Revision f5c7f5dfbaf0d2f7d946d0fe86f08e6bcb36ed0d authored by Matt Caswell on 30 June 2016, 12:17:08 UTC, committed by Matt Caswell on 22 August 2016, 09:53:55 UTC
DTLS can handle out of order record delivery. Additionally since handshake messages can be bigger than will fit into a single packet, the messages can be fragmented across multiple records (as with normal TLS). That means that the messages can arrive mixed up, and we have to reassemble them. We keep a queue of buffered messages that are "from the future", i.e. messages we're not ready to deal with yet but have arrived early. The messages held there may not be full yet - they could be one or more fragments that are still in the process of being reassembled. The code assumes that we will eventually complete the reassembly and when that occurs the complete message is removed from the queue at the point that we need to use it. However, DTLS is also tolerant of packet loss. To get around that DTLS messages can be retransmitted. If we receive a full (non-fragmented) message from the peer after previously having received a fragment of that message, then we ignore the message in the queue and just use the non-fragmented version. At that point the queued message will never get removed. Additionally the peer could send "future" messages that we never get to in order to complete the handshake. Each message has a sequence number (starting from 0). We will accept a message fragment for the current message sequence number, or for any sequence up to 10 into the future. However if the Finished message has a sequence number of 2, anything greater than that in the queue is just left there. So, in those two ways we can end up with "orphaned" data in the queue that will never get removed - except when the connection is closed. At that point all the queues are flushed. An attacker could seek to exploit this by filling up the queues with lots of large messages that are never going to be used in order to attempt a DoS by memory exhaustion. I will assume that we are only concerned with servers here. It does not seem reasonable to be concerned about a memory exhaustion attack on a client. They are unlikely to process enough connections for this to be an issue. A "long" handshake with many messages might be 5 messages long (in the incoming direction), e.g. ClientHello, Certificate, ClientKeyExchange, CertificateVerify, Finished. So this would be message sequence numbers 0 to 4. Additionally we can buffer up to 10 messages in the future. Therefore the maximum number of messages that an attacker could send that could get orphaned would typically be 15. The maximum size that a DTLS message is allowed to be is defined by max_cert_list, which by default is 100k. Therefore the maximum amount of "orphaned" memory per connection is 1500k. Message sequence numbers get reset after the Finished message, so renegotiation will not extend the maximum number of messages that can be orphaned per connection. As noted above, the queues do get cleared when the connection is closed. Therefore in order to mount an effective attack, an attacker would have to open many simultaneous connections. Issue reported by Quan Luo. CVE-2016-2179 Reviewed-by: Richard Levitte <levitte@openssl.org>
1 parent 5dfd038
ssl_test.c
/*
* Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <stdio.h>
#include <string.h>
#include <openssl/conf.h>
#include <openssl/err.h>
#include <openssl/ssl.h>
#include "handshake_helper.h"
#include "ssl_test_ctx.h"
#include "testutil.h"
static CONF *conf = NULL;
/* Currently the section names are of the form test-<number>, e.g. test-15. */
#define MAX_TESTCASE_NAME_LENGTH 100
typedef struct ssl_test_ctx_test_fixture {
const char *test_case_name;
char test_app[MAX_TESTCASE_NAME_LENGTH];
} SSL_TEST_FIXTURE;
static SSL_TEST_FIXTURE set_up(const char *const test_case_name)
{
SSL_TEST_FIXTURE fixture;
fixture.test_case_name = test_case_name;
return fixture;
}
static const char *print_alert(int alert)
{
return alert ? SSL_alert_desc_string_long(alert) : "no alert";
}
static int check_result(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
if (result->result != test_ctx->expected_result) {
fprintf(stderr, "ExpectedResult mismatch: expected %s, got %s.\n",
ssl_test_result_name(test_ctx->expected_result),
ssl_test_result_name(result->result));
return 0;
}
return 1;
}
static int check_alerts(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
if (result->client_alert_sent != result->client_alert_received) {
fprintf(stderr, "Client sent alert %s but server received %s\n.",
print_alert(result->client_alert_sent),
print_alert(result->client_alert_received));
/*
* We can't bail here because the peer doesn't always get far enough
* to process a received alert. Specifically, in protocol version
* negotiation tests, we have the following scenario.
* Client supports TLS v1.2 only; Server supports TLS v1.1.
* Client proposes TLS v1.2; server responds with 1.1;
* Client now sends a protocol alert, using TLS v1.2 in the header.
* The server, however, rejects the alert because of version mismatch
* in the record layer; therefore, the server appears to never
* receive the alert.
