{"id":"CVE-2026-89675","state":"PUBLISHED","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).","publishedAt":"2026-09-11T19:45:59.635Z","updatedAt":"2026-10-19T08:50:48.585Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3","status":"affected","lessThan":"9031493ef7369d5c59c4bacc96f0c85965f09a98","versionType":"git"},{"version":"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3","status":"affected","lessThan":"a385cf5e016b748babf94cc664e43a26e17db117","versionType":"git"},{"version":"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3","status":"affected","lessThan":"62c0f6eaf050bb9284c1f9cac6ed1770092e6b95","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4proc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.20","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.20","versionType":"semver"},{"version":"6.18.51","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4proc.c"]}],"references":["https://git.kernel.org/stable/c/9031493ef7369d5c59c4bacc96f0c85965f09a98","https://git.kernel.org/stable/c/a385cf5e016b748babf94cc664e43a26e17db117","https://git.kernel.org/stable/c/62c0f6eaf050bb9284c1f9cac6ed1770092e6b95"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89675.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89675","state":"PUBLISHED","datePublished":"2026-09-11T19:45:59.635Z","dateUpdated":"2026-10-19T08:50:48.585Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.747Z"},"containers":{"cna":{"title":"nfsd: fix UAF in async copy cancel and shutdown","descriptions":[{"lang":"en","value":"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)."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3","status":"affected","lessThan":"9031493ef7369d5c59c4bacc96f0c85965f09a98","versionType":"git"},{"version":"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3","status":"affected","lessThan":"a385cf5e016b748babf94cc664e43a26e17db117","versionType":"git"},{"version":"e0639dc5805a9d4faaa2c07ad98fa853b9529dd3","status":"affected","lessThan":"62c0f6eaf050bb9284c1f9cac6ed1770092e6b95","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4proc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.20","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.20","versionType":"semver"},{"version":"6.18.51","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4proc.c"]}],"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"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - The flaw is in nfsd's NFSv4.2 OP_COPY and OP_OFFLOAD_CANCEL handlers (nfsd4_copy/nfsd4_offload_cancel in fs/nfsd/nfs4proc.c), reached by sending COMPOUND RPCs over TCP port 2049 to the in-kernel NFS server; no local access to the host is required.\nAC:L - The attacker controls both sides of the race by starting an async COPY then issuing OFFLOAD_CANCEL or DESTROY_CLIENTID, and can stall CB_OFFLOAD replies so the embedded callback stays in flight on freed memory; the window is retryable and does not depend on uninfluenced victim state.\nPR:N - Under AUTH_SYS, the default NFS configuration, the server verifies no secret; EXCHANGE_ID, CREATE_SESSION, and OPEN succeed for any host permitted by the export, so a remote NFSv4.2 client needs no kernel-verified credentials or local privileges on the server.\nUI:N - The attacker's own NFS client issues COPY and OFFLOAD_CANCEL (or DESTROY_CLIENTID) against an already-running nfsd export; no administrator or other user action on the server is required.\nS:U - Impact is kernel heap use-after-free and nfsd state corruption within the same host kernel security authority; it does not cross a VM, hypervisor, or IOMMU boundary.\nC:H - Use-after-free of the nfsd4_copy object (including its embedded nfsd4_callback), nfsd_file src/dst objects, and the copy kthread task_struct allows slab reuse that can be leveraged for arbitrary kernel memory reads.\nI:H - The same UAFs enable heap spraying and arbitrary writes; CB_OFFLOAD work and rpc_task callbacks invoke cb_ops function pointers that live inside the freed copy, supporting control-flow hijack.\nA:H - Concurrent release_copy_files() double-puts nfsd_file, kthread_stop() can touch a self-reaped task_struct, and the copy kthread can NULL-dereference nf_dst after teardown, each of which oopses or panics the kernel."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:50:48.585Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.20","versionEndExcluding":"6.18.51"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.20","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.20","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-89675","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T19:25:50.674765Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:26:48.362Z"}}]}}}