation in the Linux kernel prior to versions 5.19.17 and 6.0.2 is vulnerable to buffer overflow. A client can force the send buffer to shrink by sending an RPC message with garbage data, leading to writes beyond the allocated buffer space.

A bug was found in the Linux kernel NFSD (NFS server) module where the export reference (svc_export) was leaked when reaping open and lock stateids. The free_ol_stateid_reaplist() function freed stateids directly via ->sc_free(), bypassing the nfs4_put_stid() path that releases the export reference. As a result, the reference was never dropped, pinning the export and blocking unmount for the lifetime of the stateid.

In the Linux kernel, the nfsd module failed to reset the write verifier when an async COPY writeback failed. When writeback failed, the server reported NFS_UNSTABLE to the NFS client but did not rotate the verifier, so after COMMIT the client treated the data as durable even though the write had failed.

In the Linux kernel, nfsd_dispatch() did not restore rq_status_counter to an even value on all exit paths (cache-hit, drop, encode-error). The counter left odd caused the lockless reader in nfsd_nl_rpc_status_get_dumpit() to treat rqstp fields as stable and read past the end of the 8-element ops array.

In the Linux kernel, _nfsd_copy_file_range() sampled the writeback error cursor (dst->f_wb_err) after the copy loop instead of before it. Concurrent COMMIT or stable WRITE could advance the cursor, so the writeback error went undetected and NFSD4_COPY_F_COMMITTED was set despite the failed write.