#include "config.h"
#include <stdlib.h>
#include <fcntl.h>
#ifdef HAVE_TIME_H
#include <time.h>
#endif
#include <sys/time.h>
#include <sys/types.h>
#include "sldns/sbuffer.h"
#include "util/config_file.h"
#include "util/net_help.h"
#include "util/netevent.h"
#include "util/log.h"
#include "dnscrypt/cert.h"
#include "dnscrypt/dnscrypt.h"
#include <ctype.h>
/**
* \file
* dnscrypt functions for encrypting DNS packets.
*/
#define DNSCRYPT_QUERY_BOX_OFFSET \
(DNSCRYPT_MAGIC_HEADER_LEN + crypto_box_PUBLICKEYBYTES + crypto_box_HALF_NONCEBYTES)
// 8 bytes: magic header (CERT_MAGIC_HEADER)
// 12 bytes: the client's nonce
// 12 bytes: server nonce extension
// 16 bytes: Poly1305 MAC (crypto_box_ZEROBYTES - crypto_box_BOXZEROBYTES)
#define DNSCRYPT_REPLY_BOX_OFFSET \
(DNSCRYPT_MAGIC_HEADER_LEN + crypto_box_HALF_NONCEBYTES + crypto_box_HALF_NONCEBYTES)
/**
* Decrypt a query using the keypair that was found using dnsc_find_keypair.
* The client nonce will be extracted from the encrypted query and stored in
* client_nonce, a shared secret will be computed and stored in nmkey and the
* buffer will be decrypted inplace.
* \param[in] keypair the keypair that matches this encrypted query.
* \param[in] client_nonce where the client nonce will be stored.
* \param[in] nmkey where the shared secret key will be written.
* \param[in] buffer the encrypted buffer.
* \return 0 on success.
*/
static int
dnscrypt_server_uncurve(const KeyPair *keypair,
uint8_t client_nonce[crypto_box_HALF_NONCEBYTES],
uint8_t nmkey[crypto_box_BEFORENMBYTES],
struct sldns_buffer* buffer)
{
size_t len = sldns_buffer_limit(buffer);
uint8_t *const buf = sldns_buffer_begin(buffer);
uint8_t nonce[crypto_box_NONCEBYTES];
struct dnscrypt_query_header *query_header;
if (len <= DNSCRYPT_QUERY_HEADER_SIZE) {
return -1;
}
query_header = (struct dnscrypt_query_header *)buf;
memcpy(nmkey, query_header->publickey, crypto_box_PUBLICKEYBYTES);
if (crypto_box_beforenm(nmkey, nmkey, keypair->crypt_secretkey) != 0) {
return -1;
}
memcpy(nonce, query_header->nonce, crypto_box_HALF_NONCEBYTES);
memset(nonce + crypto_box_HALF_NONCEBYTES, 0, crypto_box_HALF_NONCEBYTES);
sldns_buffer_set_at(buffer,
DNSCRYPT_QUERY_BOX_OFFSET - crypto_box_BOXZEROBYTES,
0, crypto_box_BOXZEROBYTES);
if (crypto_box_open_afternm
(buf + DNSCRYPT_QUERY_BOX_OFFSET - crypto_box_BOXZEROBYTES,
buf + DNSCRYPT_QUERY_BOX_OFFSET - crypto_box_BOXZEROBYTES,
len - DNSCRYPT_QUERY_BOX_OFFSET + crypto_box_BOXZEROBYTES, nonce,
nmkey) != 0) {
return -1;
}
while (*sldns_buffer_at(buffer, --len) == 0)
;
if (*sldns_buffer_at(buffer, len) != 0x80) {
return -1;
}
memcpy(client_nonce, nonce, crypto_box_HALF_NONCEBYTES);
memmove(sldns_buffer_begin(buffer),
sldns_buffer_at(buffer, DNSCRYPT_QUERY_HEADER_SIZE),
len - DNSCRYPT_QUERY_HEADER_SIZE);
sldns_buffer_set_position(buffer, 0);
sldns_buffer_set_limit(buffer, len - DNSCRYPT_QUERY_HEADER_SIZE);
return 0;
}
/**
* Add random padding to a buffer, according to a client nonce.
