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
ssltestlib.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 <string.h>
#include "ssltestlib.h"
static int tls_dump_new(BIO *bi);
static int tls_dump_free(BIO *a);
static int tls_dump_read(BIO *b, char *out, int outl);
static int tls_dump_write(BIO *b, const char *in, int inl);
static long tls_dump_ctrl(BIO *b, int cmd, long num, void *ptr);
static int tls_dump_gets(BIO *bp, char *buf, int size);
static int tls_dump_puts(BIO *bp, const char *str);
/* Choose a sufficiently large type likely to be unused for this custom BIO */
# define BIO_TYPE_TLS_DUMP_FILTER (0x80 | BIO_TYPE_FILTER)
# define BIO_TYPE_MEMPACKET_TEST 0x81
static BIO_METHOD *method_tls_dump = NULL;
static BIO_METHOD *method_mempacket_test = NULL;
/* Note: Not thread safe! */
const BIO_METHOD *bio_f_tls_dump_filter(void)
{
if (method_tls_dump == NULL) {
method_tls_dump = BIO_meth_new(BIO_TYPE_TLS_DUMP_FILTER,
"TLS dump filter");
if ( method_tls_dump == NULL
|| !BIO_meth_set_write(method_tls_dump, tls_dump_write)
|| !BIO_meth_set_read(method_tls_dump, tls_dump_read)
|| !BIO_meth_set_puts(method_tls_dump, tls_dump_puts)
|| !BIO_meth_set_gets(method_tls_dump, tls_dump_gets)
|| !BIO_meth_set_ctrl(method_tls_dump, tls_dump_ctrl)
|| !BIO_meth_set_create(method_tls_dump, tls_dump_new)
|| !BIO_meth_set_destroy(method_tls_dump, tls_dump_free))
return NULL;
}
return method_tls_dump;
}
void bio_f_tls_dump_filter_free(void)
{
BIO_meth_free(method_tls_dump);
}
static int tls_dump_new(BIO *bio)
{
BIO_set_init(bio, 1);
return 1;
}
static int tls_dump_free(BIO *bio)
{
BIO_set_init(bio, 0);
return 1;
}
static void copy_flags(BIO *bio)
{
int flags;
BIO *next = BIO_next(bio);
flags = BIO_test_flags(next, BIO_FLAGS_SHOULD_RETRY | BIO_FLAGS_RWS);
BIO_clear_flags(bio, BIO_FLAGS_SHOULD_RETRY | BIO_FLAGS_RWS);
BIO_set_flags(bio, flags);
}
#define RECORD_CONTENT_TYPE 0
#define RECORD_VERSION_HI 1
#define RECORD_VERSION_LO 2
#define RECORD_EPOCH_HI 3
#define RECORD_EPOCH_LO 4
#define RECORD_SEQUENCE_START 5
#define RECORD_SEQUENCE_END 10
#define RECORD_LEN_HI 11
#define RECORD_LEN_LO 12
#define MSG_TYPE 0
#define MSG_LEN_HI 1
#define MSG_LEN_MID 2
#define MSG_LEN_LO 3
#define MSG_SEQ_HI 4
#define MSG_SEQ_LO 5
#define MSG_FRAG_OFF_HI 6
#define MSG_FRAG_OFF_MID 7
#define MSG_FRAG_OFF_LO 8
#define MSG_FRAG_LEN_HI 9
#define MSG_FRAG_LEN_MID 10
#define MSG_FRAG_LEN_LO 11
static void dump_data(const char *data, int len)
{
int rem, i, content, reclen, msglen, fragoff, fraglen, epoch;
unsigned char *rec;
printf("---- START OF PACKET ----\n");
rem = len;
rec = (unsigned char *)data;
while (rem > 0) {
if (rem != len)
printf("*\n");
printf("*---- START OF RECORD ----\n");
if (rem < DTLS1_RT_HEADER_LENGTH) {
printf("*---- RECORD TRUNCATED ----\n");
break;
}
content = rec[RECORD_CONTENT_TYPE];
printf("** Record Content-type: %d\n", content);
printf("** Record Version: %02x%02x\n",
rec[RECORD_VERSION_HI], rec[RECORD_VERSION_LO]);
epoch = (rec[RECORD_EPOCH_HI] << 8) | rec[RECORD_EPOCH_LO];
printf("** Record Epoch: %d\n", epoch);
printf("** Record Sequence: ");
