From: Miklos Szeredi <mszeredi@suse.cz>
On mount propagation, let the owner of the clone be inherited from the

parent into which it has been propagated.
If the parent has the "nosuid" flag, set this flag for the child as

well.  This is needed for the suid-less namespace (use case #2 in the

first patch header), where all mounts are owned by the user and have

the nosuid flag set.  In this case the propagated mount needs to have

nosuid, otherwise a suid executable may be misused by the user.
Similar treatment is not needed for "nodev", because devices can't be

abused this way: the user is not able to gain privileges to devices by

rearranging the mount namespace.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

---
Index: linux/fs/namespace.c

===================================================================

--- linux.orig/fs/namespace.c	2008-01-16 13:25:09.000000000 +0100

+++ linux/fs/namespace.c	2008-01-16 13:25:11.000000000 +0100

@@ -506,10 +506,10 @@ static int reserve_user_mount(void)

 	return err;

 }
-static void __set_mnt_user(struct vfsmount *mnt)

+static void __set_mnt_user(struct vfsmount *mnt, uid_t owner)

 {

 	WARN_ON(mnt->mnt_flags & MNT_USER);

-	mnt->mnt_uid = current->fsuid;

+	mnt->mnt_uid = owner;

 	mnt->mnt_flags |= MNT_USER;
 	if (!capable(CAP_SETUID))

@@ -520,7 +520,7 @@ static void __set_mnt_user(struct vfsmou
 static void set_mnt_user(struct vfsmount *mnt)

 {

-	__set_mnt_user(mnt);

+	__set_mnt_user(mnt, current->fsuid);

 	spin_lock(&vfsmount_lock);

 	nr_user_mounts++;

 	spin_unlock(&vfsmount_lock);

@@ -536,7 +536,7 @@ static void clear_mnt_user(struct vfsmou

 }
 static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,

-					int flag)

+					int flag, uid_t owner)

 {

 	struct super_block *sb = old->mnt_sb;

 	struct vfsmount *mnt;

@@ -560,7 +560,10 @@ static struct vfsmount *clone_mnt(struct

 	/* don't copy the MNT_USER flag */

 	mnt->mnt_flags &= ~MNT_USER;

 ...
[ message continues ]

As discussed many months ago this does seem like the most appropriate

behavior for propagation.
--