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/* Copyright (C) 2021 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include "contrib/net.h"
#include "knot/include/module.h"
#include "knot/conf/schema.h"
#include "knot/query/capture.h" // Forces static module!
#include "knot/query/requestor.h" // Forces static module!
#define MOD_REMOTE "\x06""remote"
#define MOD_ADDRESS "\x07""address"
#define MOD_TCP_FASTOPEN "\x0C""tcp-fastopen"
#define MOD_TIMEOUT "\x07""timeout"
#define MOD_FALLBACK "\x08""fallback"
#define MOD_CATCH_NXDOMAIN "\x0E""catch-nxdomain"
const yp_item_t dnsproxy_conf[] = {
{ MOD_REMOTE, YP_TREF, YP_VREF = { C_RMT }, YP_FNONE,
{ knotd_conf_check_ref } },
{ MOD_TIMEOUT, YP_TINT, YP_VINT = { 0, INT32_MAX, 500 } },
{ MOD_ADDRESS, YP_TNET, YP_VNONE, YP_FMULTI },
{ MOD_FALLBACK, YP_TBOOL, YP_VBOOL = { true } },
{ MOD_TCP_FASTOPEN, YP_TBOOL, YP_VNONE },
{ MOD_CATCH_NXDOMAIN, YP_TBOOL, YP_VNONE },
{ NULL }
};
int dnsproxy_conf_check(knotd_conf_check_args_t *args)
{
knotd_conf_t rmt = knotd_conf_check_item(args, MOD_REMOTE);
if (rmt.count == 0) {
args->err_str = "no remote server specified";
return KNOT_EINVAL;
}
return KNOT_EOK;
}
typedef struct {
struct sockaddr_storage remote;
struct sockaddr_storage via;
knotd_conf_t addr;
bool fallback;
bool tfo;
bool catch_nxdomain;
int timeout;
} dnsproxy_t;
static knotd_state_t dnsproxy_fwd(knotd_state_t state, knot_pkt_t *pkt,
knotd_qdata_t *qdata, knotd_mod_t *mod)
{
assert(pkt && qdata && mod);
dnsproxy_t *proxy = knotd_mod_ctx(mod);
/* Forward only queries ending with REFUSED (no zone) or NXDOMAIN (if configured) */
if (proxy->fallback && !(qdata->rcode == KNOT_RCODE_REFUSED ||
(qdata->rcode == KNOT_RCODE_NXDOMAIN && proxy->catch_nxdomain))) {
return state;
}
/* Forward from specified addresses only if configured. */
if (proxy->addr.count > 0) {
const struct sockaddr_storage *addr = knotd_qdata_remote_addr(qdata);
if (!knotd_conf_addr_range_match(&proxy->addr, addr)) {
return state;
}
}
/* Forward also original TSIG. */
if (qdata->query->tsig_rr != NULL && !proxy->fallback) {
knot_tsig_append(qdata->query->wire, &qdata->query->size,
qdata->query->max_size, qdata->query->tsig_rr);
}
/* Capture layer context. */
const knot_layer_api_t *capture = query_capture_api();
struct capture_param capture_param = {
.sink = pkt
};
/* Create a forwarding request. */
knot_requestor_t re;
int ret = knot_requestor_init(&re, capture, &capture_param, qdata->mm);
if (ret != KNOT_EOK) {
return state; /* Ignore, not enough memory. */
}
knot_request_flag_t flags = KNOT_REQUEST_NONE;
if (!net_is_stream(qdata->params->socket)) {
flags = KNOT_REQUEST_UDP;
} else if (proxy->tfo) {
flags = KNOT_REQUEST_TFO;
}
const struct sockaddr_storage *dst = &proxy->remote;
const struct sockaddr_storage *src = &proxy->via;
knot_request_t *req = knot_request_make(re.mm, dst, src, qdata->query, NULL,
flags);
if (req == NULL) {
knot_requestor_clear(&re);
return state; /* Ignore, not enough memory. */
}
/* Forward request. */
ret = knot_requestor_exec(&re, req, proxy->timeout);
knot_request_free(req, re.mm);
knot_requestor_clear(&re);
/* Check result. */
if (ret != KNOT_EOK) {
qdata->rcode = KNOT_RCODE_SERVFAIL;
return KNOTD_STATE_FAIL; /* Forwarding failed, SERVFAIL. */
} else {
qdata->rcode = knot_pkt_ext_rcode(pkt);
}
/* Respond also with TSIG. */
if (pkt->tsig_rr != NULL && !proxy->fallback) {
knot_tsig_append(pkt->wire, &pkt->size, pkt->max_size, pkt->tsig_rr);
}
return (proxy->fallback ? KNOTD_STATE_DONE : KNOTD_STATE_FINAL);
}
int dnsproxy_load(knotd_mod_t *mod)
{
dnsproxy_t *proxy = calloc(1, sizeof(*proxy));
if (proxy == NULL) {
return KNOT_ENOMEM;
}
knotd_conf_t remote = knotd_conf_mod(mod, MOD_REMOTE);
knotd_conf_t conf = knotd_conf(mod, C_RMT, C_ADDR, &remote);
if (conf.count > 0) {
proxy->remote = conf.multi[0].addr;
knotd_conf_free(&conf);
}
conf = knotd_conf(mod, C_RMT, C_VIA, &remote);
if (conf.count > 0) {
proxy->via = conf.multi[0].addr;
knotd_conf_free(&conf);
}
proxy->addr = knotd_conf_mod(mod, MOD_ADDRESS);
conf = knotd_conf_mod(mod, MOD_TIMEOUT);
proxy->timeout = conf.single.integer;
conf = knotd_conf_mod(mod, MOD_FALLBACK);
proxy->fallback = conf.single.boolean;
conf = knotd_conf_mod(mod, MOD_TCP_FASTOPEN);
proxy->tfo = conf.single.boolean;
conf = knotd_conf_mod(mod, MOD_CATCH_NXDOMAIN);
proxy->catch_nxdomain = conf.single.boolean;
knotd_mod_ctx_set(mod, proxy);
if (proxy->fallback) {
return knotd_mod_hook(mod, KNOTD_STAGE_END, dnsproxy_fwd);
} else {
return knotd_mod_hook(mod, KNOTD_STAGE_BEGIN, dnsproxy_fwd);
}
}
void dnsproxy_unload(knotd_mod_t *mod)
{
dnsproxy_t *ctx = knotd_mod_ctx(mod);
if (ctx != NULL) {
knotd_conf_free(&ctx->addr);
}
free(ctx);
}
KNOTD_MOD_API(dnsproxy, KNOTD_MOD_FLAG_SCOPE_ANY,
dnsproxy_load, dnsproxy_unload, dnsproxy_conf, dnsproxy_conf_check);
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