FAILED: patch "[PATCH] NFSD: Prevent client use-after-free during delegation revoke" failed to apply to 6.1-stable tree

PATCH New [email protected] 2 participants 3 messages Sep 3 – Sep 6

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[email protected]

author maintainer

2026-09-03 13:45 UTC #0 lore raw

The patch below does not apply to the 6.1-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 <[email protected]>.

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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 4683ca76b3b7e5808338491c6eb3c20e6b4894d5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090336-pleat-borough-58de@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 4683ca76b3b7e5808338491c6eb3c20e6b4894d5 Mon Sep 17 00:00:00 2001
From: Chuck Lever <[email protected]>
Date: Thu, 9 Jul 2026 13:40:25 -0400
Subject: [PATCH] NFSD: Prevent client use-after-free during delegation revoke

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 [email protected]

Reviewed-by NeilBrown <[email protected]>

Reviewed-by Jeff Layton <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Chuck Lever <[email protected]>

fs/nfsd/netns.h +4 -2

index 03724bef10a7..a7bd7b67fa4f 100644
@@ -115,7 +115,8 @@ struct nfsd_net {
 	struct list_head client_lru;
 	struct list_head close_lru;
 
-	/* protects del_recall_lru and delegation hash/unhash */
+	/* protects del_recall_lru and delegation hash/unhash;
+	 * nests outside client_lock */
 	spinlock_t deleg_lock ____cacheline_aligned;
 	struct list_head del_recall_lru;

@@ -124,7 +125,8 @@ 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 deleg_lock */
 	spinlock_t client_lock;
 
 	/* protects blocked_locks_lru */

fs/nfsd/nfs4state.c +23 -0

index e000ed3e96e9..efeb2a2e9c8f 100644
@@ -7457,6 +7457,7 @@ 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;

@@ -7485,6 +7486,18 @@ 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);
 		refcount_inc(&dp->dl_stid.sc_count);
 		unhash_delegation_locked(dp, SC_STATUS_REVOKED);
 		list_add(&dp->dl_recall_lru, &reaplist);

@@ -7493,8 +7506,18 @@ 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);

Sasha Levin

maintainer

2026-09-06 15:57 UTC #1 lore raw

PATCH 1/2 nfsd: disallow file locking and delegations for NFSv4 reexport

From: Mike Snitzer <[email protected]>

[ Upstream commit 9254c8ae9b8172d9ad26e620a4bbc604a1efa7fa ]

We do not and cannot support file locking with NFS reexport over NFSv4.x for the same reason we don't do it for NFSv3: NFS reexport server reboot cannot allow clients to recover locks because the source NFS server has not rebooted, and so it is not in grace. Since the source NFS server is not in grace, it cannot offer any guarantees that the file won't have been changed between the locks getting lost and any attempt to recover/reclaim them. The same applies to delegations and any associated locks, so disallow them too.

Clients are no longer allowed to get file locks or delegations from a reexport server, any attempts will fail with operation not supported.

Update the "Reboot recovery" section accordingly in Documentation/filesystems/nfs/reexport.rst

Signed-off-by Mike Snitzer <[email protected]>

Reviewed-by Jeff Layton <[email protected]>

Signed-off-by Chuck Lever <[email protected]>

Stable-dep-of: 4683ca76b3b7 ("NFSD: Prevent client use-after-free during delegation revoke")

Signed-off-by Sasha Levin <[email protected]>

---
 Documentation/filesystems/nfs/reexport.rst | 10 ++-
 fs/nfs/export.c                            |  3 +-
 fs/nfsd/netns.h                            |  3 +
 fs/nfsd/nfs4state.c                        | 91 ++++++++++++++--------
 fs/nfsd/state.h                            |  2 +
 include/linux/exportfs.h                   |  1 +
 6 files changed, 74 insertions(+), 36 deletions(-)

Documentation/filesystems/nfs/reexport.rst +7 -3

index ff9ae4a46530a..044be965d75e2 100644
@@ -26,9 +26,13 @@ Reboot recovery
 ---------------
 
 The NFS protocol's normal reboot recovery mechanisms don't work for the
-case when the reexport server reboots.  Clients will lose any locks
-they held before the reboot, and further IO will result in errors.
-Closing and reopening files should clear the errors.
+case when the reexport server reboots because the source server has not
+rebooted, and so it is not in grace.  Since the source server is not in
+grace, it cannot offer any guarantees that the file won't have been
+changed between the locks getting lost and any attempt to recover them.
+The same applies to delegations and any associated locks.  Clients are
+not allowed to get file locks or delegations from a reexport server, any
+attempts will fail with operation not supported.
 
