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1 // Copyright 2013 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #include "net/socket/ssl_session_cache_openssl.h" | |
6 | |
7 #include <list> | |
8 #include <map> | |
9 | |
10 #include <openssl/rand.h> | |
11 #include <openssl/ssl.h> | |
12 | |
13 #include "base/containers/hash_tables.h" | |
14 #include "base/lazy_instance.h" | |
15 #include "base/logging.h" | |
16 #include "base/synchronization/lock.h" | |
17 | |
18 namespace net { | |
19 | |
20 namespace { | |
21 | |
22 // A helper class to lazily create a new EX_DATA index to map SSL_CTX handles | |
23 // to their corresponding SSLSessionCacheOpenSSLImpl object. | |
24 class SSLContextExIndex { | |
25 public: | |
26 SSLContextExIndex() { | |
27 context_index_ = SSL_CTX_get_ex_new_index(0, NULL, NULL, NULL, NULL); | |
28 DCHECK_NE(-1, context_index_); | |
29 session_index_ = SSL_SESSION_get_ex_new_index(0, NULL, NULL, NULL, NULL); | |
30 DCHECK_NE(-1, session_index_); | |
31 } | |
32 | |
33 int context_index() const { return context_index_; } | |
34 int session_index() const { return session_index_; } | |
35 | |
36 private: | |
37 int context_index_; | |
38 int session_index_; | |
39 }; | |
40 | |
41 // static | |
42 base::LazyInstance<SSLContextExIndex>::Leaky s_ssl_context_ex_instance = | |
43 LAZY_INSTANCE_INITIALIZER; | |
44 | |
45 // Retrieve the global EX_DATA index, created lazily on first call, to | |
46 // be used with SSL_CTX_set_ex_data() and SSL_CTX_get_ex_data(). | |
47 static int GetSSLContextExIndex() { | |
48 return s_ssl_context_ex_instance.Get().context_index(); | |
49 } | |
50 | |
51 // Retrieve the global EX_DATA index, created lazily on first call, to | |
52 // be used with SSL_SESSION_set_ex_data() and SSL_SESSION_get_ex_data(). | |
53 static int GetSSLSessionExIndex() { | |
54 return s_ssl_context_ex_instance.Get().session_index(); | |
55 } | |
56 | |
57 // Helper struct used to store session IDs in a SessionIdIndex container | |
58 // (see definition below). To save memory each entry only holds a pointer | |
59 // to the session ID buffer, which must outlive the entry itself. On the | |
60 // other hand, a hash is included to minimize the number of hashing | |
61 // computations during cache operations. | |
62 struct SessionId { | |
63 SessionId(const unsigned char* a_id, unsigned a_id_len) | |
64 : id(a_id), id_len(a_id_len), hash(ComputeHash(a_id, a_id_len)) {} | |
65 | |
66 explicit SessionId(const SessionId& other) | |
67 : id(other.id), id_len(other.id_len), hash(other.hash) {} | |
68 | |
69 explicit SessionId(SSL_SESSION* session) | |
70 : id(session->session_id), | |
71 id_len(session->session_id_length), | |
72 hash(ComputeHash(session->session_id, session->session_id_length)) {} | |
73 | |
74 bool operator==(const SessionId& other) const { | |
75 return hash == other.hash && id_len == other.id_len && | |
76 !memcmp(id, other.id, id_len); | |
77 } | |
78 | |
79 const unsigned char* id; | |
80 unsigned id_len; | |
81 size_t hash; | |
82 | |
83 private: | |
84 // Session ID are random strings of bytes. This happens to compute the same | |
85 // value as std::hash<std::string> without the extra string copy. See | |
86 // base/containers/hash_tables.h. Other hashing computations are possible, | |
87 // this one is just simple enough to do the job. | |
88 size_t ComputeHash(const unsigned char* id, unsigned id_len) { | |
