UBUNTU-CVE-2026-89682: Use After Free

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix fcachedisposal UAF by inlining dispose state into nfsdnet nfsdfiledisposelistdelayed() 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 nfsdfcachedisposal that is freed by nfsdfreefcachedisposalnet() during per-net teardown. The global shrinker, laundrette, and fsnotify callbacks can still be inside nfsdfiledisposelistdelayed() dereferencing that pointer, causing a use-after-free. Inline the spinlock and freeme list directly into struct nfsdnet (as fcachedisposelock and fcachedisposelist), eliminating the separately allocated struct nfsdfcachedisposal entirely. These fields now have the same lifetime as the net namespace itself, so there is no dangling pointer to chase. nfsdfilecachestartnet() now just initializes the inline fields and cannot fail due to allocation. nfsdfilecacheshutdownnet() drains the inline list directly instead of freeing a separate struct. The alloc/free helpers are removed.