ipv6: streamline addrconf_set_dstaddr

Factor out a addrconf_set_sit_dstaddr helper for the actual work if we
found a SIT device, and only hold the rtnl lock around the device lookup
and that new helper, as there is no point in holding it over a
copy_from_user call.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -2783,6 +2783,38 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len, bool sllao)
 	in6_dev_put(in6_dev);
 }
 
+static int addrconf_set_sit_dstaddr(struct net *net, struct net_device *dev,
+		struct in6_ifreq *ireq)
+{
+	struct ip_tunnel_parm p = { };
+	mm_segment_t oldfs = get_fs();
+	struct ifreq ifr;
+	int err;
+
+	if (!(ipv6_addr_type(&ireq->ifr6_addr) & IPV6_ADDR_COMPATv4))
+		return -EADDRNOTAVAIL;
+
+	p.iph.daddr = ireq->ifr6_addr.s6_addr32[3];
+	p.iph.version = 4;
+	p.iph.ihl = 5;
+	p.iph.protocol = IPPROTO_IPV6;
+	p.iph.ttl = 64;
+	ifr.ifr_ifru.ifru_data = (__force void __user *)&p;
+
+	if (!dev->netdev_ops->ndo_do_ioctl)
+		return -EOPNOTSUPP;
+	set_fs(KERNEL_DS);
+	err = dev->netdev_ops->ndo_do_ioctl(dev, &ifr, SIOCADDTUNNEL);
+	set_fs(oldfs);
+	if (err)
+		return err;
+
+	dev = __dev_get_by_name(net, p.name);
+	if (!dev)
+		return -ENOBUFS;
+	return dev_open(dev, NULL);
+}
+
 /*
  *	Set destination address.
  *	Special case for SIT interfaces where we create a new "virtual"
@@ -2790,62 +2822,19 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len, bool sllao)
  */
 int addrconf_set_dstaddr(struct net *net, void __user *arg)
 {
-	struct in6_ifreq ireq;
 	struct net_device *dev;
-	int err = -EINVAL;
+	struct in6_ifreq ireq;
+	int err = -ENODEV;
 
 	if (!IS_ENABLED(CONFIG_IPV6_SIT))
 		return -ENODEV;
-
-	rtnl_lock();
-
-	err = -EFAULT;
 	if (copy_from_user(&ireq, arg, sizeof(struct in6_ifreq)))
-		goto err_exit;
+		return -EFAULT;
 
+	rtnl_lock();
 	dev = __dev_get_by_index(net, ireq.ifr6_ifindex);
-
-	err = -ENODEV;
-	if (!dev)
-		goto err_exit;
-
-	if (dev->type == ARPHRD_SIT) {
-		const struct net_device_ops *ops = dev->netdev_ops;
-		struct ifreq ifr;
-		struct ip_tunnel_parm p;
-
-		err = -EADDRNOTAVAIL;
-		if (!(ipv6_addr_type(&ireq.ifr6_addr) & IPV6_ADDR_COMPATv4))
-			goto err_exit;
-
-		memset(&p, 0, sizeof(p));
-		p.iph.daddr = ireq.ifr6_addr.s6_addr32[3];
-		p.iph.saddr = 0;
-		p.iph.version = 4;
-		p.iph.ihl = 5;
-		p.iph.protocol = IPPROTO_IPV6;
-		p.iph.ttl = 64;
-		ifr.ifr_ifru.ifru_data = (__force void __user *)&p;
-
-		if (ops->ndo_do_ioctl) {
-			mm_segment_t oldfs = get_fs();
-
-			set_fs(KERNEL_DS);
-			err = ops->ndo_do_ioctl(dev, &ifr, SIOCADDTUNNEL);
-			set_fs(oldfs);
-		} else
-			err = -EOPNOTSUPP;
-
-		if (err == 0) {
-			err = -ENOBUFS;
-			dev = __dev_get_by_name(net, p.name);
-			if (!dev)
-				goto err_exit;
-			err = dev_open(dev, NULL);
-		}
-	}
-
-err_exit:
+	if (dev && dev->type == ARPHRD_SIT)
+		err = addrconf_set_sit_dstaddr(net, dev, &ireq);
 	rtnl_unlock();
 	return err;
 }