1 // Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #include <openssl/ssl.h>
16
17 #include <assert.h>
18 #include <string.h>
19
20 #include <openssl/bytestring.h>
21 #include <openssl/err.h>
22 #include <openssl/mem.h>
23
24 #include "../crypto/internal.h"
25 #include "internal.h"
26
27
28 BSSL_NAMESPACE_BEGIN
29
30 // kMaxEmptyRecords is the number of consecutive, empty records that will be
31 // processed. Without this limit an attacker could send empty records at a
32 // faster rate than we can process and cause record processing to loop
33 // forever.
34 static const uint8_t kMaxEmptyRecords = 32;
35
36 // kMaxEarlyDataSkipped is the maximum number of rejected early data bytes that
37 // will be skipped. Without this limit an attacker could send records at a
38 // faster rate than we can process and cause trial decryption to loop forever.
39 // This value should be slightly above kMaxEarlyDataAccepted, which is measured
40 // in plaintext.
41 static const size_t kMaxEarlyDataSkipped = 16384;
42
43 // kMaxWarningAlerts is the number of consecutive warning alerts that will be
44 // processed.
45 static const uint8_t kMaxWarningAlerts = 4;
46
47 // ssl_needs_record_splitting returns one if |ssl|'s current outgoing cipher
48 // state needs record-splitting and zero otherwise.
ssl_needs_record_splitting(const SSL * ssl)49 bool ssl_needs_record_splitting(const SSL *ssl) {
50 return !CRYPTO_fuzzer_mode_enabled() &&
51 !ssl->s3->aead_write_ctx->is_null_cipher() &&
52 ssl_protocol_version(ssl) < TLS1_1_VERSION &&
53 (ssl->mode & SSL_MODE_CBC_RECORD_SPLITTING) != 0 &&
54 SSL_CIPHER_is_block_cipher(ssl->s3->aead_write_ctx->cipher());
55 }
56
ssl_record_prefix_len(const SSL * ssl)57 size_t ssl_record_prefix_len(const SSL *ssl) {
58 assert(!SSL_is_dtls(ssl));
59 return SSL3_RT_HEADER_LENGTH + ssl->s3->aead_read_ctx->ExplicitNonceLen();
60 }
61
skip_early_data(SSL * ssl,uint8_t * out_alert,size_t consumed)62 static ssl_open_record_t skip_early_data(SSL *ssl, uint8_t *out_alert,
63 size_t consumed) {
64 ssl->s3->early_data_skipped += consumed;
65 if (ssl->s3->early_data_skipped < consumed) {
66 ssl->s3->early_data_skipped = kMaxEarlyDataSkipped + 1;
67 }
68
69 if (ssl->s3->early_data_skipped > kMaxEarlyDataSkipped) {
70 OPENSSL_PUT_ERROR(SSL, SSL_R_TOO_MUCH_SKIPPED_EARLY_DATA);
71 *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
72 return ssl_open_record_error;
73 }
74
75 return ssl_open_record_discard;
76 }
77
tls_record_version(const SSL * ssl)78 static uint16_t tls_record_version(const SSL *ssl) {
79 if (ssl->s3->version == 0) {
80 // Before the version is determined, outgoing records use TLS 1.0 for
81 // historical compatibility requirements.
82 return TLS1_VERSION;
83 }
84
85 // TLS 1.3 freezes the record version at TLS 1.2. Previous ones use the
86 // version itself.
87 return ssl_protocol_version(ssl) >= TLS1_3_VERSION ? TLS1_2_VERSION
88 : ssl->s3->version;
89 }
90
tls_open_record(SSL * ssl,uint8_t * out_type,Span<uint8_t> * out,size_t * out_consumed,uint8_t * out_alert,Span<uint8_t> in)91 ssl_open_record_t tls_open_record(SSL *ssl, uint8_t *out_type,
92 Span<uint8_t> *out, size_t *out_consumed,
93 uint8_t *out_alert, Span<uint8_t> in) {
94 *out_consumed = 0;
95 if (ssl->s3->read_shutdown == ssl_shutdown_close_notify) {
96 return ssl_open_record_close_notify;
97 }
98
99 // If there is an unprocessed handshake message or we are already buffering
100 // too much, stop before decrypting another handshake record.
