nfsd: fix fcache_disposal UAF by inlining dispose state into nfsd_net

Overview

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix fcache_disposal UAF by inlining dispose state into nfsd_net

nfsd_file_dispose_list_delayed() defers fput() to nfsd service threads via a per-net freeme queue, preventing the shrinker and GC worker from bearing the cost of closing files (see ffb402596147). However, the queue lives in a separately-allocated struct nfsd_fcache_disposal that is freed by nfsd_free_fcache_disposal_net() during per-net teardown. The global shrinker, laundrette, and fsnotify callbacks can still be inside nfsd_file_dispose_list_delayed() dereferencing that pointer, causing a use-after-free.

Inline the spinlock and freeme list directly into struct nfsd_net (as fcache_dispose_lock and fcache_dispose_list), eliminating the separately allocated struct nfsd_fcache_disposal entirely. These fields now have the same lifetime as the net namespace itself, so there is no dangling pointer to chase.

nfsd_file_cache_start_net() now just initializes the inline fields and cannot fail due to allocation. nfsd_file_cache_shutdown_net() drains the inline list directly instead of freeing a separate struct. The alloc/free helpers are removed.

Affected

• Linux >= 1463b38e7cf34d4cc60f41daff459ad807b2e408 < e6c3a43d0a41f03abae3764fc82a59369360c7e0
• Linux >= 1463b38e7cf34d4cc60f41daff459ad807b2e408 < 9c8ac7c2b9b150e13b7ad0d0fae54f17747dce67
• Linux >= 1463b38e7cf34d4cc60f41daff459ad807b2e408 < ba0ee9e04b7a0356c28d5a2fe445db675d24e572
• Linux >= 1463b38e7cf34d4cc60f41daff459ad807b2e408 < cadc9036d5a8209f89e7026ddba7cfb1c716b03c
• Linux >= 1463b38e7cf34d4cc60f41daff459ad807b2e408 < bbf13732f74351d21c5e0e8dd9bd8e1c48dc35d4
• Linux e8f923e1e9fcc0832a12c8a2461792e5a9544c03
• Linux 3bc94fb44f10ef852723e1aeaac6794c5ab16aec
• Linux >= 5.10.220 < 5.11
• Linux >= 5.15.154 < 5.16
• Linux 5.17

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-10-21 · vex