for (i = RECORD_SEQUENCE_START; i <= RECORD_SEQUENCE_END; i++)
printf("%02x", rec[i]);
reclen = (rec[RECORD_LEN_HI] << 8) | rec[RECORD_LEN_LO];
printf("\n** Record Length: %d\n", reclen);
/* Now look at message */
rec += DTLS1_RT_HEADER_LENGTH;
rem -= DTLS1_RT_HEADER_LENGTH;
if (content == SSL3_RT_HANDSHAKE) {
printf("**---- START OF HANDSHAKE MESSAGE FRAGMENT ----\n");
if (epoch > 0) {
printf("**---- HANDSHAKE MESSAGE FRAGMENT ENCRYPTED ----\n");
} else if (rem < DTLS1_HM_HEADER_LENGTH
|| reclen < DTLS1_HM_HEADER_LENGTH) {
printf("**---- HANDSHAKE MESSAGE FRAGMENT TRUNCATED ----\n");
} else {
printf("*** Message Type: %d\n", rec[MSG_TYPE]);
msglen = (rec[MSG_LEN_HI] << 16) | (rec[MSG_LEN_MID] << 8)
| rec[MSG_LEN_LO];
printf("*** Message Length: %d\n", msglen);
printf("*** Message sequence: %d\n",
(rec[MSG_SEQ_HI] << 8) | rec[MSG_SEQ_LO]);
fragoff = (rec[MSG_FRAG_OFF_HI] << 16)
| (rec[MSG_FRAG_OFF_MID] << 8)
| rec[MSG_FRAG_OFF_LO];
printf("*** Message Fragment offset: %d\n", fragoff);
fraglen = (rec[MSG_FRAG_LEN_HI] << 16)
| (rec[MSG_FRAG_LEN_MID] << 8)
| rec[MSG_FRAG_LEN_LO];
printf("*** Message Fragment len: %d\n", fraglen);
if (fragoff + fraglen > msglen)
printf("***---- HANDSHAKE MESSAGE FRAGMENT INVALID ----\n");
else if(reclen < fraglen)
printf("**---- HANDSHAKE MESSAGE FRAGMENT TRUNCATED ----\n");
else
printf("**---- END OF HANDSHAKE MESSAGE FRAGMENT ----\n");
}
}
if (rem < reclen) {
printf("*---- RECORD TRUNCATED ----\n");
rem = 0;
} else {
rec += reclen;
rem -= reclen;
printf("*---- END OF RECORD ----\n");
}
}
printf("---- END OF PACKET ----\n\n");
fflush(stdout);
}
static int tls_dump_read(BIO *bio, char *out, int outl)
{
int ret;
BIO *next = BIO_next(bio);
ret = BIO_read(next, out, outl);
copy_flags(bio);
if (ret > 0) {
dump_data(out, ret);
}
return ret;
}
static int tls_dump_write(BIO *bio, const char *in, int inl)
{
int ret;
BIO *next = BIO_next(bio);
ret = BIO_write(next, in, inl);
copy_flags(bio);
return ret;
}
static long tls_dump_ctrl(BIO *bio, int cmd, long num, void *ptr)
{
long ret;
BIO *next = BIO_next(bio);
if (next == NULL)
return 0;
switch (cmd) {
case BIO_CTRL_DUP:
ret = 0L;
break;
default:
ret = BIO_ctrl(next, cmd, num, ptr);
break;
}
return ret;
}
static int tls_dump_gets(BIO *bio, char *buf, int size)
{
/* We don't support this - not needed anyway */
return -1;
}
static int tls_dump_puts(BIO *bio, const char *str)
{
return tls_dump_write(bio, str, strlen(str));
}
struct mempacket_st {
unsigned char *data;
int len;
unsigned int num;
unsigned int type;
};
static void mempacket_free(MEMPACKET *pkt)
{
if (pkt->data != NULL)
OPENSSL_free(pkt->data);
OPENSSL_free(pkt);
}
typedef struct mempacket_test_ctx_st {
STACK_OF(MEMPACKET) *pkts;
unsigned int epoch;
unsigned int currrec;
unsigned int currpkt;
unsigned int lastpkt;
unsigned int noinject;
} MEMPACKET_TEST_CTX;
static int mempacket_test_new(BIO *bi);
static int mempacket_test_free(BIO *a);
static int mempacket_test_read(BIO *b, char *out, int outl);
static int mempacket_test_write(BIO *b, const char *in, int inl);
static long mempacket_test_ctrl(BIO *b, int cmd, long num, void *ptr);
