xref: /linux/net/netfilter/nf_conntrack_helper.c (revision 91ec2035134982b98fab0609a9fd8480e8217dc1)

// SPDX-License-Identifier: GPL-2.0-only
/* Helper handling for netfilter. */

/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
 * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
 */

#include <linux/types.h>
#include <linux/netfilter.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/vmalloc.h>
#include <linux/stddef.h>
#include <linux/random.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/netdevice.h>
#include <linux/rculist.h>
#include <linux/rtnetlink.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_conntrack_ecache.h>
#include <net/netfilter/nf_conntrack_extend.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_l4proto.h>
#include <net/netfilter/nf_conntrack_seqadj.h>
#include <net/netfilter/nf_log.h>
#include <net/ip.h>

static DEFINE_MUTEX(nf_ct_helper_mutex);
struct hlist_head *nf_ct_helper_hash __read_mostly;
EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
unsigned int nf_ct_helper_hsize __read_mostly;
EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
static unsigned int nf_ct_helper_count __read_mostly;

static DEFINE_MUTEX(nf_ct_nat_helpers_mutex);
static struct list_head nf_ct_nat_helpers __read_mostly;

static unsigned int helper_hash(const char *name, u8 protonum)
{
	static u32 seed;
	u32 initval;

	get_random_once(&seed, sizeof(seed));

	initval = seed ^ protonum;

	return jhash(name, strlen(name), initval) % nf_ct_helper_hsize;
}

struct nf_conntrack_helper *
__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
{
	struct nf_conntrack_helper *h;
	unsigned int i;

	if (!nf_ct_helper_hash)
		return NULL;

	i = helper_hash(name, protonum);

	hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
		if (strcmp(h->name, name))
			continue;
		if (h->nfproto != NFPROTO_UNSPEC && h->nfproto != l3num)
			continue;
		if (h->l4proto == protonum)
			return h;
	}
	return NULL;
}
EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);

struct nf_conntrack_helper *
nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
{
	struct nf_conntrack_helper *h;

	rcu_read_lock();

	h = __nf_conntrack_helper_find(name, l3num, protonum);
#ifdef CONFIG_MODULES
	if (h == NULL) {
		rcu_read_unlock();
		if (request_module("nfct-helper-%s", name) == 0) {
			rcu_read_lock();
			h = __nf_conntrack_helper_find(name, l3num, protonum);
		} else {
			return h;
		}
	}
#endif
	if (h != NULL && !try_module_get(h->me))
		h = NULL;
	if (h != NULL && !refcount_inc_not_zero(&h->ct_refcnt)) {
		module_put(h->me);
		h = NULL;
	}

	rcu_read_unlock();

	return h;
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);

void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
{
	module_put(helper->me);
	if (refcount_dec_and_test(&helper->ct_refcnt))
		kfree_rcu(helper, rcu);
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);

static struct nf_conntrack_nat_helper *
nf_conntrack_nat_helper_find(const char *mod_name)
{
	struct nf_conntrack_nat_helper *cur;
	bool found = false;

	list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) {
		if (!strcmp(cur->mod_name, mod_name)) {
			found = true;
			break;
		}
	}
	return found ? cur : NULL;
}

int
nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
{
	struct nf_conntrack_helper *h;
	struct nf_conntrack_nat_helper *nat;
	char mod_name[NF_CT_HELPER_NAME_LEN];
	int ret = 0;

	rcu_read_lock();
	h = __nf_conntrack_helper_find(name, l3num, protonum);
	if (!h) {
		rcu_read_unlock();
		return -ENOENT;
	}

	nat = nf_conntrack_nat_helper_find(h->nat_mod_name);
	if (!nat) {
		snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name);
		rcu_read_unlock();
		request_module("%s", mod_name);

		rcu_read_lock();
		nat = nf_conntrack_nat_helper_find(mod_name);
		if (!nat) {
			rcu_read_unlock();
			return -ENOENT;
		}
	}

	if (!try_module_get(nat->module))
		ret = -ENOENT;

	rcu_read_unlock();
	return ret;
}
EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get);

void nf_nat_helper_put(struct nf_conntrack_helper *helper)
{
	struct nf_conntrack_nat_helper *nat;

	nat = nf_conntrack_nat_helper_find(helper->nat_mod_name);
	if (WARN_ON_ONCE(!nat))
		return;

	module_put(nat->module);
}
EXPORT_SYMBOL_GPL(nf_nat_helper_put);

struct nf_conn_help *
nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
{
	struct nf_conn_help *help;

	help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
	if (help) {
		__set_bit(IPS_HELPER_BIT, &ct->status);
		INIT_HLIST_HEAD(&help->expectations);
	}
	return help;
}
EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);

int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
			      gfp_t flags)
{
	struct nf_conntrack_helper *helper = NULL;
	struct nf_conn_help *help;

	/* We already got a helper explicitly attached (e.g. nft_ct) */
	if (test_bit(IPS_HELPER_BIT, &ct->status))
		return 0;

	if (WARN_ON_ONCE(!tmpl))
		return 0;

	help = nfct_help(tmpl);
	if (help)
		helper = rcu_dereference(help->helper);

	help = nfct_help(ct);

	if (helper == NULL) {
		if (help) {
			struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);