*/
/* return 0; */
}
if (result->server_alert_sent != result->server_alert_received) {
fprintf(stderr, "Server sent alert %s but client received %s\n.",
print_alert(result->server_alert_sent),
print_alert(result->server_alert_received));
/* return 0; */
}
/* Tolerate an alert if one wasn't explicitly specified in the test. */
if (test_ctx->expected_client_alert
/*
* The info callback alert value is computed as
* (s->s3->send_alert[0] << 8) | s->s3->send_alert[1]
* where the low byte is the alert code and the high byte is other stuff.
*/
&& (result->client_alert_sent & 0xff) != test_ctx->expected_client_alert) {
fprintf(stderr, "ClientAlert mismatch: expected %s, got %s.\n",
print_alert(test_ctx->expected_client_alert),
print_alert(result->client_alert_sent));
return 0;
}
if (test_ctx->expected_server_alert
&& (result->server_alert_sent & 0xff) != test_ctx->expected_server_alert) {
fprintf(stderr, "ServerAlert mismatch: expected %s, got %s.\n",
print_alert(test_ctx->expected_server_alert),
print_alert(result->server_alert_sent));
return 0;
}
if (result->client_num_fatal_alerts_sent > 1) {
fprintf(stderr, "Client sent %d fatal alerts.\n",
result->client_num_fatal_alerts_sent);
return 0;
}
if (result->server_num_fatal_alerts_sent > 1) {
fprintf(stderr, "Server sent %d alerts.\n",
result->server_num_fatal_alerts_sent);
return 0;
}
return 1;
}
static int check_protocol(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
if (result->client_protocol != result->server_protocol) {
fprintf(stderr, "Client has protocol %s but server has %s\n.",
ssl_protocol_name(result->client_protocol),
ssl_protocol_name(result->server_protocol));
return 0;
}
if (test_ctx->expected_protocol) {
if (result->client_protocol != test_ctx->expected_protocol) {
fprintf(stderr, "Protocol mismatch: expected %s, got %s.\n",
ssl_protocol_name(test_ctx->expected_protocol),
ssl_protocol_name(result->client_protocol));
return 0;
}
}
return 1;
}
static int check_servername(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
if (result->servername != test_ctx->expected_servername) {
fprintf(stderr, "Client ServerName mismatch, expected %s, got %s\n.",
ssl_servername_name(test_ctx->expected_servername),
ssl_servername_name(result->servername));
return 0;
}
return 1;
}
static int check_session_ticket(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
if (test_ctx->session_ticket_expected == SSL_TEST_SESSION_TICKET_IGNORE)
return 1;
if (result->session_ticket != test_ctx->session_ticket_expected) {
fprintf(stderr, "Client SessionTicketExpected mismatch, expected %s, got %s\n.",
ssl_session_ticket_name(test_ctx->session_ticket_expected),
ssl_session_ticket_name(result->session_ticket));
return 0;
}
return 1;
}
#ifndef OPENSSL_NO_NEXTPROTONEG
static int check_npn(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
int ret = 1;
ret &= strings_equal("NPN Negotiated (client vs server)",
result->client_npn_negotiated,
result->server_npn_negotiated);
ret &= strings_equal("ExpectedNPNProtocol",
test_ctx->expected_npn_protocol,
result->client_npn_negotiated);
return ret;
}
#endif
static int check_alpn(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
int ret = 1;
ret &= strings_equal("ALPN Negotiated (client vs server)",
result->client_alpn_negotiated,
result->server_alpn_negotiated);
ret &= strings_equal("ExpectedALPNProtocol",
test_ctx->expected_alpn_protocol,
result->client_alpn_negotiated);
return ret;
}
static int check_resumption(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
if (result->client_resumed != result->server_resumed) {
fprintf(stderr, "Resumption mismatch (client vs server): %d vs %d\n",
result->client_resumed, result->server_resumed);
return 0;
}
if (result->client_resumed != test_ctx->resumption_expected) {
fprintf(stderr, "ResumptionExpected mismatch: %d vs %d\n",
test_ctx->resumption_expected, result->client_resumed);
return 0;
}
return 1;
}
/*
* This could be further simplified by constructing an expected
* HANDSHAKE_RESULT, and implementing comparison methods for
* its fields.
