Fix race condition with CancelCheck().

components/safe_browsing_db/v4_local_database_manager.cc

 // 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.
 
 // This file should not be build on Android but is currently getting built.
 // TODO(vakh): Fix that: http://crbug.com/621647
 
 #include "components/safe_browsing_db/v4_local_database_manager.h"
 
 #include <vector>
@@ skipping 517 matching lines @@
     queued_checks_.push_back(std::move(check));
     return false;
   }
 
   FullHashToStoreAndHashPrefixesMap full_hash_to_store_and_hash_prefixes;
   if (!GetPrefixMatches(check, &full_hash_to_store_and_hash_prefixes)) {
     return true;
   }
 
   // Post on the IO thread to enforce async behavior.
+  pending_clients_.insert(check->client);
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE,
       base::Bind(&V4LocalDatabaseManager::PerformFullHashCheck, this,
                  base::Passed(std::move(check)),
                  full_hash_to_store_and_hash_prefixes));
 
   return false;
 }
 
 bool V4LocalDatabaseManager::HandleHashSynchronously(
@@ skipping 48 matching lines @@
 
 void V4LocalDatabaseManager::PerformFullHashCheck(
     std::unique_ptr<PendingCheck> check,
     const FullHashToStoreAndHashPrefixesMap&
         full_hash_to_store_and_hash_prefixes) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
   DCHECK(enabled_);
   DCHECK(!full_hash_to_store_and_hash_prefixes.empty());
 
-  pending_clients_.insert(check->client);
-
   v4_get_hash_protocol_manager_->GetFullHashes(
       full_hash_to_store_and_hash_prefixes,
       base::Bind(&V4LocalDatabaseManager::OnFullHashResponse,
                  weak_factory_.GetWeakPtr(), base::Passed(std::move(check))));
 }
 
 void V4LocalDatabaseManager::ProcessQueuedChecks() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  for (auto& it : queued_checks_) {
+
+  // Steal the queue to protect against reentrant CancelCheck() calls.
+  QueuedChecks checks;
+  checks.swap(queued_checks_);
+
+  for (auto& it : checks) {
     FullHashToStoreAndHashPrefixesMap full_hash_to_store_and_hash_prefixes;
     if (!GetPrefixMatches(it, &full_hash_to_store_and_hash_prefixes)) {
       RespondToClient(std::move(it));
     } else {
+      pending_clients_.insert(it->client);
       PerformFullHashCheck(std::move(it), full_hash_to_store_and_hash_prefixes);
     }
   }
-  queued_checks_.clear();
 }
 
 void V4LocalDatabaseManager::RespondSafeToQueuedChecks() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  for (std::unique_ptr<PendingCheck>& it : queued_checks_) {
+
+  // Steal the queue to protect against reentrant CancelCheck() calls.
+  QueuedChecks checks;
+  checks.swap(queued_checks_);
+
+  for (std::unique_ptr<PendingCheck>& it : checks) {
     RespondToClient(std::move(it));
   }
-  queued_checks_.clear();
 }
 
 void V4LocalDatabaseManager::RespondToClient(
     std::unique_ptr<PendingCheck> check) {
   DCHECK(check.get());
 
   if (check->client_callback_type == ClientCallbackType::CHECK_BROWSE_URL) {
     DCHECK_EQ(1u, check->urls.size());
     // TODO(vakh): Remove these CHECKs after fixing bugs 660293, 660359.
     CHECK(check.get());
@@ skipping 56 matching lines @@
                             db_updated_callback_);
 }
 
 bool V4LocalDatabaseManager::AreStoresAvailableNow(
     const StoresToCheck& stores_to_check) const {
   return enabled_ && v4_database_ &&
          v4_database_->AreStoresAvailable(stores_to_check);
 }
 
 }  // namespace safe_browsing