			RCU_INIT_POINTER(help->helper, NULL);
			if (tmp && refcount_dec_and_test(&tmp->ct_refcnt))
				kfree_rcu(tmp, rcu);
		}
		return 0;
	}

	if (help == NULL) {
		help = nf_ct_helper_ext_add(ct, flags);
		if (help == NULL)
			return -ENOMEM;
	} else {
		/* We only allow helper re-assignment of the same sort since
		 * we cannot reallocate the helper extension area.
		 */
		struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);

		if (tmp) {
			if (tmp->help != helper->help) {
				RCU_INIT_POINTER(help->helper, NULL);
				if (refcount_dec_and_test(&tmp->ct_refcnt))
					kfree_rcu(tmp, rcu);
			}
			return 0;
		}
	}

	if (refcount_inc_not_zero(&helper->ct_refcnt))
		rcu_assign_pointer(help->helper, helper);

	return 0;
}
EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);

void nf_ct_helper_destroy(struct nf_conn *ct)
{
	struct nf_conn_help *help = nfct_help(ct);
	struct nf_conntrack_helper *helper;

	if (help) {
		rcu_read_lock();
		helper = rcu_dereference(help->helper);
		if (helper && helper->destroy)
			helper->destroy(ct);
		rcu_read_unlock();
	}
}

static LIST_HEAD(nf_ct_helper_expectfn_list);

void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
{
	spin_lock_bh(&nf_conntrack_expect_lock);
	list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
	spin_unlock_bh(&nf_conntrack_expect_lock);
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);

void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
{
	spin_lock_bh(&nf_conntrack_expect_lock);
	list_del_rcu(&n->head);
	spin_unlock_bh(&nf_conntrack_expect_lock);
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);

static bool expect_iter_expectfn(struct nf_conntrack_expect *exp, void *data)
{
	const struct nf_ct_helper_expectfn *n = data;

	/* Relies on registered expectfn descriptors having unique ->expectfn
	 * pointers, which holds for the in-tree NAT helpers.
	 */
	return exp->expectfn == n->expectfn;
}

/* Destroy expectations still pointing at @n->expectfn; call after the
 * caller's RCU grace period so none outlives the (often modular) callback.
 */
void nf_ct_helper_expectfn_destroy(const struct nf_ct_helper_expectfn *n)
{
	nf_ct_expect_iterate_destroy(expect_iter_expectfn, (void *)n);
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_destroy);

/* Caller should hold the rcu lock */
struct nf_ct_helper_expectfn *
nf_ct_helper_expectfn_find_by_name(const char *name)
{
	struct nf_ct_helper_expectfn *cur;
	bool found = false;

	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
		if (!strcmp(cur->name, name)) {
			found = true;
			break;
		}
	}
	return found ? cur : NULL;
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);

/* Caller should hold the rcu lock */
struct nf_ct_helper_expectfn *
nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
{
	struct nf_ct_helper_expectfn *cur;
	bool found = false;

	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
		if (cur->expectfn == symbol) {
			found = true;
			break;
		}
	}
	return found ? cur : NULL;
}
EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);

__printf(3, 4)
void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
		      const char *fmt, ...)
{
	const char *helper_name = "(null)";
	const struct nf_conn_help *help;
	struct va_format vaf;
	va_list args;

	va_start(args, fmt);

	vaf.fmt = fmt;
	vaf.va = &args;

	help = nfct_help(ct);
	if (help) {
		const struct nf_conntrack_helper *helper;

		helper = rcu_dereference(help->helper);
		if (helper)
			helper_name = helper->name;
	}

	nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
		      "helper %s dropping packet: %pV ", helper_name, &vaf);

	va_end(args);
}
EXPORT_SYMBOL_GPL(nf_ct_helper_log);

int __nf_conntrack_helper_register(struct nf_conntrack_helper *me)
{
	struct nf_conntrack_helper *cur;
	unsigned int h;
	int ret = 0, i;

	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);

	if (!nf_ct_helper_hash)
		return -ENOENT;

	for (i = 0; i <= me->expect_class_max; i++) {
		if (!me->expect_policy[i].max_expected)
			me->expect_policy[i].max_expected = NF_CT_EXPECT_MAX_CNT;

		if (me->expect_policy[i].max_expected > NF_CT_EXPECT_MAX_CNT)
			return -EINVAL;
	}

	h = helper_hash(me->name, me->l4proto);
	mutex_lock(&nf_ct_helper_mutex);
	hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
		if (!strcmp(cur->name, me->name) &&
		    (cur->nfproto == NFPROTO_UNSPEC ||
		     cur->nfproto == me->nfproto) &&
		    cur->l4proto == me->l4proto) {
			ret = -EBUSY;
			goto out;
		}
	}

	refcount_set(&me->ct_refcnt, 1);
	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
	nf_ct_helper_count++;
out:
	mutex_unlock(&nf_ct_helper_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(__nf_conntrack_helper_register);

