netfilter: xt_osf: Add missing permission checks

netfilter: xt_osf: Add missing permission checks

The capability check in nfnetlink_rcv() verifies that the caller
has CAP_NET_ADMIN in the namespace that "owns" the netlink socket.
However, xt_osf_fingers is shared by all net namespaces on the
system.  An unprivileged user can create user and net namespaces
in which he holds CAP_NET_ADMIN to bypass the netlink_net_capable()
check:

    vpnns -- nfnl_osf -f /tmp/pf.os

    vpnns -- nfnl_osf -f /tmp/pf.os -d

These non-root operations successfully modify the systemwide OS
fingerprint list.  Add new capable() checks so that they can't.

Signed-off-by: Kevin Cernekee <cernekee@chromium.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
(cherry picked from commit 916a27901de01446bcf57ecca4783f6cff493309)

Orabug: 29037831
CVE: CVE-2017-17450

Signed-off-by: John Donnelly <john.p.donnelly@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>