ipv4: Refactor fib_check_nh

fib_check_nh is currently huge covering multiple uses cases - device only,
device + gateway, and device + gateway with ONLINK. The next patch adds
validation checks for IPv6 which only further complicates it. So, break
fib_check_nh into 2 helpers - one for gateway validation and one for device
only.
Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_semantics.c

@@ -885,23 +885,18 @@ bool fib_metrics_match(struct fib_config *cfg, struct fib_info *fi)
  *					|
  *					|-> {local prefix} (terminal node)
  */
-static int fib_check_nh(struct fib_config *cfg, struct fib_nh *nh,
-			struct netlink_ext_ack *extack)
+static int fib_check_nh_v4_gw(struct net *net, struct fib_nh *nh, u32 table,
+			      u8 scope, struct netlink_ext_ack *extack)
 {
-	int err = 0;
-	struct net *net;
 	struct net_device *dev;
-
-	net = cfg->fc_nlinfo.nl_net;
-	if (nh->fib_nh_gw4) {
 	struct fib_result res;
+	int err;
 
 	if (nh->fib_nh_flags & RTNH_F_ONLINK) {
 		unsigned int addr_type;
 
-			if (cfg->fc_scope >= RT_SCOPE_LINK) {
-				NL_SET_ERR_MSG(extack,
-					       "Nexthop has invalid scope");
+		if (scope >= RT_SCOPE_LINK) {
+			NL_SET_ERR_MSG(extack, "Nexthop has invalid scope");
 			return -EINVAL;
 		}
 		dev = __dev_get_by_index(net, nh->fib_nh_oif);
@@ -910,15 +905,12 @@ static int fib_check_nh(struct fib_config *cfg, struct fib_nh *nh,
 			return -ENODEV;
 		}
 		if (!(dev->flags & IFF_UP)) {
-				NL_SET_ERR_MSG(extack,
-					       "Nexthop device is not up");
+			NL_SET_ERR_MSG(extack, "Nexthop device is not up");
 			return -ENETDOWN;
 		}
-			addr_type = inet_addr_type_dev_table(net, dev,
-							     nh->fib_nh_gw4);
+		addr_type = inet_addr_type_dev_table(net, dev, nh->fib_nh_gw4);
 		if (addr_type != RTN_UNICAST) {
-				NL_SET_ERR_MSG(extack,
-					       "Nexthop has invalid gateway");
+			NL_SET_ERR_MSG(extack, "Nexthop has invalid gateway");
 			return -EINVAL;
 		}
 		if (!netif_carrier_ok(dev))
@@ -933,7 +925,7 @@ static int fib_check_nh(struct fib_config *cfg, struct fib_nh *nh,
 		struct fib_table *tbl = NULL;
 		struct flowi4 fl4 = {
 			.daddr = nh->fib_nh_gw4,
-				.flowi4_scope = cfg->fc_scope + 1,
+			.flowi4_scope = scope + 1,
 			.flowi4_oif = nh->fib_nh_oif,
 			.flowi4_iif = LOOPBACK_IFINDEX,
 		};
@@ -942,8 +934,8 @@ static int fib_check_nh(struct fib_config *cfg, struct fib_nh *nh,
 		if (fl4.flowi4_scope < RT_SCOPE_LINK)
 			fl4.flowi4_scope = RT_SCOPE_LINK;
 
-			if (cfg->fc_table)
-				tbl = fib_get_table(net, cfg->fc_table);
+		if (table)
+			tbl = fib_get_table(net, table);
 
 		if (tbl)
 			err = fib_table_lookup(tbl, &fl4, &res,
@@ -960,12 +952,11 @@ static int fib_check_nh(struct fib_config *cfg, struct fib_nh *nh,
 		}
 
 		if (err) {
-				NL_SET_ERR_MSG(extack,
-					       "Nexthop has invalid gateway");
-				rcu_read_unlock();
-				return err;
+			NL_SET_ERR_MSG(extack, "Nexthop has invalid gateway");
+			goto out;
 		}
 	}
+
 	err = -EINVAL;
 	if (res.type != RTN_UNICAST && res.type != RTN_LOCAL) {
 		NL_SET_ERR_MSG(extack, "Nexthop has invalid gateway");
@@ -983,15 +974,25 @@ static int fib_check_nh(struct fib_config *cfg, struct fib_nh *nh,
 	if (!netif_carrier_ok(dev))
 		nh->fib_nh_flags |= RTNH_F_LINKDOWN;
 	err = (dev->flags & IFF_UP) ? 0 : -ENETDOWN;
-	} else {
+out:
+	rcu_read_unlock();
+	return err;
+}
+
+static int fib_check_nh_nongw(struct net *net, struct fib_nh *nh,
+			      struct netlink_ext_ack *extack)
+{
 	struct in_device *in_dev;
+	int err;
 
 	if (nh->fib_nh_flags & (RTNH_F_PERVASIVE | RTNH_F_ONLINK)) {
 		NL_SET_ERR_MSG(extack,
 			       "Invalid flags for nexthop - PERVASIVE and ONLINK can not be set");
 		return -EINVAL;
 	}
+
 	rcu_read_lock();
+
 	err = -ENODEV;
 	in_dev = inetdev_by_index(net, nh->fib_nh_oif);
 	if (!in_dev)
@@ -1001,18 +1002,33 @@ static int fib_check_nh(struct fib_config *cfg, struct fib_nh *nh,
 		NL_SET_ERR_MSG(extack, "Device for nexthop is not up");
 		goto out;
 	}
+
 	nh->fib_nh_dev = in_dev->dev;
 	dev_hold(nh->fib_nh_dev);
 	nh->fib_nh_scope = RT_SCOPE_HOST;
 	if (!netif_carrier_ok(nh->fib_nh_dev))
 		nh->fib_nh_flags |= RTNH_F_LINKDOWN;
 	err = 0;
-	}
 out:
 	rcu_read_unlock();
 	return err;
 }
 
+static int fib_check_nh(struct fib_config *cfg, struct fib_nh *nh,
+			struct netlink_ext_ack *extack)
+{
+	struct net *net = cfg->fc_nlinfo.nl_net;
+	u32 table = cfg->fc_table;
+	int err;
+
+	if (nh->fib_nh_gw_family == AF_INET)
+		err = fib_check_nh_v4_gw(net, nh, table, cfg->fc_scope, extack);
+	else
+		err = fib_check_nh_nongw(net, nh, extack);
+
+	return err;
+}
+
 static inline unsigned int fib_laddr_hashfn(__be32 val)
 {
 	unsigned int mask = (fib_info_hash_size - 1);