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>

include/uapi/linux/nexthop.h

+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_NEXTHOP_H
+#define _UAPI_LINUX_NEXTHOP_H
+
+#include <linux/types.h>
+
+struct nhmsg {
+	unsigned char	nh_family;
+	unsigned char	nh_scope;     /* return only */
+	unsigned char	nh_protocol;  /* Routing protocol that installed nh */
+	unsigned char	resvd;
+	unsigned int	nh_flags;     /* RTNH_F flags */
+};
+
+/* entry in a nexthop group */
+struct nexthop_grp {
+	__u32	id;	  /* nexthop id - must exist */
+	__u8	weight;   /* weight of this nexthop */
+	__u8	resvd1;
+	__u16	resvd2;
+};
+
+enum {
+	NEXTHOP_GRP_TYPE_MPATH,  /* default type if not specified */
+	__NEXTHOP_GRP_TYPE_MAX,
+};
+
+#define NEXTHOP_GRP_TYPE_MAX (__NEXTHOP_GRP_TYPE_MAX - 1)
+
+enum {
+	NHA_UNSPEC,
+	NHA_ID,		/* u32; id for nexthop. id == 0 means auto-assign */
+
+	NHA_GROUP,	/* array of nexthop_grp */
+	NHA_GROUP_TYPE,	/* u16 one of NEXTHOP_GRP_TYPE */
+	/* if NHA_GROUP attribute is added, no other attributes can be set */
+
+	NHA_BLACKHOLE,	/* flag; nexthop used to blackhole packets */
+	/* if NHA_BLACKHOLE is added, OIF, GATEWAY, ENCAP can not be set */
+
+	NHA_OIF,	/* u32; nexthop device */
+	NHA_GATEWAY,	/* be32 (IPv4) or in6_addr (IPv6) gw address */
+	NHA_ENCAP_TYPE, /* u16; lwt encap type */
+	NHA_ENCAP,	/* lwt encap data */
+
+	/* NHA_OIF can be appended to dump request to return only
+	 * nexthops using given device
+	 */
+	NHA_GROUPS,	/* flag; only return nexthop groups in dump */
+	NHA_MASTER,	/* u32;  only return nexthops with given master dev */
+
+	__NHA_MAX,
+};
+
+#define NHA_MAX	(__NHA_MAX - 1)
+#endif

include/uapi/linux/rtnetlink.h

@@ -157,6 +157,13 @@ enum {
 	RTM_GETCHAIN,
 #define RTM_GETCHAIN RTM_GETCHAIN
 
+	RTM_NEWNEXTHOP = 104,
+#define RTM_NEWNEXTHOP	RTM_NEWNEXTHOP
+	RTM_DELNEXTHOP,
+#define RTM_DELNEXTHOP	RTM_DELNEXTHOP
+	RTM_GETNEXTHOP,
+#define RTM_GETNEXTHOP	RTM_GETNEXTHOP
+
 	__RTM_MAX,
 #define RTM_MAX		(((__RTM_MAX + 3) & ~3) - 1)
 };
@@ -342,6 +349,7 @@ enum rtattr_type_t {
 	RTA_IP_PROTO,
 	RTA_SPORT,
 	RTA_DPORT,
+	RTA_NH_ID,
 	__RTA_MAX
 };
 
@@ -704,6 +712,8 @@ enum rtnetlink_groups {
 #define RTNLGRP_IPV4_MROUTE_R	RTNLGRP_IPV4_MROUTE_R
 	RTNLGRP_IPV6_MROUTE_R,
 #define RTNLGRP_IPV6_MROUTE_R	RTNLGRP_IPV6_MROUTE_R
+	RTNLGRP_NEXTHOP,
+#define RTNLGRP_NEXTHOP		RTNLGRP_NEXTHOP
 	__RTNLGRP_MAX
 };
 #define RTNLGRP_MAX	(__RTNLGRP_MAX - 1)

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;