net: nexthop uapi

New UAPI for nexthops as standalone objects:
- defines netlink ancillary header, struct nhmsg
- RTM commands for nexthop objects, RTM_*NEXTHOP,
- RTNLGRP for nexthop notifications, RTNLGRP_NEXTHOP,
- Attributes for creating nexthops, NHA_*
- Attribute for route specs to specify a nexthop by id, RTA_NH_ID.

The nexthop attributes and semantics follow the route and RTA ones for
device, gateway and lwt encap. Unique to nexthop objects are a blackhole
and a group which contains references to other nexthop objects. With the
exception of blackhole and group, nexthop objects MUST contain a device.
Gateway and encap are optional. Nexthop groups can only reference other
pre-existing nexthops by id. If the NHA_ID attribute is present that id
is used for the nexthop. If not specified, one is auto assigned.

Dump requests can include attributes:
- NHA_GROUPS to return only nexthop groups,
- NHA_MASTER to limit dumps to nexthops with devices enslaved to the
  given master (e.g., VRF)
- NHA_OIF to limit dumps to nexthops using given device

nlmsg_route_perms in selinux code is updated for the new RTM comands.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

security/selinux/nlmsgtab.c

@@ -83,6 +83,9 @@ static const struct nlmsg_perm nlmsg_route_perms[] =
 	{ RTM_NEWCHAIN,		NETLINK_ROUTE_SOCKET__NLMSG_WRITE },
 	{ RTM_DELCHAIN,		NETLINK_ROUTE_SOCKET__NLMSG_WRITE },
 	{ RTM_GETCHAIN,		NETLINK_ROUTE_SOCKET__NLMSG_READ  },
+	{ RTM_NEWNEXTHOP,	NETLINK_ROUTE_SOCKET__NLMSG_WRITE },
+	{ RTM_DELNEXTHOP,	NETLINK_ROUTE_SOCKET__NLMSG_WRITE },
+	{ RTM_GETNEXTHOP,	NETLINK_ROUTE_SOCKET__NLMSG_READ  },
 };
 
 static const struct nlmsg_perm nlmsg_tcpdiag_perms[] =
@@ -166,7 +169,7 @@ int selinux_nlmsg_lookup(u16 sclass, u16 nlmsg_type, u32 *perm)
 		 * structures at the top of this file with the new mappings
 		 * before updating the BUILD_BUG_ON() macro!
 		 */
-		BUILD_BUG_ON(RTM_MAX != (RTM_NEWCHAIN + 3));
+		BUILD_BUG_ON(RTM_MAX != (RTM_NEWNEXTHOP + 3));
 		err = nlmsg_perm(nlmsg_type, perm, nlmsg_route_perms,
 				 sizeof(nlmsg_route_perms));
 		break;