Commit message: netfilter: add back stackpointer size checks

The rationale for removing the check is only correct for rulesets
generated by ip(6)tables.

In iptables, a jump can only occur to a user-defined chain, i.e.
because we size the stack based on number of user-defined chains we
cannot exceed stack size.

However, the underlying binary format has no such restriction,
and the validation step only ensures that the jump target is a
valid rule start point.

IOW, its possible to build a rule blob that has no user-defined
chains but does contain a jump.

If this happens, no jump stack gets allocated and crash occurs
because no jumpstack was allocated.

Fixes: 7814b6ec6d0d6 ("netfilter: xtables: don't save/restore jumpstack offset")
Reported-by: syzbot+e783f671527912cd9403@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
CVE: CVE-2018-1065
CWE: CWE-476
Vulnerability description: The netfilter subsystem in the Linux kernel through 4.15.7 mishandles the case of a rule blob that contains a jump but lacks a user-defined chain, which allows local users to cause a denial of service (NULL pointer dereference) by leveraging the CAP_NET_RAW or CAP_NET_ADMIN capability, related to arpt_do_table in net/ipv4/netfilter/arp_tables.c, ipt_do_table in net/ipv4/netfilter/ip_tables.c, and ip6t_do_table in net/ipv6/netfilter/ip6_tables.c.

Project: linux

static inline int arp_packet_match(const struct arphdr *arphdr,
				   struct net_device *dev,
				   const char *indev,
				   const char *outdev,
				   const struct arpt_arp *arpinfo)
{
	const char *arpptr = (char *)(arphdr + 1);
	const char *src_devaddr, *tgt_devaddr;
	__be32 src_ipaddr, tgt_ipaddr;
	long ret;

	if (NF_INVF(arpinfo, ARPT_INV_ARPOP,
		    (arphdr->ar_op & arpinfo->arpop_mask) != arpinfo->arpop))
		return 0;

	if (NF_INVF(arpinfo, ARPT_INV_ARPHRD,
		    (arphdr->ar_hrd & arpinfo->arhrd_mask) != arpinfo->arhrd))
		return 0;

	if (NF_INVF(arpinfo, ARPT_INV_ARPPRO,
		    (arphdr->ar_pro & arpinfo->arpro_mask) != arpinfo->arpro))
		return 0;

	if (NF_INVF(arpinfo, ARPT_INV_ARPHLN,
		    (arphdr->ar_hln & arpinfo->arhln_mask) != arpinfo->arhln))
		return 0;

	src_devaddr = arpptr;
	arpptr += dev->addr_len;
	memcpy(&src_ipaddr, arpptr, sizeof(u32));
	arpptr += sizeof(u32);
	tgt_devaddr = arpptr;
	arpptr += dev->addr_len;
	memcpy(&tgt_ipaddr, arpptr, sizeof(u32));

	if (NF_INVF(arpinfo, ARPT_INV_SRCDEVADDR,
		    arp_devaddr_compare(&arpinfo->src_devaddr, src_devaddr,
					dev->addr_len)) ||
	    NF_INVF(arpinfo, ARPT_INV_TGTDEVADDR,
		    arp_devaddr_compare(&arpinfo->tgt_devaddr, tgt_devaddr,
					dev->addr_len)))
		return 0;

	if (NF_INVF(arpinfo, ARPT_INV_SRCIP,
		    (src_ipaddr & arpinfo->smsk.s_addr) != arpinfo->src.s_addr) ||
	    NF_INVF(arpinfo, ARPT_INV_TGTIP,
		    (tgt_ipaddr & arpinfo->tmsk.s_addr) != arpinfo->tgt.s_addr))
		return 0;

	/* Look for ifname matches.  */
	ret = ifname_compare(indev, arpinfo->iniface, arpinfo->iniface_mask);

	if (NF_INVF(arpinfo, ARPT_INV_VIA_IN, ret != 0))
		return 0;

	ret = ifname_compare(outdev, arpinfo->outiface, arpinfo->outiface_mask);

	if (NF_INVF(arpinfo, ARPT_INV_VIA_OUT, ret != 0))
		return 0;

	return 1;
}

Project: linux

static inline int check_target(struct arpt_entry *e, const char *name)
{
	struct xt_entry_target *t = arpt_get_target(e);
	struct xt_tgchk_param par = {
		.table     = name,
		.entryinfo = e,
		.target    = t->u.kernel.target,
		.targinfo  = t->data,
		.hook_mask = e->comefrom,
		.family    = NFPROTO_ARP,
	};

	return xt_check_target(&par, t->u.target_size - sizeof(*t), 0, false);
}

Project: linux

static inline void cleanup_entry(struct arpt_entry *e)
{
	struct xt_tgdtor_param par;
	struct xt_entry_target *t;

	t = arpt_get_target(e);
	par.target   = t->u.kernel.target;
	par.targinfo = t->data;
	par.family   = NFPROTO_ARP;
	if (par.target->destroy != NULL)
		par.target->destroy(&par);
	module_put(par.target->me);
	xt_percpu_counter_free(&e->counters);
}