101 if (!tls_can_accept_handshake_data(ssl, out_alert)) {
102 return ssl_open_record_error;
103 }
104
105 CBS cbs = CBS(in);
106
107 // Decode the record header.
108 uint8_t type;
109 uint16_t version, ciphertext_len;
110 if (!CBS_get_u8(&cbs, &type) || //
111 !CBS_get_u16(&cbs, &version) || //
112 !CBS_get_u16(&cbs, &ciphertext_len)) {
113 *out_consumed = SSL3_RT_HEADER_LENGTH;
114 return ssl_open_record_partial;
115 }
116
117 bool version_ok;
118 if (ssl->s3->aead_read_ctx->is_null_cipher()) {
119 // Only check the first byte. Enforcing beyond that can prevent decoding
120 // version negotiation failure alerts.
121 version_ok = (version >> 8) == SSL3_VERSION_MAJOR;
122 } else {
123 version_ok = version == tls_record_version(ssl);
124 }
125
126 if (!version_ok) {
127 OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_VERSION_NUMBER);
128 *out_alert = SSL_AD_PROTOCOL_VERSION;
129 return ssl_open_record_error;
130 }
131
132 // Check the ciphertext length.
133 if (ciphertext_len > SSL3_RT_MAX_ENCRYPTED_LENGTH) {
134 OPENSSL_PUT_ERROR(SSL, SSL_R_ENCRYPTED_LENGTH_TOO_LONG);
135 *out_alert = SSL_AD_RECORD_OVERFLOW;
136 return ssl_open_record_error;
137 }
138
139 // Extract the body.
140 CBS body;
141 if (!CBS_get_bytes(&cbs, &body, ciphertext_len)) {
142 *out_consumed = SSL3_RT_HEADER_LENGTH + (size_t)ciphertext_len;
143 return ssl_open_record_partial;
144 }
145
146 Span<const uint8_t> header = in.subspan(0, SSL3_RT_HEADER_LENGTH);
147 ssl_do_msg_callback(ssl, 0 /* read */, SSL3_RT_HEADER, header);
148
149 *out_consumed = in.size() - CBS_len(&cbs);
150
151 // In TLS 1.3, during the handshake, skip ChangeCipherSpec records.
152 static const uint8_t kChangeCipherSpec[] = {SSL3_MT_CCS};
153 if (ssl_has_final_version(ssl) &&
154 ssl_protocol_version(ssl) >= TLS1_3_VERSION && SSL_in_init(ssl) &&
155 type == SSL3_RT_CHANGE_CIPHER_SPEC &&
156 Span<const uint8_t>(body) == kChangeCipherSpec) {
157 ssl->s3->empty_record_count++;
158 if (ssl->s3->empty_record_count > kMaxEmptyRecords) {
159 OPENSSL_PUT_ERROR(SSL, SSL_R_TOO_MANY_EMPTY_FRAGMENTS);
160 *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
161 return ssl_open_record_error;
162 }
163 return ssl_open_record_discard;
164 }
165
166 // Skip early data received when expecting a second ClientHello if we rejected
167 // 0RTT.
168 if (ssl->s3->skip_early_data && //
169 ssl->s3->aead_read_ctx->is_null_cipher() && //
170 type == SSL3_RT_APPLICATION_DATA) {
171 return skip_early_data(ssl, out_alert, *out_consumed);
172 }
173
174 // Ensure the sequence number update does not overflow.
175 if (ssl->s3->read_sequence + 1 == 0) {
176 OPENSSL_PUT_ERROR(SSL, ERR_R_OVERFLOW);
177 *out_alert = SSL_AD_INTERNAL_ERROR;
178 return ssl_open_record_error;
179 }
180
181 // Decrypt the body in-place.
