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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
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| Linux | Linux | affected |
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Solution
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Workaround
No workaround given by the vendor.
Sat, 12 Sep 2026 00:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-825 | |
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Fri, 11 Sep 2026 23:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | NFSD: Prevent post-shutdown use-after-free in unlock_filesystem | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-11T19:45:49.086Z
Reserved: 2026-09-11T19:38:34.744Z
Link: CVE-2026-89661
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-11T20:19:52.413
Modified: 2026-09-11T20:19:52.413
Link: CVE-2026-89661
Redhat
OpenCVE Enrichment
Updated: 2026-09-12T04:45:07Z