--- id: CVE-2026-89675 title: 'nfsd: fix UAF in async copy cancel and shutdown' summary: |- In the Linux kernel, the following vulnerability has been resolved: nfsd: fix UAF in async copy cancel and shutdown An async copy could be freed or used after free while a teardown caller (OFFLOAD_CANCEL, nfsd4_shutdown_copy, nfsd4_can… severity: critical cvss: 9.8 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H' cvssSource: cna cwe: - CWE-825 vendor: Linux product: Linux affected: - >- Linux >= e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 < 9031493ef7369d5c59c4bacc96f0c85965f09a98 - >- Linux >= e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 < a385cf5e016b748babf94cc664e43a26e17db117 - >- Linux >= e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 < 62c0f6eaf050bb9284c1f9cac6ed1770092e6b95 - Linux 4.20 ssvc: exploitation: none automatable: 'yes' technicalImpact: total timestamp: '2026-10-16T19:25:50.674765Z' published: '2026-09-11' updated: '2026-10-19' sourceUpdated: '2026-10-19T08:50:48.585Z' source: CVEORG sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89675' references: - url: 'https://git.kernel.org/stable/c/9031493ef7369d5c59c4bacc96f0c85965f09a98' - url: 'https://git.kernel.org/stable/c/a385cf5e016b748babf94cc664e43a26e17db117' - url: 'https://git.kernel.org/stable/c/62c0f6eaf050bb9284c1f9cac6ed1770092e6b95' - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89675.json - url: 'https://access.redhat.com/security/cve/CVE-2026-89675' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532272' - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89675' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89675' - url: >- https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89675.mbox tags: - cve.org - csaf - vex - red-hat - score-dispute epss: 0.00442 epssPercentile: 0.38243 scores: cna: 9.8 vendor: 7 ingestedAt: '2026-09-14T15:23:07.473Z' --- ## Overview In the Linux kernel, the following vulnerability has been resolved: nfsd: fix UAF in async copy cancel and shutdown An async copy could be freed or used after free while a teardown caller (OFFLOAD_CANCEL, nfsd4_shutdown_copy, nfsd4_cancel_copy_by_sb) raced the copy kthread: - find_async_copy() bumped copy->refcount but left the copy on clp->async_copies, so the reaper's cleanup_async_copy() could run release_copy_files() concurrently with a cancel/shutdown caller. Both put and NULL nf_src/nf_dst without a common lock, double-putting the nfsd_file and freeing it early. - nfsd4_do_async_copy() set NFSD4_COPY_F_STOPPED before its final uses of the copy (nfsd_update_cmtime_attr() on copy->nf_dst, nfsd4_send_cb_offload()). nfsd4_stop_copy() treats a set STOPPED bit as "kthread done, skip kthread_stop()", so a teardown caller ran release_copy_files() -- which puts and NULLs nf_dst -- while the kthread still dereferenced it (NULL/UAF). - copy->copy_task was never pinned. The one-shot kthread self-reaps on return, so kthread_stop()'s get_task_struct() could touch a freed task_struct. - co_cb is embedded in the copy, but nfsd4_send_cb_offload() held a reference only on the client, so a concurrent teardown could free the copy while the CB_OFFLOAD callback was in flight. Fix the teardown lifetime as a whole: - find_async_copy() unlinks the copy (clear cp_clp, list_del_init) under async_lock; the cancel, shutdown, and sb-cancel paths drop the list-membership reference via nfs4_put_copy() after nfsd4_stop_copy(). Drop the now-redundant list_del fixup from cleanup_async_copy(). - Because unlinking hides the copy from the reaper, its cleanup_async_copy() can no longer remove the copy's s2s_cp_stateids entry; the cancel/shutdown/sb-cancel paths now call nfs4_free_copy_state() themselves (while cp_clp is still valid) so the entry does not dangle at freed memory for the laundromat and manage_cpntf_state() to dereference. - Give the kthread its own reference, taken in nfsd4_copy() before wake_up_process() and dropped at the end of nfsd4_do_async_copy(); call wake_up_process() before list_add(). - Pin the task_struct with get_task_struct() in nfsd4_copy(), released in nfs4_put_copy(), so kthread_stop() is safe whenever the kthread exits. Set NFSD4_COPY_F_STOPPED only in nfsd4_stop_copy(), which now always kthread_stop()s before release_copy_files(); completion is still reported via NFSD4_COPY_F_COMPLETED, so nfsd4_has_active_async_copies() is unaffected. Each teardown caller removes the copy from clp->async_copies first, so kthread_stop() runs exactly once. - Take a copy reference in nfsd4_send_cb_offload(), dropped in nfsd4_cb_offload_release(). The kthread still holds its own reference there, so the refcount_inc() cannot race the final free. - Read cp_clp with smp_load_acquire() to pair with the unordered set_bit()/clear_bit() writers (Documentation/atomic_bitops.rst). ## Affected - `Linux >= e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 < 9031493ef7369d5c59c4bacc96f0c85965f09a98` - `Linux >= e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 < a385cf5e016b748babf94cc664e43a26e17db117` - `Linux >= e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 < 62c0f6eaf050bb9284c1f9cac6ed1770092e6b95` - `Linux 4.20` ## Remediation Refer to the linked advisories for vendor-supplied fixes and affected version ranges. ## Vendor advisories - **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89675.json)