182 if (!ssl->s3->aead_read_ctx->Open(
183 out, type, version, ssl->s3->read_sequence, header,
184 Span(const_cast<uint8_t *>(CBS_data(&body)), CBS_len(&body)))) {
185 if (ssl->s3->skip_early_data && !ssl->s3->aead_read_ctx->is_null_cipher()) {
186 ERR_clear_error();
187 return skip_early_data(ssl, out_alert, *out_consumed);
188 }
189
190 OPENSSL_PUT_ERROR(SSL, SSL_R_DECRYPTION_FAILED_OR_BAD_RECORD_MAC);
191 *out_alert = SSL_AD_BAD_RECORD_MAC;
192 return ssl_open_record_error;
193 }
194
195 ssl->s3->skip_early_data = false;
196 ssl->s3->read_sequence++;
197
198 // TLS 1.3 hides the record type inside the encrypted data.
199 bool has_padding = !ssl->s3->aead_read_ctx->is_null_cipher() &&
200 ssl_protocol_version(ssl) >= TLS1_3_VERSION;
201
202 // If there is padding, the plaintext limit includes the padding, but includes
203 // extra room for the inner content type.
204 size_t plaintext_limit =
205 has_padding ? SSL3_RT_MAX_PLAIN_LENGTH + 1 : SSL3_RT_MAX_PLAIN_LENGTH;
206 if (out->size() > plaintext_limit) {
207 OPENSSL_PUT_ERROR(SSL, SSL_R_DATA_LENGTH_TOO_LONG);
208 *out_alert = SSL_AD_RECORD_OVERFLOW;
209 return ssl_open_record_error;
210 }
211
212 if (has_padding) {
213 // The outer record type is always application_data.
214 if (type != SSL3_RT_APPLICATION_DATA) {
215 OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_OUTER_RECORD_TYPE);
216 *out_alert = SSL_AD_DECODE_ERROR;
217 return ssl_open_record_error;
218 }
219
220 do {
221 if (out->empty()) {
222 OPENSSL_PUT_ERROR(SSL, SSL_R_DECRYPTION_FAILED_OR_BAD_RECORD_MAC);
223 *out_alert = SSL_AD_DECRYPT_ERROR;
224 return ssl_open_record_error;
225 }
226 type = out->back();
227 *out = out->subspan(0, out->size() - 1);
228 } while (type == 0);
229 }
230
231 // Limit the number of consecutive empty records.
232 if (out->empty()) {
233 ssl->s3->empty_record_count++;
234 if (ssl->s3->empty_record_count > kMaxEmptyRecords) {
235 OPENSSL_PUT_ERROR(SSL, SSL_R_TOO_MANY_EMPTY_FRAGMENTS);
236 *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
237 return ssl_open_record_error;
238 }
239 // Apart from the limit, empty records are returned up to the caller. This
240 // allows the caller to reject records of the wrong type.
241 } else {
242 ssl->s3->empty_record_count = 0;
243 }
244
245 if (type == SSL3_RT_ALERT) {
246 return ssl_process_alert(ssl, out_alert, *out);
247 }
248
249 // Handshake messages may not interleave with any other record type.
250 if (type != SSL3_RT_HANDSHAKE && //
251 tls_has_unprocessed_handshake_data(ssl)) {
252 OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_RECORD);
253 *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
254 return ssl_open_record_error;
255 }
256
257 ssl->s3->warning_alert_count = 0;
258
259 *out_type = type;
260 return ssl_open_record_success;
261 }
262
do_seal_record(SSL * ssl,uint8_t * out_prefix,uint8_t * out,uint8_t * out_suffix,uint8_t type,const uint8_t * in,const size_t in_len)263 static bool do_seal_record(SSL *ssl, uint8_t *out_prefix, uint8_t *out,
264 uint8_t *out_suffix, uint8_t type, const uint8_t *in,
265 const size_t in_len) {
266 SSLAEADContext *aead = ssl->s3->aead_write_ctx.get();
267 uint8_t *extra_in = NULL;
268 size_t extra_in_len = 0;
269 if (!aead->is_null_cipher() && ssl_protocol_version(ssl) >= TLS1_3_VERSION) {
270 // TLS 1.3 hides the actual record type inside the encrypted data.
