[PATCH 5.15.y 2/3] NFSD: Consolidate the revocation-path client unpin

[Sasha Levin <sashal@kernel.org>]

From: Chuck Lever <cel@kernel.org>

[ Upstream commit 3308cf3f11ed23c79f9f3f90b34bbbad3e3a6ea9 ]

The client use-after-free fixes in the state-revocation paths left
four open-coded copies of one idiom: drop a cl_rpc_users pin without
renewing the client's lease, waking force_expire_client() when the
last pin drops on a client it is tearing down.  The accompanying "do
not renew" rationale was documented at only one of the four sites.

put_client_renew_locked() and put_client_renew() already carry the
same pin-drop logic, but they renew a non-expired client's lease and
so would resurrect the client whose state is being revoked.  Factor
the common pin-drop into __put_client_locked(), parameterized by
whether to renew.  The renew helpers pass true; the new
put_client_no_renew_locked() and put_client_no_renew() pass false and
carry the revocation paths, which must not revive the client they are
tearing down.  No change in behavior.

Reviewed-by: NeilBrown <neil@brown.name>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260709-cel-v4-6-1d519d9be0cb@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
Stable-dep-of: 9026932ac8be ("NFSD: Prevent client use-after-free during blocked-lock reaping")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/nfs4state.c | 47 +++++++++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 19 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index a29b7e317b16a..4468c24145687 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -205,18 +205,28 @@ renew_client_locked(struct nfs4_client *clp)
 	clp->cl_state = NFSD4_ACTIVE;
 }
 
+/*
+ * Finish a cl_rpc_users unpin with the client_lock held. A
+ * revocation walk clears @renew so the client whose state it is
+ * revoking is not revived; every other caller renews the lease of
+ * a still-active client.
+ */
+static void __put_client_locked(struct nfs4_client *clp, bool renew)
+{
+	if (is_client_expired(clp))
+		wake_up_all(&expiry_wq);
+	else if (renew)
+		renew_client_locked(clp);
+}
+
 static void put_client_renew_locked(struct nfs4_client *clp)
 {
 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
 
 	lockdep_assert_held(&nn->client_lock);
 
-	if (!atomic_dec_and_test(&clp->cl_rpc_users))
-		return;
-	if (!is_client_expired(clp))
-		renew_client_locked(clp);
-	else
-		wake_up_all(&expiry_wq);
+	if (atomic_dec_and_test(&clp->cl_rpc_users))
+		__put_client_locked(clp, true);
 }
 
 static void put_client_renew(struct nfs4_client *clp)
@@ -225,10 +235,17 @@ static void put_client_renew(struct nfs4_client *clp)
 
 	if (!atomic_dec_and_lock(&clp->cl_rpc_users, &nn->client_lock))
 		return;
-	if (!is_client_expired(clp))
-		renew_client_locked(clp);
-	else
-		wake_up_all(&expiry_wq);
+	__put_client_locked(clp, true);
+	spin_unlock(&nn->client_lock);
+}
+
+static void put_client_no_renew(struct nfs4_client *clp)
+{
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+
+	if (!atomic_dec_and_lock(&clp->cl_rpc_users, &nn->client_lock))
+		return;
+	__put_client_locked(clp, false);
 	spin_unlock(&nn->client_lock);
 }
 
@@ -6232,15 +6249,7 @@ nfs4_laundromat(struct nfsd_net *nn)
 		clp = dp->dl_stid.sc_client;
 		list_del_init(&dp->dl_recall_lru);
 		revoke_delegation(dp);
-		/*
-		 * Unpin without renewing: put_client_renew() would
-		 * renew the reaped client's lease.
-		 */
-		if (atomic_dec_and_lock(&clp->cl_rpc_users, &nn->client_lock)) {
-			if (is_client_expired(clp))
-				wake_up_all(&expiry_wq);
-			spin_unlock(&nn->client_lock);
-		}
+		put_client_no_renew(clp);
 	}
 
 	spin_lock(&nn->client_lock);
-- 
2.53.0