CVE-2026-93221

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.