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// Copyright 2016 The Chromium Authors. All rights reserved.
// 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 "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),
requests_(0u),
cache_hits_(0u) {
CertDatabase::GetInstance()->AddObserver(this);
}
CachingCertVerifier::~CachingCertVerifier() {
CertDatabase::GetInstance()->RemoveObserver(this);
}
int CachingCertVerifier::Verify(const CertVerifier::RequestParams& params,
CRLSet* crl_set,
CertVerifyResult* verify_result,
const CompletionCallback& 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();
CompletionCallback caching_callback = base::Bind(
&CachingCertVerifier::OnRequestFinished, base::Unretained(this), params,
start_time, callback, verify_result);
int result = verifier_->Verify(params, crl_set, verify_result,
caching_callback, out_req, net_log);
if (result != ERR_IO_PENDING) {
// Synchronous completion; add directly to cache.
AddResultToCache(params, start_time, *verify_result, result);
}
return result;
}
bool CachingCertVerifier::SupportsOCSPStapling() {
return verifier_->SupportsOCSPStapling();
}
bool CachingCertVerifier::AddEntry(const RequestParams& params,
int error,
const CertVerifyResult& verify_result,
base::Time verification_time) {
// If the cache is full, don't bother.
if (cache_.size() == cache_.max_entries())
return false;
// If there is an existing entry, don't bother updating it.
const CertVerificationCache::value_type* entry =
cache_.Get(params, CacheValidityPeriod(base::Time::Now()));
if (entry)
return false;
// Otherwise, go and add it.
AddResultToCache(params, verification_time, verify_result, error);
return true;
}
CachingCertVerifier::CachedResult::CachedResult() : error(ERR_FAILED) {}
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(const RequestParams& params,
base::Time start_time,
const CompletionCallback& callback,
CertVerifyResult* verify_result,
int error) {
AddResultToCache(params, start_time, *verify_result, error);
// Now chain to the user's callback, which may delete |this|.
callback.Run(error);
}
void CachingCertVerifier::AddResultToCache(
const RequestParams& params,
base::Time start_time,
const CertVerifyResult& verify_result,
int error) {
// 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::TimeDelta::FromSeconds(kTTLSecs)));
}
void CachingCertVerifier::VisitEntries(CacheVisitor* visitor) const {
DCHECK(visitor);
CacheValidityPeriod now(base::Time::Now());
CacheExpirationFunctor expiration_cmp;
for (CertVerificationCache::Iterator it(cache_); it.HasNext(); it.Advance()) {
if (!expiration_cmp(now, it.expiration()))
continue;
if (!visitor->VisitEntry(it.key(), it.value().error, it.value().result,
it.expiration().verification_time,
it.expiration().expiration_time)) {
break;
}
}
}
void CachingCertVerifier::OnCertDBChanged() {
ClearCache();
}
void CachingCertVerifier::ClearCache() {
cache_.Clear();
}
size_t CachingCertVerifier::GetCacheSize() const {
return cache_.size();
}
} // namespace net
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