From 5ff9d8a65ce80efb509ce4e8051394e9ed2cd942 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Fri, 29 Mar 2013 21:04:39 -0700
Subject: vfs: Lock in place mounts from more privileged users
When creating a less privileged mount namespace or propogating mounts
from a more privileged to a less privileged mount namespace lock the
submounts so they may not be unmounted individually in the child mount
namespace revealing what is under them.
This enforces the reasonable expectation that it is not possible to
see under a mount point. Most of the time mounts are on empty
directories and revealing that does not matter, however I have seen an
occassionaly sloppy configuration where there were interesting things
concealed under a mount point that probably should not be revealed.
Expirable submounts are not locked because they will eventually
unmount automatically so whatever is under them already needs
to be safe for unprivileged users to access.
From a practical standpoint these restrictions do not appear to be
significant for unprivileged users of the mount namespace. Recursive
bind mounts and pivot_root continues to work, and mounts that are
created in a mount namespace may be unmounted there. All of which
means that the common idiom of keeping a directory of interesting
files and using pivot_root to throw everything else away continues to
work just fine.
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
include/linux/mount.h | 1 +
1 file changed, 1 insertion(+)
(limited to 'include/linux/mount.h')
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 73005f9957e..38cd98f112a 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -48,6 +48,7 @@ struct mnt_namespace;
#define MNT_INTERNAL 0x4000
#define MNT_LOCK_READONLY 0x400000
+#define MNT_LOCKED 0x800000
struct vfsmount {
struct dentry *mnt_root; /* root of the mounted tree */
--
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