ipv4: Check return of dev_set_allmulti

allmulti might overflow.
Commit: "netdevice: Fix promiscuity and allmulti overflow" in net-next makes
dev_set_promiscuity/allmulti return error number if overflow happened.

Here, we check the positive increment for allmulti to get error return.

PS: For unwinding tunnel creating, we let ipip->ioctl() to handle it.
Signed-off-by: Wang Chen <wangchen@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ipmr.c

@@ -118,6 +118,31 @@ static struct timer_list ipmr_expire_timer;
 
 /* Service routines creating virtual interfaces: DVMRP tunnels and PIMREG */
 
+static void ipmr_del_tunnel(struct net_device *dev, struct vifctl *v)
+{
+	dev_close(dev);
+
+	dev = __dev_get_by_name(&init_net, "tunl0");
+	if (dev) {
+		struct ifreq ifr;
+		mm_segment_t	oldfs;
+		struct ip_tunnel_parm p;
+
+		memset(&p, 0, sizeof(p));
+		p.iph.daddr = v->vifc_rmt_addr.s_addr;
+		p.iph.saddr = v->vifc_lcl_addr.s_addr;
+		p.iph.version = 4;
+		p.iph.ihl = 5;
+		p.iph.protocol = IPPROTO_IPIP;
+		sprintf(p.name, "dvmrp%d", v->vifc_vifi);
+		ifr.ifr_ifru.ifru_data = (__force void __user *)&p;
+
+		oldfs = get_fs(); set_fs(KERNEL_DS);
+		dev->do_ioctl(dev, &ifr, SIOCDELTUNNEL);
+		set_fs(oldfs);
+	}
+}
+
 static
 struct net_device *ipmr_new_tunnel(struct vifctl *v)
 {
@@ -389,6 +414,7 @@ static int vif_add(struct vifctl *vifc, int mrtsock)
 	struct vif_device *v = &vif_table[vifi];
 	struct net_device *dev;
 	struct in_device *in_dev;
+	int err;
 
 	/* Is vif busy ? */
 	if (VIF_EXISTS(vifi))
@@ -406,18 +432,31 @@ static int vif_add(struct vifctl *vifc, int mrtsock)
 		dev = ipmr_reg_vif();
 		if (!dev)
 			return -ENOBUFS;
+		err = dev_set_allmulti(dev, 1);
+		if (err) {
+			unregister_netdevice(dev);
+			return err;
+		}
 		break;
 #endif
 	case VIFF_TUNNEL:
 		dev = ipmr_new_tunnel(vifc);
 		if (!dev)
 			return -ENOBUFS;
+		err = dev_set_allmulti(dev, 1);
+		if (err) {
+			ipmr_del_tunnel(dev, vifc);
+			return err;
+		}
 		break;
 	case 0:
 		dev = ip_dev_find(&init_net, vifc->vifc_lcl_addr.s_addr);
 		if (!dev)
 			return -EADDRNOTAVAIL;
 		dev_put(dev);
+		err = dev_set_allmulti(dev, 1);
+		if (err)
+			return err;
 		break;
 	default:
 		return -EINVAL;
@@ -426,7 +465,6 @@ static int vif_add(struct vifctl *vifc, int mrtsock)
 	if ((in_dev = __in_dev_get_rtnl(dev)) == NULL)
 		return -EADDRNOTAVAIL;
 	IPV4_DEVCONF(in_dev->cnf, MC_FORWARDING)++;
-	dev_set_allmulti(dev, +1);
 	ip_rt_multicast_event(in_dev);
 
 	/*