linux-kernel - [PATCH v2] nfsd: remove long-standing revoked delegations by force

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250903115918.788159-1-lilingfeng3@huawei.com>
Date: Wed, 3 Sep 2025 19:59:18 +0800
From: Li Lingfeng <lilingfeng3@...wei.com>
To: <chuck.lever@...cle.com>, <jlayton@...nel.org>, <neil@...wn.name>,
	<okorniev@...hat.com>, <Dai.Ngo@...cle.com>, <tom@...pey.com>,
	<linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <yukuai1@...weicloud.com>, <houtao1@...wei.com>, <yi.zhang@...wei.com>,
	<yangerkun@...wei.com>, <lilingfeng@...weicloud.com>,
	<lilingfeng3@...wei.com>, <zhangjian496@...wei.com>, <bcodding@...hat.com>
Subject: [PATCH v2] nfsd: remove long-standing revoked delegations by force

When file access conflicts occur between clients, the server recalls
delegations. If the client holding delegation fails to return it after
a recall, nfs4_laundromat adds the delegation to cl_revoked list.
This causes subsequent SEQUENCE operations to set the
SEQ4_STATUS_RECALLABLE_STATE_REVOKED flag, forcing the client to
validate all delegations and return the revoked one.

However, if the client fails to return the delegation like this:
nfs4_laundromat                       nfsd4_delegreturn
 unhash_delegation_locked
 list_add // add dp to reaplist
          // by dl_recall_lru
 list_del_init // delete dp from
               // reaplist
                                       destroy_delegation
                                        unhash_delegation_locked
                                         // do nothing but return false
 revoke_delegation
 list_add // add dp to cl_revoked
          // by dl_recall_lru

The delegation will remain in the server's cl_revoked list while the
client marks it revoked and won't find it upon detecting
SEQ4_STATUS_RECALLABLE_STATE_REVOKED.
This leads to a loop:
the server persistently sets SEQ4_STATUS_RECALLABLE_STATE_REVOKED, and the
client repeatedly tests all delegations, severely impacting performance
when numerous delegations exist.

Since abnormal delegations are removed from flc_lease via nfs4_laundromat
--> revoke_delegation --> destroy_unhashed_deleg -->
nfs4_unlock_deleg_lease --> kernel_setlease, and do not block new open
requests indefinitely, retaining such a delegation on the server is
unnecessary.

Reported-by: Zhang Jian <zhangjian496@...wei.com>
Fixes: 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED")
Closes: https://lore.kernel.org/all/ff8debe9-6877-4cf7-ba29-fc98eae0ffa0@huawei.com/
Signed-off-by: Li Lingfeng <lilingfeng3@...wei.com>
---
  Changes in v2:
  1) Set SC_STATUS_CLOSED unconditionally in destroy_delegation();
  2) Determine whether to remove the delegation based on SC_STATUS_CLOSED,
     rather than by timeout;
  3) Modify the commit message.
 fs/nfsd/nfs4state.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 88c347957da5..bb9e1df4e41f 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1336,6 +1336,11 @@ static void destroy_delegation(struct nfs4_delegation *dp)
 
 	spin_lock(&state_lock);
 	unhashed = unhash_delegation_locked(dp, SC_STATUS_CLOSED);
+	/*
+	 * Unconditionally set SC_STATUS_CLOSED, regardless of whether the
+	 * delegation is hashed, to mark the current delegation as invalid.
+	 */
+	dp->dl_stid.sc_status |= SC_STATUS_CLOSED;
 	spin_unlock(&state_lock);
 	if (unhashed)
 		destroy_unhashed_deleg(dp);
@@ -4326,6 +4331,8 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	int buflen;
 	struct net *net = SVC_NET(rqstp);
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct list_head *pos, *next;
+	struct nfs4_delegation *dp;
 
 	if (resp->opcnt != 1)
 		return nfserr_sequence_pos;
@@ -4470,6 +4477,19 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	default:
 		seq->status_flags = 0;
 	}
+	if (!list_empty(&clp->cl_revoked)) {
+		spin_lock(&clp->cl_lock);
+		list_for_each_safe(pos, next, &clp->cl_revoked) {
+			dp = list_entry(pos, struct nfs4_delegation, dl_recall_lru);
+			if (dp->dl_stid.sc_status & SC_STATUS_CLOSED) {
+				list_del_init(&dp->dl_recall_lru);
+				spin_unlock(&clp->cl_lock);
+				nfs4_put_stid(&dp->dl_stid);
+				spin_lock(&clp->cl_lock);
+			}
+		}
+		spin_unlock(&clp->cl_lock);
+	}
 	if (!list_empty(&clp->cl_revoked))
 		seq->status_flags |= SEQ4_STATUS_RECALLABLE_STATE_REVOKED;
 	if (atomic_read(&clp->cl_admin_revoked))
-- 
2.46.1