FAILED: patch "[PATCH] NFSD: Prevent client use-after-free during blocked-lock" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] NFSD: Prevent client use-after-free during blocked-lock" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 9026932ac8be4d0ae01db47f23619a98cc57b671
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090333-gutter-request-d440@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9026932ac8be4d0ae01db47f23619a98cc57b671 Mon Sep 17 00:00:00 2001
From: Chuck Lever <cel@kernel.org>
Date: Thu, 9 Jul 2026 13:40:30 -0400
Subject: [PATCH] NFSD: Prevent client use-after-free during blocked-lock
 reaping

A bare lock owner -- its only remaining reference a blocked lock on
nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but
no reference keeping the client alive. When the per-net laundromat
reaps such a lock, freeing the nbl drops the owner reference
held through flc_owner, and the final nfs4_put_stateowner()
takes the client's cl_lock. Because the laundromat detaches the
nbl first, __destroy_client() no longer finds it, so a concurrent
force_expire_client() can free the client before nfs4_put_stateowner()
runs, dereferencing cl_lock in freed memory.

Pin the client with cl_rpc_users before dropping
nn->blocked_locks_lock, and skip clients already expiring, whose
blocked locks __destroy_client() frees while holding an owner
reference. Take nn->client_lock outside nn->blocked_locks_lock.
Every other site holds nn->blocked_locks_lock as a leaf, acquiring
no further lock, so placing nn->client_lock outside it cannot form
a lock-order cycle.

Fixes: 7919d0a27f1e ("nfsd: add a LRU list for blocked locks")
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260709-cel-v4-7-1d519d9be0cb@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 142ba7d80539..4acd02f1642c 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -357,6 +357,16 @@ free_blocked_lock(struct nfsd4_blocked_lock *nbl)
 	kref_put(&nbl->nbl_kref, free_nbl);
 }
 
+/* A blocked lock's flc_owner is its nfs4_lockowner. */
+static struct nfs4_client *
+nbl_client(struct nfsd4_blocked_lock *nbl)
+{
+	struct nfs4_lockowner *lo;
+
+	lo = (struct nfs4_lockowner *)nbl->nbl_lock.c.flc_owner;
+	return lo->lo_owner.so_client;
+}
+
 static void
 remove_blocked_locks(struct nfs4_lockowner *lo)
 {
@@ -7591,22 +7601,29 @@ nfs4_laundromat(struct nfsd_net *nn)
 	 * indefinitely once the lock does become free.
 	 */
 	BUG_ON(!list_empty(&reaplist));
+	spin_lock(&nn->client_lock);
 	spin_lock(&nn->blocked_locks_lock);
-	while (!list_empty(&nn->blocked_locks_lru)) {
-		nbl = list_first_entry(&nn->blocked_locks_lru,
-					struct nfsd4_blocked_lock, nbl_lru);
+	list_for_each_safe(pos, next, &nn->blocked_locks_lru) {
+		nbl = list_entry(pos, struct nfsd4_blocked_lock, nbl_lru);
 		if (!state_expired(&lt, nbl->nbl_time))
 			break;
+		clp = nbl_client(nbl);
+		if (is_client_expired(clp))
+			continue;
+		atomic_inc(&clp->cl_rpc_users);
 		list_move(&nbl->nbl_lru, &reaplist);
 		list_del_init(&nbl->nbl_list);
 	}
 	spin_unlock(&nn->blocked_locks_lock);
+	spin_unlock(&nn->client_lock);
 
 	while (!list_empty(&reaplist)) {
 		nbl = list_first_entry(&reaplist,
 					struct nfsd4_blocked_lock, nbl_lru);
+		clp = nbl_client(nbl);
 		list_del_init(&nbl->nbl_lru);
 		free_blocked_lock(nbl);
+		put_client_no_renew(clp);
 	}
 #ifdef CONFIG_NFSD_V4_2_INTER_SSC
 	/* service the server-to-server copy delayed unmount list */

