X-Git-Url: https://git.openssl.org/gitweb/?p=openssl.git;a=blobdiff_plain;f=ssl%2Fd1_lib.c;h=eb6a0f8295f1d46fa0e20de531b8fdd5ef7ecbbe;hp=a20f30a5c21d2b414f23f7816867db138cbe433b;hb=67f78eadd00ce1c3a5bbde5e42530c1a61d363a2;hpb=0485d5406a3b76dd02e73c1c7dcabebe64f9f8a2 diff --git a/ssl/d1_lib.c b/ssl/d1_lib.c index a20f30a5c2..eb6a0f8295 100644 --- a/ssl/d1_lib.c +++ b/ssl/d1_lib.c @@ -13,21 +13,18 @@ #include #include "ssl_locl.h" -#if defined(OPENSSL_SYS_VMS) -# include -#elif defined(OPENSSL_SYS_VXWORKS) +#if defined(OPENSSL_SYS_VXWORKS) # include #elif !defined(OPENSSL_SYS_WIN32) # include #endif static void get_current_time(struct timeval *t); -static int dtls1_set_handshake_header(SSL *s, int type, unsigned long len); static int dtls1_handshake_write(SSL *s); -static unsigned int dtls1_link_min_mtu(void); +static size_t dtls1_link_min_mtu(void); /* XDTLS: figure out the right values */ -static const unsigned int g_probable_mtu[] = { 1500, 512, 256 }; +static const size_t g_probable_mtu[] = { 1500, 512, 256 }; const SSL3_ENC_METHOD DTLSv1_enc_data = { tls1_enc, @@ -36,14 +33,13 @@ const SSL3_ENC_METHOD DTLSv1_enc_data = { tls1_generate_master_secret, tls1_change_cipher_state, tls1_final_finish_mac, - TLS1_FINISH_MAC_LENGTH, TLS_MD_CLIENT_FINISH_CONST, TLS_MD_CLIENT_FINISH_CONST_SIZE, TLS_MD_SERVER_FINISH_CONST, TLS_MD_SERVER_FINISH_CONST_SIZE, tls1_alert_code, tls1_export_keying_material, SSL_ENC_FLAG_DTLS | SSL_ENC_FLAG_EXPLICIT_IV, - DTLS1_HM_HEADER_LENGTH, dtls1_set_handshake_header, + dtls1_close_construct_packet, dtls1_handshake_write }; @@ -54,15 +50,14 @@ const SSL3_ENC_METHOD DTLSv1_2_enc_data = { tls1_generate_master_secret, tls1_change_cipher_state, tls1_final_finish_mac, - TLS1_FINISH_MAC_LENGTH, TLS_MD_CLIENT_FINISH_CONST, TLS_MD_CLIENT_FINISH_CONST_SIZE, TLS_MD_SERVER_FINISH_CONST, TLS_MD_SERVER_FINISH_CONST_SIZE, tls1_alert_code, tls1_export_keying_material, SSL_ENC_FLAG_DTLS | SSL_ENC_FLAG_EXPLICIT_IV | SSL_ENC_FLAG_SIGALGS | SSL_ENC_FLAG_SHA256_PRF | SSL_ENC_FLAG_TLS1_2_CIPHERS, - DTLS1_HM_HEADER_LENGTH, dtls1_set_handshake_header, + dtls1_close_construct_packet, dtls1_handshake_write }; @@ -114,6 +109,12 @@ int dtls1_new(SSL *s) } static void dtls1_clear_queues(SSL *s) +{ + dtls1_clear_received_buffer(s); + dtls1_clear_sent_buffer(s); +} + +void dtls1_clear_received_buffer(SSL *s) { pitem *item = NULL; hm_fragment *frag = NULL; @@ -123,6 +124,12 @@ static void dtls1_clear_queues(SSL *s) dtls1_hm_fragment_free(frag); pitem_free(item); } +} + +void dtls1_clear_sent_buffer(SSL *s) +{ + pitem *item = NULL; + hm_fragment *frag = NULL; while ((item = pqueue_pop(s->d1->sent_messages)) != NULL) { frag = (hm_fragment *)item->data; @@ -131,6 +138,7 @@ static void dtls1_clear_queues(SSL *s) } } + void dtls1_free(SSL *s) { DTLS_RECORD_LAYER_free(&s->rlayer); @@ -150,8 +158,8 @@ void dtls1_clear(SSL *s) { pqueue *buffered_messages; pqueue *sent_messages; - unsigned int mtu; - unsigned int link_mtu; + size_t mtu; + size_t link_mtu; DTLS_RECORD_LAYER_clear(&s->rlayer); @@ -179,10 +187,13 @@ void dtls1_clear(SSL *s) } ssl3_clear(s); - if (s->options & SSL_OP_CISCO_ANYCONNECT) - s->client_version = s->version = DTLS1_BAD_VER; - else if (s->method->version == DTLS_ANY_VERSION) + + if (s->method->version == DTLS_ANY_VERSION) s->version = DTLS_MAX_VERSION; +#ifndef OPENSSL_NO_DTLS1_METHOD + else if (s->options & SSL_OP_CISCO_ANYCONNECT) + s->client_version = s->version = DTLS1_BAD_VER; +#endif else s->version = s->method->version; } @@ -322,12 +333,12 @@ void dtls1_stop_timer(SSL *s) BIO_ctrl(SSL_get_rbio(s), BIO_CTRL_DGRAM_SET_NEXT_TIMEOUT, 0, &(s->d1->next_timeout)); /* Clear retransmission buffer */ - dtls1_clear_record_buffer(s); + dtls1_clear_sent_buffer(s); } int dtls1_check_timeout_num(SSL *s) { - unsigned int mtu; + size_t mtu; s->d1->timeout.num_alerts++; @@ -335,8 +346,7 @@ int dtls1_check_timeout_num(SSL *s) if (s->d1->timeout.num_alerts > 2 && !(SSL_get_options(s) & SSL_OP_NO_QUERY_MTU)) { mtu = - BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_GET_FALLBACK_MTU, 0, - NULL); + BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_GET_FALLBACK_MTU, 0, NULL); if (mtu < s->d1->mtu) s->d1->mtu = mtu; } @@ -366,12 +376,6 @@ int dtls1_handle_timeout(SSL *s) if (s->d1->timeout.read_timeouts > DTLS1_TMO_READ_COUNT) { s->d1->timeout.read_timeouts = 1; } -#ifndef OPENSSL_NO_HEARTBEATS - if (s->tlsext_hb_pending) { - s->tlsext_hb_pending = 0; - return dtls1_heartbeat(s); - } -#endif dtls1_start_timer(s); return dtls1_retransmit_buffered_messages(s); @@ -388,24 +392,21 @@ static void get_current_time(struct timeval *t) GetSystemTime(&st); SystemTimeToFileTime(&st, &now.ft); + /* re-bias to 1/1/1970 */ # ifdef __MINGW32__ now.ul -= 116444736000000000ULL; # else - now.ul -= 116444736000000000UI64; /* re-bias to 1/1/1970 */ + /* *INDENT-OFF* */ + now.ul -= 116444736000000000UI64; + /* *INDENT-ON* */ # endif t->tv_sec = (long)(now.ul / 10000000); t->tv_usec = ((int)(now.ul % 10000000)) / 10; -#elif defined(OPENSSL_SYS_VMS) - struct timeb tb; - ftime(&tb); - t->tv_sec = (long)tb.time; - t->tv_usec = (long)tb.millitm * 1000; #else gettimeofday(t, NULL); #endif } - #define LISTEN_SUCCESS 2 #define LISTEN_SEND_VERIFY_REQUEST 1 @@ -416,14 +417,19 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) unsigned char cookie[DTLS1_COOKIE_LENGTH]; unsigned char seq[SEQ_NUM_SIZE]; const unsigned char *data; - unsigned char *p, *buf; - unsigned long reclen, fragoff, fraglen, msglen; + unsigned char *buf; + size_t fragoff, fraglen, msglen; unsigned int rectype, versmajor, msgseq, msgtype, clientvers, cookielen; BIO *rbio, *wbio; BUF_MEM *bufm; BIO_ADDR *tmpclient = NULL; PACKET pkt, msgpkt, msgpayload, session, cookiepkt; + if (s->handshake_func == NULL) { + /* Not properly initialized yet */ + SSL_set_accept_state(s); + } + /* Ensure there is no state left over from a previous invocation */ if (!SSL_clear(s)) return -1; @@ -433,7 +439,7 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) rbio = SSL_get_rbio(s); wbio = SSL_get_wbio(s); - if(!rbio || !wbio) { + if (!rbio || !wbio) { SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_BIO_NOT_SET); return -1; } @@ -487,7 +493,7 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) n = BIO_read(rbio, buf, SSL3_RT_MAX_PLAIN_LENGTH); if (n <= 0) { - if(BIO_should_retry(rbio)) { + if (BIO_should_retry(rbio)) { /* Non-blocking IO */ goto end; } @@ -528,7 +534,7 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) goto