FAILED: patch "[PATCH] NFSD: Hold net reference for the lifetime of" failed to apply to 5.15-stable tree

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 <[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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x e7fcf179b82d3a3730fd8615da01b087cc654d0b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026032038-dimly-tiring-d92b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From e7fcf179b82d3a3730fd8615da01b087cc654d0b Mon Sep 17 00:00:00 2001
From: Chuck Lever <[email protected]>
Date: Thu, 19 Feb 2026 16:50:17 -0500
Subject: [PATCH] NFSD: Hold net reference for the lifetime of
/proc/fs/nfs/exports fd

The /proc/fs/nfs/exports proc entry is created at module init and persists for the module's lifetime. exports_proc_open() captures the caller's current network namespace and stores its svc_export_cache in seq->private, but takes no reference on the namespace. If the namespace is subsequently torn down (e.g. container destruction after the opener does setns() to a different namespace), nfsd_net_exit() calls nfsd_export_shutdown() which frees the cache. Subsequent reads on the still-open fd dereference the freed cache_detail, walking a freed hash table.

Hold a reference on the struct net for the lifetime of the open file descriptor. This prevents nfsd_net_exit() from running -- and thus prevents nfsd_export_shutdown() from freeing the cache -- while any exports fd is open. cache_detail already stores its net pointer (cd->net, set by cache_create_net()), so exports_release() can retrieve it without additional per-file storage.

index fe3b3f206aa9..d67c169526d0 100644
@@ -149,9 +149,19 @@ static int exports_net_open(struct net *net, struct file *file)
 
 	seq = file->private_data;
 	seq->private = nn->svc_export_cache;
+	get_net(net);
 	return 0;
 }
 
+static int exports_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq = file->private_data;
+	struct cache_detail *cd = seq->private;
+
+	put_net(cd->net);
+	return seq_release(inode, file);
+}
+
 static int exports_nfsd_open(struct inode *inode, struct file *file)
 {
 	return exports_net_open(inode->i_sb->s_fs_info, file);

@@ -161,7 +171,7 @@ static const struct file_operations exports_nfsd_operations = {
 	.open		= exports_nfsd_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release,
+	.release	= exports_release,
 };
 
 static int export_features_show(struct seq_file *m, void *v)

@@ -1376,7 +1386,7 @@ static const struct proc_ops exports_proc_ops = {
 	.proc_open	= exports_proc_open,
 	.proc_read	= seq_read,
 	.proc_lseek	= seq_lseek,
-	.proc_release	= seq_release,
+	.proc_release	= exports_release,
 };
 
 static int create_proc_exports_entry(void)

From: Tom Rix <[email protected]>

[ Upstream commit 340086da9a87820b40601141a0e9e87c954ac006 ]

gcc with W=1 and ! CONFIG_PROC_FS fs/nfsd/nfsctl.c:161:30: error: ‘exports_proc_ops’
defined but not used [-Werror=unused-const-variable=]

  161 | static const struct proc_ops exports_proc_ops = {
      |                              ^~~~~~~~~~~~~~~~

The only use of exports_proc_ops is when CONFIG_PROC_FS is defined, so its definition should be likewise conditional.

Stable-dep-of: e7fcf179b82d ("NFSD: Hold net reference for the lifetime of /proc/fs/nfs/exports fd")

---
 fs/nfsd/nfsctl.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

index ba2eaf3744efa..e3d34fb7fce5a 100644
@@ -155,18 +155,6 @@ static int exports_net_open(struct net *net, struct file *file)
 	return 0;
 }
 
-static int exports_proc_open(struct inode *inode, struct file *file)
-{
-	return exports_net_open(current->nsproxy->net_ns, file);
-}
-
-static const struct proc_ops exports_proc_ops = {
-	.proc_open	= exports_proc_open,
-	.proc_read	= seq_read,
-	.proc_lseek	= seq_lseek,
-	.proc_release	= seq_release,
-};
-
 static int exports_nfsd_open(struct inode *inode, struct file *file)
 {
 	return exports_net_open(inode->i_sb->s_fs_info, file);

@@ -1423,6 +1411,19 @@ static struct file_system_type nfsd_fs_type = {
 MODULE_ALIAS_FS("nfsd");
 
 #ifdef CONFIG_PROC_FS
+
+static int exports_proc_open(struct inode *inode, struct file *file)
+{
+	return exports_net_open(current->nsproxy->net_ns, file);
+}
+
+static const struct proc_ops exports_proc_ops = {
+	.proc_open	= exports_proc_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= seq_release,
+};
+
 static int create_proc_exports_entry(void)
 {
 	struct proc_dir_entry *entry;

2.51.0

From: Chuck Lever <[email protected]>

[ Upstream commit e7fcf179b82d3a3730fd8615da01b087cc654d0b ]

The /proc/fs/nfs/exports proc entry is created at module init and persists for the module's lifetime. exports_proc_open() captures the caller's current network namespace and stores its svc_export_cache in seq->private, but takes no reference on the namespace. If the namespace is subsequently torn down (e.g. container destruction after the opener does setns() to a different namespace), nfsd_net_exit() calls nfsd_export_shutdown() which frees the cache. Subsequent reads on the still-open fd dereference the freed cache_detail, walking a freed hash table.

Hold a reference on the struct net for the lifetime of the open file descriptor. This prevents nfsd_net_exit() from running -- and thus prevents nfsd_export_shutdown() from freeing the cache -- while any exports fd is open. cache_detail already stores its net pointer (cd->net, set by cache_create_net()), so exports_release() can retrieve it without additional per-file storage.

---
 fs/nfsd/nfsctl.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

index e3d34fb7fce5a..bc30cf413c92e 100644
@@ -152,9 +152,19 @@ static int exports_net_open(struct net *net, struct file *file)
 
 	seq = file->private_data;
 	seq->private = nn->svc_export_cache;
+	get_net(net);
 	return 0;
 }
 
+static int exports_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq = file->private_data;
+	struct cache_detail *cd = seq->private;
+
+	put_net(cd->net);
+	return seq_release(inode, file);
+}
+
 static int exports_nfsd_open(struct inode *inode, struct file *file)
 {
 	return exports_net_open(inode->i_sb->s_fs_info, file);

@@ -164,7 +174,7 @@ static const struct file_operations exports_nfsd_operations = {
 	.open		= exports_nfsd_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release,
+	.release	= exports_release,
 };
 
 static int export_features_show(struct seq_file *m, void *v)

@@ -1421,7 +1431,7 @@ static const struct proc_ops exports_proc_ops = {
 	.proc_open	= exports_proc_open,
 	.proc_read	= seq_read,
 	.proc_lseek	= seq_lseek,
-	.proc_release	= seq_release,
+	.proc_release	= exports_release,
 };
 
 static int create_proc_exports_entry(void)

2.51.0