{"id":"CVE-2026-89675","revision":"49cdac9571134d6e85f5e85460846428","records":[{"revision":"49cdac9571134d6e85f5e85460846428","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-89675","aliases":[],"title":"nfsd: fix UAF in async copy cancel and shutdown","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix UAF in async copy cancel and shutdown\n\nAn async copy could be freed or used after free while a teardown caller\n(OFFLOAD_CANCEL, nfsd4_shutdown_copy, nfsd4_cancel_copy_by_sb) raced the\ncopy kthread:\n\n  - find_async_copy() bumped copy->refcount but left the copy on\n    clp->async_copies, so the reaper's cleanup_async_copy() could run\n    release_copy_files() concurrently with a cancel/shutdown caller. Both\n    put and NULL nf_src/nf_dst without a common lock, double-putting the\n    nfsd_file and freeing it early.\n\n  - nfsd4_do_async_copy() set NFSD4_COPY_F_STOPPED before its final uses\n    of the copy (nfsd_update_cmtime_attr() on copy->nf_dst,\n    nfsd4_send_cb_offload()). nfsd4_stop_copy() treats a set STOPPED bit\n    as \"kthread done, skip kthread_stop()\", so a teardown caller ran\n    release_copy_files() -- which puts and NULLs nf_dst -- while the\n    kthread still dereferenced it (NULL/UAF).\n\n  - copy->copy_task was never pinned. The one-shot kthread self-reaps on\n    return, so kthread_stop()'s get_task_struct() could touch a freed\n    task_struct.\n\n  - co_cb is embedded in the copy, but nfsd4_send_cb_offload() held a\n    reference only on the client, so a concurrent teardown could free\n    the copy while the CB_OFFLOAD callback was in flight.\n\nFix the teardown lifetime as a whole:\n\n  - find_async_copy() unlinks the copy (clear cp_clp, list_del_init)\n    under async_lock; the cancel, shutdown, and sb-cancel paths drop the\n    list-membership reference via nfs4_put_copy() after nfsd4_stop_copy().\n    Drop the now-redundant list_del fixup from cleanup_async_copy().\n\n  - Because unlinking hides the copy from the reaper, its\n    cleanup_async_copy() can no longer remove the copy's s2s_cp_stateids\n    entry; the cancel/shutdown/sb-cancel paths now call\n    nfs4_free_copy_state() themselves (while cp_clp is still valid) so\n    the entry does not dangle at freed memory for the laundromat and\n    manage_cpntf_state() to dereference.\n\n  - Give the kthread its own reference, taken in nfsd4_copy() before\n    wake_up_process() and dropped at the end of nfsd4_do_async_copy();\n    call wake_up_process() before list_add().\n\n  - Pin the task_struct with get_task_struct() in nfsd4_copy(), released\n    in nfs4_put_copy(), so kthread_stop() is safe whenever the kthread\n    exits. Set NFSD4_COPY_F_STOPPED only in nfsd4_stop_copy(), which now\n    always kthread_stop()s before release_copy_files(); completion is\n    still reported via NFSD4_COPY_F_COMPLETED, so\n    nfsd4_has_active_async_copies() is unaffected. Each teardown caller\n    removes the copy from clp->async_copies first, so kthread_stop() runs\n    exactly once.\n\n  - Take a copy reference in nfsd4_send_cb_offload(), dropped in\n    nfsd4_cb_offload_release(). The kthread still holds its own reference\n    there, so the refcount_inc() cannot race the final free.\n\n  - Read cp_clp with smp_load_acquire() to pair with the unordered\n    set_bit()/clear_bit() writers (Documentation/atomic_bitops.rst).","state":0,"publishedAt":"2026-09-11T19:45:59.635+00:00","modifiedAt":"2026-10-19T08:50:48.585+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"fs/nfsd/nfs4proc.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3\",\n                            \"lessThan\": \"9031493ef7369d5c59c4bacc96f0c85965f09a98\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3\",\n                            \"lessThan\": \"a385cf5e016b748babf94cc664e43a26e17db117\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3\",\n                            \"lessThan\": \"62c0f6eaf050bb9284c1f9cac6ed1770092e6b95\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"fs/nfsd/nfs4proc.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"4.20\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"4.20\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.51\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.2.4\",\n                            \"lessThanOrEqual\": \"7.2.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.3\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","score":9.8,"severity":"CRITICAL"}],"references":["https://git.kernel.org/stable/c/9031493ef7369d5c59c4bacc96f0c85965f09a98","https://git.kernel.org/stable/c/a385cf5e016b748babf94cc664e43a26e17db117","https://git.kernel.org/stable/c/62c0f6eaf050bb9284c1f9cac6ed1770092e6b95"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-89675","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-89675","identifiers":["CVE-2026-89675"]},"retained":false,"historicalAffected":[]}],"coverage":[]}