// 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_log.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 bool nf_ct_auto_assign_helper __read_mostly = false;
module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
MODULE_PARM_DESC(nf_conntrack_helper,
                 "Enable automatic conntrack helper assignment (default 0)");

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

/* Stupid hash, but collision free for the default registrations of the
 * helpers currently in the kernel. */
static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
{
        return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
                (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
}

static struct nf_conntrack_helper *
__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
{
        struct nf_conntrack_helper *helper;
        struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
        unsigned int h;

        if (!nf_ct_helper_count)
                return NULL;

        h = helper_hash(tuple);
        hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) {
                if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
                        return helper;
        }
        return NULL;
}

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

        for (i = 0; i < nf_ct_helper_hsize; i++) {
                hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
                        if (strcmp(h->name, name))
                                continue;

                        if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
                            h->tuple.src.l3num != l3num)
                                continue;

                        if (h->tuple.dst.protonum == 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->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)
{
        refcount_dec(&helper->refcnt);
        module_put(helper->me);
}
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(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)
                INIT_HLIST_HEAD(&help->expectations);
        else
                pr_debug("failed to add helper extension area");
        return help;
}
EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);

static struct nf_conntrack_helper *
nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
{
        struct nf_conntrack_net *cnet = nf_ct_pernet(net);

        if (!cnet->sysctl_auto_assign_helper) {
                if (cnet->auto_assign_helper_warned)
                        return NULL;
                if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
                        return NULL;
                pr_info("nf_conntrack: default automatic helper assignment "
                        "has been turned off for security reasons and CT-based "
                        "firewall rule not found. Use the iptables CT target "
                        "to attach helpers instead.\n");
                cnet->auto_assign_helper_warned = true;
                return NULL;
        }

        return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
}

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;
        struct net *net = nf_ct_net(ct);

        /* We already got a helper explicitly attached. The function
         * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
         * the helper up again. Since now the user is in full control of
         * making consistent helper configurations, skip this automatic
         * re-lookup, otherwise we'll lose the helper.
         */
        if (test_bit(IPS_HELPER_BIT, &ct->status))
                return 0;

        if (tmpl != NULL) {
                help = nfct_help(tmpl);
                if (help != NULL) {
                        helper = help->helper;
                        set_bit(IPS_HELPER_BIT, &ct->status);
                }
        }

        help = nfct_help(ct);

        if (helper == NULL) {
                helper = nf_ct_lookup_helper(ct, net);
                if (helper == NULL) {
                        if (help)
                                RCU_INIT_POINTER(help->helper, NULL);
                        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 && tmp->help != helper->help) {
                        RCU_INIT_POINTER(help->helper, NULL);
                        return 0;
                }
        }

        rcu_assign_pointer(help->helper, helper);

        return 0;
}
EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);

/* appropriate ct lock protecting must be taken by caller */
static int unhelp(struct nf_conn *ct, void *me)
{
        struct nf_conn_help *help = nfct_help(ct);

        if (help && rcu_dereference_raw(help->helper) == me) {
                nf_conntrack_event(IPCT_HELPER, ct);
                RCU_INIT_POINTER(help->helper, NULL);
        }

        /* We are not intended to delete this conntrack. */
        return 0;
}

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);

/* 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 struct nf_conn_help *help;
        const struct nf_conntrack_helper *helper;
        struct va_format vaf;
        va_list args;

        va_start(args, fmt);

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

        /* Called from the helper function, this call never fails */
        help = nfct_help(ct);

        /* rcu_read_lock()ed by nf_hook_thresh */
        helper = rcu_dereference(help->helper);

        nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
                      "nf_ct_%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_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
        unsigned int h = helper_hash(&me->tuple);
        struct nf_conntrack_helper *cur;
        int ret = 0, i;

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

        if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
                return -EINVAL;

        mutex_lock(&nf_ct_helper_mutex);
        for (i = 0; i < nf_ct_helper_hsize; i++) {
                hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
                        if (!strcmp(cur->name, me->name) &&
                            (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
                             cur->tuple.src.l3num == me->tuple.src.l3num) &&
                            cur->tuple.dst.protonum == me->tuple.dst.protonum) {
                                ret = -EEXIST;
                                goto out;
                        }
                }
        }

        /* avoid unpredictable behaviour for auto_assign_helper */
        if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
                hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
                        if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
                                                     &mask)) {
                                ret = -EEXIST;
                                goto out;
                        }
                }
        }
        refcount_set(&me->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);

static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
{
        struct nf_conn_help *help = nfct_help(exp->master);
        const struct nf_conntrack_helper *me = data;
        const struct nf_conntrack_helper *this;

        if (exp->helper == me)
                return true;

        this = rcu_dereference_protected(help->helper,
                                         lockdep_is_held(&nf_conntrack_expect_lock));
        return this == me;
}

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);

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

        nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
        nf_ct_iterate_destroy(unhelp, me);

        /* Maybe someone has gotten the helper already when unhelp above.
         * So need to wait it.
         */
        synchronize_rcu();
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);

void nf_ct_helper_init(struct nf_conntrack_helper *helper,
                       u16 l3num, u16 protonum, const char *name,
                       u16 default_port, u16 spec_port, u32 id,
                       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)
{
        helper->tuple.src.l3num = l3num;
        helper->tuple.dst.protonum = protonum;
        helper->tuple.src.u.all = htons(spec_port);
        helper->expect_policy = exp_pol;
        helper->expect_class_max = expect_class_max;
        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);

        if (spec_port == default_port)
                snprintf(helper->name, sizeof(helper->name), "%s", name);
        else
                snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
}
EXPORT_SYMBOL_GPL(nf_ct_helper_init);

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

        for (i = 0; i < n; i++) {
                err = nf_conntrack_helper_register(&helper[i]);
                if (err < 0)
                        goto err;
        }

        return err;
err:
        if (i > 0)
                nf_conntrack_helpers_unregister(helper, 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]);
}
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);

static const struct nf_ct_ext_type helper_extend = {
        .len    = sizeof(struct nf_conn_help),
        .align  = __alignof__(struct nf_conn_help),
        .id     = NF_CT_EXT_HELPER,
};

void nf_conntrack_helper_pernet_init(struct net *net)
{
        struct nf_conntrack_net *cnet = nf_ct_pernet(net);

        cnet->sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
}

int nf_conntrack_helper_init(void)
{
        int ret;
        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;

        ret = nf_ct_extend_register(&helper_extend);
        if (ret < 0) {
                pr_err("nf_ct_helper: Unable to register helper extension.\n");
                goto out_extend;
        }

        INIT_LIST_HEAD(&nf_ct_nat_helpers);
        return 0;
out_extend:
        kvfree(nf_ct_helper_hash);
        return ret;
}

void nf_conntrack_helper_fini(void)
{
        nf_ct_extend_unregister(&helper_extend);
        kvfree(nf_ct_helper_hash);
}