* The length has to depend on the query in order to avoid reply attacks.
*
* @param buf a buffer
* @param len the initial size of the buffer
* @param max_len the maximum size
* @param nonce a nonce, made of the client nonce repeated twice
* @param secretkey
* @return the new size, after padding
*/
size_t
dnscrypt_pad(uint8_t *buf, const size_t len, const size_t max_len,
const uint8_t *nonce, const uint8_t *secretkey)
{
uint8_t *buf_padding_area = buf + len;
size_t padded_len;
uint32_t rnd;
// no padding
if (max_len < len + DNSCRYPT_MIN_PAD_LEN)
return len;
assert(nonce[crypto_box_HALF_NONCEBYTES] == nonce[0]);
crypto_stream((unsigned char *)&rnd, (unsigned long long)sizeof(rnd), nonce,
secretkey);
padded_len =
len + DNSCRYPT_MIN_PAD_LEN + rnd % (max_len - len -
DNSCRYPT_MIN_PAD_LEN + 1);
padded_len += DNSCRYPT_BLOCK_SIZE - padded_len % DNSCRYPT_BLOCK_SIZE;
if (padded_len > max_len)
padded_len = max_len;
memset(buf_padding_area, 0, padded_len - len);
*buf_padding_area = 0x80;
return padded_len;
}
uint64_t
dnscrypt_hrtime(void)
{
struct timeval tv;
uint64_t ts = (uint64_t)0U;
int ret;
ret = gettimeofday(&tv, NULL);
if (ret == 0) {
ts = (uint64_t)tv.tv_sec * 1000000U + (uint64_t)tv.tv_usec;
} else {
log_err("gettimeofday: %s", strerror(errno));
}
return ts;
}
/**
* Add the server nonce part to once.
* The nonce is made half of client nonce and the seconf half of the server
* nonce, both of them of size crypto_box_HALF_NONCEBYTES.
* \param[in] nonce: a uint8_t* of size crypto_box_NONCEBYTES
*/
static void
add_server_nonce(uint8_t *nonce)
{
uint64_t ts;
uint64_t tsn;
uint32_t suffix;
ts = dnscrypt_hrtime();
// TODO? dnscrypt-wrapper does some logic with context->nonce_ts_last
// unclear if we really need it, so skipping it for now.
tsn = (ts << 10) | (randombytes_random() & 0x3ff);
#if (BYTE_ORDER == LITTLE_ENDIAN)
tsn =
(((uint64_t)htonl((uint32_t)tsn)) << 32) | htonl((uint32_t)(tsn >> 32));
#endif
memcpy(nonce + crypto_box_HALF_NONCEBYTES, &tsn, 8);
suffix = randombytes_random();
memcpy(nonce + crypto_box_HALF_NONCEBYTES + 8, &suffix, 4);
}
/**
* Encrypt a reply using the keypair that was used with the query.
* The client nonce will be extracted from the encrypted query and stored in
* The buffer will be encrypted inplace.
* \param[in] keypair the keypair that matches this encrypted query.
* \param[in] client_nonce client nonce used during the query
* \param[in] nmkey shared secret key used during the query.
* \param[in] buffer the buffer where to encrypt the reply.
* \param[in] udp if whether or not it is a UDP query.
* \param[in] max_udp_size configured max udp size.
* \return 0 on success.
