FAILED: patch "[PATCH] NFSD: Hold net reference for the lifetime of" failed to apply to 6.1-stable tree

[<gregkh@linuxfoundation.org>]

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 <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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x e7fcf179b82d3a3730fd8615da01b087cc654d0b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026032034-freeing-unlimited-383f@gregkh' --subject-prefix 'PATCH 6.1.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 <chuck.lever@oracle.com>
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.

Reported-by: Misbah Anjum N <misanjum@linux.ibm.com>
Closes: https://lore.kernel.org/linux-nfs/dcd371d3a95815a84ba7de52cef447b8@linux.ibm.com/
Fixes: 96d851c4d28d ("nfsd: use proper net while reading "exports" file")
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: NeilBrown <neil@brown.name>
Tested-by: Olga Kornievskaia <okorniev@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index fe3b3f206aa9..d67c169526d0 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -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)