selinux: Implement mptcp_add_subflow hook

Newly added subflows should inherit the LSM label from the associated
msk socket regarless current context.

This patch implements the above copying sid and class from the msk
context, deleting the existing subflow label, if any, and then
re-creating a new one.

The new helper reuses the selinux_netlbl_sk_security_free() function,
and the latter can end-up being called multiple times with the same
argument; we additionally need to make it idempotent.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
2 files changed