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Privacy aware DNS Cookies 

Track source IP address in an efficient manner to make sure the same cookie will not be sent from different source IP addresses.
This commit is contained in:
Willem Toorop 2020-04-09 16:24:34 +02:00
parent de13a0c32d
commit 9ecd3fde1c
6 changed files with 200 additions and 118 deletions
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9
src/context.c
View File

@ -953,9 +953,12 @@ upstream_init(getdns_upstream *upstream,
(void) getdns_eventloop_event_init(
&upstream->finished_event, upstream, NULL, NULL, NULL);
upstream->has_client_cookie = 0;
upstream->has_prev_client_cookie = 0;
upstream->has_server_cookie = 0;
upstream->server_cookie_len = 0;
(void) memset(&upstream->server_cookie, 0,
sizeof(upstream->server_cookie));
upstream->src_addr_checked = 0;
(void) memset(&upstream->src_addr, 0, sizeof(upstream->src_addr));
upstream->src_addr_len = 0;
upstream->tsig_alg = GETDNS_NO_TSIG;
upstream->tsig_dname_len = 0;

16
src/context.h
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@ -243,15 +243,13 @@ typedef struct getdns_upstream {
unsigned is_sync_loop : 1;
/* EDNS cookies */
uint32_t secret;
uint8_t client_cookie[8];
uint8_t prev_client_cookie[8];
uint8_t server_cookie[32];
unsigned has_client_cookie : 1;
unsigned has_prev_client_cookie : 1;
unsigned has_server_cookie : 1;
unsigned server_cookie_len : 5;
uint8_t server_cookie[40];
size_t server_cookie_len;
uint64_t src_addr_checked;
struct sockaddr_storage src_addr;
socklen_t src_addr_len;
char src_addr_str[INET6_ADDRSTRLEN];
/* TSIG */
uint8_t tsig_dname[256];

2
src/request-internal.c
View File

@ -210,6 +210,8 @@ network_req_init(getdns_network_req *net_req, getdns_dns_req *owner,
memset(&net_req->event, 0, sizeof(net_req->event));
net_req->keepalive_sent = 0;
net_req->badcookie_retry = 0;
net_req->cookie_sent = 0;
memset(&net_req->client_cookie, 0, sizeof(net_req->client_cookie));
net_req->write_queue_tail = NULL;
/* Some fields to record info for return_call_reporting */
net_req->debug_tls_auth_status = GETDNS_AUTH_NONE;

