vfs: Carefully propogate mounts across user namespaces

As a matter of policy MNT_READONLY should not be changable if the
original mounter had more privileges than creator of the mount
namespace.

Add the flag CL_UNPRIVILEGED to note when we are copying a mount from
a mount namespace that requires more privileges to a mount namespace
that requires fewer privileges.

When the CL_UNPRIVILEGED flag is set cause clone_mnt to set MNT_NO_REMOUNT
if any of the mnt flags that should never be changed are set.

This protects both mount propagation and the initial creation of a less
privileged mount namespace.

Cc: [email protected]
Acked-by: Serge Hallyn <[email protected]>
Reported-by: Andy Lutomirski <[email protected]>
Signed-off-by: "Eric W. Biederman" <[email protected]>

0 files changed, 0 insertions, 0 deletions