271 extra_in = &type;
272 extra_in_len = 1;
273 }
274
275 size_t suffix_len, ciphertext_len;
276 if (!aead->SuffixLen(&suffix_len, in_len, extra_in_len) ||
277 !aead->CiphertextLen(&ciphertext_len, in_len, extra_in_len)) {
278 OPENSSL_PUT_ERROR(SSL, SSL_R_RECORD_TOO_LARGE);
279 return false;
280 }
281
282 assert(in == out || !buffers_alias(in, in_len, out, in_len));
283 assert(!buffers_alias(in, in_len, out_prefix, ssl_record_prefix_len(ssl)));
284 assert(!buffers_alias(in, in_len, out_suffix, suffix_len));
285
286 if (extra_in_len) {
287 out_prefix[0] = SSL3_RT_APPLICATION_DATA;
288 } else {
289 out_prefix[0] = type;
290 }
291
292 uint16_t record_version = tls_record_version(ssl);
293 out_prefix[1] = record_version >> 8;
294 out_prefix[2] = record_version & 0xff;
295 out_prefix[3] = ciphertext_len >> 8;
296 out_prefix[4] = ciphertext_len & 0xff;
297 Span<const uint8_t> header = Span(out_prefix, SSL3_RT_HEADER_LENGTH);
298
299 // Ensure the sequence number update does not overflow.
300 if (ssl->s3->write_sequence + 1 == 0) {
301 OPENSSL_PUT_ERROR(SSL, ERR_R_OVERFLOW);
302 return false;
303 }
304
305 if (!aead->SealScatter(out_prefix + SSL3_RT_HEADER_LENGTH, out, out_suffix,
306 out_prefix[0], record_version, ssl->s3->write_sequence,
307 header, in, in_len, extra_in, extra_in_len)) {
308 return false;
309 }
310
311 ssl->s3->write_sequence++;
312 ssl_do_msg_callback(ssl, 1 /* write */, SSL3_RT_HEADER, header);
313 return true;
314 }
315
tls_seal_scatter_prefix_len(const SSL * ssl,uint8_t type,size_t in_len)316 static size_t tls_seal_scatter_prefix_len(const SSL *ssl, uint8_t type,
317 size_t in_len) {
318 size_t ret = SSL3_RT_HEADER_LENGTH;
319 if (type == SSL3_RT_APPLICATION_DATA && in_len > 1 &&
320 ssl_needs_record_splitting(ssl)) {
321 // In the case of record splitting, the 1-byte record (of the 1/n-1 split)
322 // will be placed in the prefix, as will four of the five bytes of the
323 // record header for the main record. The final byte will replace the first
324 // byte of the plaintext that was used in the small record.
325 ret += ssl_cipher_get_record_split_len(ssl->s3->aead_write_ctx->cipher());
326 ret += SSL3_RT_HEADER_LENGTH - 1;
327 } else {
328 ret += ssl->s3->aead_write_ctx->ExplicitNonceLen();
329 }
330 return ret;
331 }
332
tls_seal_scatter_suffix_len(const SSL * ssl,size_t * out_suffix_len,uint8_t type,size_t in_len)333 static bool tls_seal_scatter_suffix_len(const SSL *ssl, size_t *out_suffix_len,
334 uint8_t type, size_t in_len) {
335 size_t extra_in_len = 0;
336 if (!ssl->s3->aead_write_ctx->is_null_cipher() &&
337 ssl_protocol_version(ssl) >= TLS1_3_VERSION) {
338 // TLS 1.3 adds an extra byte for encrypted record type.
339 extra_in_len = 1;
340 }
341 // clang-format off
342 if (type == SSL3_RT_APPLICATION_DATA &&
343 in_len > 1 &&
344 ssl_needs_record_splitting(ssl)) {
345 // With record splitting enabled, the first byte gets sealed into a separate
346 // record which is written into the prefix.