[PATCH 5.15.y 1/3] NFSD: Prevent client use-after-free during delegation revoke

[Sasha Levin]

From: Chuck Lever <cel@kernel.org>

[ Upstream commit 4683ca76b3b7e5808338491c6eb3c20e6b4894d5 ]

A delegation stateid holds only a bare pointer to its owning
nfs4_client and does not keep it alive.  The client survives its
stateids only because __destroy_client() drains cl_delegations and
cl_revoked before free_client() runs.

nfs4_laundromat() breaks that invariant: it unhashes an
expired delegation from cl_delegations, drops deleg_lock, then
revoke_delegation() relinks it onto cl_revoked under cl_lock.  In that
window the delegation is on neither list, so client_has_state() can
report no remaining state.

Every teardown path first requires cl_rpc_users to be zero, but
the laundromat holds no such reference.  A client whose recalled
delegation has just timed out can therefore reach free_client()
while revoke_delegation() is still about to dereference cl_lock,
a use-after-free.

Pin the client with cl_rpc_users across the revoke so teardown blocks
until it completes, then reap the delegation from cl_revoked.  A client
already expiring reaps its own, so skip it and leave the delegation on
del_recall_lru.

Fixes: 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED")
Cc: stable@vger.kernel.org
Reviewed-by: NeilBrown <neil@brown.name>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260709-cel-v4-2-1d519d9be0cb@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/netns.h     |  3 ++-
 fs/nfsd/nfs4state.c | 29 ++++++++++++++++++++++++++---
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index be0c8f1ce4e3e..ad457a1b48157 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -105,7 +105,8 @@ struct nfsd_net {
 
 	struct delayed_work laundromat_work;
 
-	/* client_lock protects the client lru list and session hash table */
+	/* client_lock protects the client lru list and session hash
+	 * table; nests inside state_lock */
 	spinlock_t client_lock;
 
 	/* protects blocked_locks_lru */
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index e6c0b1520973e..a29b7e317b16a 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -91,9 +91,9 @@ static void nfsd4_file_hash_remove(struct nfs4_file *fi);
 /* Locking: */
 
 /*
- * Currently used for the del_recall_lru and file hash table.  In an
- * effort to decrease the scope of the client_mutex, this spinlock may
- * eventually cover more:
+ * Currently used for the del_recall_lru and file hash table. It nests
+ * outside client_lock. In an effort to decrease the scope of the
+ * client_mutex, this spinlock may eventually cover more:
  */
 static DEFINE_SPINLOCK(state_lock);
 
@@ -6184,6 +6184,7 @@ nfs4_laundromat(struct nfsd_net *nn)
 		.new_timeo = nn->nfsd4_lease
 	};
 	struct nfs4_cpntf_state *cps;
+	struct nfs4_client *clp;
 	copy_stateid_t *cps_t;
 	int i;
 
@@ -6209,6 +6210,18 @@ nfs4_laundromat(struct nfsd_net *nn)
 		dp = list_entry (pos, struct nfs4_delegation, dl_recall_lru);
 		if (!state_expired(&lt, dp->dl_time))
 			break;
+		clp = dp->dl_stid.sc_client;
+		spin_lock(&nn->client_lock);
+		if (is_client_expired(clp)) {
+			spin_unlock(&nn->client_lock);
+			continue;
+		}
+		/*
+		 * Pin without reviving: get_client_locked() would
+		 * flip a courtesy client back to NFSD4_ACTIVE.
+		 */
+		atomic_inc(&clp->cl_rpc_users);
+		spin_unlock(&nn->client_lock);
 		WARN_ON(!unhash_delegation_locked(dp));
 		list_add(&dp->dl_recall_lru, &reaplist);
 	}
@@ -6216,8 +6229,18 @@ nfs4_laundromat(struct nfsd_net *nn)
 	while (!list_empty(&reaplist)) {
 		dp = list_first_entry(&reaplist, struct nfs4_delegation,
 					dl_recall_lru);
+		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);
+		}
 	}
 
 	spin_lock(&nn->client_lock);
-- 
2.53.0

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

[Sasha Levin]

