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Side by Side Diff: net/socket/ssl_session_cache_openssl.cc

Issue 994263002: Rewrite session cache in OpenSSL ports. (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: reebase Created 5 years, 8 months ago
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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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