Project: linux

static int do_arpt_get_ctl(struct sock *sk, int cmd, void __user *user, int *len)
{
	int ret;

	if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
		return -EPERM;

	switch (cmd) {
	case ARPT_SO_GET_INFO:
		ret = get_info(sock_net(sk), user, len, 0);
		break;

	case ARPT_SO_GET_ENTRIES:
		ret = get_entries(sock_net(sk), user, len);
		break;

	case ARPT_SO_GET_REVISION_TARGET: {
		struct xt_get_revision rev;

		if (*len != sizeof(rev)) {
			ret = -EINVAL;
			break;
		}
		if (copy_from_user(&rev, user, sizeof(rev)) != 0) {
			ret = -EFAULT;
			break;
		}
		rev.name[sizeof(rev.name)-1] = 0;

		try_then_request_module(xt_find_revision(NFPROTO_ARP, rev.name,
							 rev.revision, 1, &ret),
					"arpt_%s", rev.name);
		break;
	}

	default:
		ret = -EINVAL;
	}

	return ret;
}

Project: linux

__do_replace(struct net *net, const char *name, unsigned int valid_hooks,
	     struct xt_table_info *newinfo, unsigned int num_counters,
	     void __user *counters_ptr)
{
	int ret;
	struct xt_table *t;
	struct xt_table_info *oldinfo;
	struct xt_counters *counters;
	struct ipt_entry *iter;

	ret = 0;
	counters = vzalloc(num_counters * sizeof(struct xt_counters));
	if (!counters) {
		ret = -ENOMEM;
		goto out;
	}

	t = xt_request_find_table_lock(net, AF_INET, name);
	if (IS_ERR(t)) {
		ret = PTR_ERR(t);
		goto free_newinfo_counters_untrans;
	}

	/* You lied! */
	if (valid_hooks != t->valid_hooks) {
		ret = -EINVAL;
		goto put_module;
	}

	oldinfo = xt_replace_table(t, num_counters, newinfo, &ret);
	if (!oldinfo)
		goto put_module;

	/* Update module usage count based on number of rules */
	if ((oldinfo->number > oldinfo->initial_entries) ||
	    (newinfo->number <= oldinfo->initial_entries))
		module_put(t->me);
	if ((oldinfo->number > oldinfo->initial_entries) &&
	    (newinfo->number <= oldinfo->initial_entries))
		module_put(t->me);

	get_old_counters(oldinfo, counters);

	/* Decrease module usage counts and free resource */
	xt_entry_foreach(iter, oldinfo->entries, oldinfo->size)
		cleanup_entry(iter, net);

	xt_free_table_info(oldinfo);
	if (copy_to_user(counters_ptr, counters,
			 sizeof(struct xt_counters) * num_counters) != 0) {
		/* Silent error, can't fail, new table is already in place */
		net_warn_ratelimited("iptables: counters copy to user failed while replacing table\n");
	}
	vfree(counters);
	xt_table_unlock(t);
	return ret;

 put_module:
	module_put(t->me);
	xt_table_unlock(t);
 free_newinfo_counters_untrans:
	vfree(counters);
 out:
	return ret;
}

Project: linux

copy_entries_to_user(unsigned int total_size,
		     const struct xt_table *table,
		     void __user *userptr)
{
	unsigned int off, num;
	const struct ipt_entry *e;
	struct xt_counters *counters;
	const struct xt_table_info *private = table->private;
	int ret = 0;
	const void *loc_cpu_entry;

	counters = alloc_counters(table);
	if (IS_ERR(counters))
		return PTR_ERR(counters);

	loc_cpu_entry = private->entries;

	/* FIXME: use iterator macros --RR */
	/* ... then go back and fix counters and names */
	for (off = 0, num = 0; off < total_size; off += e->next_offset, num++){
		unsigned int i;
		const struct xt_entry_match *m;
		const struct xt_entry_target *t;

		e = loc_cpu_entry + off;
		if (copy_to_user(userptr + off, e, sizeof(*e))) {
			ret = -EFAULT;
			goto free_counters;
		}
		if (copy_to_user(userptr + off
				 + offsetof(struct ipt_entry, counters),
				 &counters[num],
				 sizeof(counters[num])) != 0) {
			ret = -EFAULT;
			goto free_counters;
		}

		for (i = sizeof(struct ipt_entry);
		     i < e->target_offset;
		     i += m->u.match_size) {
			m = (void *)e + i;

			if (xt_match_to_user(m, userptr + off + i)) {
				ret = -EFAULT;
				goto free_counters;
			}
		}

		t = ipt_get_target_c(e);
		if (xt_target_to_user(t, userptr + off + e->target_offset)) {
			ret = -EFAULT;
			goto free_counters;
		}
	}

 free_counters:
	vfree(counters);
	return ret;
}

Project: linux

do_replace(struct net *net, const void __user *user, unsigned int len)
{
	int ret;
	struct ipt_replace tmp;
	struct xt_table_info *newinfo;
	void *loc_cpu_entry;
	struct ipt_entry *iter;

	if (copy_from_user(&tmp, user, sizeof(tmp)) != 0)
		return -EFAULT;