end; } - if (rectype != SSL3_RT_HANDSHAKE) { + if (rectype != SSL3_RT_HANDSHAKE) { SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_UNEXPECTED_MESSAGE); goto end; } @@ -565,10 +571,10 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) /* Finished processing the record header, now process the message */ if (!PACKET_get_1(&msgpkt, &msgtype) - || !PACKET_get_net_3(&msgpkt, &msglen) + || !PACKET_get_net_3_len(&msgpkt, &msglen) || !PACKET_get_net_2(&msgpkt, &msgseq) - || !PACKET_get_net_3(&msgpkt, &fragoff) - || !PACKET_get_net_3(&msgpkt, &fraglen) + || !PACKET_get_net_3_len(&msgpkt, &fragoff) + || !PACKET_get_net_3_len(&msgpkt, &fraglen) || !PACKET_get_sub_packet(&msgpkt, &msgpayload, fraglen) || PACKET_remaining(&msgpkt) != 0) { SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_LENGTH_MISMATCH); @@ -581,7 +587,7 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) } /* Message sequence number can only be 0 or 1 */ - if(msgseq > 2) { + if (msgseq > 2) { SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_INVALID_SEQUENCE_NUMBER); goto end; } @@ -645,8 +651,7 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) return -1; } if (s->ctx->app_verify_cookie_cb(s, PACKET_data(&cookiepkt), - PACKET_remaining(&cookiepkt)) == - 0) { + (unsigned int)PACKET_remaining(&cookiepkt)) == 0) { /* * We treat invalid cookies in the same was as no cookie as * per RFC6347 @@ -659,6 +664,10 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) } if (next == LISTEN_SEND_VERIFY_REQUEST) { + WPACKET wpkt; + unsigned int version; + size_t wreclen; + /* * There was no cookie in the ClientHello so we need to send a * HelloVerifyRequest. If this fails we do not worry about trying @@ -682,66 +691,81 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) return -1; } - p = &buf[DTLS1_RT_HEADER_LENGTH]; - msglen = dtls_raw_hello_verify_request(p + DTLS1_HM_HEADER_LENGTH, - cookie, cookielen); - - *p++ = DTLS1_MT_HELLO_VERIFY_REQUEST; - - /* Message length */ - l2n3(msglen, p); - - /* Message sequence number is always 0 for a HelloVerifyRequest */ - s2n(0, p); - - /* - * We never fragment a HelloVerifyRequest, so fragment offset is 0 - * and fragment length is message length - */ - l2n3(0, p); - l2n3(msglen, p); - - /* Set reclen equal to length of whole handshake message */ - reclen = msglen + DTLS1_HM_HEADER_LENGTH; - - /* Add the record header */ - p = buf; - - *(p++) = SSL3_RT_HANDSHAKE; /* * Special case: for hello verify request, client version 1.0 and we * haven't decided which version to use yet send back using version * 1.0 header: otherwise some clients will ignore it. */ - if (s->method->version == DTLS_ANY_VERSION) { - *(p++) = DTLS1_VERSION >> 8; - *(p++) = DTLS1_VERSION & 0xff; - } else { - *(p++) = s->version >> 8; - *(p++) = s->version & 0xff; + version = (s->method->version == DTLS_ANY_VERSION) ? DTLS1_VERSION + : s->version; + + /* Construct the record and message headers */ + if (!WPACKET_init(&wpkt, s->init_buf) + || !WPACKET_put_bytes_u8(&wpkt, SSL3_RT_HANDSHAKE) + || !WPACKET_put_bytes_u16(&wpkt, version) + /* + * Record sequence number is always the same as in the + * received ClientHello + */ + || !WPACKET_memcpy(&wpkt, seq, SEQ_NUM_SIZE) + /* End