Commit message: ipv6: do not free rt if FIB_LOOKUP_NOREF is set on suppress rule

Commit 7d9e5f422150 removed references from certain dsts, but accounting
for this never translated down into the fib6 suppression code. This bug
was triggered by WireGuard users who use wg-quick(8), which uses the
"suppress-prefix" directive to ip-rule(8) for routing all of their
internet traffic without routing loops. The test case added here
causes the reference underflow by causing packets to evaluate a suppress
rule.

Fixes: 7d9e5f422150 ("ipv6: convert major tx path to use RT6_LOOKUP_F_DST_NOREF")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Acked-by: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2021-3892
CWE: CWE-401
Vulnerability description: Rejected reason: DO NOT USE THIS CANDIDATE NUMBER. ConsultIDs: CVE-2019-18198. Reason: This candidate is a reservation duplicate of CVE-2019-18198. Notes: All CVE users should reference CVE-2019-18198 instead of this candidate. All references and descriptions in this candidate have been removed to prevent accidental usage

Project: linux
File: fib6_rules.c

bool fib6_rule_default(const struct fib_rule *rule)
{
	if (!fib6_rule_matchall(rule) || rule->action != FR_ACT_TO_TBL ||
	    rule->l3mdev)
		return false;
	if (rule->table != RT6_TABLE_LOCAL && rule->table != RT6_TABLE_MAIN)
		return false;
	return true;
}

Project: linux
File: fib6_rules.c

static int fib6_rule_saddr(struct net *net, struct fib_rule *rule, int flags,
			   struct flowi6 *flp6, const struct net_device *dev)
{
	struct fib6_rule *r = (struct fib6_rule *)rule;

	/* If we need to find a source address for this traffic,
	 * we check the result if it meets requirement of the rule.
	 */
	if ((rule->flags & FIB_RULE_FIND_SADDR) &&
	    r->src.plen && !(flags & RT6_LOOKUP_F_HAS_SADDR)) {
		struct in6_addr saddr;

		if (ipv6_dev_get_saddr(net, dev, &flp6->daddr,
				       rt6_flags2srcprefs(flags), &saddr))
			return -EAGAIN;

		if (!ipv6_prefix_equal(&saddr, &r->src.addr, r->src.plen))
			return -EAGAIN;

		flp6->saddr = saddr;
	}

	return 0;
}

Project: linux
File: fib6_rules.c

static int __fib6_rule_action(struct fib_rule *rule, struct flowi *flp,
			      int flags, struct fib_lookup_arg *arg)
{
	struct fib6_result *res = arg->result;
	struct flowi6 *flp6 = &flp->u.ip6;
	struct rt6_info *rt = NULL;
	struct fib6_table *table;
	struct net *net = rule->fr_net;
	pol_lookup_t lookup = arg->lookup_ptr;
	int err = 0;
	u32 tb_id;

	switch (rule->action) {
	case FR_ACT_TO_TBL:
		break;
	case FR_ACT_UNREACHABLE:
		err = -ENETUNREACH;
		rt = net->ipv6.ip6_null_entry;
		goto discard_pkt;
	default:
	case FR_ACT_BLACKHOLE:
		err = -EINVAL;
		rt = net->ipv6.ip6_blk_hole_entry;
		goto discard_pkt;
	case FR_ACT_PROHIBIT:
		err = -EACCES;
		rt = net->ipv6.ip6_prohibit_entry;
		goto discard_pkt;
	}

	tb_id = fib_rule_get_table(rule, arg);
	table = fib6_get_table(net, tb_id);
	if (!table) {
		err = -EAGAIN;
		goto out;
	}

	rt = lookup(net, table, flp6, arg->lookup_data, flags);
	if (rt != net->ipv6.ip6_null_entry) {
		err = fib6_rule_saddr(net, rule, flags, flp6,
				      ip6_dst_idev(&rt->dst)->dev);

		if (err == -EAGAIN)
			goto again;

		err = rt->dst.error;
		if (err != -EAGAIN)
			goto out;
	}
again:
	ip6_rt_put_flags(rt, flags);
	err = -EAGAIN;
	rt = NULL;
	goto out;

discard_pkt:
	if (!(flags & RT6_LOOKUP_F_DST_NOREF))
		dst_hold(&rt->dst);
out:
	res->rt6 = rt;
	return err;
}