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

[PATCH 5.15.y 3/3] NFSD: Prevent client use-after-free during blocked-lock reaping

[Sasha Levin]

From: Chuck Lever <cel@kernel.org>

[ Upstream commit 9026932ac8be4d0ae01db47f23619a98cc57b671 ]

A bare lock owner -- its only remaining reference a blocked lock on
nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but
no reference keeping the client alive. When the per-net laundromat
reaps such a lock, freeing the nbl drops the owner reference
held through flc_owner, and the final nfs4_put_stateowner()
takes the client's cl_lock. Because the laundromat detaches the
nbl first, __destroy_client() no longer finds it, so a concurrent
force_expire_client() can free the client before nfs4_put_stateowner()
runs, dereferencing cl_lock in freed memory.

Pin the client with cl_rpc_users before dropping
nn->blocked_locks_lock, and skip clients already expiring, whose
blocked locks __destroy_client() frees while holding an owner
reference. Take nn->client_lock outside nn->blocked_locks_lock.
Every other site holds nn->blocked_locks_lock as a leaf, acquiring
no further lock, so placing nn->client_lock outside it cannot form
a lock-order cycle.

Fixes: 7919d0a27f1e ("nfsd: add a LRU list for blocked locks")
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260709-cel-v4-7-1d519d9be0cb@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
[ adapted nbl_lock.c.flc_owner access to the older nbl_lock.fl_owner layout ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/nfs4state.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 4468c24145687..e08dcfd2e75b9 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -346,6 +346,16 @@ free_blocked_lock(struct nfsd4_blocked_lock *nbl)
 	kref_put(&nbl->nbl_kref, free_nbl);
 }
 
+/* A blocked lock's fl_owner is its nfs4_lockowner. */
+static struct nfs4_client *
+nbl_client(struct nfsd4_blocked_lock *nbl)
+{
+	struct nfs4_lockowner *lo;
+
+	lo = (struct nfs4_lockowner *)nbl->nbl_lock.fl_owner;
+	return lo->lo_owner.so_client;
+}
+
 static void
 remove_blocked_locks(struct nfs4_lockowner *lo)
 {
@@ -6279,22 +6289,29 @@ nfs4_laundromat(struct nfsd_net *nn)
 	 * indefinitely once the lock does become free.
 	 */
 	BUG_ON(!list_empty(&reaplist));
+	spin_lock(&nn->client_lock);
 	spin_lock(&nn->blocked_locks_lock);
-	while (!list_empty(&nn->blocked_locks_lru)) {
-		nbl = list_first_entry(&nn->blocked_locks_lru,
-					struct nfsd4_blocked_lock, nbl_lru);
+	list_for_each_safe(pos, next, &nn->blocked_locks_lru) {
+		nbl = list_entry(pos, struct nfsd4_blocked_lock, nbl_lru);
 		if (!state_expired(&lt, nbl->nbl_time))
 			break;
+		clp = nbl_client(nbl);
+		if (is_client_expired(clp))
+			continue;
+		atomic_inc(&clp->cl_rpc_users);
 		list_move(&nbl->nbl_lru, &reaplist);
 		list_del_init(&nbl->nbl_list);
 	}
 	spin_unlock(&nn->blocked_locks_lock);
+	spin_unlock(&nn->client_lock);
 
 	while (!list_empty(&reaplist)) {
 		nbl = list_first_entry(&reaplist,
 					struct nfsd4_blocked_lock, nbl_lru);
+		clp = nbl_client(nbl);
 		list_del_init(&nbl->nbl_lru);
 		free_blocked_lock(nbl);
+		put_client_no_renew(clp);
 	}
 #ifdef CONFIG_NFSD_V4_2_INTER_SSC
 	/* service the server-to-server copy delayed unmount list */
-- 
2.53.0