89 size_t result = 0; | |
90 for (unsigned n = 0; n < id_len; ++n) { | |
91 result = (result * 131) + id[n]; | |
92 } | |
93 return result; | |
94 } | |
95 }; | |
96 | |
97 } // namespace | |
98 | |
99 } // namespace net | |
100 | |
101 namespace BASE_HASH_NAMESPACE { | |
102 | |
103 template <> | |
104 struct hash<net::SessionId> { | |
105 std::size_t operator()(const net::SessionId& entry) const { | |
106 return entry.hash; | |
107 } | |
108 }; | |
109 | |
110 } // namespace BASE_HASH_NAMESPACE | |
111 | |
112 namespace net { | |
113 | |
114 // Implementation of the real SSLSessionCache. | |
115 // | |
116 // The implementation is inspired by base::MRUCache, except that the deletor | |
117 // also needs to remove the entry from other containers. In a nutshell, this | |
118 // uses several basic containers: | |
119 // | |
120 // |ordering_| is a doubly-linked list of SSL_SESSION handles, ordered in | |
121 // MRU order. | |
122 // | |
123 // |key_index_| is a hash table mapping unique cache keys (e.g. host/port | |
124 // values) to a single iterator of |ordering_|. It is used to efficiently | |
125 // find the cached session associated with a given key. | |
126 // | |
127 // |id_index_| is a hash table mapping SessionId values to iterators | |
128 // of |key_index_|. If is used to efficiently remove sessions from the cache, | |
129 // as well as check for the existence of a session ID value in the cache. | |
130 // | |
131 // SSL_SESSION objects are reference-counted, and owned by the cache. This | |
132 // means that their reference count is incremented when they are added, and | |
133 // decremented when they are removed. | |
134 // | |
135 // Assuming an average key size of 100 characters, each node requires the | |
136 // following memory usage on 32-bit Android, when linked against STLport: | |
137 // | |
138 // 12 (ordering_ node, including SSL_SESSION handle) | |
139 // 100 (key characters) | |
140 // + 24 (std::string header/minimum size) | |
141 // + 8 (key_index_ node, excluding the 2 lines above for the key). | |
142 // + 20 (id_index_ node) | |
143 // -------- | |
144 // 164 bytes/node | |
145 // | |
146 // Hence, 41 KiB for a full cache with a maximum of 1024 entries, excluding | |
147 // the size of SSL_SESSION objects and heap fragmentation. | |
148 // | |
149 | |
150 class SSLSessionCacheOpenSSLImpl { | |
151 public: | |
152 // Construct new instance. This registers various hooks into the SSL_CTX | |
153 // context |ctx|. OpenSSL will call back during SSL connection | |
154 // operations. |key_func| is used to map a SSL handle to a unique cache | |
155 // string, according to the client's preferences. | |
156 SSLSessionCacheOpenSSLImpl(SSL_CTX* ctx, | |
157 const SSLSessionCacheOpenSSL::Config& config) | |
158 : ctx_(ctx), config_(config), expiration_check_(0) { | |
159 DCHECK(ctx); | |
160 | |
161 // NO_INTERNAL_STORE disables OpenSSL's builtin cache, and | |
162 // NO_AUTO_CLEAR disables the call to SSL_CTX_flush_sessions | |
163 // every 256 connections (this number is hard-coded in the library | |
164 // and can't be changed). | |
165 SSL_CTX_set_session_cache_mode(ctx_, | |
166 SSL_SESS_CACHE_CLIENT | | |
167 SSL_SESS_CACHE_NO_INTERNAL_STORE | | |
168 SSL_SESS_CACHE_NO_AUTO_CLEAR); | |
169 | |
170 SSL_CTX_sess_set_new_cb(ctx_, NewSessionCallbackStatic); | |
171 SSL_CTX_sess_set_remove_cb(ctx_, RemoveSessionCallbackStatic); | |