of record, start sub packet for message */ + || !WPACKET_start_sub_packet_u16(&wpkt) + /* Message type */ + || !WPACKET_put_bytes_u8(&wpkt, + DTLS1_MT_HELLO_VERIFY_REQUEST) + /* + * Message length - doesn't follow normal TLS convention: + * the length isn't the last thing in the message header. + * We'll need to fill this in later when we know the + * length. Set it to zero for now + */ + || !WPACKET_put_bytes_u24(&wpkt, 0) + /* + * Message sequence number is always 0 for a + * HelloVerifyRequest + */ + || !WPACKET_put_bytes_u16(&wpkt, 0) + /* + * We never fragment a HelloVerifyRequest, so fragment + * offset is 0 + */ + || !WPACKET_put_bytes_u24(&wpkt, 0) + /* + * Fragment length is the same as message length, but + * this *is* the last thing in the message header so we + * can just start a sub-packet. No need to come back + * later for this one. + */ + || !WPACKET_start_sub_packet_u24(&wpkt) + /* Create the actual HelloVerifyRequest body */ + || !dtls_raw_hello_verify_request(&wpkt, cookie, cookielen) + /* Close message body */ + || !WPACKET_close(&wpkt) + /* Close record body */ + || !WPACKET_close(&wpkt) + || !WPACKET_get_total_written(&wpkt, &wreclen) + || !WPACKET_finish(&wpkt)) { + SSLerr(SSL_F_DTLSV1_LISTEN, ERR_R_INTERNAL_ERROR); + WPACKET_cleanup(&wpkt); + /* This is fatal */ + return -1; } /* - * Record sequence number is always the same as in the received - * ClientHello - */ - memcpy(p, seq, SEQ_NUM_SIZE); - p += SEQ_NUM_SIZE; - - /* Length */ - s2n(reclen, p); - - /* - * Set reclen equal to length of whole record including record - * header + * Fix up the message len in the message header. Its the same as the + * fragment len which has been filled in by WPACKET, so just copy + * that. Destination for the message len is after the record header + * plus one byte for the message content type. The source is the + * last 3 bytes of the message header */ - reclen += DTLS1_RT_HEADER_LENGTH; + memcpy(&buf[DTLS1_RT_HEADER_LENGTH + 1], + &buf[DTLS1_RT_HEADER_LENGTH + DTLS1_HM_HEADER_LENGTH - 3], + 3); if (s->msg_callback) s->msg_callback(1, 0, SSL3_RT_HEADER, buf, DTLS1_RT_HEADER_LENGTH, s, s->msg_callback_arg); - if ((tmpclient = BIO_ADDR_new()) == NULL) { SSLerr(SSL_F_DTLSV1_LISTEN, ERR_R_MALLOC_FAILURE); goto end; @@ -752,14 +776,15 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) * maybe they're not. We ignore errors here - some BIOs do not * support this. */ - if(BIO_dgram_get_peer(rbio, tmpclient) > 0) { + if (BIO_dgram_get_peer(rbio, tmpclient) > 0) { (void)BIO_dgram_set_peer(wbio, tmpclient); } BIO_ADDR_free(tmpclient); tmpclient = NULL; - if (BIO_write(wbio, buf, reclen) < (int)reclen) { - if(BIO_should_retry(wbio)) { + /* TODO(size_t): convert this call */ + if (BIO_write(wbio, buf, wreclen) < (int)wreclen) { + if (BIO_should_retry(wbio)) { /* * Non-blocking IO...but we're stateless, so we're just * going to drop this packet. @@ -770,7 +795,7 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) } if (BIO_flush(wbio) <= 0) { - if(BIO_should_retry(wbio)) { + if (BIO_should_retry(wbio)) { /* * Non-blocking IO...but we're stateless, so we're just * going to drop this packet. @@ -802,13 +827,15 @@ int DTLSv1_listen(SSL *s, BIO_ADDR *client) */ ossl_statem_set_hello_verify_done(s); - /* Some BIOs may not support this. If we fail we clear the client address */ + /* + * Some BIOs may not support this. If we fail we clear the client address + */ if (BIO_dgram_get_peer(rbio, client) <= 0) BIO_ADDR_clear(client); ret = 1; clearpkt = 0; -end: + end: BIO_ADDR_free(tmpclient); BIO_ctrl(SSL_get_rbio(s), BIO_CTRL_DGRAM_SET_PEEK_MODE, 0, NULL); if (clearpkt) { @@ -819,185 +846,11 @@ end: } #endif -static int dtls1_set_handshake_header(SSL *s, int htype, unsigned long len) -{ - dtls1_set_message_header(s, htype, len, 0, len); - s->init_num = (int)len + DTLS1_HM_HEADER_LENGTH; - s->init_off = 0; - /* Buffer the message to handle re-xmits */ - - if (!dtls1_buffer_message(s, 0)) - return 0; - - return 1; -} - static int dtls1_handshake_write(SSL *s) { return dtls1_do_write(s, SSL3_RT_HANDSHAKE); } -#ifndef OPENSSL_NO_HEARTBEATS - -#define HEARTBEAT_SIZE(payload, padding) ( \ - 1 /* heartbeat type */ + \ - 2 /* heartbeat length */ + \ - (payload) + (padding)) - -#define HEARTBEAT_SIZE_STD(payload) HEARTBEAT_SIZE(payload, 16) - -int dtls1_process_heartbeat(SSL *s, unsigned char *p, unsigned int length) -{ - unsigned char *pl; - unsigned short hbtype; - unsigned int payload; - unsigned int padding = 16; /* Use minimum padding */ - - if (s->msg_callback) - s->msg_callback(0, s->version, DTLS1_RT_HEARTBEAT, - p, length, s, s->msg_callback_arg); - - /* Read type and payload length */ - if (HEARTBEAT_SIZE_STD(0) > length) - return 0; /* silently discard */ - if (length > SSL3_RT_MAX_PLAIN_LENGTH) - return 0; /* silently discard per RFC 6520 sec. 4 */ - - hbtype = *p++; - n2s(p, payload); - if (HEARTBEAT_SIZE_STD(payload) > length) - return 0; /* silently discard per RFC 6520 sec. 4 */ - pl = p; - - if (hbtype == TLS1_HB_REQUEST) { - unsigned char *buffer, *bp; - unsigned int write_length = HEARTBEAT_SIZE(payload, padding); - int r; - - if (write_length > SSL3_RT_MAX_PLAIN_LENGTH) - return 0; - - /* Allocate memory for the response. */ - buffer = OPENSSL_malloc(write_length); - if (buffer == NULL) - return -1; - bp = buffer; - - /* Enter response type, length and copy payload */ - *bp++ = TLS1_HB_RESPONSE; - s2n(payload, bp); - memcpy(bp, pl, payload); - bp += payload; - /* Random padding */ - if (RAND_bytes(bp, padding) <= 0) { - OPENSSL_free(buffer); - return -1; - } - - r = dtls1_write_bytes(s, DTLS1_RT_HEARTBEAT, buffer, write_length); - - if (r >= 0 && s->msg_callback) - s->msg_callback(1, s->version, DTLS1_RT_HEARTBEAT, - buffer, write_length, s, s->msg_callback_arg); - - OPENSSL_free(buffer); - - if (r < 0) - return r; - } else if (hbtype == TLS1_HB_RESPONSE) { - unsigned int seq; - - /* - * We only send sequence numbers (2 bytes unsigned int), and 16 - * random bytes, so we just try to read the sequence number - */ - n2s(pl, seq); - - if (payload == 18 && seq == s->tlsext_hb_seq) { - dtls1_stop_timer(s); - s->tlsext_hb_seq++; - s->tlsext_hb_pending = 0; - } - } - - return 0; -} - -int dtls1_heartbeat(SSL *s) -{ - unsigned char *buf, *p; - int ret = -1; - unsigned int payload = 18; /* Sequence number + random bytes */ - unsigned int padding = 16; /* Use minimum padding */ - unsigned int size; - - /* Only send if peer supports and accepts HB requests... */ - if (!