Project: linux
File: fib6_rules.c

static int fib6_rule_delete(struct fib_rule *rule)
{
	struct net *net = rule->fr_net;

	if (net->ipv6.fib6_rules_require_fldissect &&
	    fib_rule_requires_fldissect(rule))
		net->ipv6.fib6_rules_require_fldissect--;

	return 0;
}

Project: linux
File: fib6_rules.c

static int fib6_rule_compare(struct fib_rule *rule, struct fib_rule_hdr *frh,
			     struct nlattr **tb)
{
	struct fib6_rule *rule6 = (struct fib6_rule *) rule;

	if (frh->src_len && (rule6->src.plen != frh->src_len))
		return 0;

	if (frh->dst_len && (rule6->dst.plen != frh->dst_len))
		return 0;

	if (frh->tos && (rule6->tclass != frh->tos))
		return 0;

	if (frh->src_len &&
	    nla_memcmp(tb[FRA_SRC], &rule6->src.addr, sizeof(struct in6_addr)))
		return 0;

	if (frh->dst_len &&
	    nla_memcmp(tb[FRA_DST], &rule6->dst.addr, sizeof(struct in6_addr)))
		return 0;

	return 1;
}

Project: linux
File: fib6_rules.c

static int fib6_rule_fill(struct fib_rule *rule, struct sk_buff *skb,
			  struct fib_rule_hdr *frh)
{
	struct fib6_rule *rule6 = (struct fib6_rule *) rule;

	frh->dst_len = rule6->dst.plen;
	frh->src_len = rule6->src.plen;
	frh->tos = rule6->tclass;

	if ((rule6->dst.plen &&
	     nla_put_in6_addr(skb, FRA_DST, &rule6->dst.addr)) ||
	    (rule6->src.plen &&
	     nla_put_in6_addr(skb, FRA_SRC, &rule6->src.addr)))
		goto nla_put_failure;
	return 0;

nla_put_failure:
	return -ENOBUFS;
}

Project: linux
File: fib6_rules.c

static int __net_init fib6_rules_net_init(struct net *net)
{
	struct fib_rules_ops *ops;
	int err = -ENOMEM;

	ops = fib_rules_register(&fib6_rules_ops_template, net);
	if (IS_ERR(ops))
		return PTR_ERR(ops);

	err = fib_default_rule_add(ops, 0, RT6_TABLE_LOCAL, 0);
	if (err)
		goto out_fib6_rules_ops;

	err = fib_default_rule_add(ops, 0x7FFE, RT6_TABLE_MAIN, 0);
	if (err)
		goto out_fib6_rules_ops;

	net->ipv6.fib6_rules_ops = ops;
	net->ipv6.fib6_rules_require_fldissect = 0;
out:
	return err;

out_fib6_rules_ops:
	fib_rules_unregister(ops);
	goto out;
}

Project: linux
File: fib6_rules.c

static bool fib6_rule_matchall(const struct fib_rule *rule)
{
	struct fib6_rule *r = container_of(rule, struct fib6_rule, common);

	if (r->dst.plen || r->src.plen || r->tclass)
		return false;
	return fib_rule_matchall(rule);
}

Project: linux
File: fib6_rules.c

static int fib6_rule_match(struct fib_rule *rule, struct flowi *fl, int flags)
{
	struct fib6_rule *r = (struct fib6_rule *) rule;
	struct flowi6 *fl6 = &fl->u.ip6;

	if (r->dst.plen &&
	    !ipv6_prefix_equal(&fl6->daddr, &r->dst.addr, r->dst.plen))
		return 0;