172 SSL_CTX_set_generate_session_id(ctx_, GenerateSessionIdStatic); | |
173 SSL_CTX_set_timeout(ctx_, config_.timeout_seconds); | |
174 | |
175 SSL_CTX_set_ex_data(ctx_, GetSSLContextExIndex(), this); | |
176 } | |
177 | |
178 // Destroy this instance. Must happen before |ctx_| is destroyed. | |
179 ~SSLSessionCacheOpenSSLImpl() { | |
180 Flush(); | |
181 SSL_CTX_set_ex_data(ctx_, GetSSLContextExIndex(), NULL); | |
182 SSL_CTX_sess_set_new_cb(ctx_, NULL); | |
183 SSL_CTX_sess_set_remove_cb(ctx_, NULL); | |
184 SSL_CTX_set_generate_session_id(ctx_, NULL); | |
185 } | |
186 | |
187 // Return the number of items in this cache. | |
188 size_t size() const { return key_index_.size(); } | |
189 | |
190 // Retrieve the cache key from |ssl| and look for a corresponding | |
191 // cached session ID. If one is found, call SSL_set_session() to associate | |
192 // it with the |ssl| connection. | |
193 // | |
194 // Will also check for expired sessions every |expiration_check_count| | |
195 // calls. | |
196 // | |
197 // Return true if a cached session ID was found, false otherwise. | |
198 bool SetSSLSession(SSL* ssl) { | |
199 std::string cache_key = config_.key_func(ssl); | |
200 if (cache_key.empty()) | |
201 return false; | |
202 | |
203 return SetSSLSessionWithKey(ssl, cache_key); | |
204 } | |
205 | |
206 // Variant of SetSSLSession to be used when the client already has computed | |
207 // the cache key. Avoid a call to the configuration's |key_func| function. | |
208 bool SetSSLSessionWithKey(SSL* ssl, const std::string& cache_key) { | |
209 base::AutoLock locked(lock_); | |
210 | |
211 DCHECK_EQ(config_.key_func(ssl), cache_key); | |
212 | |
213 if (++expiration_check_ >= config_.expiration_check_count) { | |
214 expiration_check_ = 0; | |
215 FlushExpiredSessionsLocked(); | |
216 } | |
217 | |
218 KeyIndex::iterator it = key_index_.find(cache_key); | |
219 if (it == key_index_.end()) | |
220 return false; | |
221 | |
222 SSL_SESSION* session = *it->second; | |
223 DCHECK(session); | |
224 | |
225 DVLOG(2) << "Lookup session: " << session << " for " << cache_key; | |
226 | |
227 void* session_is_good = | |
228 SSL_SESSION_get_ex_data(session, GetSSLSessionExIndex()); | |
229 if (!session_is_good) | |
230 return false; // Session has not yet been marked good. Treat as a miss. | |
231 | |
232 // Move to front of MRU list. | |
233 ordering_.push_front(session); | |
234 ordering_.erase(it->second); | |
235 it->second = ordering_.begin(); | |
236 | |
237 return SSL_set_session(ssl, session) == 1; | |
238 } | |
239 | |
240 void MarkSSLSessionAsGood(SSL* ssl) { | |
241 SSL_SESSION* session = SSL_get_session(ssl); | |
242 if (!session) | |
243 return; | |
244 | |
245 // Mark the session as good, allowing it to be used for future connections. | |
246 SSL_SESSION_set_ex_data( | |
247 session, GetSSLSessionExIndex(), reinterpret_cast<void*>(1)); | |
248 } | |
249 | |
250 // Flush all entries from the cache. | |
251 void Flush() { | |
252 base::AutoLock lock(lock_); | |
253 id_index_.clear(); | |
254 key_index_.clear(); | |
255 while (!ordering_.empty()) { | |
256 SSL_SESSION* session = ordering_.front(); | |
257 ordering_.pop_front(); | |
258 SSL_SESSION_free(session); | |
259 } | |
260 } | |
261 | |
262 private: | |
263 // Type for list of SSL_SESSION handles, ordered in MRU order. | |
264 typedef std::list<SSL_SESSION*> MRUSessionList; | |
