GHSA-R3MG-G23P-86C9
Vulnerability from github – Published: 2026-09-24 18:31 – Updated: 2026-09-25 06:30In 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.
{
"affected": [],
"aliases": [
"CVE-2026-93221"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-24T16:17:17Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: convert nfsd_net boolean flags to unsigned long flags word\n\nnfsd_net contains several boolean fields that are accessed from\nconcurrent contexts without serialization. In particular,\nnfsd4_end_grace() guards its drain path with a plain bool:\n\n if (nn-\u003egrace_ended)\n return;\n nn-\u003egrace_ended = true;\n\nThe read and the write are independent, and nothing in struct\nnfsd_net serializes them. At least two contexts can reach this\ncode with no lock held:\n\n laundromat path\n laundry_wq kworker\n nfs4_laundromat()\n nfsd4_end_grace()\n\n RECLAIM_COMPLETE path\n nfsd compound kthread\n nfsd4_reclaim_complete()\n inc_reclaim_complete()\n nfsd4_end_grace()\n\nBoth callers can observe grace_ended == false on different CPUs,\nboth store true, and both proceed into nfsd4_record_grace_done(),\nwhich invokes the active client_tracking_ops-\u003egrace_done callback.\nFor tracking ops that drain reclaim_str_hashtbl (legacy_tracking_ops\nvia nfsd4_recdir_purge_old, and the cld v1+ ops via\nnfsd4_cld_grace_done), grace_done calls nfs4_release_reclaim(),\nwhich walks every bucket of reclaim_str_hashtbl with no lock and\ncalls nfs4_remove_reclaim_record() (list_del + kfree) on each\nentry. Two concurrent walkers corrupt the list and double-free\nevery nfs4_client_reclaim. A concurrent nfsd4_find_reclaim_client()\niterating the same bucket reads through freed memory.\n\nA third call site exists in nfs4_state_start_net() on the\nskip_grace startup path, but it runs under nfsd_mutex before any\nclient has connected and before the laundromat\u0027s first delayed\nwork fires, so it cannot race with the two callers above.\n\nReplace the scattered boolean fields in nfsd_net with a single\nunsigned long flags word and an enum nfsd_net_flag for the bit\npositions. The grace_ended race is fixed by using\ntest_and_set_bit(), which is atomic on all architectures. The\nremaining flags (grace_end_forced, in_grace, somebody_reclaimed,\ntrack_reclaim_completes, nfsd_net_up, lockd_up) are converted to\nuse test_bit/set_bit/clear_bit for consistency. This avoids\nsub-word cmpxchg issues on architectures like Hexagon that only\nsupport word-sized atomic operations.",
"id": "GHSA-r3mg-g23p-86c9",
"modified": "2026-09-25T06:30:27Z",
"published": "2026-09-24T18:31:22Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-93221"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/11a5fe42e1811f793e04ef885b639ea7668f439d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/df5922fe09a8131c793ffa86adf204999b0470f8"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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