*/
static int
dnscrypt_server_curve(const KeyPair *keypair,
uint8_t client_nonce[crypto_box_HALF_NONCEBYTES],
uint8_t nmkey[crypto_box_BEFORENMBYTES],
struct sldns_buffer* buffer,
uint8_t udp,
size_t max_udp_size)
{
size_t dns_reply_len = sldns_buffer_limit(buffer);
size_t max_len = dns_reply_len + DNSCRYPT_MAX_PADDING + DNSCRYPT_REPLY_HEADER_SIZE;
size_t max_reply_size = max_udp_size - 20U - 8U;
uint8_t nonce[crypto_box_NONCEBYTES];
uint8_t *boxed;
uint8_t *const buf = sldns_buffer_begin(buffer);
size_t len = sldns_buffer_limit(buffer);
if(udp){
if (max_len > max_reply_size)
max_len = max_reply_size;
}
memcpy(nonce, client_nonce, crypto_box_HALF_NONCEBYTES);
memcpy(nonce + crypto_box_HALF_NONCEBYTES, client_nonce,
crypto_box_HALF_NONCEBYTES);
boxed = buf + DNSCRYPT_REPLY_BOX_OFFSET;
memmove(boxed + crypto_box_MACBYTES, buf, len);
len = dnscrypt_pad(boxed + crypto_box_MACBYTES, len,
max_len - DNSCRYPT_REPLY_HEADER_SIZE, nonce,
keypair->crypt_secretkey);
sldns_buffer_set_at(buffer,
DNSCRYPT_REPLY_BOX_OFFSET - crypto_box_BOXZEROBYTES,
0, crypto_box_ZEROBYTES);
// add server nonce extension
add_server_nonce(nonce);
if (crypto_box_afternm
(boxed - crypto_box_BOXZEROBYTES, boxed - crypto_box_BOXZEROBYTES,
len + crypto_box_ZEROBYTES, nonce, nmkey) != 0) {
return -1;
}
sldns_buffer_write_at(buffer, 0, DNSCRYPT_MAGIC_RESPONSE, DNSCRYPT_MAGIC_HEADER_LEN);
sldns_buffer_write_at(buffer, DNSCRYPT_MAGIC_HEADER_LEN, nonce, crypto_box_NONCEBYTES);
sldns_buffer_set_limit(buffer, len + DNSCRYPT_REPLY_HEADER_SIZE);
return 0;
}
/**
* Read the content of fname into buf.
* \param[in] fname name of the file to read.
* \param[in] buf the buffer in which to read the content of the file.
* \param[in] count number of bytes to read.
* \return 0 on success.
*/
static int
dnsc_read_from_file(char *fname, char *buf, size_t count)
{
int fd;
fd = open(fname, O_RDONLY);
if (fd == -1) {
return -1;
}
if (read(fd, buf, count) != (ssize_t)count) {
close(fd);
return -2;
}
close(fd);
return 0;
}
/**
* Parse certificates files provided by the configuration and load them into
* dnsc_env.
* \param[in] env the dnsc_env structure to load the certs into.
* \param[in] cfg the configuration.
* \return the number of certificates loaded.
*/
static int
dnsc_parse_certs(struct dnsc_env *env, struct config_file *cfg)
{
struct config_strlist *head;
size_t signed_cert_id;
env->signed_certs_count = 0U;
for (head = cfg->dnscrypt_provider_cert; head; head = head->next) {
env->signed_certs_count++;
}
env->signed_certs = sodium_allocarray(env->signed_certs_count,
sizeof *env->signed_certs);
signed_cert_id = 0U;
for(head = cfg->dnscrypt_provider_cert; head; head = head->next, signed_cert_id++) {
if(dnsc_read_from_file(
head->str,
(char *)(env->signed_certs + signed_cert_id),
sizeof(struct SignedCert)) != 0) {
fatal_exit("dnsc_parse_certs: failed to load %s: %s", head->str, strerror(errno));
}
verbose(VERB_OPS, "Loaded cert %s", head->str);
}
return signed_cert_id;
}
/**
* Helper function to convert a binary key into a printable fingerprint.
* \param[in] fingerprint the buffer in which to write the printable key.
* \param[in] key the key to convert.
