commit: 90563b198e4c6674c63672fae1923da467215f45
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Date: Fri, 22 Mar 2013 03:10:15 -0700
Subject: vfs: Add a mount flag to lock read only bind mounts
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
restriction.
Add a MNT_LOCK_READONLY mount flag to indicate that a mount must
remain read-only.
CC: stable@xxxxxxxxxxxxxxx
Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
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 a303522..8505b5e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1713,6 +1713,9 @@ 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));
else
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 */
--
1.7.10.4
--
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