CVE-2025-21900: NFSv4: Fix a deadlock when recovering state on a sillyrenamed file

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-04-01 · updated 2026-07-30
Weakness: CWE-667

Description

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.

Affected products

Linux kernel: from 6.11 before 6.12.18; from 6.13 before 6.13.6; 6.14-rc1, 6.14-rc2, 6.14-rc3, 6.14-rc4 — fixed in 6.12.18, 6.13.6

How to fix

Upgrade to a fixed version: Linux kernel 6.12.18, 6.13.6. Check the vendor advisory for mitigations.

References

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