/*-
* Copyright (c) 2010-2019 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This material is based upon work partially supported by The
* NetBSD Foundation under a contract with Mindaugas Rasiukevicius.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

/*
* NPF interface for the Application Level Gateways (ALGs).
*/

#ifdef _KERNEL
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: npf_alg.c,v 1.22 2020/05/30 14:16:56 rmind Exp $");

#include <sys/param.h>
#include <sys/types.h>

#include <sys/kmem.h>
#include <sys/module.h>
#endif

#include "npf_impl.h"

/*
* NAT ALG description structure.  For more compact use of cache,
* the functions are separated in their own arrays.  The number of
* ALGs is expected to be very small.
*/

struct npf_alg {
       const char *    na_name;
       unsigned        na_slot;
};

struct npf_algset {
       /* List of ALGs and the count. */
       npf_alg_t       alg_list[NPF_MAX_ALGS];
       unsigned        alg_count;

       /* Matching, inspection and translation functions. */
       npfa_funcs_t    alg_funcs[NPF_MAX_ALGS];
};

#define NPF_ALG_PREF    "npf_alg_"
#define NPF_ALG_PREFLEN (sizeof(NPF_ALG_PREF) - 1)

void
npf_alg_init(npf_t *npf)
{
       npf_algset_t *aset;

       aset = kmem_zalloc(sizeof(npf_algset_t), KM_SLEEP);
       npf->algset = aset;
}

void
npf_alg_fini(npf_t *npf)
{
       npf_algset_t *aset = npf->algset;

       kmem_free(aset, sizeof(npf_algset_t));
}

static npf_alg_t *
npf_alg_lookup(npf_t *npf, const char *name)
{
       npf_algset_t *aset = npf->algset;

       KASSERT(npf_config_locked_p(npf));

       for (unsigned i = 0; i < aset->alg_count; i++) {
               npf_alg_t *alg = &aset->alg_list[i];
               const char *aname = alg->na_name;

               if (aname && strcmp(aname, name) == 0)
                       return alg;
       }
       return NULL;
}

npf_alg_t *
npf_alg_construct(npf_t *npf, const char *name)
{
       npf_alg_t *alg;

       npf_config_enter(npf);
       if ((alg = npf_alg_lookup(npf, name)) == NULL) {
               char modname[NPF_ALG_PREFLEN + 64];

               snprintf(modname, sizeof(modname), "%s%s", NPF_ALG_PREF, name);
               npf_config_exit(npf);

               if (module_autoload(modname, MODULE_CLASS_MISC) != 0) {
                       return NULL;
               }
               npf_config_enter(npf);
               alg = npf_alg_lookup(npf, name);
       }
       npf_config_exit(npf);
       return alg;
}

/*
* npf_alg_register: register application-level gateway.
*/
npf_alg_t *
npf_alg_register(npf_t *npf, const char *name, const npfa_funcs_t *funcs)
{
       npf_algset_t *aset = npf->algset;
       npfa_funcs_t *afuncs;
       npf_alg_t *alg;
       unsigned i;

       npf_config_enter(npf);
       if (npf_alg_lookup(npf, name) != NULL) {
               npf_config_exit(npf);
               return NULL;
       }

       /* Find a spare slot. */
       for (i = 0; i < NPF_MAX_ALGS; i++) {
               alg = &aset->alg_list[i];
               if (alg->na_name == NULL) {
                       break;
               }
       }
       if (i == NPF_MAX_ALGS) {
               npf_config_exit(npf);
               return NULL;
       }

       /* Register the ALG. */
       alg->na_name = name;
       alg->na_slot = i;

       /*
        * Assign the functions.  Make sure the 'destroy' gets visible first.
        */
       afuncs = &aset->alg_funcs[i];
       atomic_store_relaxed(&afuncs->destroy, funcs->destroy);
       membar_producer();
       atomic_store_relaxed(&afuncs->translate, funcs->translate);
       atomic_store_relaxed(&afuncs->inspect, funcs->inspect);
       atomic_store_relaxed(&afuncs->match, funcs->match);
       membar_producer();

       atomic_store_relaxed(&aset->alg_count, MAX(aset->alg_count, i + 1));
       npf_config_exit(npf);

       return alg;
}

/*
* npf_alg_unregister: unregister application-level gateway.
*/
int
npf_alg_unregister(npf_t *npf, npf_alg_t *alg)
{
       npf_algset_t *aset = npf->algset;
       unsigned i = alg->na_slot;
       npfa_funcs_t *afuncs;

       /* Deactivate the functions first. */
       npf_config_enter(npf);
       afuncs = &aset->alg_funcs[i];
       atomic_store_relaxed(&afuncs->match, NULL);
       atomic_store_relaxed(&afuncs->translate, NULL);
       atomic_store_relaxed(&afuncs->inspect, NULL);
       npf_config_sync(npf);

