CVE-2026-89682nfsd: fix fcache_disposal UAF by inlining dispose state into nfsd_net

Official description

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 packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/41fe0e804bbf1110c0aba2ebdfc729efb240d8a6
• https://git.kernel.org/stable/c/e6c3a43d0a41f03abae3764fc82a59369360c7e0
• https://git.kernel.org/stable/c/9c8ac7c2b9b150e13b7ad0d0fae54f17747dce67
• https://git.kernel.org/stable/c/ba0ee9e04b7a0356c28d5a2fe445db675d24e572
• https://git.kernel.org/stable/c/cadc9036d5a8209f89e7026ddba7cfb1c716b03c
• https://git.kernel.org/stable/c/bbf13732f74351d21c5e0e8dd9bd8e1c48dc35d4