static int mempacket_test_gets(BIO *bp, char *buf, int size);
static int mempacket_test_puts(BIO *bp, const char *str);
const BIO_METHOD *bio_s_mempacket_test(void)
{
if (method_mempacket_test == NULL) {
method_mempacket_test = BIO_meth_new(BIO_TYPE_MEMPACKET_TEST,
"Mem Packet Test");
if ( method_mempacket_test == NULL
|| !BIO_meth_set_write(method_mempacket_test, mempacket_test_write)
|| !BIO_meth_set_read(method_mempacket_test, mempacket_test_read)
|| !BIO_meth_set_puts(method_mempacket_test, mempacket_test_puts)
|| !BIO_meth_set_gets(method_mempacket_test, mempacket_test_gets)
|| !BIO_meth_set_ctrl(method_mempacket_test, mempacket_test_ctrl)
|| !BIO_meth_set_create(method_mempacket_test, mempacket_test_new)
|| !BIO_meth_set_destroy(method_mempacket_test, mempacket_test_free))
return NULL;
}
return method_mempacket_test;
}
void bio_s_mempacket_test_free(void)
{
BIO_meth_free(method_mempacket_test);
}
static int mempacket_test_new(BIO *bio)
{
MEMPACKET_TEST_CTX *ctx = OPENSSL_zalloc(sizeof(*ctx));
if (ctx == NULL)
return 0;
ctx->pkts = sk_MEMPACKET_new_null();
if (ctx->pkts == NULL) {
OPENSSL_free(ctx);
return 0;
}
BIO_set_init(bio, 1);
BIO_set_data(bio, ctx);
return 1;
}
static int mempacket_test_free(BIO *bio)
{
MEMPACKET_TEST_CTX *ctx = BIO_get_data(bio);
sk_MEMPACKET_pop_free(ctx->pkts, mempacket_free);
OPENSSL_free(ctx);
BIO_set_data(bio, NULL);
BIO_set_init(bio, 0);
return 1;
}
/* Record Header values */
#define EPOCH_HI 4
#define EPOCH_LO 5
#define RECORD_SEQUENCE 10
#define RECORD_LEN_HI 11
#define RECORD_LEN_LO 12
#define STANDARD_PACKET 0
static int mempacket_test_read(BIO *bio, char *out, int outl)
{
MEMPACKET_TEST_CTX *ctx = BIO_get_data(bio);
MEMPACKET *thispkt;
unsigned char *rec;
int rem;
unsigned int seq, offset, len, epoch;
BIO_clear_retry_flags(bio);
thispkt = sk_MEMPACKET_value(ctx->pkts, 0);
if (thispkt == NULL || thispkt->num != ctx->currpkt) {
/* Probably run out of data */
BIO_set_retry_read(bio);
return -1;
}
sk_MEMPACKET_shift(ctx->pkts);
ctx->currpkt++;
if (outl > thispkt->len)
outl = thispkt->len;
if (thispkt->type != INJECT_PACKET_IGNORE_REC_SEQ) {
/*
* Overwrite the record sequence number. We strictly number them in
* the order received. Since we are actually a reliable transport
* we know that there won't be any re-ordering. We overwrite to deal
* with any packets that have been injected
*/
rem = thispkt->len;
rec = thispkt->data;
while (rem > 0) {
if (rem < DTLS1_RT_HEADER_LENGTH) {
return -1;
}
epoch = (rec[EPOCH_HI] << 8) | rec[EPOCH_LO];
if (epoch != ctx->epoch) {
ctx->epoch = epoch;
ctx->currrec = 0;
}
seq = ctx->currrec;
offset = 0;
do {
rec[RECORD_SEQUENCE - offset] = seq & 0xFF;
seq >>= 8;
offset++;
} while (seq > 0);
ctx->currrec++;
len = ((rec[RECORD_LEN_HI] << 8) | rec[RECORD_LEN_LO])
+ DTLS1_RT_HEADER_LENGTH;
rec += len;
rem -= len;
}
}
memcpy(out, thispkt->data, outl);
mempacket_free(thispkt);
return outl;
}
int mempacket_test_inject(BIO *bio, const char *in, int inl, int pktnum,
int type)
{
MEMPACKET_TEST_CTX *ctx = BIO_get_data(bio);
MEMPACKET *thispkt, *looppkt, *nextpkt;
int i;
if (ctx == NULL)