*/
void
dnsc_key_to_fingerprint(char fingerprint[80U], const uint8_t * const key)
{
const size_t fingerprint_size = 80U;
size_t fingerprint_pos = (size_t) 0U;
size_t key_pos = (size_t) 0U;
for (;;) {
assert(fingerprint_size > fingerprint_pos);
snprintf(&fingerprint[fingerprint_pos],
fingerprint_size - fingerprint_pos, "%02X%02X",
key[key_pos], key[key_pos + 1U]);
key_pos += 2U;
if (key_pos >= crypto_box_PUBLICKEYBYTES) {
break;
}
fingerprint[fingerprint_pos + 4U] = ':';
fingerprint_pos += 5U;
}
}
/**
* Find the keypair matching a DNSCrypt query.
* \param[in] dnscenv The DNSCrypt enviroment, which contains the list of keys
* supported by the server.
* \param[in] buffer The encrypted DNS query.
* \return a KeyPair * if we found a key pair matching the query, NULL otherwise.
*/
static const KeyPair *
dnsc_find_keypair(struct dnsc_env* dnscenv, struct sldns_buffer* buffer)
{
const KeyPair *keypairs = dnscenv->keypairs;
struct dnscrypt_query_header *dnscrypt_header;
size_t i;
if (sldns_buffer_limit(buffer) < DNSCRYPT_QUERY_HEADER_SIZE) {
return NULL;
}
dnscrypt_header = (struct dnscrypt_query_header *)sldns_buffer_begin(buffer);
for (i = 0U; i < dnscenv->keypairs_count; i++) {
if (memcmp(keypairs[i].crypt_publickey, dnscrypt_header->magic_query,
DNSCRYPT_MAGIC_HEADER_LEN) == 0) {
return &keypairs[i];
}
}
return NULL;
}
/**
* Insert local-zone and local-data into configuration.
* In order to be able to serve certs over TXT, we can reuse the local-zone and
* local-data config option. The zone and qname are infered from the
* provider_name and the content of the TXT record from the certificate content.
* returns the number of certtificate TXT record that were loaded.
* < 0 in case of error.
*/
static int
dnsc_load_local_data(struct dnsc_env* dnscenv, struct config_file *cfg)
{
size_t i, j;
// Insert 'local-zone: "2.dnscrypt-cert.example.com" deny'
if(!cfg_str2list_insert(&cfg->local_zones,
strdup(dnscenv->provider_name),
strdup("deny"))) {
log_err("Could not load dnscrypt local-zone: %s deny",
dnscenv->provider_name);
return -1;
}
// Add local data entry of type:
// 2.dnscrypt-cert.example.com 86400 IN TXT "DNSC......"
for(i=0; i<dnscenv->signed_certs_count; i++) {
const char *ttl_class_type = " 86400 IN TXT \"";
struct SignedCert *cert = dnscenv->signed_certs + i;
uint16_t rrlen = strlen(dnscenv->provider_name) +
strlen(ttl_class_type) +
4 * sizeof(struct SignedCert) + // worst case scenario
1 + // trailing double quote
1;
char *rr = malloc(rrlen);
if(!rr) {
log_err("Could not allocate memory");
return -2;
}
snprintf(rr, rrlen - 1, "%s 86400 IN TXT \"", dnscenv->provider_name);
for(j=0; j<sizeof(struct SignedCert); j++) {
int c = (int)*((const uint8_t *) cert + j);
if (isprint(c) && c != '"' && c != '\\') {
snprintf(rr + strlen(rr), rrlen - 1 - strlen(rr), "%c", c);
} else {
snprintf(rr + strlen(rr), rrlen - 1 - strlen(rr), "\\%03d", c);
}
}
snprintf(rr + strlen(rr), rrlen - 1 - strlen(rr), "\"");
cfg_strlist_insert(&cfg->local_data, strdup(rr));
free(rr);
}
return dnscenv->signed_certs_count;
}
/**
* Parse the secret key files from `dnscrypt-secret-key` config and populates
* a list of secret/public keys supported by dnscrypt listener.
* \param[in] env The dnsc_env structure which will hold the keypairs.
* \param[in] cfg The config with the secret key file paths.
