linux-kernel - [PATCH 1/5] initmpfs v2: replace MS

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Date:	Tue, 16 Jul 2013 16:45:19 -0700 (PDT)
From:	Rob Landley <rob@...dley.net>
To:	linux-kernel@...r.kernel.org
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 1/5] initmpfs v2: replace MS_NOUSER in initramfs

From: Rob Landley <rob@...dley.net>

Mounting MS_NOUSER prevents --bind mounts from rootfs. Prevent new rootfs
mounts with a different mechanism that doesn't affect bind mounts.

Signed-off-by: Rob Landley <rob@...dley.net>
---

 fs/ramfs/inode.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c
index c24f1e1..14b9c35 100644
--- a/fs/ramfs/inode.c
+++ b/fs/ramfs/inode.c
@@ -247,7 +247,12 @@ struct dentry *ramfs_mount(struct file_system_type *fs_type,
 static struct dentry *rootfs_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
-	return mount_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super);
+	static unsigned long once;
+
+	if (test_and_set_bit(1, &once))
+		return ERR_PTR(-ENODEV);
+
+	return mount_nodev(fs_type, flags, data, ramfs_fill_super);
 }
 
 static void ramfs_kill_sb(struct super_block *sb)
--
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