Commit message: ipv6: don't set DST_NOCOUNT for remotely added routes

DST_NOCOUNT should only be used if an authorized user adds routes
locally. In case of routes which are added on behalf of router
advertisments this flag must not get used as it allows an unlimited
number of routes getting added remotely.

Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2014-2309
CWE: CWE-119
Vulnerability description: The ip6_route_add function in net/ipv6/route.c in the Linux kernel through 3.13.6 does not properly count the addition of routes, which allows remote attackers to cause a denial of service (memory consumption) via a flood of ICMPv6 Router Advertisement packets.

Project: net
File: route.c

int ip6_route_add(struct fib6_config *cfg)
{
	int err;
	struct net *net = cfg->fc_nlinfo.nl_net;
	struct rt6_info *rt = NULL;
	struct net_device *dev = NULL;
	struct inet6_dev *idev = NULL;
	struct fib6_table *table;
	int addr_type;

	if (cfg->fc_dst_len > 128 || cfg->fc_src_len > 128)
		return -EINVAL;
#ifndef CONFIG_IPV6_SUBTREES
	if (cfg->fc_src_len)
		return -EINVAL;
#endif
	if (cfg->fc_ifindex) {
		err = -ENODEV;
		dev = dev_get_by_index(net, cfg->fc_ifindex);
		if (!dev)
			goto out;
		idev = in6_dev_get(dev);
		if (!idev)
			goto out;
	}

	if (cfg->fc_metric == 0)
		cfg->fc_metric = IP6_RT_PRIO_USER;

	err = -ENOBUFS;
	if (cfg->fc_nlinfo.nlh &&
	    !(cfg->fc_nlinfo.nlh->nlmsg_flags & NLM_F_CREATE)) {
		table = fib6_get_table(net, cfg->fc_table);
		if (!table) {
			pr_warn("NLM_F_CREATE should be specified when creating new route\n");
			table = fib6_new_table(net, cfg->fc_table);
		}
	} else {
		table = fib6_new_table(net, cfg->fc_table);
	}

	if (!table)
		goto out;

	rt = ip6_dst_alloc(net, NULL, DST_NOCOUNT, table);

	if (!rt) {
		err = -ENOMEM;
		goto out;
	}

	if (cfg->fc_flags & RTF_EXPIRES)
		rt6_set_expires(rt, jiffies +
				clock_t_to_jiffies(cfg->fc_expires));
	else
		rt6_clean_expires(rt);

	if (cfg->fc_protocol == RTPROT_UNSPEC)
		cfg->fc_protocol = RTPROT_BOOT;
	rt->rt6i_protocol = cfg->fc_protocol;

	addr_type = ipv6_addr_type(&cfg->fc_dst);

	if (addr_type & IPV6_ADDR_MULTICAST)
		rt->dst.input = ip6_mc_input;
	else if (cfg->fc_flags & RTF_LOCAL)
		rt->dst.input = ip6_input;
	else
		rt->dst.input = ip6_forward;

	rt->dst.output = ip6_output;

	ipv6_addr_prefix(&rt->rt6i_dst.addr, &cfg->fc_dst, cfg->fc_dst_len);
	rt->rt6i_dst.plen = cfg->fc_dst_len;
	if (rt->rt6i_dst.plen == 128)
	       rt->dst.flags |= DST_HOST;

	if (!(rt->dst.flags & DST_HOST) && cfg->fc_mx) {
		u32 *metrics = kzalloc(sizeof(u32) * RTAX_MAX, GFP_KERNEL);
		if (!metrics) {
			err = -ENOMEM;
			goto out;
		}
		dst_init_metrics(&rt->dst, metrics, 0);
	}
#ifdef CONFIG_IPV6_SUBTREES
	ipv6_addr_prefix(&rt->rt6i_src.addr, &cfg->fc_src, cfg->fc_src_len);
	rt->rt6i_src.plen = cfg->fc_src_len;
#endif

	rt->rt6i_metric = cfg->fc_metric;