265 // Type for a dictionary from unique cache keys to session list nodes. | |
266 typedef base::hash_map<std::string, MRUSessionList::iterator> KeyIndex; | |
267 // Type for a dictionary from SessionId values to key index nodes. | |
268 typedef base::hash_map<SessionId, KeyIndex::iterator> SessionIdIndex; | |
269 | |
270 // Return the key associated with a given session, or the empty string if | |
271 // none exist. This shall only be used for debugging. | |
272 std::string SessionKey(SSL_SESSION* session) { | |
273 if (!session) | |
274 return std::string("<null-session>"); | |
275 | |
276 if (session->session_id_length == 0) | |
277 return std::string("<empty-session-id>"); | |
278 | |
279 SessionIdIndex::iterator it = id_index_.find(SessionId(session)); | |
280 if (it == id_index_.end()) | |
281 return std::string("<unknown-session>"); | |
282 | |
283 return it->second->first; | |
284 } | |
285 | |
286 // Remove a given |session| from the cache. Lock must be held. | |
287 void RemoveSessionLocked(SSL_SESSION* session) { | |
288 lock_.AssertAcquired(); | |
289 DCHECK(session); | |
290 DCHECK_GT(session->session_id_length, 0U); | |
291 SessionId session_id(session); | |
292 SessionIdIndex::iterator id_it = id_index_.find(session_id); | |
293 if (id_it == id_index_.end()) { | |
294 LOG(ERROR) << "Trying to remove unknown session from cache: " << session; | |
295 return; | |
296 } | |
297 KeyIndex::iterator key_it = id_it->second; | |
298 DCHECK(key_it != key_index_.end()); | |
299 DCHECK_EQ(session, *key_it->second); | |
300 | |
301 id_index_.erase(session_id); | |
302 ordering_.erase(key_it->second); | |
303 key_index_.erase(key_it); | |
304 | |
305 SSL_SESSION_free(session); | |
306 | |
307 DCHECK_EQ(key_index_.size(), id_index_.size()); | |
308 } | |
309 | |
310 // Used internally to flush expired sessions. Lock must be held. | |
311 void FlushExpiredSessionsLocked() { | |
312 lock_.AssertAcquired(); | |
313 | |
314 // Unfortunately, OpenSSL initializes |session->time| with a time() | |
315 // timestamps, which makes mocking / unit testing difficult. | |
316 long timeout_secs = static_cast<long>(::time(NULL)); | |
317 MRUSessionList::iterator it = ordering_.begin(); | |
318 while (it != ordering_.end()) { | |
319 SSL_SESSION* session = *it++; | |
320 | |
321 // Important, use <= instead of < here to allow unit testing to | |
322 // work properly. That's because unit tests that check the expiration | |
323 // behaviour will use a session timeout of 0 seconds. | |
324 if (session->time + session->timeout <= timeout_secs) { | |
325 DVLOG(2) << "Expiring session " << session << " for " | |
326 << SessionKey(session); | |
327 RemoveSessionLocked(session); | |
328 } | |
329 } | |
330 } | |
331 | |
332 // Retrieve the cache associated with a given SSL context |ctx|. | |
333 static SSLSessionCacheOpenSSLImpl* GetCache(SSL_CTX* ctx) { | |
334 DCHECK(ctx); | |
335 void* result = SSL_CTX_get_ex_data(ctx, GetSSLContextExIndex()); | |
336 DCHECK(result); | |
337 return reinterpret_cast<SSLSessionCacheOpenSSLImpl*>(result); | |
338 } | |
339 | |
340 // Called by OpenSSL when a new |session| was created and added to a given | |
341 // |ssl| connection. Note that the session's reference count was already | |
342 // incremented before the function is entered. The function must return 1 | |
343 // to indicate that it took ownership of the session, i.e. that the caller | |
