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CVE-2026-89670— nfsd: hold rcu across localio cmpxchg retry

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Linux 内核中，以下漏洞已得到修复： nfsd：在 localio cmpxchg 重试过程中保持 RCU 锁 对象通过 释放（filecache.c:296），而 在创建时未设置 （filecache.c:789 处的 ），因此在 RCU 宽限期（grace period）结束后，承载已释放 的 slab 页可被自由回收。 在 的 重试代码块中，使用 加载指针后，调用 （即 ），但此时并未持有 。该函数的唯一调用者 在调用此辅助函数之前已释放了 ，因此没有外层读者端临界区覆盖该加载操作。 若回收后的对象在

AI Predicted 5.5 Difficulty: Hard

Affected Version Matrix 10

VendorProduct Version RangeStatus
Linux Linux e6f7e1487ab528a6c653bd0d42812ff2942846cd< 763c0bad872368304db718f79af7e93048885c67 affected
e6f7e1487ab528a6c653bd0d42812ff2942846cd< 559570f91a7d4d199a72105e4980bef791f4cbf1 affected
e6f7e1487ab528a6c653bd0d42812ff2942846cd< 58884694978a3d7d111edb433d7fd6a6c5af2f34 affected
986a21ace186433e0397a59491646edad8c8d636 affected
6.15.3< 6.16 affected
6.16 affected
< 6.16 unaffected
6.18.50≤ 6.18.* unaffected
… +2 more rows
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I. Basic Information for CVE-2026-89670

Vulnerability Information
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Vulnerability Title
nfsd: hold rcu across localio cmpxchg retry
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: nfsd: hold rcu across localio cmpxchg retry nfsd_file objects are freed via call_rcu (filecache.c:296), and nfsd_file_slab is created without SLAB_TYPESAFE_BY_RCU (KMEM_CACHE(nfsd_file, 0) at filecache.c:789), so the slab page backing a freed nfsd_file becomes freely reclaimable once the RCU grace period elapses. The again: retry block in nfsd_open_local_fh() loads a pointer with cmpxchg and then calls nfsd_file_get(new) (which is refcount_inc_not_zero) without holding rcu_read_lock. The sole caller nfs_open_local_fh() drops rcu_read_lock before invoking this helper, so no outer reader-side critical section covers the load. CPU 0 (nfsd_open_local_fh) CPU 1 (nfsd_file_put_local) ----- ----- new = cmpxchg(pnf, NULL, ...) nf = xchg(pnf, NULL) nfsd_file_put(nf) last ref -> call_rcu() /* grace period elapses; slab page recycled */ nfsd_file_get(new) refcount_inc_not_zero(&new->nf_ref) /* operates on recycled memory */ A non-zero word at the nf_ref offset of the recycled object makes the refcount bump appear to succeed, and the caller then dereferences new->nf_net and new->nf_file out of freed memory. Fix by taking rcu_read_lock() immediately before the cmpxchg and releasing it on all three exits of the if (new) block: the goto-again retry, the lost-race cleanup path, and the install-succeeded path. nfsd_file_put() and nfsd_net_put() stay outside the RCU section so they remain free to block.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux e6f7e1487ab528a6c653bd0d42812ff2942846cd ~ 763c0bad872368304db718f79af7e93048885c67 -
Linux Linux 6.16 -

II. Public POCs for CVE-2026-89670

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III. Intelligence Information for CVE-2026-89670

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Patches & Fixes for CVE-2026-89670 (2)

Other References for CVE-2026-89670 (1)

Same Patch Batch · Linux · 2026-09-11 · 431 CVEs total

CVE-2026-89491 ocfs2: cluster: don't sleep while holding o2hb_live_lock in o2hb_region_pin()
CVE-2026-89477 sctp: fix NULL deref on untransmitted RECONF completion
CVE-2026-89478 sctp: drop a chunk if its transport was removed
CVE-2026-89479 sctp: stop processing a packet once its association is deleted
CVE-2026-89480 nvme-tcp: reject a read that transferred too few bytes
CVE-2026-89482 nvme-tcp: do not accept C2HData based on blk_rq_payload_bytes() alone
CVE-2026-89481 nvme-tcp: fix host memory disclosure on R2T for a read command
CVE-2026-89483 nvme: zero the discard fallback page
CVE-2026-89484 lockd: fix NULL dereference on lockowner allocation failure
CVE-2026-89485 lockd: pin next file across nlm_inspect_file lock-drop
CVE-2026-89486 ipmi: Fix use-after-free of cmd_rcvr in _ipmi_destroy_user()
CVE-2026-89487 openvswitch: only skb_tx_error() a packet we are about to drop
CVE-2026-89488 openvswitch: Fix CT limit teardown use-after-free
CVE-2026-89489 openrisc: fix arbitrary kernel memory access via or1k_atomic syscall
CVE-2026-89500 ring-buffer: Make cpu_buffer::free_page a buffer_data_read_page
CVE-2026-89497 orangefs: skip leading spaces before parsing client debug masks
CVE-2026-89498 orangefs: fix double-free of trailer_buf on readdir copy failure
CVE-2026-89499 ring-buffer: Stop remote reader update when page swap fails
CVE-2026-89496 ocfs2: always run deallocs on copy-on-write completion
CVE-2026-89501 ring-buffer: Hold cpu_buffer::lock when resizing a subbuf

Showing top 20 of 431 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-89670

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