	/* We cannot add true routes via loopback here,
	   they would result in kernel looping; promote them to reject routes
	 */
	if ((cfg->fc_flags & RTF_REJECT) ||
	    (dev && (dev->flags & IFF_LOOPBACK) &&
	     !(addr_type & IPV6_ADDR_LOOPBACK) &&
	     !(cfg->fc_flags & RTF_LOCAL))) {
		/* hold loopback dev/idev if we haven't done so. */
		if (dev != net->loopback_dev) {
			if (dev) {
				dev_put(dev);
				in6_dev_put(idev);
			}
			dev = net->loopback_dev;
			dev_hold(dev);
			idev = in6_dev_get(dev);
			if (!idev) {
				err = -ENODEV;
				goto out;
			}
		}
		rt->rt6i_flags = RTF_REJECT|RTF_NONEXTHOP;
		switch (cfg->fc_type) {
		case RTN_BLACKHOLE:
			rt->dst.error = -EINVAL;
			rt->dst.output = dst_discard;
			rt->dst.input = dst_discard;
			break;
		case RTN_PROHIBIT:
			rt->dst.error = -EACCES;
			rt->dst.output = ip6_pkt_prohibit_out;
			rt->dst.input = ip6_pkt_prohibit;
			break;
		case RTN_THROW:
		default:
			rt->dst.error = (cfg->fc_type == RTN_THROW) ? -EAGAIN
					: -ENETUNREACH;
			rt->dst.output = ip6_pkt_discard_out;
			rt->dst.input = ip6_pkt_discard;
			break;
		}
		goto install_route;
	}

	if (cfg->fc_flags & RTF_GATEWAY) {
		const struct in6_addr *gw_addr;
		int gwa_type;

		gw_addr = &cfg->fc_gateway;
		rt->rt6i_gateway = *gw_addr;
		gwa_type = ipv6_addr_type(gw_addr);

		if (gwa_type != (IPV6_ADDR_LINKLOCAL|IPV6_ADDR_UNICAST)) {
			struct rt6_info *grt;

			/* 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
			 */
			err = -EINVAL;
			if (!(gwa_type & IPV6_ADDR_UNICAST))
				goto out;

			grt = rt6_lookup(net, gw_addr, NULL, cfg->fc_ifindex, 1);

			err = -EHOSTUNREACH;
			if (!grt)
				goto out;
			if (dev) {
				if (dev != grt->dst.dev) {
					ip6_rt_put(grt);
					goto out;
				}
			} else {
				dev = grt->dst.dev;
				idev = grt->rt6i_idev;
				dev_hold(dev);
				in6_dev_hold(grt->rt6i_idev);
			}
			if (!(grt->rt6i_flags & RTF_GATEWAY))
				err = 0;
			ip6_rt_put(grt);

			if (err)
				goto out;
		}
		err = -EINVAL;
		if (!dev || (dev->flags & IFF_LOOPBACK))
			goto out;
	}

	err = -ENODEV;
	if (!dev)
		goto out;

	if (!ipv6_addr_any(&cfg->fc_prefsrc)) {
		if (!ipv6_chk_addr(net, &cfg->fc_prefsrc, dev, 0)) {
			err = -EINVAL;
			goto out;
		}
		rt->rt6i_prefsrc.addr = cfg->fc_prefsrc;
		rt->rt6i_prefsrc.plen = 128;
	} else
		rt->rt6i_prefsrc.plen = 0;

	rt->rt6i_flags = cfg->fc_flags;

install_route:
	if (cfg->fc_mx) {
		struct nlattr *nla;
		int remaining;

		nla_for_each_attr(nla, cfg->fc_mx, cfg->fc_mx_len, remaining) {
			int type = nla_type(nla);

			if (type) {
				if (type > RTAX_MAX) {
					err = -EINVAL;
					goto out;
				}

				dst_metric_set(&rt->dst, type, nla_get_u32(nla));
			}
		}
	}

	rt->dst.dev = dev;
	rt->rt6i_idev = idev;
	rt->rt6i_table = table;

	cfg->fc_nlinfo.nl_net = dev_net(dev);

	return __ip6_ins_rt(rt, &cfg->fc_nlinfo);

out:
	if (dev)
		dev_put(dev);
	if (idev)
		in6_dev_put(idev);
	if (rt)
		dst_free(&rt->dst);
	return err;
}