(s->tlsext_heartbeat & SSL_DTLSEXT_HB_ENABLED) || - s->tlsext_heartbeat & SSL_DTLSEXT_HB_DONT_SEND_REQUESTS) { - SSLerr(SSL_F_DTLS1_HEARTBEAT, SSL_R_TLS_HEARTBEAT_PEER_DOESNT_ACCEPT); - return -1; - } - - /* ...and there is none in flight yet... */ - if (s->tlsext_hb_pending) { - SSLerr(SSL_F_DTLS1_HEARTBEAT, SSL_R_TLS_HEARTBEAT_PENDING); - return -1; - } - - /* ...and no handshake in progress. */ - if (SSL_in_init(s) || ossl_statem_get_in_handshake(s)) { - SSLerr(SSL_F_DTLS1_HEARTBEAT, SSL_R_UNEXPECTED_MESSAGE); - return -1; - } - - /*- - * Create HeartBeat message, we just use a sequence number - * as payload to distinguish different messages and add - * some random stuff. - */ - size = HEARTBEAT_SIZE(payload, padding); - buf = OPENSSL_malloc(size); - if (buf == NULL) { - SSLerr(SSL_F_DTLS1_HEARTBEAT, ERR_R_MALLOC_FAILURE); - return -1; - } - p = buf; - /* Message Type */ - *p++ = TLS1_HB_REQUEST; - /* Payload length (18 bytes here) */ - s2n(payload, p); - /* Sequence number */ - s2n(s->tlsext_hb_seq, p); - /* 16 random bytes */ - if (RAND_bytes(p, 16) <= 0) { - SSLerr(SSL_F_DTLS1_HEARTBEAT, ERR_R_INTERNAL_ERROR); - goto err; - } - p += 16; - /* Random padding */ - if (RAND_bytes(p, padding) <= 0) { - SSLerr(SSL_F_DTLS1_HEARTBEAT, ERR_R_INTERNAL_ERROR); - goto err; - } - - ret = dtls1_write_bytes(s, DTLS1_RT_HEARTBEAT, buf, size); - if (ret >= 0) { - if (s->msg_callback) - s->msg_callback(1, s->version, DTLS1_RT_HEARTBEAT, - buf, size, - s, s->msg_callback_arg); - - dtls1_start_timer(s); - s->tlsext_hb_pending = 1; - } - - err: - OPENSSL_free(buf); - - return ret; -} -#endif - int dtls1_shutdown(SSL *s) { int ret; @@ -1045,7 +898,7 @@ int dtls1_query_mtu(SSL *s) /* Set to min mtu */ s->d1->mtu = dtls1_min_mtu(s); BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_SET_MTU, - s->d1->mtu, NULL); + (long)s->d1->mtu, NULL); } } else return 0; @@ -1053,13 +906,49 @@ int dtls1_query_mtu(SSL *s) return 1; } -static unsigned int dtls1_link_min_mtu(void) +static size_t dtls1_link_min_mtu(void) { return (g_probable_mtu[(sizeof(g_probable_mtu) / sizeof(g_probable_mtu[0])) - 1]); } -unsigned int dtls1_min_mtu(SSL *s) +size_t dtls1_min_mtu(SSL *s) { return dtls1_link_min_mtu() - BIO_dgram_get_mtu_overhead(SSL_get_wbio(s)); } + +size_t DTLS_get_data_mtu(const SSL *s) +{ + size_t mac_overhead, int_overhead, blocksize, ext_overhead; + const SSL_CIPHER *ciph = SSL_get_current_cipher(s); + size_t mtu = s->d1->mtu; + + if (ciph == NULL) + return 0; + + if (!ssl_cipher_get_overhead(ciph, &mac_overhead, &int_overhead, + &blocksize, &ext_overhead)) + return 0; + + if (SSL_READ_ETM(s)) + ext_overhead += mac_overhead; + else + int_overhead += mac_overhead; + + /* Subtract external overhead (e.g. IV/nonce, separate MAC) */ + if (ext_overhead + DTLS1_RT_HEADER_LENGTH >= mtu) + return 0; + mtu -= ext_overhead + DTLS1_RT_HEADER_LENGTH; + + /* Round encrypted payload down to cipher block size (for CBC etc.) + * No check for overflow since 'mtu % blocksize' cannot exceed mtu. */ + if (blocksize) + mtu -= (mtu % blocksize); + + /* Subtract internal overhead (e.g. CBC padding len byte) */ + if (int_overhead >= mtu) + return 0; + mtu -= int_overhead; + + return mtu; +}