278
src/stub.c
View File

@ -33,6 +33,10 @@
#include "config.h"
#ifndef USE_WINSOCK
#include <netdb.h>
#endif
/* Intercept and do not sent out COM DS queries with TLS
* For debugging purposes only. Never commit with this turned on.
*/
@ -53,6 +57,7 @@
#include "general.h"
#include "pubkey-pinning.h"
/* WSA TODO:
* STUB_TCP_RETRY added to deal with edge triggered event loops (versus
* level triggered). See also lines containing WSA TODO below...
@ -73,10 +78,6 @@
/* Arbritray number of message for EDNS keepalive resend*/
#define EDNS_KEEPALIVE_RESEND 5
static time_t secret_rollover_time = 0;
static uint32_t secret = 0;
static uint32_t prev_secret = 0;
static void upstream_read_cb(void *userarg);
static void upstream_write_cb(void *userarg);
static void upstream_idle_timeout_cb(void *userarg);
@ -97,47 +98,6 @@ uint64_t _getdns_get_time_as_uintt64();
/* General utility functions */
/*****************************/
static void
rollover_secret()
{
time_t now = 0;
/* Create and roll server secrets */
if (time(&now) <= secret_rollover_time)
return;
/* Remember previous secret, in to keep answering on rollover
* boundary with old cookie.
*/
prev_secret = secret;
secret = arc4random();
/* Next rollover over EDNS_COOKIE_ROLLOVER_TIME with 30% jitter,
* I.e. some offset + or - 15% of the future point in time.
*/
secret_rollover_time = now + (EDNS_COOKIE_ROLLOVER_TIME / 20 * 17)
+ arc4random_uniform(EDNS_COOKIE_ROLLOVER_TIME / 10 * 3);
}
static void
calc_new_cookie(getdns_upstream *upstream, uint8_t *cookie)
{
unsigned char md_value[GETDNS_TLS_MAX_DIGEST_LENGTH];
size_t md_len;
size_t i;
sa_family_t af = upstream->addr.ss_family;
void *sa_addr = ((struct sockaddr*)&upstream->addr)->sa_data;
size_t addr_len = ( af == AF_INET6 ? sizeof(struct sockaddr_in6)
: af == AF_INET ? sizeof(struct sockaddr_in)
: 0 ) - sizeof(sa_family_t);
_getdns_tls_cookie_sha256(secret, sa_addr, addr_len, md_value, &md_len);
(void) memset(cookie, 0, 8);
for (i = 0; i < md_len; i++)
cookie[i % 8] ^= md_value[i];
}
static getdns_return_t
attach_edns_client_subnet_private(getdns_network_req *req)
{
@ -169,46 +129,59 @@ static getdns_return_t
attach_edns_cookie(getdns_network_req *req)
{
getdns_upstream *upstream = req->upstream;
uint16_t sz;
void* val;
uint8_t buf[8 + 32]; /* server cookies can be no larger than 32 bytes */
rollover_secret();
if (!upstream->has_client_cookie) {
calc_new_cookie(upstream, upstream->client_cookie);
upstream->secret = secret;
upstream->has_client_cookie = 1;
if (upstream->server_cookie_len) {
if (!req->badcookie_retry && bind(req->fd, (struct sockaddr *)
&upstream->src_addr, upstream->src_addr_len)) {
sz = 8;
val = upstream->client_cookie;
} else if (upstream->secret != secret) {
memcpy( upstream->prev_client_cookie
, upstream->client_cookie, 8);
upstream->has_prev_client_cookie = 1;
calc_new_cookie(upstream, upstream->client_cookie);
upstream->secret = secret;
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_INFO,
"%-40s : Upstream : %s with source address: %s. "
"Renewing Client Cookie.\n", upstream->addr_str,
strerror(errno), upstream->src_addr_str);
sz = 8;
val = upstream->client_cookie;
} else if (!upstream->has_server_cookie) {
sz = 8;
val = upstream->client_cookie;
} else {
sz = 8 + upstream->server_cookie_len;
memcpy(buf, upstream->client_cookie, 8);
memcpy(buf+8, upstream->server_cookie, upstream->server_cookie_len);
val = buf;
upstream->server_cookie_len = 0;
upstream->src_addr_checked = 0;
} else
return _getdns_network_req_add_upstream_option(
req, EDNS_COOKIE_OPCODE,
upstream->server_cookie_len,
upstream->server_cookie);
}
return _getdns_network_req_add_upstream_option(req, EDNS_COOKIE_OPCODE, sz, val);
if (_getdns_get_now_ms() - upstream->src_addr_checked < 3600000) {
/* This upstream has been registered to *not* support cookies.
* We will recheck one hour after this was registered.