347 in_len -= 1;
348 }
349 // clang-format on
350 return ssl->s3->aead_write_ctx->SuffixLen(out_suffix_len, in_len,
351 extra_in_len);
352 }
353
354 // tls_seal_scatter_record seals a new record of type |type| and body |in| and
355 // splits it between |out_prefix|, |out|, and |out_suffix|. Exactly
356 // |tls_seal_scatter_prefix_len| bytes are written to |out_prefix|, |in_len|
357 // bytes to |out|, and |tls_seal_scatter_suffix_len| bytes to |out_suffix|. It
358 // returns one on success and zero on error. If enabled,
359 // |tls_seal_scatter_record| implements TLS 1.0 CBC 1/n-1 record splitting and
360 // may write two records concatenated.
tls_seal_scatter_record(SSL * ssl,uint8_t * out_prefix,uint8_t * out,uint8_t * out_suffix,uint8_t type,const uint8_t * in,size_t in_len)361 static bool tls_seal_scatter_record(SSL *ssl, uint8_t *out_prefix, uint8_t *out,
362 uint8_t *out_suffix, uint8_t type,
363 const uint8_t *in, size_t in_len) {
364 if (type == SSL3_RT_APPLICATION_DATA && in_len > 1 &&
365 ssl_needs_record_splitting(ssl)) {
366 assert(ssl->s3->aead_write_ctx->ExplicitNonceLen() == 0);
367 const size_t prefix_len = SSL3_RT_HEADER_LENGTH;
368
369 // Write the 1-byte fragment into |out_prefix|.
370 uint8_t *split_body = out_prefix + prefix_len;
371 uint8_t *split_suffix = split_body + 1;
372
373 if (!do_seal_record(ssl, out_prefix, split_body, split_suffix, type, in,
374 1)) {
375 return false;
376 }
377
378 size_t split_record_suffix_len;
379 if (!ssl->s3->aead_write_ctx->SuffixLen(&split_record_suffix_len, 1, 0)) {
380 assert(false);
381 return false;
382 }
383 const size_t split_record_len = prefix_len + 1 + split_record_suffix_len;
384 assert(SSL3_RT_HEADER_LENGTH + ssl_cipher_get_record_split_len(
385 ssl->s3->aead_write_ctx->cipher()) ==
386 split_record_len);
387
388 // Write the n-1-byte fragment. The header gets split between |out_prefix|
389 // (header[:-1]) and |out| (header[-1:]).
390 uint8_t tmp_prefix[SSL3_RT_HEADER_LENGTH];
391 if (!do_seal_record(ssl, tmp_prefix, out + 1, out_suffix, type, in + 1,
392 in_len - 1)) {
393 return false;
394 }
395 assert(tls_seal_scatter_prefix_len(ssl, type, in_len) ==
396 split_record_len + SSL3_RT_HEADER_LENGTH - 1);
397 OPENSSL_memcpy(out_prefix + split_record_len, tmp_prefix,
398 SSL3_RT_HEADER_LENGTH - 1);
399 OPENSSL_memcpy(out, tmp_prefix + SSL3_RT_HEADER_LENGTH - 1, 1);
400 return true;
401 }
402
403 return do_seal_record(ssl, out_prefix, out, out_suffix, type, in, in_len);
404 }
405
tls_seal_record(SSL * ssl,uint8_t * out,size_t * out_len,size_t max_out_len,uint8_t type,const uint8_t * in,size_t in_len)406 bool tls_seal_record(SSL *ssl, uint8_t *out, size_t *out_len,
407 size_t max_out_len, uint8_t type, const uint8_t *in,
408 size_t in_len) {
409 if (buffers_alias(in, in_len, out, max_out_len)) {
410 OPENSSL_PUT_ERROR(SSL, SSL_R_OUTPUT_ALIASES_INPUT);
411 return false;
412 }
413
414 const size_t prefix_len = tls_seal_scatter_prefix_len(ssl, type, in_len);
415 size_t suffix_len;
416 if (!tls_seal_scatter_suffix_len(ssl, &suffix_len, type, in_len)) {
417 return false;
418 }
419 if (in_len + prefix_len < in_len ||
420 prefix_len + in_len + suffix_len < prefix_len + in_len) {
421 OPENSSL_PUT_ERROR(SSL, SSL_R_RECORD_TOO_LARGE);
422 return false;
423 }
424 if (max_out_len < in_len + prefix_len + suffix_len) {
425 OPENSSL_PUT_ERROR(SSL, SSL_R_BUFFER_TOO_SMALL);
426 return false;
427 }
428
429 uint8_t *prefix = out;
430 uint8_t *body = out + prefix_len;
431 uint8_t *suffix = body + in_len;
432 if (!tls_seal_scatter_record(ssl, prefix, body, suffix, type, in, in_len)) {
433 return false;
434 }
435
436 *out_len = prefix_len + in_len + suffix_len;
437 return true;
438 }
439
ssl_process_alert(SSL * ssl,uint8_t * out_alert,Span<const uint8_t> in)440 enum ssl_open_record_t ssl_process_alert(SSL *ssl, uint8_t *out_alert,
441 Span<const uint8_t> in) {
442 // Alerts records may not contain fragmented or multiple alerts.
