Code: void fib_del_ifaddr(struct in_ifaddr *ifa, struct in_ifaddr *iprim)
{
	struct in_device *in_dev = ifa->ifa_dev;
	struct net_device *dev = in_dev->dev;
	struct in_ifaddr *ifa1;
	struct in_ifaddr *prim = ifa, *prim1 = NULL;
	__be32 brd = ifa->ifa_address | ~ifa->ifa_mask;
	__be32 any = ifa->ifa_address & ifa->ifa_mask;
#define LOCAL_OK	1
#define BRD_OK		2
#define BRD0_OK		4
#define BRD1_OK		8
	unsigned int ok = 0;
	int subnet = 0;		/* Primary network */
	int gone = 1;		/* Address is missing */
	int same_prefsrc = 0;	/* Another primary with same IP */

	if (ifa->ifa_flags & IFA_F_SECONDARY) {
		prim = inet_ifa_byprefix(in_dev, any, ifa->ifa_mask);
		if (!prim) {
			pr_warn("%s: bug: prim == NULL\n", __func__);
			return;
		}
		if (iprim && iprim != prim) {
			pr_warn("%s: bug: iprim != prim\n", __func__);
			return;
		}
	} else if (!ipv4_is_zeronet(any) &&
		   (any != ifa->ifa_local || ifa->ifa_prefixlen < 32)) {
		if (!(ifa->ifa_flags & IFA_F_NOPREFIXROUTE))
			fib_magic(RTM_DELROUTE,
				  dev->flags & IFF_LOOPBACK ? RTN_LOCAL : RTN_UNICAST,
				  any, ifa->ifa_prefixlen, prim);
 		subnet = 1;
 	}
 
 	/* Deletion is more complicated than add.
 	 * We should take care of not to delete too much :-)
 	 *
	 * Scan address list to be sure that addresses are really gone.
	 */

	for (ifa1 = in_dev->ifa_list; ifa1; ifa1 = ifa1->ifa_next) {
		if (ifa1 == ifa) {
			/* promotion, keep the IP */
			gone = 0;
			continue;
		}
		/* Ignore IFAs from our subnet */
		if (iprim && ifa1->ifa_mask == iprim->ifa_mask &&
		    inet_ifa_match(ifa1->ifa_address, iprim))
			continue;

		/* Ignore ifa1 if it uses different primary IP (prefsrc) */
		if (ifa1->ifa_flags & IFA_F_SECONDARY) {
			/* Another address from our subnet? */
			if (ifa1->ifa_mask == prim->ifa_mask &&
			    inet_ifa_match(ifa1->ifa_address, prim))
				prim1 = prim;
			else {
				/* We reached the secondaries, so
				 * same_prefsrc should be determined.
				 */
				if (!same_prefsrc)
					continue;
				/* Search new prim1 if ifa1 is not
				 * using the current prim1
				 */
				if (!prim1 ||
				    ifa1->ifa_mask != prim1->ifa_mask ||
				    !inet_ifa_match(ifa1->ifa_address, prim1))
					prim1 = inet_ifa_byprefix(in_dev,
							ifa1->ifa_address,
							ifa1->ifa_mask);
				if (!prim1)
					continue;
				if (prim1->ifa_local != prim->ifa_local)
					continue;
			}
		} else {
			if (prim->ifa_local != ifa1->ifa_local)
				continue;
			prim1 = ifa1;
			if (prim != prim1)
				same_prefsrc = 1;
		}
		if (ifa->ifa_local == ifa1->ifa_local)
			ok |= LOCAL_OK;
		if (ifa->ifa_broadcast == ifa1->ifa_broadcast)
			ok |= BRD_OK;
		if (brd == ifa1->ifa_broadcast)
			ok |= BRD1_OK;
		if (any == ifa1->ifa_broadcast)
			ok |= BRD0_OK;
		/* primary has network specific broadcasts */
		if (prim1 == ifa1 && ifa1->ifa_prefixlen < 31) {
			__be32 brd1 = ifa1->ifa_address | ~ifa1->ifa_mask;
			__be32 any1 = ifa1->ifa_address & ifa1->ifa_mask;

			if (!ipv4_is_zeronet(any1)) {
				if (ifa->ifa_broadcast == brd1 ||
				    ifa->ifa_broadcast == any1)
					ok |= BRD_OK;
				if (brd == brd1 || brd == any1)
					ok |= BRD1_OK;
				if (any == brd1 || any == any1)
					ok |= BRD0_OK;
			}
 		}
 	}
 
 	if (!(ok & BRD_OK))
 		fib_magic(RTM_DELROUTE, RTN_BROADCAST, ifa->ifa_broadcast, 32, prim);
 	if (subnet && ifa->ifa_prefixlen < 31) {
		if (!(ok & BRD1_OK))
			fib_magic(RTM_DELROUTE, RTN_BROADCAST, brd, 32, prim);
		if (!(ok & BRD0_OK))
			fib_magic(RTM_DELROUTE, RTN_BROADCAST, any, 32, prim);
	}
	if (!(ok & LOCAL_OK)) {
		unsigned int addr_type;

		fib_magic(RTM_DELROUTE, RTN_LOCAL, ifa->ifa_local, 32, prim);

		/* Check, that this local address finally disappeared. */
		addr_type = inet_addr_type_dev_table(dev_net(dev), dev,
						     ifa->ifa_local);
		if (gone && addr_type != RTN_LOCAL) {
			/* And the last, but not the least thing.
			 * We must flush stray FIB entries.
			 *
			 * First of all, we scan fib_info list searching
			 * for stray nexthop entries, then ignite fib_flush.
			 */
			if (fib_sync_down_addr(dev_net(dev), ifa->ifa_local))
				fib_flush(dev_net(dev));
		}
	}
#undef LOCAL_OK
#undef BRD_OK
#undef BRD0_OK
#undef BRD1_OK
}

Vulnerability Type: DoS 
CWE ID: CWE-399
Summary: The IPv4 implementation in the Linux kernel before 4.5.2 mishandles destruction of device objects, which allows guest OS users to cause a denial of service (host OS networking outage) by arranging for a large number of IP addresses.
Commit Message: ipv4: Don't do expensive useless work during inetdev destroy.

When an inetdev is destroyed, every address assigned to the interface
is removed.  And in this scenerio we do two pointless things which can
be very expensive if the number of assigned interfaces is large:

1) Address promotion.  We are deleting all addresses, so there is no
   point in doing this.

2) A full nf conntrack table purge for every address.  We only need to
   do this once, as is already caught by the existing
   masq_dev_notifier so masq_inet_event() can skip this.

Reported-by: Solar Designer <solar@openwall.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Tested-by: Cyrill Gorcunov <gorcunov@openvz.org>