*/
return 0;
}
/* Try to get a new server cookie for this upstream
* Explicitly connect on UDP only.
*/
if (req->fd >= 0 && connect(req->fd,
(struct sockaddr*)&upstream->addr, upstream->addr_len)) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_WARNING,
"%-40s : Upstream : Could not connect(): %s. "
"Required for privacy aware Cookies. Cookies disabled.\n",
upstream->addr_str, strerror(errno));
/* Don't recheck for another hour */
upstream->src_addr_checked = _getdns_get_now_ms();
return 0;
}
/* Create new client cookie */
req->cookie_sent = 1;
gldns_write_uint32(req->client_cookie, arc4random());
gldns_write_uint32(req->client_cookie + 4, arc4random());
return _getdns_network_req_add_upstream_option(
req, EDNS_COOKIE_OPCODE, 8, req->client_cookie);
}
/* Will find a matching OPT RR, but leaves the caller to validate it
*
* Returns 2 when found
* 0 when not found
* and 1 on FORMERR
*/
#define MATCH_OPT_FOUND 2
#define MATCH_OPT_NOT_FOUND 0
#define MATCH_OPT_ERROR 1
static int
match_edns_opt_rr(uint16_t code, getdns_network_req *netreq,
const uint8_t **position, uint16_t *option_len)
@ -234,7 +207,7 @@ match_edns_opt_rr(uint16_t code, getdns_network_req *netreq,
}
if (! rr_iter) {
netreq->response_opt = NO_OPT_RR;
return 0; /* No OPT, no options cookie */
return MATCH_OPT_NOT_FOUND;
}
pos = netreq->response_opt = rr_iter->rr_type + 8;
@ -253,10 +226,10 @@ match_edns_opt_rr(uint16_t code, getdns_network_req *netreq,
if (pos + 2 > rr_iter->nxt
|| pos + 2 + gldns_read_uint16(pos) > rr_iter->nxt) {
netreq->response_opt = NO_OPT_RR;
return 1; /* FORMERR */
return MATCH_OPT_ERROR;
}
} else if (netreq->response_opt == NO_OPT_RR)
return 0; /* No OPT, no options */
return MATCH_OPT_NOT_FOUND;
else
/* Reuse earlier found option */
pos = netreq->response_opt;;
@ -269,17 +242,17 @@ match_edns_opt_rr(uint16_t code, getdns_network_req *netreq,
opt_code = gldns_read_uint16(pos); pos += 2;
opt_len = gldns_read_uint16(pos); pos += 2;
if (pos + opt_len > rdata_end)
return 1; /* FORMERR */
return MATCH_OPT_ERROR;
if (opt_code == code)
break;
pos += opt_len; /* Skip unknown options */
}
if (pos >= rdata_end || opt_code != code)
return 0; /* Everything OK,
* the searched for option was just not found. */
return MATCH_OPT_NOT_FOUND;
*position = pos;
*option_len = opt_len;
return 2;
return MATCH_OPT_FOUND;
}
/* TODO: Test combinations of EDNS0 options*/
@ -289,33 +262,126 @@ match_and_process_server_cookie(
{
const uint8_t *position = NULL;
uint16_t option_len = 0;
int gai_r;
int found = match_edns_opt_rr(EDNS_COOKIE_OPCODE, netreq,
&position, &option_len);
if (found != 2)
return found;
if (found == MATCH_OPT_ERROR) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_WARNING,
"%-40s : Upstream : Error getting Cookie option.\n",
upstream->addr_str);
if (option_len < 16 || option_len > 40)
return 1; /* FORMERR */
if (!upstream->has_client_cookie)
return 1; /* Cookie reply, but we didn't sent one */
if (memcmp(upstream->client_cookie, position, 8) != 0) {
if (!upstream->has_prev_client_cookie)
return 1; /* Cookie didn't match */
if (memcmp(upstream->prev_client_cookie, position, 8) != 0)
return 1; /* Previous cookie didn't match either */
upstream->has_server_cookie = 0;
return 0; /* Don't store server cookie, because it
* is for our previous client cookie
*/
return 1; /* Discard and wait for better response */
}
else if (found == MATCH_OPT_NOT_FOUND) {
/* Option not found, server does not support cookies */
if (upstream->server_cookie_len > 8) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_ERR,
"%-40s : Upstream : Server did not return "
" DNS Cookie. Response discarded.\n",
upstream->addr_str);
return 1; /* Discard response */
} else if (netreq->cookie_sent) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_INFO,
"%-40s : Upstream : Does not support DNS Cookies"