	/* overflow check */
	if (tmp.num_counters >= INT_MAX / sizeof(struct xt_counters))
		return -ENOMEM;
	if (tmp.num_counters == 0)
		return -EINVAL;

	tmp.name[sizeof(tmp.name)-1] = 0;

	newinfo = xt_alloc_table_info(tmp.size);
	if (!newinfo)
		return -ENOMEM;

	loc_cpu_entry = newinfo->entries;
	if (copy_from_user(loc_cpu_entry, user + sizeof(tmp),
			   tmp.size) != 0) {
		ret = -EFAULT;
		goto free_newinfo;
	}

	ret = translate_table(net, newinfo, loc_cpu_entry, &tmp);
	if (ret != 0)
		goto free_newinfo;

	ret = __do_replace(net, tmp.name, tmp.valid_hooks, newinfo,
			   tmp.num_counters, tmp.counters);
	if (ret)
		goto free_newinfo_untrans;
	return 0;

 free_newinfo_untrans:
	xt_entry_foreach(iter, loc_cpu_entry, newinfo->size)
		cleanup_entry(iter, net);
 free_newinfo:
	xt_free_table_info(newinfo);
	return ret;
}

Project: linux

static void cleanup_entry(struct ip6t_entry *e, struct net *net)
{
	struct xt_tgdtor_param par;
	struct xt_entry_target *t;
	struct xt_entry_match *ematch;

	/* Cleanup all matches */
	xt_ematch_foreach(ematch, e)
		cleanup_match(ematch, net);
	t = ip6t_get_target(e);

	par.net      = net;
	par.target   = t->u.kernel.target;
	par.targinfo = t->data;
	par.family   = NFPROTO_IPV6;
	if (par.target->destroy != NULL)
		par.target->destroy(&par);
	module_put(par.target->me);
	xt_percpu_counter_free(&e->counters);
}

Project: linux

translate_table(struct net *net, struct xt_table_info *newinfo, void *entry0,
		const struct ip6t_replace *repl)
{
	struct xt_percpu_counter_alloc_state alloc_state = { 0 };
	struct ip6t_entry *iter;
	unsigned int *offsets;
	unsigned int i;
	int ret = 0;

	newinfo->size = repl->size;
	newinfo->number = repl->num_entries;

	/* Init all hooks to impossible value. */
	for (i = 0; i < NF_INET_NUMHOOKS; i++) {
		newinfo->hook_entry[i] = 0xFFFFFFFF;
		newinfo->underflow[i] = 0xFFFFFFFF;
	}

	offsets = xt_alloc_entry_offsets(newinfo->number);
	if (!offsets)
		return -ENOMEM;
	i = 0;
	/* Walk through entries, checking offsets. */
	xt_entry_foreach(iter, entry0, newinfo->size) {
		ret = check_entry_size_and_hooks(iter, newinfo, entry0,
						 entry0 + repl->size,
						 repl->hook_entry,
						 repl->underflow,
						 repl->valid_hooks);
		if (ret != 0)
			goto out_free;
		if (i < repl->num_entries)
			offsets[i] = (void *)iter - entry0;
		++i;
		if (strcmp(ip6t_get_target(iter)->u.user.name,
		    XT_ERROR_TARGET) == 0)
			++newinfo->stacksize;
	}

	ret = -EINVAL;
	if (i != repl->num_entries)
		goto out_free;

	/* Check hooks all assigned */
	for (i = 0; i < NF_INET_NUMHOOKS; i++) {
		/* Only hooks which are valid */
		if (!(repl->valid_hooks & (1 << i)))
			continue;
		if (newinfo->hook_entry[i] == 0xFFFFFFFF)
			goto out_free;
		if (newinfo->underflow[i] == 0xFFFFFFFF)
			goto out_free;
	}

	if (!mark_source_chains(newinfo, repl->valid_hooks, entry0, offsets)) {
		ret = -ELOOP;
		goto out_free;
	}
	kvfree(offsets);

	/* Finally, each sanity check must pass */
	i = 0;
	xt_entry_foreach(iter, entry0, newinfo->size) {
		ret = find_check_entry(iter, net, repl->name, repl->size,
				       &alloc_state);
		if (ret != 0)
			break;
		++i;
	}

	if (ret != 0) {
		xt_entry_foreach(iter, entry0, newinfo->size) {
			if (i-- == 0)
				break;
			cleanup_entry(iter, net);
		}
		return ret;
	}

	return ret;
 out_free:
	kvfree(offsets);
	return ret;
}