nfsd: convert nfsd_net boolean flags to unsigned long flags word

Summary

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.

Timeline

1. Sep 24, 2026, 3:10 PM UTCCVE published
2. Oct 21, 2026, 12:52 PM UTCRecord last updated

Affected versions

• Linux 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 Linux

  5.2

• KernelLinux

  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

References 5