int nf_conntrack_helper_register(struct nf_conntrack_helper *me,
				 struct nf_conntrack_helper **helper_ptr)
{
	struct nf_conntrack_helper *new_helper;
	int err;

	new_helper = kzalloc_obj(*new_helper, GFP_KERNEL_ACCOUNT);
	if (!new_helper)
		return -ENOMEM;

	memcpy(new_helper, me, sizeof(*new_helper));
	*helper_ptr = new_helper;

	err = __nf_conntrack_helper_register(new_helper);
	if (err < 0)
		goto err_helper;

	return 0;

err_helper:
	*helper_ptr = NULL;
	kfree(new_helper);

	return err;
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);

static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
{
	const struct nf_conntrack_helper *me = data;
	const struct nf_conntrack_helper *this;

	this = rcu_dereference_protected(exp->helper,
					 lockdep_is_held(&nf_conntrack_expect_lock));
	if (this == me)
		return true;

	this = rcu_dereference_protected(exp->assign_helper,
					 lockdep_is_held(&nf_conntrack_expect_lock));
	return this == me;
}

void nf_conntrack_helper_release(struct nf_conntrack_helper *me)
{
	nf_ct_expect_iterate_destroy(expect_iter_me, me);

	if (refcount_dec_and_test(&me->ct_refcnt))
		kfree_rcu(me, rcu);
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_release);

void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
{
	mutex_lock(&nf_ct_helper_mutex);
	hlist_del_rcu(&me->hnode);
	nf_ct_helper_count--;
	mutex_unlock(&nf_ct_helper_mutex);

	/* This helper is going away, disable it. */
	rcu_assign_pointer(me->help, NULL);

	/* Make sure every nothing is still using the helper unless its a
	 * connection in the hash.
	 */
	synchronize_rcu();

	nf_conntrack_helper_release(me);
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);

void nf_ct_helper_init(struct nf_conntrack_helper *helper,
		       u8 l3num, u16 protonum, const char *name,
		       const struct nf_conntrack_expect_policy *exp_pol,
		       u32 expect_class_max,
		       int (*help)(struct sk_buff *skb, unsigned int protoff,
				   struct nf_conn *ct,
				   enum ip_conntrack_info ctinfo),
		       int (*from_nlattr)(struct nlattr *attr,
					  struct nf_conn *ct),
		       struct module *module)
{
	memset(helper, 0, sizeof(*helper));

	helper->nfproto = l3num;
	helper->l4proto = protonum;

	rcu_assign_pointer(helper->help, help);
	helper->from_nlattr = from_nlattr;
	helper->me = module;
	snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
		 NF_NAT_HELPER_PREFIX "%s", name);

	snprintf(helper->name, sizeof(helper->name), "%s", name);

	if (WARN_ON_ONCE(expect_class_max >= NF_CT_MAX_EXPECT_CLASSES))
		return;

	memcpy(helper->expect_policy, exp_pol,
	       (expect_class_max + 1) * sizeof(*exp_pol));
	helper->expect_class_max = expect_class_max;
}
EXPORT_SYMBOL_GPL(nf_ct_helper_init);

int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
				  unsigned int n, struct nf_conntrack_helper **helper_ptr)
{
	struct nf_conntrack_helper *new_helper;
	unsigned int i;
	int err = 0;

	for (i = 0; i < n; i++) {
		new_helper = kzalloc_obj(*new_helper, GFP_KERNEL_ACCOUNT);
		if (!new_helper) {
			err = -ENOMEM;
			goto err;
		}

		memcpy(new_helper, &helper[i], sizeof(*new_helper));
		helper_ptr[i] = new_helper;

		err = __nf_conntrack_helper_register(new_helper);
		if (err < 0) {
			helper_ptr[i] = NULL;
			goto err_helper;
		}
	}

	return err;
err_helper:
	kfree(new_helper);
err:
	if (i > 0)
		nf_conntrack_helpers_unregister(helper_ptr, i);
	return err;
}
EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);

void nf_conntrack_helpers_unregister(struct nf_conntrack_helper **helper,
				     unsigned int n)
{
	while (n-- > 0) {
		nf_conntrack_helper_unregister(helper[n]);
		helper[n] = NULL;
	}
}
EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);

void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
{
	mutex_lock(&nf_ct_nat_helpers_mutex);
	list_add_rcu(&nat->list, &nf_ct_nat_helpers);
	mutex_unlock(&nf_ct_nat_helpers_mutex);
}
EXPORT_SYMBOL_GPL(nf_nat_helper_register);

void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
{
	mutex_lock(&nf_ct_nat_helpers_mutex);
	list_del_rcu(&nat->list);
	mutex_unlock(&nf_ct_nat_helpers_mutex);
}
EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);

int nf_conntrack_helper_init(void)
{
	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
	nf_ct_helper_hash =
		nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
	if (!nf_ct_helper_hash)
		return -ENOMEM;

	INIT_LIST_HEAD(&nf_ct_nat_helpers);
	return 0;
}

void nf_conntrack_helper_fini(void)
{
	kvfree(nf_ct_helper_hash);
	nf_ct_helper_hash = NULL;
}