443 if (in.size() != 2) {
444 *out_alert = SSL_AD_DECODE_ERROR;
445 OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_ALERT);
446 return ssl_open_record_error;
447 }
448
449 ssl_do_msg_callback(ssl, 0 /* read */, SSL3_RT_ALERT, in);
450
451 const uint8_t alert_level = in[0];
452 const uint8_t alert_descr = in[1];
453
454 uint16_t alert = (alert_level << 8) | alert_descr;
455 ssl_do_info_callback(ssl, SSL_CB_READ_ALERT, alert);
456
457 if (alert_level == SSL3_AL_WARNING) {
458 if (alert_descr == SSL_AD_CLOSE_NOTIFY) {
459 ssl->s3->read_shutdown = ssl_shutdown_close_notify;
460 return ssl_open_record_close_notify;
461 }
462
463 // Warning alerts do not exist in TLS 1.3, but RFC 8446 section 6.1
464 // continues to define user_canceled as a signal to cancel the handshake,
465 // without specifying how to handle it. JDK11 misuses it to signal
466 // full-duplex connection close after the handshake. As a workaround, skip
467 // user_canceled as in TLS 1.2. This matches NSS and OpenSSL.
468 if (ssl_has_final_version(ssl) &&
469 ssl_protocol_version(ssl) >= TLS1_3_VERSION &&
470 alert_descr != SSL_AD_USER_CANCELLED) {
471 *out_alert = SSL_AD_DECODE_ERROR;
472 OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_ALERT);
473 return ssl_open_record_error;
474 }
475
476 ssl->s3->warning_alert_count++;
477 if (ssl->s3->warning_alert_count > kMaxWarningAlerts) {
478 *out_alert = SSL_AD_UNEXPECTED_MESSAGE;
479 OPENSSL_PUT_ERROR(SSL, SSL_R_TOO_MANY_WARNING_ALERTS);
480 return ssl_open_record_error;
481 }
482 return ssl_open_record_discard;
483 }
484
485 if (alert_level == SSL3_AL_FATAL) {
486 OPENSSL_PUT_ERROR(SSL, SSL_AD_REASON_OFFSET + alert_descr);
487 ERR_add_error_dataf("SSL alert number %d", alert_descr);
488 *out_alert = 0; // No alert to send back to the peer.
489 return ssl_open_record_error;
490 }
491
492 *out_alert = SSL_AD_ILLEGAL_PARAMETER;
493 OPENSSL_PUT_ERROR(SSL, SSL_R_UNKNOWN_ALERT_TYPE);
494 return ssl_open_record_error;
495 }
496
497 BSSL_NAMESPACE_END
498
499 using namespace bssl;
500
SSL_max_seal_overhead(const SSL * ssl)501 size_t SSL_max_seal_overhead(const SSL *ssl) {
502 if (SSL_is_dtls(ssl)) {
503 // TODO(crbug.com/381113363): Use the 0-RTT epoch if writing 0-RTT.
504 return dtls_max_seal_overhead(ssl, ssl->d1->write_epoch.epoch());
505 }
506
507 size_t ret = SSL3_RT_HEADER_LENGTH;
508 ret += ssl->s3->aead_write_ctx->MaxOverhead();
509 // TLS 1.3 needs an extra byte for the encrypted record type.
510 if (!ssl->s3->aead_write_ctx->is_null_cipher() &&
511 ssl_protocol_version(ssl) >= TLS1_3_VERSION) {
512 ret += 1;
513 }
514 if (ssl_needs_record_splitting(ssl)) {
515 ret *= 2;
516 }
517 return ret;
518 }
519