[ 3.5.y.z extended stable ] Patch "vfs: Add a mount flag to lock read only bind mounts" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Wed Apr 3 10:50:23 UTC 2013

This is a note to let you know that I have just added a patch titled

    vfs: Add a mount flag to lock read only bind mounts

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From 777a11be9c4b612497dfc1252b1b836e5663a656 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm at xmission.com>
Date: Fri, 22 Mar 2013 03:10:15 -0700
Subject: [PATCH] vfs: Add a mount flag to lock read only bind mounts

commit 90563b198e4c6674c63672fae1923da467215f45 upstream.

When a read-only bind mount is copied from mount namespace in a higher
privileged user namespace to a mount namespace in a lesser privileged
user namespace, it should not be possible to remove the the read-only

Add a MNT_LOCK_READONLY mount flag to indicate that a mount must
remain read-only.

Acked-by: Serge Hallyn <serge.hallyn at canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 fs/namespace.c        | 3 +++
 include/linux/mount.h | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 1e4a5fe..c8cd18c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1641,6 +1641,9 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
 	if (readonly_request == __mnt_is_readonly(mnt))
 		return 0;

+	if (mnt->mnt_flags & MNT_LOCK_READONLY)
+		return -EPERM;
 	if (readonly_request)
 		error = mnt_make_readonly(real_mount(mnt));
diff --git a/include/linux/mount.h b/include/linux/mount.h
index d7029f4..73005f9 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -47,6 +47,8 @@ struct mnt_namespace;

 #define MNT_INTERNAL	0x4000

+#define MNT_LOCK_READONLY	0x400000
 struct vfsmount {
 	struct dentry *mnt_root;	/* root of the mounted tree */
 	struct super_block *mnt_sb;	/* pointer to superblock */

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