linux-kernel - [PATCH 5.10 02/23] devtmpfs regression fix: reconfigure on each mount

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Message-Id: <20220118160451.327507632@linuxfoundation.org>
Date:   Tue, 18 Jan 2022 17:05:42 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>,
        Al Viro <viro@...iv.linux.org.uk>, NeilBrown <neilb@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.10 02/23] devtmpfs regression fix: reconfigure on each mount

From: NeilBrown <neilb@...e.de>

commit a6097180d884ddab769fb25588ea8598589c218c upstream.

Prior to Linux v5.4 devtmpfs used mount_single() which treats the given
mount options as "remount" options, so it updates the configuration of
the single super_block on each mount.

Since that was changed, the mount options used for devtmpfs are ignored.
This is a regression which affect systemd - which mounts devtmpfs with
"-o mode=755,size=4m,nr_inodes=1m".

This patch restores the "remount" effect by calling reconfigure_single()

Fixes: d401727ea0d7 ("devtmpfs: don't mix {ramfs,shmem}_fill_super() with mount_single()")
Acked-by: Christian Brauner <christian.brauner@...ntu.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: NeilBrown <neilb@...e.de>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/base/devtmpfs.c    |    7 +++++++
 fs/super.c                 |    4 ++--
 include/linux/fs_context.h |    2 ++
 3 files changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -59,8 +59,15 @@ static struct dentry *public_dev_mount(s
 		      const char *dev_name, void *data)
 {
 	struct super_block *s = mnt->mnt_sb;
+	int err;
+
 	atomic_inc(&s->s_active);
 	down_write(&s->s_umount);
+	err = reconfigure_single(s, flags, data);
+	if (err < 0) {
+		deactivate_locked_super(s);
+		return ERR_PTR(err);
+	}
 	return dget(s->s_root);
 }
 
--- a/fs/super.c
+++ b/fs/super.c
@@ -1472,8 +1472,8 @@ struct dentry *mount_nodev(struct file_s
 }
 EXPORT_SYMBOL(mount_nodev);
 
-static int reconfigure_single(struct super_block *s,
-			      int flags, void *data)
+int reconfigure_single(struct super_block *s,
+		       int flags, void *data)
 {
 	struct fs_context *fc;
 	int ret;
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -140,6 +140,8 @@ extern int generic_parse_monolithic(stru
 extern int vfs_get_tree(struct fs_context *fc);
 extern void put_fs_context(struct fs_context *fc);
 extern void fc_drop_locked(struct fs_context *fc);
+int reconfigure_single(struct super_block *s,
+		       int flags, void *data);
 
 /*
  * sget() wrappers to be called from the ->get_tree() op.