CVE-2025-21900

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

NFSv4: Fix a deadlock when recovering state on a sillyrenamed file

If the file is sillyrenamed, and slated for delete on close, it is possible for a server reboot to triggeer an open reclaim, with can again race with the application call to close(). When that happens, the call to put_nfs_open_context() can trigger a synchronous delegreturn call which deadlocks because it is not marked as privileged.

Instead, ensure that the call to nfs4_inode_return_delegation_on_close() catches the delegreturn, and schedules it asynchronously.

This vulnerability is rated as Moderate severity because triggering the deadlock requires an uncommon race condition between remote server state recovery and a local application closing an unlinked file. The issue is limited to NFSv4 clients actively handling deleted-on-close files during an NFS server restart, resulting in a denial of service. The flaw cannot be exploited to gain unauthorized access, elevate privileges, or compromise data confidentiality and integrity.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.