# CVE-2026-93221: nfsd: convert nfsd_net boolean flags to unsigned long flags word

CVE-2026-93221 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-93221, released September 24, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-93221
- Priority: High
- CVSS: 8.1 (Important)
- EPSS: 0.0042
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 24, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-93221

## Description

In the Linux kernel, the following vulnerability has been resolved:  nfsd: convert nfsd_net boolean flags to unsigned long flags word  nfsd_net contains several boolean fields that are accessed from concurrent contexts without serialization.  In particular, nfsd4_end_grace() guards its drain path with a plain bool:      if (nn->grace_ended)             return;     nn->grace_ended = true;  The read and the write are independent, and nothing in struct nfsd_net serializes them.  At least two contexts can reach this code with no lock held:      laundromat path       laundry_wq kworker         nfs4_laundromat()           nfsd4_end_grace()      RECLAIM_COMPLETE path       nfsd compound kthread         nfsd4_reclaim_complete()           inc_reclaim_complete()             nfsd4_end_grace()  Both callers can observe grace_ended == false on different CPUs, both store true, and both proceed into nfsd4_record_grace_done(), which invokes the active client_tracking_ops->grace_done callback. For tracking ops that drain reclaim_str_hashtbl (legacy_tracking_ops via nfsd4_recdir_purge_old, and the cld v1+ ops via nfsd4_cld_grace_done), grace_done calls nfs4_release_reclaim(), which walks every bucket of reclaim_str_hashtbl with no lock and calls nfs4_remove_reclaim_record() (list_del + kfree) on each entry.  Two concurrent walkers corrupt the list and double-free every nfs4_client_reclaim.  A concurrent nfsd4_find_reclaim_client() iterating the same bucket reads through freed memory.  A third call site exists in nfs4_state_start_net() on the skip_grace startup path, but it runs under nfsd_mutex before any client has connected and before the laundromat's first delayed work fires, so it cannot race with the two callers above.  Replace the scattered boolean fields in nfsd_net with a single unsigned long flags word and an enum nfsd_net_flag for the bit positions.  The grace_ended race is fixed by using test_and_set_bit(), which is atomic on all architectures.  The remaining flags (grace_end_forced, in_grace, somebody_reclaimed, track_reclaim_completes, nfsd_net_up, lockd_up) are converted to use test_bit/set_bit/clear_bit for consistency.  This avoids sub-word cmpxchg issues on architectures like Hexagon that only support word-sized atomic operations.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-93221](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93221.md) | Sep 24, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-93221](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93221.md) | Sep 24, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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