*/
static int
dnsc_parse_keys(struct dnsc_env *env, struct config_file *cfg)
{
struct config_strlist *head;
size_t keypair_id;
env->keypairs_count = 0U;
for (head = cfg->dnscrypt_secret_key; head; head = head->next) {
env->keypairs_count++;
}
env->keypairs = sodium_allocarray(env->keypairs_count,
sizeof *env->keypairs);
keypair_id = 0U;
for(head = cfg->dnscrypt_secret_key; head; head = head->next, keypair_id++) {
char fingerprint[80];
if(dnsc_read_from_file(
head->str,
(char *)(env->keypairs[keypair_id].crypt_secretkey),
crypto_box_SECRETKEYBYTES) != 0) {
fatal_exit("dnsc_parse_keys: failed to load %s: %s", head->str, strerror(errno));
}
verbose(VERB_OPS, "Loaded key %s", head->str);
if (crypto_scalarmult_base(env->keypairs[keypair_id].crypt_publickey,
env->keypairs[keypair_id].crypt_secretkey) != 0) {
fatal_exit("dnsc_parse_keys: could not generate public key from %s", head->str);
}
dnsc_key_to_fingerprint(fingerprint, env->keypairs[keypair_id].crypt_publickey);
verbose(VERB_OPS, "Crypt public key fingerprint for %s: %s", head->str, fingerprint);
}
return keypair_id;
}
/**
* #########################################################
* ############# Publicly accessible functions #############
* #########################################################
*/
int
dnsc_handle_curved_request(struct dnsc_env* dnscenv,
struct comm_reply* repinfo)
{
struct comm_point* c = repinfo->c;
repinfo->is_dnscrypted = 0;
if( !c->dnscrypt ) {
return 1;
}
// Attempt to decrypt the query. If it is not crypted, we may still need
// to serve the certificate.
verbose(VERB_ALGO, "handle request called on DNSCrypt socket");
if ((repinfo->keypair = dnsc_find_keypair(dnscenv, c->buffer)) != NULL) {
if(dnscrypt_server_uncurve(repinfo->keypair,
repinfo->client_nonce,
repinfo->nmkey,
c->buffer) != 0){
verbose(VERB_ALGO, "dnscrypt: Failed to uncurve");
comm_point_drop_reply(repinfo);
return 0;
}
repinfo->is_dnscrypted = 1;
sldns_buffer_rewind(c->buffer);
}
return 1;
}
int
dnsc_handle_uncurved_request(struct comm_reply *repinfo)
{
if(!repinfo->c->dnscrypt) {
return 1;
}
sldns_buffer_copy(repinfo->c->dnscrypt_buffer, repinfo->c->buffer);
if(!repinfo->is_dnscrypted) {
return 1;
}
if(dnscrypt_server_curve(repinfo->keypair,
repinfo->client_nonce,
repinfo->nmkey,
repinfo->c->dnscrypt_buffer,
repinfo->c->type == comm_udp,
repinfo->max_udp_size) != 0){
verbose(VERB_ALGO, "dnscrypt: Failed to curve cached missed answer");
comm_point_drop_reply(repinfo);
return 0;
}
return 1;
}
struct dnsc_env *
dnsc_create(void)
{
struct dnsc_env *env;
if (sodium_init() == -1) {
fatal_exit("dnsc_create: could not initialize libsodium.");
}
env = (struct dnsc_env *) calloc(1, sizeof(struct dnsc_env));
return env;
}
int
dnsc_apply_cfg(struct dnsc_env *env, struct config_file *cfg)
{
if(dnsc_parse_certs(env, cfg) <= 0) {
fatal_exit("dnsc_apply_cfg: no cert file loaded");
}
if(dnsc_parse_keys(env, cfg) <= 0) {
fatal_exit("dnsc_apply_cfg: no key file loaded");
}
randombytes_buf(env->hash_key, sizeof env->hash_key);
env->provider_name = cfg->dnscrypt_provider;
if(dnsc_load_local_data(env, cfg) <= 0) {
fatal_exit("dnsc_apply_cfg: could not load local data");
}
return 0;
}