*/
static int check_test(HANDSHAKE_RESULT *result, SSL_TEST_CTX *test_ctx)
{
int ret = 1;
ret &= check_result(result, test_ctx);
ret &= check_alerts(result, test_ctx);
if (result->result == SSL_TEST_SUCCESS) {
ret &= check_protocol(result, test_ctx);
ret &= check_servername(result, test_ctx);
ret &= check_session_ticket(result, test_ctx);
ret &= (result->session_ticket_do_not_call == 0);
#ifndef OPENSSL_NO_NEXTPROTONEG
ret &= check_npn(result, test_ctx);
#endif
ret &= check_alpn(result, test_ctx);
ret &= check_resumption(result, test_ctx);
}
return ret;
}
static int execute_test(SSL_TEST_FIXTURE fixture)
{
int ret = 0;
SSL_CTX *server_ctx = NULL, *server2_ctx = NULL, *client_ctx = NULL,
*resume_server_ctx = NULL, *resume_client_ctx = NULL;
SSL_TEST_CTX *test_ctx = NULL;
HANDSHAKE_RESULT *result = NULL;
test_ctx = SSL_TEST_CTX_create(conf, fixture.test_app);
if (test_ctx == NULL)
goto err;
#ifndef OPENSSL_NO_DTLS
if (test_ctx->method == SSL_TEST_METHOD_DTLS) {
server_ctx = SSL_CTX_new(DTLS_server_method());
if (test_ctx->extra.server.servername_callback !=
SSL_TEST_SERVERNAME_CB_NONE) {
server2_ctx = SSL_CTX_new(DTLS_server_method());
TEST_check(server2_ctx != NULL);
}
client_ctx = SSL_CTX_new(DTLS_client_method());
if (test_ctx->handshake_mode == SSL_TEST_HANDSHAKE_RESUME) {
resume_server_ctx = SSL_CTX_new(DTLS_server_method());
resume_client_ctx = SSL_CTX_new(DTLS_client_method());
TEST_check(resume_server_ctx != NULL);
TEST_check(resume_client_ctx != NULL);
}
}
#endif
if (test_ctx->method == SSL_TEST_METHOD_TLS) {
server_ctx = SSL_CTX_new(TLS_server_method());
/* SNI on resumption isn't supported/tested yet. */
if (test_ctx->extra.server.servername_callback !=
SSL_TEST_SERVERNAME_CB_NONE) {
server2_ctx = SSL_CTX_new(TLS_server_method());
TEST_check(server2_ctx != NULL);
}
client_ctx = SSL_CTX_new(TLS_client_method());
if (test_ctx->handshake_mode == SSL_TEST_HANDSHAKE_RESUME) {
resume_server_ctx = SSL_CTX_new(TLS_server_method());
resume_client_ctx = SSL_CTX_new(TLS_client_method());
TEST_check(resume_server_ctx != NULL);
TEST_check(resume_client_ctx != NULL);
}
}
TEST_check(server_ctx != NULL);
TEST_check(client_ctx != NULL);
TEST_check(CONF_modules_load(conf, fixture.test_app, 0) > 0);
if (!SSL_CTX_config(server_ctx, "server")
|| !SSL_CTX_config(client_ctx, "client")) {
goto err;
}
if (server2_ctx != NULL && !SSL_CTX_config(server2_ctx, "server2"))
goto err;
if (resume_server_ctx != NULL
&& !SSL_CTX_config(resume_server_ctx, "resume-server"))
goto err;
if (resume_client_ctx != NULL
&& !SSL_CTX_config(resume_client_ctx, "resume-client"))
goto err;
result = do_handshake(server_ctx, server2_ctx, client_ctx,
resume_server_ctx, resume_client_ctx, test_ctx);
ret = check_test(result, test_ctx);
err:
CONF_modules_unload(0);
SSL_CTX_free(server_ctx);
SSL_CTX_free(server2_ctx);
SSL_CTX_free(client_ctx);
SSL_CTX_free(resume_server_ctx);
SSL_CTX_free(resume_client_ctx);
SSL_TEST_CTX_free(test_ctx);
if (ret != 1)
ERR_print_errors_fp(stderr);
HANDSHAKE_RESULT_free(result);
return ret;
}
static void tear_down(SSL_TEST_FIXTURE fixture)
{
}
#define SETUP_SSL_TEST_FIXTURE() \
SETUP_TEST_FIXTURE(SSL_TEST_FIXTURE, set_up)
#define EXECUTE_SSL_TEST() \
EXECUTE_TEST(execute_test, tear_down)
static int test_handshake(int idx)
{
SETUP_SSL_TEST_FIXTURE();
BIO_snprintf(fixture.test_app, sizeof(fixture.test_app),
"test-%d", idx);
EXECUTE_SSL_TEST();
}
int main(int argc, char **argv)
{
int result = 0;
long num_tests;
if (argc != 2)
return 1;
conf = NCONF_new(NULL);
TEST_check(conf != NULL);
/* argv[1] should point to the test conf file */
TEST_check(NCONF_load(conf, argv[1], NULL) > 0);
TEST_check(NCONF_get_number_e(conf, NULL, "num_tests", &num_tests));
ADD_ALL_TESTS(test_handshake, (int)(num_tests));
result = run_tests(argv[0]);
return result;
}
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