From 7b4f8a1586c42d3afc3c0ac779af2db7ab1a5c55 Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Thu, 9 Jul 2026 13:40:28 -0400 Subject: [PATCH] NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup nfs40_clean_admin_revoked() takes a stateid reference under clp->cl_lock, drops nn->client_lock, and calls nfsd4_drop_revoked_stid(), which dereferences the stateid's client through s->sc_client->cl_lock. The stateid reference does not pin the client, so a teardown racing the dropped lock can free the client while nfsd4_drop_revoked_stid() is still using it. This cleanup runs from the laundromat, so a periodic sweep can race force_expire_client() driven by a write to the clients//ctl file. Skip a client that is already expiring and otherwise pin it with cl_rpc_users under client_lock before dropping the lock, matching nfsd4_revoke_states(). Fixes: d688d8585e6b ("nfsd: allow admin-revoked NFSv4.0 state to be freed.") Cc: stable@vger.kernel.org Reviewed-by: NeilBrown Reviewed-by: Jeff Layton Link: https://patch.msgid.link/20260709-cel-v4-5-1d519d9be0cb@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/nfs4state.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index 9de535a2a4bb..445a0f40d5ff 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -7452,16 +7452,22 @@ static void nfs40_clean_admin_revoked(struct nfsd_net *nn, if (atomic_read(&clp->cl_admin_revoked) == 0) continue; + if (is_client_expired(clp)) + continue; spin_lock(&clp->cl_lock); idr_for_each_entry_ul(&clp->cl_stateids, stid, tmp, id) if (stid->sc_status & SC_STATUS_ADMIN_REVOKED) { refcount_inc(&stid->sc_count); + atomic_inc(&clp->cl_rpc_users); spin_unlock(&nn->client_lock); /* this function drops ->cl_lock */ nfsd4_drop_revoked_stid(stid); nfs4_put_stid(stid); spin_lock(&nn->client_lock); + if (atomic_dec_and_test(&clp->cl_rpc_users) && + is_client_expired(clp)) + wake_up_all(&expiry_wq); goto retry; } spin_unlock(&clp->cl_lock);