	/*
	 * If FIB_RULE_FIND_SADDR is set and we do not have a
	 * source address for the traffic, we defer check for
	 * source address.
	 */
	if (r->src.plen) {
		if (flags & RT6_LOOKUP_F_HAS_SADDR) {
			if (!ipv6_prefix_equal(&fl6->saddr, &r->src.addr,
					       r->src.plen))
				return 0;
		} else if (!(r->common.flags & FIB_RULE_FIND_SADDR))
			return 0;
	}

	if (r->tclass && r->tclass != ip6_tclass(fl6->flowlabel))
		return 0;

	if (rule->ip_proto && (rule->ip_proto != fl6->flowi6_proto))
		return 0;

	if (fib_rule_port_range_set(&rule->sport_range) &&
	    !fib_rule_port_inrange(&rule->sport_range, fl6->fl6_sport))
		return 0;

	if (fib_rule_port_range_set(&rule->dport_range) &&
	    !fib_rule_port_inrange(&rule->dport_range, fl6->fl6_dport))
		return 0;

	return 1;
}

Project: linux
File: fib6_rules.c

int __init fib6_rules_init(void)
{
	return register_pernet_subsys(&fib6_rules_net_ops);
}

Project: linux
File: fib6_rules.c

int fib6_rules_dump(struct net *net, struct notifier_block *nb)
{
	return fib_rules_dump(net, nb, AF_INET6);
}

Project: linux
File: fib6_rules.c

static bool fib6_rule_suppress(struct fib_rule *rule, struct fib_lookup_arg *arg)
{
	struct fib6_result *res = arg->result;
	struct rt6_info *rt = res->rt6;
	struct net_device *dev = NULL;

	if (!rt)
		return false;

	if (rt->rt6i_idev)
		dev = rt->rt6i_idev->dev;

	/* do not accept result if the route does
	 * not meet the required prefix length
	 */
	if (rt->rt6i_dst.plen <= rule->suppress_prefixlen)
		goto suppress_route;

	/* do not accept result if the route uses a device
	 * belonging to a forbidden interface group
	 */
	if (rule->suppress_ifgroup != -1 && dev && dev->group == rule->suppress_ifgroup)
		goto suppress_route;

	return false;

suppress_route:
	if (!(arg->flags & FIB_LOOKUP_NOREF))
		ip6_rt_put(rt);
	return true;
}

Project: linux
File: fib6_rules.c

static size_t fib6_rule_nlmsg_payload(struct fib_rule *rule)
{
	return nla_total_size(16) /* dst */
	       + nla_total_size(16); /* src */
}

Project: linux
File: fib6_rules.c

static int fib6_rule_action_alt(struct fib_rule *rule, struct flowi *flp,
				int flags, struct fib_lookup_arg *arg)
{
	struct fib6_result *res = arg->result;
	struct flowi6 *flp6 = &flp->u.ip6;
	struct net *net = rule->fr_net;
	struct fib6_table *table;
	int err, *oif;
	u32 tb_id;

	switch (rule->action) {
	case FR_ACT_TO_TBL:
		break;
	case FR_ACT_UNREACHABLE:
		return -ENETUNREACH;
	case FR_ACT_PROHIBIT:
		return -EACCES;
	case FR_ACT_BLACKHOLE:
	default:
		return -EINVAL;
	}

	tb_id = fib_rule_get_table(rule, arg);
	table = fib6_get_table(net, tb_id);
	if (!table)
		return -EAGAIN;

	oif = (int *)arg->lookup_data;
	err = fib6_table_lookup(net, table, *oif, flp6, res, flags);
	if (!err && res->f6i != net->ipv6.fib6_null_entry)
		err = fib6_rule_saddr(net, rule, flags, flp6,
				      res->nh->fib_nh_dev);
	else
		err = -EAGAIN;

	return err;
}

Project: linux
File: fib6_rules.c

void fib6_rules_cleanup(void)
{
	unregister_pernet_subsys(&fib6_rules_net_ops);
}