return -1;
/* We only allow injection before we've started writing any data */
if (pktnum >= 0) {
if (ctx->noinject)
return -1;
} else {
ctx->noinject = 1;
}
thispkt = OPENSSL_malloc(sizeof(MEMPACKET));
if (thispkt == NULL)
return -1;
thispkt->data = OPENSSL_malloc(inl);
if (thispkt->data == NULL) {
mempacket_free(thispkt);
return -1;
}
memcpy(thispkt->data, in, inl);
thispkt->len = inl;
thispkt->num = (pktnum >= 0) ? (unsigned int)pktnum : ctx->lastpkt;
thispkt->type = type;
for(i = 0; (looppkt = sk_MEMPACKET_value(ctx->pkts, i)) != NULL; i++) {
/* Check if we found the right place to insert this packet */
if (looppkt->num > thispkt->num) {
if (sk_MEMPACKET_insert(ctx->pkts, thispkt, i) == 0) {
mempacket_free(thispkt);
return -1;
}
/* If we're doing up front injection then we're done */
if (pktnum >= 0)
return inl;
/*
* We need to do some accounting on lastpkt. We increment it first,
* but it might now equal the value of injected packets, so we need
* to skip over those
*/
ctx->lastpkt++;
do {
i++;
nextpkt = sk_MEMPACKET_value(ctx->pkts, i);
if (nextpkt != NULL && nextpkt->num == ctx->lastpkt)
ctx->lastpkt++;
else
return inl;
} while(1);
} else if(looppkt->num == thispkt->num) {
if (!ctx->noinject) {
/* We injected two packets with the same packet number! */
return -1;
}
ctx->lastpkt++;
thispkt->num++;
}
}
/*
* We didn't find any packets with a packet number equal to or greater than
* this one, so we just add it onto the end
*/
if (!sk_MEMPACKET_push(ctx->pkts, thispkt)) {
mempacket_free(thispkt);
return -1;
}
if (pktnum < 0)
ctx->lastpkt++;
return inl;
}
static int mempacket_test_write(BIO *bio, const char *in, int inl)
{
return mempacket_test_inject(bio, in, inl, -1, STANDARD_PACKET);
}
static long mempacket_test_ctrl(BIO *bio, int cmd, long num, void *ptr)
{
long ret = 1;
MEMPACKET_TEST_CTX *ctx = BIO_get_data(bio);
MEMPACKET *thispkt;
switch (cmd) {
case BIO_CTRL_EOF:
ret = (long)(sk_MEMPACKET_num(ctx->pkts) == 0);
break;
case BIO_CTRL_GET_CLOSE:
ret = BIO_get_shutdown(bio);
break;
case BIO_CTRL_SET_CLOSE:
BIO_set_shutdown(bio, (int)num);
break;
case BIO_CTRL_WPENDING:
ret = 0L;
break;
case BIO_CTRL_PENDING:
thispkt = sk_MEMPACKET_value(ctx->pkts, 0);
if (thispkt == NULL)
ret = 0;
else
ret = thispkt->len;
break;
case BIO_CTRL_FLUSH:
ret = 1;
break;
case BIO_CTRL_RESET:
case BIO_CTRL_DUP:
case BIO_CTRL_PUSH:
case BIO_CTRL_POP:
default:
ret = 0;
break;
}
return ret;
}
static int mempacket_test_gets(BIO *bio, char *buf, int size)
{
/* We don't support this - not needed anyway */
return -1;
}
static int mempacket_test_puts(BIO *bio, const char *str)
{
return mempacket_test_write(bio, str, strlen(str));
}
int create_ssl_ctx_pair(const SSL_METHOD *sm, const SSL_METHOD *cm,
SSL_CTX **sctx, SSL_CTX **cctx, char *certfile,
char *privkeyfile)
{
SSL_CTX *serverctx = NULL;
SSL_CTX *clientctx = NULL;
serverctx = SSL_CTX_new(sm);
clientctx = SSL_CTX_new(cm);
if (serverctx == NULL || clientctx == NULL) {
printf("Failed to create SSL_CTX\n");
goto err;
}
if (SSL_CTX_use_certificate_file(serverctx, certfile,
SSL_FILETYPE_PEM) <= 0) {
printf("Failed to load server certificate\n");