       /*
        * Finally, unregister the ALG.  We leave the 'destroy' callback
        * as the following will invoke it for the relevant connections.
        */
       npf_ruleset_freealg(npf_config_natset(npf), alg);
       atomic_store_relaxed(&afuncs->destroy, NULL);
       alg->na_name = NULL;
       npf_config_exit(npf);

       return 0;
}

/*
* npf_alg_match: call the ALG matching inspectors.
*
*      The purpose of the "matching" inspector function in the ALG API
*      is to determine whether this connection matches the ALG criteria
*      i.e. is concerning the ALG.  If yes, ALG can associate itself with
*      the given NAT state structure and set/save an arbitrary parameter.
*      This is done using the using the npf_nat_setalg() function.
*
*      => This is called when the packet matches the dynamic NAT policy
*         and the NAT state entry is being created for it [NAT-ESTABLISH].
*/
bool
npf_alg_match(npf_cache_t *npc, npf_nat_t *nt, int di)
{
       npf_t *npf = npc->npc_ctx;
       npf_algset_t *aset = npf->algset;
       bool match = false;
       unsigned count;
       int s;

       KASSERTMSG(npf_iscached(npc, NPC_IP46), "expecting protocol number");

       s = npf_config_read_enter(npf);
       count = atomic_load_relaxed(&aset->alg_count);
       for (unsigned i = 0; i < count; i++) {
               const npfa_funcs_t *f = &aset->alg_funcs[i];
               bool (*match_func)(npf_cache_t *, npf_nat_t *, int);

               match_func = atomic_load_relaxed(&f->match);
               if (match_func && match_func(npc, nt, di)) {
                       match = true;
                       break;
               }
       }
       npf_config_read_exit(npf, s);
       return match;
}

/*
* npf_alg_exec: execute the ALG translation processors.
*
*      The ALG function would perform any additional packet translation
*      or manipulation here.
*
*      => This is called when the packet is being translated according
*         to the dynamic NAT logic [NAT-TRANSLATE].
*/
void
npf_alg_exec(npf_cache_t *npc, npf_nat_t *nt, const npf_flow_t flow)
{
       npf_t *npf = npc->npc_ctx;
       npf_algset_t *aset = npf->algset;
       unsigned count;
       int s;

       s = npf_config_read_enter(npf);
       count = atomic_load_relaxed(&aset->alg_count);
       for (unsigned i = 0; i < count; i++) {
               const npfa_funcs_t *f = &aset->alg_funcs[i];
               bool (*translate_func)(npf_cache_t *, npf_nat_t *, npf_flow_t);

               translate_func = atomic_load_relaxed(&f->translate);
               if (translate_func) {
                       translate_func(npc, nt, flow);
               }
       }
       npf_config_read_exit(npf, s);
}

/*
* npf_alg_conn: query ALGs which may perform a custom state lookup.
*
*      The purpose of ALG connection inspection function is to provide
*      ALGs with a mechanism to override the regular connection state
*      lookup, if they need to.  For example, some ALGs may want to
*      extract and use a different n-tuple to perform a lookup.
*
*      => This is called at the beginning of the connection state lookup
*         function [CONN-LOOKUP].
*
*      => Must use the npf_conn_lookup() function to perform the custom
*         connection state lookup and return the result.
*
*      => Returning NULL will result in NPF performing a regular state
*         lookup for the packet.
*/
npf_conn_t *
npf_alg_conn(npf_cache_t *npc, int di)
{
       npf_t *npf = npc->npc_ctx;
       npf_algset_t *aset = npf->algset;
       npf_conn_t *con = NULL;
       unsigned count;
       int s;

       s = npf_config_read_enter(npf);
       count = atomic_load_relaxed(&aset->alg_count);
       for (unsigned i = 0; i < count; i++) {
               const npfa_funcs_t *f = &aset->alg_funcs[i];
               npf_conn_t *(*inspect_func)(npf_cache_t *, int);

               inspect_func = atomic_load_relaxed(&f->inspect);
               if (inspect_func && (con = inspect_func(npc, di)) != NULL) {
                       break;
               }
       }
       npf_config_read_exit(npf, s);
       return con;
}

/*
* npf_alg_destroy: free the ALG structure associated with the NAT entry.
*/
void
npf_alg_destroy(npf_t *npf, npf_alg_t *alg, npf_nat_t *nat, npf_conn_t *con)
{
       npf_algset_t *aset = npf->algset;
       const npfa_funcs_t *f = &aset->alg_funcs[alg->na_slot];
       void (*destroy_func)(npf_t *, npf_nat_t *, npf_conn_t *);

       if ((destroy_func = atomic_load_relaxed(&f->destroy)) != NULL) {
               destroy_func(npf, nat, con);
       }
}

/*
* npf_alg_export: serialise the configuration of ALGs.
*/
int
npf_alg_export(npf_t *npf, nvlist_t *nvl)
{
       npf_algset_t *aset = npf->algset;

       KASSERT(npf_config_locked_p(npf));

       for (unsigned i = 0; i < aset->alg_count; i++) {
               const npf_alg_t *alg = &aset->alg_list[i];
               nvlist_t *algdict;

               if (alg->na_name == NULL) {
                       continue;
               }
               algdict = nvlist_create(0);
               nvlist_add_string(algdict, "name", alg->na_name);
               nvlist_append_nvlist_array(nvl, "algs", algdict);
               nvlist_destroy(algdict);
       }
       return 0;
}

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