344 // should not decrement its reference count after completion. | |
345 static int NewSessionCallbackStatic(SSL* ssl, SSL_SESSION* session) { | |
346 GetCache(ssl->ctx)->OnSessionAdded(ssl, session); | |
347 return 1; | |
348 } | |
349 | |
350 // Called by OpenSSL to indicate that a session must be removed from the | |
351 // cache. This happens when SSL_CTX is destroyed. | |
352 static void RemoveSessionCallbackStatic(SSL_CTX* ctx, SSL_SESSION* session) { | |
353 GetCache(ctx)->OnSessionRemoved(session); | |
354 } | |
355 | |
356 // Called by OpenSSL to generate a new session ID. This happens during a | |
357 // SSL connection operation, when the SSL object doesn't have a session yet. | |
358 // | |
359 // A session ID is a random string of bytes used to uniquely identify the | |
360 // session between a client and a server. | |
361 // | |
362 // |ssl| is a SSL connection handle. Ignored here. | |
363 // |id| is the target buffer where the ID must be generated. | |
364 // |*id_len| is, on input, the size of the desired ID. It will be 16 for | |
365 // SSLv2, and 32 for anything else. OpenSSL allows an implementation | |
366 // to change it on output, but this will not happen here. | |
367 // | |
368 // The function must ensure the generated ID is really unique, i.e. that | |
369 // another session in the cache doesn't already use the same value. It must | |
370 // return 1 to indicate success, or 0 for failure. | |
371 static int GenerateSessionIdStatic(const SSL* ssl, | |
372 unsigned char* id, | |
373 unsigned* id_len) { | |
374 if (!GetCache(ssl->ctx)->OnGenerateSessionId(id, *id_len)) | |
375 return 0; | |
376 | |
377 return 1; | |
378 } | |
379 | |
380 // Add |session| to the cache in association with |cache_key|. If a session | |
381 // already exists, it is replaced with the new one. This assumes that the | |
382 // caller already incremented the session's reference count. | |
383 void OnSessionAdded(SSL* ssl, SSL_SESSION* session) { | |
384 base::AutoLock locked(lock_); | |
385 DCHECK(ssl); | |
386 DCHECK_GT(session->session_id_length, 0U); | |
387 std::string cache_key = config_.key_func(ssl); | |
388 KeyIndex::iterator it = key_index_.find(cache_key); | |
389 if (it == key_index_.end()) { | |
390 DVLOG(2) << "Add session " << session << " for " << cache_key; | |
391 // This is a new session. Add it to the cache. | |
392 ordering_.push_front(session); | |
393 std::pair<KeyIndex::iterator, bool> ret = | |
394 key_index_.insert(std::make_pair(cache_key, ordering_.begin())); | |
395 DCHECK(ret.second); | |
396 it = ret.first; | |
397 DCHECK(it != key_index_.end()); | |
398 } else { | |
399 // An existing session exists for this key, so replace it if needed. | |
400 DVLOG(2) << "Replace session " << *it->second << " with " << session | |
401 << " for " << cache_key; | |
402 SSL_SESSION* old_session = *it->second; | |
403 if (old_session != session) { | |
404 id_index_.erase(SessionId(old_session)); | |
405 SSL_SESSION_free(old_session); | |
406 } | |
407 ordering_.erase(it->second); | |
408 ordering_.push_front(session); | |
409 it->second = ordering_.begin(); | |
410 } | |
411 | |
412 id_index_[SessionId(session)] = it; | |
413 | |
414 if (key_index_.size() > config_.max_entries) | |
415 ShrinkCacheLocked(); | |
416 | |
417 DCHECK_EQ(key_index_.size(), id_index_.size()); | |
418 DCHECK_LE(key_index_.size(), config_.max_entries); | |
