net/ipv6: Refactor gateway validation on route add

Move gateway validation code from ip6_route_info_create into
ip6_validate_gw. Code move plus adjustments to handle the potential
reset of dev and idev and to make checkpatch happy.
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/ipv6/route.c

@@ -2550,7 +2550,7 @@ static struct rt6_info *ip6_nh_lookup_table(struct net *net,
 
 static int ip6_route_check_nh_onlink(struct net *net,
 				     struct fib6_config *cfg,
-				     struct net_device *dev,
+				     const struct net_device *dev,
 				     struct netlink_ext_ack *extack)
 {
 	u32 tbid = l3mdev_fib_table(dev) ? : RT_TABLE_MAIN;
@@ -2626,6 +2626,68 @@ static int ip6_route_check_nh(struct net *net,
 	return err;
 }
 
+static int ip6_validate_gw(struct net *net, struct fib6_config *cfg,
+			   struct net_device **_dev, struct inet6_dev **idev,
+			   struct netlink_ext_ack *extack)
+{
+	const struct in6_addr *gw_addr = &cfg->fc_gateway;
+	int gwa_type = ipv6_addr_type(gw_addr);
+	const struct net_device *dev = *_dev;
+	int err = -EINVAL;
+
+	/* if gw_addr is local we will fail to detect this in case
+	 * address is still TENTATIVE (DAD in progress). rt6_lookup()
+	 * will return already-added prefix route via interface that
+	 * prefix route was assigned to, which might be non-loopback.
+	 */
+	if (ipv6_chk_addr_and_flags(net, gw_addr,
+				    gwa_type & IPV6_ADDR_LINKLOCAL ?
+				    dev : NULL, 0, 0)) {
+		NL_SET_ERR_MSG(extack, "Invalid gateway address");
+		goto out;
+	}
+
+	if (gwa_type != (IPV6_ADDR_LINKLOCAL | IPV6_ADDR_UNICAST)) {
+		/* IPv6 strictly inhibits using not link-local
+		 * addresses as nexthop address.
+		 * Otherwise, router will not able to send redirects.
+		 * It is very good, but in some (rare!) circumstances
+		 * (SIT, PtP, NBMA NOARP links) it is handy to allow
+		 * some exceptions. --ANK
+		 * We allow IPv4-mapped nexthops to support RFC4798-type
+		 * addressing
+		 */
+		if (!(gwa_type & (IPV6_ADDR_UNICAST | IPV6_ADDR_MAPPED))) {
+			NL_SET_ERR_MSG(extack, "Invalid gateway address");
+			goto out;
+		}
+
+		if (cfg->fc_flags & RTNH_F_ONLINK)
+			err = ip6_route_check_nh_onlink(net, cfg, dev, extack);
+		else
+			err = ip6_route_check_nh(net, cfg, _dev, idev);
+
+		if (err)
+			goto out;
+	}
+
+	/* reload in case device was changed */
+	dev = *_dev;
+
+	err = -EINVAL;
+	if (!dev) {
+		NL_SET_ERR_MSG(extack, "Egress device not specified");
+		goto out;
+	} else if (dev->flags & IFF_LOOPBACK) {
+		NL_SET_ERR_MSG(extack,
+			       "Egress device can not be loopback device for this route");
+		goto out;
+	}
+	err = 0;
+out:
+	return err;
+}
+
 static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg,
 					      struct netlink_ext_ack *extack)
 {
@@ -2808,61 +2870,11 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg,
 	}
 
 	if (cfg->fc_flags & RTF_GATEWAY) {
-		const struct in6_addr *gw_addr;
-		int gwa_type;
-
-		gw_addr = &cfg->fc_gateway;
-		gwa_type = ipv6_addr_type(gw_addr);
-
-		/* if gw_addr is local we will fail to detect this in case
-		 * address is still TENTATIVE (DAD in progress). rt6_lookup()
-		 * will return already-added prefix route via interface that
-		 * prefix route was assigned to, which might be non-loopback.
-		 */
-		err = -EINVAL;
-		if (ipv6_chk_addr_and_flags(net, gw_addr,
-					    gwa_type & IPV6_ADDR_LINKLOCAL ?
-					    dev : NULL, 0, 0)) {
-			NL_SET_ERR_MSG(extack, "Invalid gateway address");
+		err = ip6_validate_gw(net, cfg, &dev, &idev, extack);
+		if (err)
 			goto out;
-		}
-		rt->rt6i_gateway = *gw_addr;
-
-		if (gwa_type != (IPV6_ADDR_LINKLOCAL|IPV6_ADDR_UNICAST)) {
-			/* IPv6 strictly inhibits using not link-local
-			   addresses as nexthop address.
-			   Otherwise, router will not able to send redirects.
-			   It is very good, but in some (rare!) circumstances
-			   (SIT, PtP, NBMA NOARP links) it is handy to allow
-			   some exceptions. --ANK
-			   We allow IPv4-mapped nexthops to support RFC4798-type
-			   addressing
-			 */
-			if (!(gwa_type & (IPV6_ADDR_UNICAST |
-					  IPV6_ADDR_MAPPED))) {
-				NL_SET_ERR_MSG(extack,
-					       "Invalid gateway address");
-				goto out;
-			}
 
-			if (cfg->fc_flags & RTNH_F_ONLINK) {
-				err = ip6_route_check_nh_onlink(net, cfg, dev,
-								extack);
-			} else {
-				err = ip6_route_check_nh(net, cfg, &dev, &idev);
-			}
-			if (err)
-				goto out;
-		}
-		err = -EINVAL;
-		if (!dev) {
-			NL_SET_ERR_MSG(extack, "Egress device not specified");
-			goto out;
-		} else if (dev->flags & IFF_LOOPBACK) {
-			NL_SET_ERR_MSG(extack,
-				       "Egress device can not be loopback device for this route");
-			goto out;
-		}
+		rt->rt6i_gateway = cfg->fc_gateway;
 	}
 
 	err = -ENODEV;