nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke
CVE-2026-89686 · published 11 Sept 2026
How serious is it
- Severity: critical, CVSS score 9.8 out of 10.
- No exploit prediction (EPSS) score yet.
- Not on the CISA list of exploited vulnerabilities.
- No public exploit in Exploit-DB.
Is your app affected by CVE-2026-89686?
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Who is affected
- Linux Linux: c5c707f96fc9a6e5a57ca5baac892673270abe3d to < d12af460df27876661707efab3a8532146cb961f, c5c707f96fc9a6e5a57ca5baac892673270abe3d to < c517f27498757e616d2a8fe6d16caad1fee422e6, c5c707f96fc9a6e5a57ca5baac892673270abe3d to < 607a56fea772c1f4f4989d8e255dd4f7192d9604, c5c707f96fc9a6e5a57ca5baac892673270abe3d to < 97bda8b4284d90897a1f1922e5082ff9e35d7c7e
- Linux Linux: 4.0
How to check
- Find out whether you run the affected product and which version, then compare it with the versions above.
How to fix
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- Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
- If a vulnerable version was live, check your logs and rotate the secrets that server could read.
The advisory
In the Linux kernel, the following vulnerability has been resolved:
nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke
nfsd4_alloc_layout_stateid reads fp->fi_deleg_file without holding
fi_lock when the parent stateid is a delegation. A concurrent delegation
revoke via the laundromat can clear fi_deleg_file under fi_lock, causing
nfsd_file_get() to return NULL and triggering the BUG_ON.
This race is client-reachable: two NFS clients can trigger it by having
one hold a delegation while another opens the same file to force a
recall. When the first client doesn't respond to the recall, the
laundromat revokes it. A concurrent LAYOUTGET from any client using the
delegation stateid hits the race window.
Fix this by taking fi_lock around the fi_deleg_file read in the
SC_TYPE_DELEG path, matching the locking discipline of the
find_any_file() arm, and replacing the BUG_ON with a graceful error
return that cleans up the partially-initialized layout stateid.
Check your whole app
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References
- git.kernel.org/stable/c/d12af460df27876661707efab3a8532146cb961f
- git.kernel.org/stable/c/c517f27498757e616d2a8fe6d16caad1fee422e6
- git.kernel.org/stable/c/607a56fea772c1f4f4989d8e255dd4f7192d9604
- git.kernel.org/stable/c/97bda8b4284d90897a1f1922e5082ff9e35d7c7e
- git.kernel.org/stable/c/ca94ba36172046be6a694a7986f6931e47ed4d51
Merged from CVE List. Last updated 26 Oct 2026. All vulnerabilities · RSS · JSON