419 } | |
420 | |
421 // Shrink the cache to ensure no more than config_.max_entries entries, | |
422 // starting with older entries first. Lock must be acquired. | |
423 void ShrinkCacheLocked() { | |
424 lock_.AssertAcquired(); | |
425 DCHECK_EQ(key_index_.size(), ordering_.size()); | |
426 DCHECK_EQ(key_index_.size(), id_index_.size()); | |
427 | |
428 while (key_index_.size() > config_.max_entries) { | |
429 MRUSessionList::reverse_iterator it = ordering_.rbegin(); | |
430 DCHECK(it != ordering_.rend()); | |
431 | |
432 SSL_SESSION* session = *it; | |
433 DCHECK(session); | |
434 DVLOG(2) << "Evicting session " << session << " for " | |
435 << SessionKey(session); | |
436 RemoveSessionLocked(session); | |
437 } | |
438 } | |
439 | |
440 // Remove |session| from the cache. | |
441 void OnSessionRemoved(SSL_SESSION* session) { | |
442 base::AutoLock locked(lock_); | |
443 DVLOG(2) << "Remove session " << session << " for " << SessionKey(session); | |
444 RemoveSessionLocked(session); | |
445 } | |
446 | |
447 // See GenerateSessionIdStatic for a description of what this function does. | |
448 bool OnGenerateSessionId(unsigned char* id, unsigned id_len) { | |
449 base::AutoLock locked(lock_); | |
450 // This mimics def_generate_session_id() in openssl/ssl/ssl_sess.cc, | |
451 // I.e. try to generate a pseudo-random bit string, and check that no | |
452 // other entry in the cache has the same value. | |
453 const size_t kMaxTries = 10; | |
454 for (size_t tries = 0; tries < kMaxTries; ++tries) { | |
455 if (RAND_pseudo_bytes(id, id_len) <= 0) { | |
456 DLOG(ERROR) << "Couldn't generate " << id_len | |
457 << " pseudo random bytes?"; | |
458 return false; | |
459 } | |
460 if (id_index_.find(SessionId(id, id_len)) == id_index_.end()) | |
461 return true; | |
462 } | |
463 DLOG(ERROR) << "Couldn't generate unique session ID of " << id_len | |
464 << "bytes after " << kMaxTries << " tries."; | |
465 return false; | |
466 } | |
467 | |
468 SSL_CTX* ctx_; | |
469 SSLSessionCacheOpenSSL::Config config_; | |
470 | |
471 // method to get the index which can later be used with SSL_CTX_get_ex_data() | |
472 // or SSL_CTX_set_ex_data(). | |
473 base::Lock lock_; // Protects access to containers below. | |
474 | |
475 MRUSessionList ordering_; | |
476 KeyIndex key_index_; | |
477 SessionIdIndex id_index_; | |
478 | |
479 size_t expiration_check_; | |
480 }; | |
481 | |
482 SSLSessionCacheOpenSSL::~SSLSessionCacheOpenSSL() { delete impl_; } | |
483 | |
484 size_t SSLSessionCacheOpenSSL::size() const { return impl_->size(); } | |
485 | |
486 void SSLSessionCacheOpenSSL::Reset(SSL_CTX* ctx, const Config& config) { | |
487 if (impl_) | |
488 delete impl_; | |
489 | |
490 impl_ = new SSLSessionCacheOpenSSLImpl(ctx, config); | |
491 } | |
492 | |
493 bool SSLSessionCacheOpenSSL::SetSSLSession(SSL* ssl) { | |
494 return impl_->SetSSLSession(ssl); | |
495 } | |
496 | |
497 bool SSLSessionCacheOpenSSL::SetSSLSessionWithKey( | |
498 SSL* ssl, | |
499 const std::string& cache_key) { | |
500 return impl_->SetSSLSessionWithKey(ssl, cache_key); | |
501 } | |
502 | |
503 void SSLSessionCacheOpenSSL::MarkSSLSessionAsGood(SSL* ssl) { | |
504 return impl_->MarkSSLSessionAsGood(ssl); | |
505 } | |
506 | |
507 void SSLSessionCacheOpenSSL::Flush() { impl_->Flush(); } | |
508 | |
509 } // namespace net | |
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