 Filehandle limits
 -----------------

fs/nfs/export.c +2 -1

index aacf6220ab44e..4412c1a355007 100644
@@ -168,5 +168,6 @@ const struct export_operations nfs_export_ops = {
 		 EXPORT_OP_CLOSE_BEFORE_UNLINK	|
 		 EXPORT_OP_REMOTE_FS		|
 		 EXPORT_OP_NOATOMIC_ATTR	|
-		 EXPORT_OP_FLUSH_ON_CLOSE,
+		 EXPORT_OP_FLUSH_ON_CLOSE	|
+		 EXPORT_OP_NOLOCKS,
 };

fs/nfsd/netns.h +3 -0

index be0c8f1ce4e3e..4ef41e18a7871 100644
@@ -98,6 +98,9 @@ struct nfsd_net {
 	 */
 	struct list_head client_lru;
 	struct list_head close_lru;
+
+	/* protects del_recall_lru and delegation hash/unhash */
+	spinlock_t deleg_lock ____cacheline_aligned;
 	struct list_head del_recall_lru;
 
 	/* protected by blocked_locks_lock */

fs/nfsd/nfs4state.c +59 ~~-32~~

226 lines not on this page · raw message

fs/nfsd/state.h +2 -0

index 53298bdcfb3d0..46ed4077fd89a 100644
@@ -97,6 +97,8 @@ struct nfs4_stid {
 #define NFS4_REVOKED_DELEG_STID 16
 #define NFS4_CLOSED_DELEG_STID 32
 #define NFS4_LAYOUT_STID 64
+/* Selector for unhashing a delegation that is about to be revoked. */
+#define SC_STATUS_REVOKED NFS4_REVOKED_DELEG_STID
 	struct list_head	sc_cp_list;
 	unsigned char		sc_type;
 	stateid_t		sc_stateid;

include/linux/exportfs.h +1 -0

index 218fc5c54e901..45916f1deff62 100644
@@ -222,6 +222,7 @@ struct export_operations {
 						  atomic attribute updates
 						*/
 #define EXPORT_OP_FLUSH_ON_CLOSE	(0x20) /* fs flushes file data on close */
+#define EXPORT_OP_NOLOCKS		(0x40) /* no file locking support */
 	unsigned long	flags;
 };

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-06 15:57 UTC #2 lore raw

PATCH 2/2 NFSD: Prevent client use-after-free during delegation revoke

From: Chuck Lever <[email protected]>

[ Upstream commit 4683ca76b3b7e5808338491c6eb3c20e6b4894d5 ]

Fixes 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED")

Cc [email protected]

Reviewed-by NeilBrown <[email protected]>

Reviewed-by Jeff Layton <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Chuck Lever <[email protected]>

Signed-off-by Sasha Levin <[email protected]>

---
 fs/nfsd/netns.h     |  6 ++++--
 fs/nfsd/nfs4state.c | 23 +++++++++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)

fs/nfsd/netns.h +4 -2

index 4ef41e18a7871..d4aff2b4eb7ad 100644
@@ -99,7 +99,8 @@ struct nfsd_net {
 	struct list_head client_lru;
 	struct list_head close_lru;
 
-	/* protects del_recall_lru and delegation hash/unhash */
+	/* protects del_recall_lru and delegation hash/unhash;
+	 * nests outside client_lock */
 	spinlock_t deleg_lock ____cacheline_aligned;
 	struct list_head del_recall_lru;

@@ -108,7 +109,8 @@ 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 deleg_lock */
 	spinlock_t client_lock;
 
 	/* protects blocked_locks_lru */

fs/nfsd/nfs4state.c +23 -0

index b3aa70adc9293..dc11a0ba2beea 100644
@@ -6196,6 +6196,7 @@ 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;

@@ -6221,6 +6222,18 @@ 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);
 		refcount_inc(&dp->dl_stid.sc_count);
 		unhash_delegation_locked(dp, SC_STATUS_REVOKED);
 		list_add(&dp->dl_recall_lru, &reaplist);

@@ -6229,8 +6242,18 @@ 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);

Signature · 1 line

2.53.0