1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
|
// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "net/cert/caching_cert_verifier.h"
#include <utility>
#include "base/bind.h"
#include "base/time/time.h"
#include "net/base/net_errors.h"
namespace net {
namespace {
// The maximum number of cache entries to use for the ExpiringCache.
const unsigned kMaxCacheEntries = 256;
// The number of seconds to cache entries.
const unsigned kTTLSecs = 1800; // 30 minutes.
} // namespace
CachingCertVerifier::CachingCertVerifier(std::unique_ptr<CertVerifier> verifier)
: verifier_(std::move(verifier)), cache_(kMaxCacheEntries) {
CertDatabase::GetInstance()->AddObserver(this);
}
CachingCertVerifier::~CachingCertVerifier() {
CertDatabase::GetInstance()->RemoveObserver(this);
}
int CachingCertVerifier::Verify(const CertVerifier::RequestParams& params,
CertVerifyResult* verify_result,
CompletionOnceCallback callback,
std::unique_ptr<Request>* out_req,
const NetLogWithSource& net_log) {
out_req->reset();
requests_++;
const CertVerificationCache::value_type* cached_entry =
cache_.Get(params, CacheValidityPeriod(base::Time::Now()));
if (cached_entry) {
++cache_hits_;
*verify_result = cached_entry->result;
return cached_entry->error;
}
base::Time start_time = base::Time::Now();
CompletionOnceCallback caching_callback = base::BindOnce(
&CachingCertVerifier::OnRequestFinished, base::Unretained(this),
config_id_, params, start_time, std::move(callback), verify_result);
int result = verifier_->Verify(params, verify_result,
std::move(caching_callback), out_req, net_log);
if (result != ERR_IO_PENDING) {
// Synchronous completion; add directly to cache.
AddResultToCache(config_id_, params, start_time, *verify_result, result);
}
return result;
}
void CachingCertVerifier::SetConfig(const CertVerifier::Config& config) {
verifier_->SetConfig(config);
config_id_++;
ClearCache();
}
CachingCertVerifier::CachedResult::CachedResult() = default;
CachingCertVerifier::CachedResult::~CachedResult() = default;
CachingCertVerifier::CacheValidityPeriod::CacheValidityPeriod(base::Time now)
: verification_time(now), expiration_time(now) {}
CachingCertVerifier::CacheValidityPeriod::CacheValidityPeriod(
base::Time now,
base::Time expiration)
: verification_time(now), expiration_time(expiration) {}
bool CachingCertVerifier::CacheExpirationFunctor::operator()(
const CacheValidityPeriod& now,
const CacheValidityPeriod& expiration) const {
// Ensure this functor is being used for expiration only, and not strict
// weak ordering/sorting. |now| should only ever contain a single
// base::Time.
// Note: DCHECK_EQ is not used due to operator<< overloading requirements.
DCHECK(now.verification_time == now.expiration_time);
// |now| contains only a single time (verification_time), while |expiration|
// contains the validity range - both when the certificate was verified and
// when the verification result should expire.
//
// If the user receives a "not yet valid" message, and adjusts their clock
// foward to the correct time, this will (typically) cause
// now.verification_time to advance past expiration.expiration_time, thus
// treating the cached result as an expired entry and re-verifying.
// If the user receives a "expired" message, and adjusts their clock
// backwards to the correct time, this will cause now.verification_time to
// be less than expiration_verification_time, thus treating the cached
// result as an expired entry and re-verifying.
// If the user receives either of those messages, and does not adjust their
// clock, then the result will be (typically) be cached until the expiration
// TTL.
//
// This algorithm is only problematic if the user consistently keeps
// adjusting their clock backwards in increments smaller than the expiration
// TTL, in which case, cached elements continue to be added. However,
// because the cache has a fixed upper bound, if no entries are expired, a
// 'random' entry will be, thus keeping the memory constraints bounded over
// time.
return now.verification_time >= expiration.verification_time &&
now.verification_time < expiration.expiration_time;
}
void CachingCertVerifier::OnRequestFinished(uint32_t config_id,
const RequestParams& params,
base::Time start_time,
CompletionOnceCallback callback,
CertVerifyResult* verify_result,
int error) {
AddResultToCache(config_id, params, start_time, *verify_result, error);
// Now chain to the user's callback, which may delete |this|.
std::move(callback).Run(error);
}
void CachingCertVerifier::AddResultToCache(
uint32_t config_id,
const RequestParams& params,
base::Time start_time,
const CertVerifyResult& verify_result,
int error) {
// If the configuration has changed since this verification was started,
// don't add it to the cache.
if (config_id != config_id_)
return;
// When caching, this uses the time that validation started as the
// beginning of the validity, rather than the time that it ended (aka
// base::Time::Now()), to account for the fact that during validation,
// the clock may have changed.
//
// If the clock has changed significantly, then this result will ideally
// be evicted and the next time the certificate is encountered, it will
// be revalidated.
//
// Because of this, it's possible for situations to arise where the
// clock was correct at the start of validation, changed to an
// incorrect time during validation (such as too far in the past or
// future), and then was reset to the correct time. If this happens,
// it's likely that the result will not be a valid/correct result,
// but will still be used from the cache because the clock was reset
// to the correct time after the (bad) validation result completed.
//
// However, this solution optimizes for the case where the clock is
// bad at the start of validation, and subsequently is corrected. In
// that situation, the result is also incorrect, but because the clock
// was corrected after validation, if the cache validity period was
// computed at the end of validation, it would continue to serve an
// invalid result for kTTLSecs.
CachedResult cached_result;
cached_result.error = error;
cached_result.result = verify_result;
cache_.Put(
params, cached_result, CacheValidityPeriod(start_time),
CacheValidityPeriod(start_time, start_time + base::Seconds(kTTLSecs)));
}
void CachingCertVerifier::OnCertDBChanged() {
config_id_++;
ClearCache();
}
void CachingCertVerifier::ClearCache() {
cache_.Clear();
}
size_t CachingCertVerifier::GetCacheSize() const {
return cache_.size();
}
} // namespace net
|