". Retrying in one hour.\n", upstream->addr_str);
upstream->src_addr_checked = _getdns_get_now_ms();
}
return 0; /* Use response */
}
assert(found == MATCH_OPT_FOUND);
if (option_len < 16 || option_len > 40) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_WARNING,
"%-40s : Upstream : "
"Unsupported Server Cookie size: %d.\n",
upstream->addr_str, (int)option_len);
return 1; /* Discard and wait for better response */
}
if (upstream->server_cookie_len > 8) {
if (memcmp(upstream->server_cookie, position, 8)) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_WARNING,
"%-40s : Upstream : DNS Cookie did not match.\n",
upstream->addr_str);
return 1; /* Discard and wait for better response */
}
/* Update server cookie */
upstream->server_cookie_len = option_len;
(void) memcpy(upstream->server_cookie, position, option_len);
return 0; /* Use response */
} else if (!netreq->cookie_sent) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_WARNING,
"%-40s : Upstream : "
"DNS Cookie received but none sent.\n",upstream->addr_str);
return 1; /* Discard and wait for better response */
}
if (memcmp(netreq->client_cookie, position, 8)) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_WARNING,
"%-40s : Upstream : DNS Cookie did not match.\n",
upstream->addr_str);
return 1; /* Discard and wait for better response */
}
/* A new client cookie matched, store server cookie but only if we
* can get the source IP address.
*/
upstream->src_addr_checked = _getdns_get_now_ms();
upstream->src_addr_len = sizeof(upstream->src_addr);
if (getsockname(netreq->fd,(struct sockaddr*)
&upstream->src_addr, &upstream->src_addr_len)) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_WARNING,
"%-40s : Upstream : Could not get source address: %s. "
"Privacy aware DNS Cookies not supported.\n",
upstream->addr_str, strerror(errno));
} else if ((gai_r = getnameinfo((struct sockaddr *)
&upstream->src_addr, upstream->src_addr_len,
upstream->src_addr_str, sizeof(upstream->src_addr_str),
NULL, 0, NI_NUMERICHOST))) {
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_WARNING,
"%-40s : Upstream : Could not print source address: %s. "
"Privacy aware DNS Cookies not supported.\n",
upstream->addr_str, gai_strerror(gai_r));
} else {
switch (upstream->src_addr.ss_family) {
case AF_INET:
((struct sockaddr_in *)&upstream->src_addr)->sin_port = 0;
break;
case AF_INET6:
((struct sockaddr_in6*)&upstream->src_addr)->sin6_port = 0;
break;
default:
return 0;
}
_getdns_upstream_log(upstream,
GETDNS_LOG_UPSTREAM_STATS, GETDNS_LOG_DEBUG,
"%-40s : Upstream : "
"Registering new Server Cookie for source address: %s.\n",
upstream->addr_str, upstream->src_addr_str);
upstream->server_cookie_len = option_len;
(void) memcpy(upstream->server_cookie, position, option_len);
return 0;
}
position += 8;
option_len -= 8;
upstream->has_server_cookie = 1;
upstream->server_cookie_len = option_len;
(void) memcpy(upstream->server_cookie, position, option_len);
return 0;
}

2
src/types-internal.h
View File

@ -247,6 +247,8 @@ typedef struct getdns_network_req
unsigned debug_udp : 1;
unsigned keepalive_sent : 1;
unsigned badcookie_retry: 1;
unsigned cookie_sent : 1;
uint8_t client_cookie[8];
/* When more space is needed for the wire_data response than is
* available in wire_data[], it will be allocated separately.

11
src/util-internal.h
View File

@ -213,6 +213,17 @@ INLINE uint64_t _getdns_ms_until_expiry(uint64_t expires)
return now_ms >= expires ? 0 : expires - now_ms;
}
INLINE uint64_t _getdns_get_now_ms2(uint64_t *now_ms)
{
struct timeval tv;
if (!now_ms) return _getdns_get_now_ms();
if (*now_ms) return *now_ms;
(void) gettimeofday(&tv, NULL);
return (*now_ms = (uint64_t)tv.tv_sec * 1000 + tv.tv_usec / 1000);
}
INLINE uint64_t _getdns_ms_until_expiry2(uint64_t expires, uint64_t *now_ms)
{
if (*now_ms == 0) *now_ms = _getdns_get_now_ms();