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CVE-2026-89685: nfsd: fix clock domain mismatch in clients_still_reclaiming()

• Severity: high (CVSS 7.5 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: 2026-09-11 · updated 2026-10-30

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix clock domain mismatch in clients_still_reclaiming() clients_still_reclaiming() computes a deadline from nn->boot_time (CLOCK_REALTIME, ~1.7 billion) but compares it against ktime_get_boottime_seconds() (CLOCK_BOOTTIME, seconds since boot). The comparison is always false — it would take ~54 years of uptime for BOOTTIME to exceed the REALTIME-derived deadline. This means any client can hold the server in grace indefinitely by sending CLAIM_PREVIOUS OPEN requests, blocking all non-reclaim operations for all other clients. Add boot_time_bt (CLOCK_BOOTTIME) alongside the existing boot_time and use it for the deadline computation. boot_time (CLOCK_REALTIME) is preserved for its cl_boot clientid-nonce role.

Affected products

• Linux: 5.6 — fixed in 7.3

How to fix

Upgrade to a fixed version: Linux 7.3. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/04c3e4456fe76e8d7c94171009df3165c3262c51
• https://git.kernel.org/stable/c/09ea3eb9a518565f5bca386e81b993ed8825f5e8
• https://git.kernel.org/stable/c/2c9efc6b692a153643d0f204b3c3632cb6b5761e
• https://git.kernel.org/stable/c/7ca44a63d9a554ba7ad05b06d88746eab08b760e
• https://git.kernel.org/stable/c/9843649196221152b6e5d138a3ce859bdaae1d96
• https://git.kernel.org/stable/c/a22ee3a2cadef44f2edeb909ae36bd72450a3a35
• https://git.kernel.org/stable/c/e92e80c5b043108029bc729b30d12c37158fb9cb
• https://git.kernel.org/stable/c/f9cec313efb2fd18d962aad738a4892bce806016

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