ipv4: Allow routes to use nexthop objects

Add support for RTA_NH_ID attribute to allow a user to specify a
nexthop id to use with a route. fc_nh_id is added to fib_config to
hold the value passed in the RTA_NH_ID attribute. If a nexthop id
is given, the gateway, device, encap and multipath attributes can
not be set.

Update fib_nh_match to check ids on a route delete.

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

include/net/ip_fib.h

@@ -40,6 +40,7 @@ struct fib_config {
 	u32			fc_flags;
 	u32			fc_priority;
 	__be32			fc_prefsrc;
+	u32			fc_nh_id;
 	struct nlattr		*fc_mx;
 	struct rtnexthop	*fc_mp;
 	int			fc_mx_len;

net/ipv4/fib_frontend.c

@@ -671,6 +671,7 @@ const struct nla_policy rtm_ipv4_policy[RTA_MAX + 1] = {
 	[RTA_IP_PROTO]		= { .type = NLA_U8 },
 	[RTA_SPORT]		= { .type = NLA_U16 },
 	[RTA_DPORT]		= { .type = NLA_U16 },
+	[RTA_NH_ID]		= { .type = NLA_U32 },
 };
 
 int fib_gw_from_via(struct fib_config *cfg, struct nlattr *nla,
@@ -808,6 +809,18 @@ static int rtm_to_fib_config(struct net *net, struct sk_buff *skb,
 			if (err < 0)
 				goto errout;
 			break;
+		case RTA_NH_ID:
+			cfg->fc_nh_id = nla_get_u32(attr);
+			break;
+		}
+	}
+
+	if (cfg->fc_nh_id) {
+		if (cfg->fc_oif || cfg->fc_gw_family ||
+		    cfg->fc_encap || cfg->fc_mp) {
+			NL_SET_ERR_MSG(extack,
+				       "Nexthop specification and nexthop id are mutually exclusive");
+			return -EINVAL;
 		}
 	}
 
@@ -834,6 +847,12 @@ static int inet_rtm_delroute(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (err < 0)
 		goto errout;
 
+	if (cfg.fc_nh_id && !nexthop_find_by_id(net, cfg.fc_nh_id)) {
+		NL_SET_ERR_MSG(extack, "Nexthop id does not exist");
+		err = -EINVAL;
+		goto errout;
+	}
+
 	tb = fib_get_table(net, cfg.fc_table);
 	if (!tb) {
 		NL_SET_ERR_MSG(extack, "FIB table does not exist");

net/ipv4/fib_semantics.c

@@ -789,6 +789,12 @@ int fib_nh_match(struct fib_config *cfg, struct fib_info *fi,
 	if (cfg->fc_priority && cfg->fc_priority != fi->fib_priority)
 		return 1;
 
+	if (cfg->fc_nh_id) {
+		if (fi->nh && cfg->fc_nh_id == fi->nh->id)
+			return 0;
+		return 1;
+	}
+
 	if (cfg->fc_oif || cfg->fc_gw_family) {
 		struct fib_nh *nh = fib_info_nh(fi, 0);
 
@@ -1302,6 +1308,15 @@ struct fib_info *fib_create_info(struct fib_config *cfg,
 		goto err_inval;
 	}
 
+	if (cfg->fc_nh_id) {
+		nh = nexthop_find_by_id(net, cfg->fc_nh_id);
+		if (!nh) {
+			NL_SET_ERR_MSG(extack, "Nexthop id does not exist");
+			goto err_inval;
+		}
+		nhs = 0;
+	}
+
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 	if (cfg->fc_mp) {
 		nhs = fib_count_nexthops(cfg->fc_mp, cfg->fc_mp_len, extack);