NFSD: Prevent post-shutdown use-after-free in unlock_filesystem

Summary

In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent post-shutdown use-after-free in unlock_filesystem Writing a filesystem path to /proc/fs/nfsd/unlock_filesystem runs nfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before the handler confirms that nn->nfsd_serv is set. Once nfsd has shut down, nfs4_state_destroy_net() has freed nn->conf_id_hashtbl but left the pointer intact, so the cancel helper iterates freed slab memory as an array of struct list_head and then dereferences a bogus nfs4_client when it takes clp->async_lock. A local administrator holding CAP_SYS_ADMIN can reach this use-after-free by stopping the server and then writing to unlock_filesystem; KASAN reports a slab-use-after-free read in nfsd4_cancel_copy_by_sb(). nfsd4_revoke_states() walks the same state tables and for that reason already runs only under nfsd_mutex with nn->nfsd_serv confirmed present. Move the async COPY cancel into that protected section so every NFSv4 state-table walker on this path observes a running server. Async copies exist only while the server runs, so gating the cancel on nn->nfsd_serv loses nothing.

Timeline

1. Sep 11, 2026, 7:45 PM UTCCVE published
2. Oct 19, 2026, 8:50 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 3daab3112f039cf849f96764019b096bb0a39d04 · fixed in 0c1a755b7212e0835398d4df5e782ea85ccd7476; From 3daab3112f039cf849f96764019b096bb0a39d04 · fixed in 292d915d3ba6fd15eeb88351fa10581683073109

• Linux Linux

  7.0

• KernelLinux

  From 7.0.0 · fixed in 7.2.4

References 2