goto err;
}
if (SSL_CTX_use_PrivateKey_file(serverctx, privkeyfile,
SSL_FILETYPE_PEM) <= 0) {
printf("Failed to load server private key\n");
}
if (SSL_CTX_check_private_key(serverctx) <= 0) {
printf("Failed to check private key\n");
goto err;
}
*sctx = serverctx;
*cctx = clientctx;
return 1;
err:
SSL_CTX_free(serverctx);
SSL_CTX_free(clientctx);
return 0;
}
#define MAXLOOPS 100000
/*
* NOTE: Transfers control of the BIOs - this function will free them on error
*/
int create_ssl_objects(SSL_CTX *serverctx, SSL_CTX *clientctx, SSL **sssl,
SSL **cssl, BIO *s_to_c_fbio, BIO *c_to_s_fbio)
{
SSL *serverssl, *clientssl;
BIO *s_to_c_bio = NULL, *c_to_s_bio = NULL;
if (*sssl == NULL)
serverssl = SSL_new(serverctx);
else
serverssl = *sssl;
if (*cssl == NULL)
clientssl = SSL_new(clientctx);
else
clientssl = *cssl;
if (serverssl == NULL || clientssl == NULL) {
printf("Failed to create SSL object\n");
goto error;
}
if (SSL_is_dtls(clientssl)) {
s_to_c_bio = BIO_new(bio_s_mempacket_test());
c_to_s_bio = BIO_new(bio_s_mempacket_test());;
} else {
s_to_c_bio = BIO_new(BIO_s_mem());
c_to_s_bio = BIO_new(BIO_s_mem());
}
if (s_to_c_bio == NULL || c_to_s_bio == NULL) {
printf("Failed to create mem BIOs\n");
goto error;
}
if (s_to_c_fbio != NULL)
s_to_c_bio = BIO_push(s_to_c_fbio, s_to_c_bio);
if (c_to_s_fbio != NULL)
c_to_s_bio = BIO_push(c_to_s_fbio, c_to_s_bio);
if (s_to_c_bio == NULL || c_to_s_bio == NULL) {
printf("Failed to create chained BIOs\n");
goto error;
}
/* Set Non-blocking IO behaviour */
BIO_set_mem_eof_return(s_to_c_bio, -1);
BIO_set_mem_eof_return(c_to_s_bio, -1);
/* Up ref these as we are passing them to two SSL objects */
BIO_up_ref(s_to_c_bio);
BIO_up_ref(c_to_s_bio);
SSL_set_bio(serverssl, c_to_s_bio, s_to_c_bio);
SSL_set_bio(clientssl, s_to_c_bio, c_to_s_bio);
/* BIOs will now be freed when SSL objects are freed */
s_to_c_bio = c_to_s_bio = NULL;
s_to_c_fbio = c_to_s_fbio = NULL;
*sssl = serverssl;
*cssl = clientssl;
return 1;
error:
SSL_free(serverssl);
SSL_free(clientssl);
BIO_free(s_to_c_bio);
BIO_free(c_to_s_bio);
BIO_free(s_to_c_fbio);
BIO_free(c_to_s_fbio);
return 0;
}
int create_ssl_connection(SSL *serverssl, SSL *clientssl)
{
int retc = -1, rets = -1, err, abortctr = 0;
int clienterr = 0, servererr = 0;
do {
err = SSL_ERROR_WANT_WRITE;
while (!clienterr && retc <= 0 && err == SSL_ERROR_WANT_WRITE) {
retc = SSL_connect(clientssl);
if (retc <= 0)
err = SSL_get_error(clientssl, retc);
}
if (!clienterr && retc <= 0 && err != SSL_ERROR_WANT_READ) {
printf("SSL_connect() failed %d, %d\n", retc, err);
clienterr = 1;
}
err = SSL_ERROR_WANT_WRITE;
while (!servererr && rets <= 0 && err == SSL_ERROR_WANT_WRITE) {
rets = SSL_accept(serverssl);
if (rets <= 0)
err = SSL_get_error(serverssl, rets);
}
if (!servererr && rets <= 0 && err != SSL_ERROR_WANT_READ) {
printf("SSL_accept() failed %d, %d\n", retc, err);
servererr = 1;
}
if (clienterr && servererr)
return 0;
if (++abortctr == MAXLOOPS) {
printf("No progress made\n");
return 0;
}
} while (retc <=0 || rets <= 0);
return 1;
}
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