linux-kernel - [PATCH] lockd: don't allow locking on reexported NFSv2/3

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Message-Id: <20251023-lockd-owner-v1-1-1d196b0183d1@kernel.org>
Date: Thu, 23 Oct 2025 09:12:39 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Chuck Lever <chuck.lever@...cle.com>, NeilBrown <neil@...wn.name>, 
 Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>, 
 Tom Talpey <tom@...pey.com>, Trond Myklebust <trondmy@...nel.org>, 
 Anna Schumaker <anna@...nel.org>
Cc: Mike Snitzer <snitzer@...nel.org>, linux-nfs@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>
Subject: [PATCH] lockd: don't allow locking on reexported NFSv2/3

Since commit 9254c8ae9b81 ("nfsd: disallow file locking and delegations
for NFSv4 reexport"), file locking when reexporting an NFS mount via
NFSv4 is expressly prohibited by nfsd. Do the same in lockd:

Add a new  nlmsvc_file_cannot_lock() helper that will test whether file
locking is allowed for a given file, and return nlm_lck_denied_nolocks
if it isn't.

Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
Regardless of how we fix the bug that Olga found recently, I think we
need to do this as well. We don't allow locking when reexporting via v4,
and I don't think we want to allow it when reexporting via v2/3 either.
---
 fs/lockd/svclock.c          | 12 ++++++++++++
 fs/lockd/svcshare.c         |  6 ++++++
 include/linux/lockd/lockd.h |  9 ++++++++-
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index c1315df4b350bbd753305b5c08550d50f67b92aa..cd42e480a7000f1b3ec7fca5ecc7fb8dc4755a09 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -495,6 +495,9 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 				(long long)lock->fl.fl_end,
 				wait);
 
+	if (nlmsvc_file_cannot_lock(file))
+		return nlm_lck_denied_nolocks;
+
 	if (!locks_can_async_lock(nlmsvc_file_file(file)->f_op)) {
 		async_block = wait;
 		wait = 0;
@@ -621,6 +624,9 @@ nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
 				(long long)lock->fl.fl_start,
 				(long long)lock->fl.fl_end);
 
+	if (nlmsvc_file_cannot_lock(file))
+		return nlm_lck_denied_nolocks;
+
 	if (locks_in_grace(SVC_NET(rqstp))) {
 		ret = nlm_lck_denied_grace_period;
 		goto out;
@@ -678,6 +684,9 @@ nlmsvc_unlock(struct net *net, struct nlm_file *file, struct nlm_lock *lock)
 				(long long)lock->fl.fl_start,
 				(long long)lock->fl.fl_end);
 
+	if (nlmsvc_file_cannot_lock(file))
+		return nlm_lck_denied_nolocks;
+
 	/* First, cancel any lock that might be there */
 	nlmsvc_cancel_blocked(net, file, lock);
 
@@ -715,6 +724,9 @@ nlmsvc_cancel_blocked(struct net *net, struct nlm_file *file, struct nlm_lock *l
 				(long long)lock->fl.fl_start,
 				(long long)lock->fl.fl_end);
 
+	if (nlmsvc_file_cannot_lock(file))
+		return nlm_lck_denied_nolocks;
+
 	if (locks_in_grace(net))
 		return nlm_lck_denied_grace_period;
 
diff --git a/fs/lockd/svcshare.c b/fs/lockd/svcshare.c
index ade4931b2da247abd23bd16923f1d2388dc6ce00..88c81ce1148d92bd29ec580ac399ac944ba5ecf8 100644
--- a/fs/lockd/svcshare.c
+++ b/fs/lockd/svcshare.c
@@ -32,6 +32,9 @@ nlmsvc_share_file(struct nlm_host *host, struct nlm_file *file,
 	struct xdr_netobj	*oh = &argp->lock.oh;
 	u8			*ohdata;
 
+	if (nlmsvc_file_cannot_lock(file))
+		return nlm_lck_denied_nolocks;
+
 	for (share = file->f_shares; share; share = share->s_next) {
 		if (share->s_host == host && nlm_cmp_owner(share, oh))
 			goto update;
@@ -72,6 +75,9 @@ nlmsvc_unshare_file(struct nlm_host *host, struct nlm_file *file,
 	struct nlm_share	*share, **shpp;
 	struct xdr_netobj	*oh = &argp->lock.oh;
 
+	if (nlmsvc_file_cannot_lock(file))
+		return nlm_lck_denied_nolocks;
+
 	for (shpp = &file->f_shares; (share = *shpp) != NULL;
 					shpp = &share->s_next) {
 		if (share->s_host == host && nlm_cmp_owner(share, oh)) {
diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index c8f0f9458f2cc035fd9161f8f2486ba76084abf1..330e38776bb20d09c20697fc38a96c161ad0313a 100644
--- a/include/linux/lockd/lockd.h
+++ b/include/linux/lockd/lockd.h
@@ -12,6 +12,7 @@
 
 /* XXX: a lot of this should really be under fs/lockd. */
 
+#include <linux/exportfs.h>
 #include <linux/in.h>
 #include <linux/in6.h>
 #include <net/ipv6.h>
@@ -307,7 +308,7 @@ void		  nlmsvc_invalidate_all(void);
 int           nlmsvc_unlock_all_by_sb(struct super_block *sb);
 int           nlmsvc_unlock_all_by_ip(struct sockaddr *server_addr);
 
-static inline struct file *nlmsvc_file_file(struct nlm_file *file)
+static inline struct file *nlmsvc_file_file(const struct nlm_file *file)
 {
 	return file->f_file[O_RDONLY] ?
 	       file->f_file[O_RDONLY] : file->f_file[O_WRONLY];
@@ -318,6 +319,12 @@ static inline struct inode *nlmsvc_file_inode(struct nlm_file *file)
 	return file_inode(nlmsvc_file_file(file));
 }
 
+static inline bool
+nlmsvc_file_cannot_lock(const struct nlm_file *file)
+{
+	return exportfs_cannot_lock(nlmsvc_file_file(file)->f_path.dentry->d_sb->s_export_op);
+}
+
 static inline int __nlm_privileged_request4(const struct sockaddr *sap)
 {
 	const struct sockaddr_in *sin = (struct sockaddr_in *)sap;

---
base-commit: 316f960d9ffb8439e0876dc2eab812e55f3ccb2a
change-id: 20251023-lockd-owner-a529e45d8622

Best regards,
-- 
Jeff Layton <jlayton@...nel.org>