Project: linux
File: fib6_rules.c

int fib6_lookup(struct net *net, int oif, struct flowi6 *fl6,
		struct fib6_result *res, int flags)
{
	int err;

	if (net->ipv6.fib6_has_custom_rules) {
		struct fib_lookup_arg arg = {
			.lookup_ptr = fib6_table_lookup,
			.lookup_data = &oif,
			.result = res,
			.flags = FIB_LOOKUP_NOREF,
		};

		l3mdev_update_flow(net, flowi6_to_flowi(fl6));

		err = fib_rules_lookup(net->ipv6.fib6_rules_ops,
				       flowi6_to_flowi(fl6), flags, &arg);
	} else {
		err = fib6_table_lookup(net, net->ipv6.fib6_local_tbl, oif,
					fl6, res, flags);
		if (err || res->f6i == net->ipv6.fib6_null_entry)
			err = fib6_table_lookup(net, net->ipv6.fib6_main_tbl,
						oif, fl6, res, flags);
	}

	return err;
}

Project: linux
File: fib6_rules.c

struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
				   const struct sk_buff *skb,
				   int flags, pol_lookup_t lookup)
{
	if (net->ipv6.fib6_has_custom_rules) {
		struct fib6_result res = {};
		struct fib_lookup_arg arg = {
			.lookup_ptr = lookup,
			.lookup_data = skb,
			.result = &res,
			.flags = FIB_LOOKUP_NOREF,
		};

		/* update flow if oif or iif point to device enslaved to l3mdev */
		l3mdev_update_flow(net, flowi6_to_flowi(fl6));

		fib_rules_lookup(net->ipv6.fib6_rules_ops,
				 flowi6_to_flowi(fl6), flags, &arg);

		if (res.rt6)
			return &res.rt6->dst;
	} else {
		struct rt6_info *rt;

		rt = lookup(net, net->ipv6.fib6_local_tbl, fl6, skb, flags);
		if (rt != net->ipv6.ip6_null_entry && rt->dst.error != -EAGAIN)
			return &rt->dst;
		ip6_rt_put_flags(rt, flags);
		rt = lookup(net, net->ipv6.fib6_main_tbl, fl6, skb, flags);
		if (rt->dst.error != -EAGAIN)
			return &rt->dst;
		ip6_rt_put_flags(rt, flags);
	}

	if (!(flags & RT6_LOOKUP_F_DST_NOREF))
		dst_hold(&net->ipv6.ip6_null_entry->dst);
	return &net->ipv6.ip6_null_entry->dst;
}

Project: linux
File: fib6_rules.c

static int fib6_rule_configure(struct fib_rule *rule, struct sk_buff *skb,
			       struct fib_rule_hdr *frh,
			       struct nlattr **tb,
			       struct netlink_ext_ack *extack)
{
	int err = -EINVAL;
	struct net *net = sock_net(skb->sk);
	struct fib6_rule *rule6 = (struct fib6_rule *) rule;

	if (rule->action == FR_ACT_TO_TBL && !rule->l3mdev) {
		if (rule->table == RT6_TABLE_UNSPEC) {
			NL_SET_ERR_MSG(extack, "Invalid table");
			goto errout;
		}

		if (fib6_new_table(net, rule->table) == NULL) {
			err = -ENOBUFS;
			goto errout;
		}
	}

	if (frh->src_len)
		rule6->src.addr = nla_get_in6_addr(tb[FRA_SRC]);

	if (frh->dst_len)
		rule6->dst.addr = nla_get_in6_addr(tb[FRA_DST]);

	rule6->src.plen = frh->src_len;
	rule6->dst.plen = frh->dst_len;
	rule6->tclass = frh->tos;

	if (fib_rule_requires_fldissect(rule))
		net->ipv6.fib6_rules_require_fldissect++;

	net->ipv6.fib6_has_custom_rules = true;
	err = 0;
errout:
	return err;
}

Project: linux
File: fib6_rules.c

unsigned int fib6_rules_seq_read(struct net *net)
{
	return fib_rules_seq_read(net, AF_INET6);
}

Project: linux
File: fib6_rules.c

static int fib6_rule_action(struct fib_rule *rule, struct flowi *flp,
			    int flags, struct fib_lookup_arg *arg)
{
	if (arg->lookup_ptr == fib6_table_lookup)
		return fib6_rule_action_alt(rule, flp, flags, arg);

	return __fib6_rule_action(rule, flp, flags, arg);
}

Project: linux
File: fib6_rules.c

static void __net_exit fib6_rules_net_exit(struct net *net)
{
	rtnl_lock();
	fib_rules_unregister(net->ipv6.fib6_rules_ops);
	rtnl_unlock();
}