nfsd: fix UAF in async copy cancel and shutdown

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89675
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:19:54 UTC
Updated2026-09-11 20:19:54 UTC
DescriptionIn 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).

Risk And Classification

EPSS: 0.001660000 probability, percentile 0.061340000 (date 2026-09-12)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 9031493ef7369d5c59c4bacc96f0c85965f09a98 git Not specified
CNA Linux Linux affected e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 a385cf5e016b748babf94cc664e43a26e17db117 git Not specified
CNA Linux Linux affected e0639dc5805a9d4faaa2c07ad98fa853b9529dd3 62c0f6eaf050bb9284c1f9cac6ed1770092e6b95 git Not specified
CNA Linux Linux affected 4.20 Not specified
CNA Linux Linux unaffected 4.20 semver Not specified
CNA Linux Linux unaffected 6.18.51 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/9031493ef7369d5c59c4bacc96f0c85965f09a98 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a385cf5e016b748babf94cc664e43a26e17db117 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/62c0f6eaf050bb9284c1f9cac6ed1770092e6b95 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

© CVE.report 2026

Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. It is the responsibility of user to evaluate the accuracy, completeness or usefulness of any information, opinion, advice or other content. EACH USER WILL BE SOLELY RESPONSIBLE FOR ANY consequences of his or her direct or indirect use of this web site. ALL WARRANTIES OF ANY KIND ARE EXPRESSLY DISCLAIMED. This site will NOT BE LIABLE FOR ANY DIRECT, INDIRECT or any other kind of loss.

CVE, CWE, and OVAL are registred trademarks of The MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. This site includes MITRE data granted under the following license.

Free CVE JSON API cve.report/api

CVE.report and Source URL Uptime Status status.cve.report