PVer4: Test checksum on startup outside the hotpath of DB load

components/safe_browsing_db/v4_store.cc

Index: components/safe_browsing_db/v4_store.cc
diff --git a/components/safe_browsing_db/v4_store.cc b/components/safe_browsing_db/v4_store.cc
index 434c6a9751fe03bb088472ff28777ca1451d2b0c..8946ccdbc056a279de7e90c1a5c44ca713e15ee3 100644
--- a/components/safe_browsing_db/v4_store.cc
+++ b/components/safe_browsing_db/v4_store.cc
@@ -13,6 +13,7 @@
 #include "components/safe_browsing_db/v4_rice.h"
 #include "components/safe_browsing_db/v4_store.h"
 #include "components/safe_browsing_db/v4_store.pb.h"
+#include "content/public/browser/browser_thread.h"
 #include "crypto/secure_hash.h"
 #include "crypto/sha2.h"
 
@@ -34,8 +35,6 @@ std::string GetUmaSuffixForStore(const base::FilePath& file_path) {
 void RecordTimeWithAndWithoutStore(const std::string& metric,
                                    base::TimeDelta time,
                                    const base::FilePath& file_path) {
-  std::string suffix = GetUmaSuffixForStore(file_path);
-
   // The histograms below are an expansion of the UMA_HISTOGRAM_LONG_TIMES
   // macro adapted to allow for a dynamically suffixed histogram name.
   // Note: The factory creates and owns the histogram.
@@ -47,6 +46,7 @@ void RecordTimeWithAndWithoutStore(const std::string& metric,
     histogram->AddTime(time);
   }
 
+  std::string suffix = GetUmaSuffixForStore(file_path);
   base::HistogramBase* histogram_suffix = base::Histogram::FactoryTimeGet(
       metric + suffix, base::TimeDelta::FromMilliseconds(1),
       base::TimeDelta::FromHours(1), 50,
@@ -174,10 +174,21 @@ std::string V4Store::DebugString() const {
                             store_path_.value().c_str(), state_base64.c_str());
 }
 
-bool V4Store::Reset() {
-  // TODO(vakh): Implement skeleton.
+void V4Store::Reset() {
+  DCHECK(task_runner_->RunsTasksOnCurrentThread());
+
+  // Posted to IO thread to avoid the race condition between
+  // |GetMatchingHashPrefix()|, which runs on the IO thread, and |Reset()|,
+  // which runs on task runner.

[Scott Hess - ex-Googler, 2016/10/05 04:42:13]

I may be reading things wrong, but I think now what happens is the manager
receives ResetDatabase() on the I/O thread, so it posts a task to the task
runner, which asks the database to reset, which asks this to reset, which posts
tasks back to the I/O thread.  Seems like a lot of work.  Since reset is only
affecting in-memory structures, it could all be on I/O thread, right?

Also, I feel like this code can't post back out to the I/O thread this way
without running the risk of use-after-free because the next task on the task
runner could be the DeleteSoon() on the owning V4Database instance.

[vakh (use Gerrit instead), 2016/10/05 23:49:32]

I've deleted the Reset code in the V4Database since it is not being called.

The other thing that I am going to do is to make V4LDBM be incharge of all write
operations that happen on the DB/store. This is to avoid the race conditions
between making changes to the store/DB and DB getting destroyed.

Here's a single-page design document of the new proposal:
https://goto.google.com/design-doc-v4store-verifychecksum

Please review it when you have the time. Meanwhile, I'll code it up in this CL.

+  content::BrowserThread::PostTask(
+      content::BrowserThread::IO, FROM_HERE,
+      base::Bind(&V4Store::ResetOnIOThread, base::Unretained(this)));
+}
+
+void V4Store::ResetOnIOThread() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  hash_prefix_map_.clear();
   state_ = "";
-  return true;
 }
 
 ApplyUpdateResult V4Store::ProcessPartialUpdateAndWriteToDisk(
@@ -201,8 +212,8 @@ ApplyUpdateResult V4Store::ProcessFullUpdateAndWriteToDisk(
   TimeTicks before = TimeTicks::Now();
   ApplyUpdateResult result = ProcessFullUpdate(response);
   if (result == APPLY_UPDATE_SUCCESS) {
-    RecordStoreWriteResult(WriteToDisk(std::move(response)));
     RecordProcessFullUpdateTime(TimeTicks::Now() - before, store_path_);
+    RecordStoreWriteResult(WriteToDisk(std::move(response)));
   }
   return result;
 }
@@ -310,7 +321,6 @@ void V4Store::ApplyUpdate(
   RecordApplyUpdateResult(apply_update_result);
 }
 
-// static
 ApplyUpdateResult V4Store::UpdateHashPrefixMapFromAdditions(
     const RepeatedPtrField<ThreatEntrySet>& additions,
     HashPrefixMap* additions_map) {
@@ -448,7 +458,29 @@ ApplyUpdateResult V4Store::MergeUpdate(const HashPrefixMap& old_prefixes_map,
                                        const HashPrefixMap& additions_map,
                                        const RepeatedField<int32>* raw_removals,
                                        const std::string& expected_checksum) {
+  DCHECK(task_runner_->RunsTasksOnCurrentThread());
   DCHECK(hash_prefix_map_.empty());
+
+  bool calculate_checksum = !expected_checksum.empty();
+  if (old_prefixes_map.empty()) {
+    // If the old map is empty, which it is at startup, then just copy over the
+    // additions map.
+    DCHECK(!raw_removals);
+    hash_prefix_map_ = additions_map;
+
+    if (calculate_checksum) {
+      // Calculate the checksum asynchronously later and if it doesn't match,
+      // reset the store. This is done so that the SafeBrowsing DB loads
+      // quickly, because navigation operations are not allowed until the DB
+      // loads.
+      task_runner_->PostTask(
+          FROM_HERE, base::Bind(&V4Store::VerifyChecksumDelayed,
+                                base::Unretained(this), expected_checksum));
+    }
+
+    return APPLY_UPDATE_SUCCESS;
+  }
+
   hash_prefix_map_.clear();
   ReserveSpaceInPrefixMap(old_prefixes_map, &hash_prefix_map_);
   ReserveSpaceInPrefixMap(additions_map, &hash_prefix_map_);
@@ -470,7 +502,6 @@ ApplyUpdateResult V4Store::MergeUpdate(const HashPrefixMap& old_prefixes_map,
   // At least one of the maps still has elements that need to be merged into the
   // new store.
 
-  bool calculate_checksum = !expected_checksum.empty();
   std::unique_ptr<crypto::SecureHash> checksum_ctx(
       crypto::SecureHash::Create(crypto::SecureHash::SHA256));
 
@@ -500,7 +531,7 @@ ApplyUpdateResult V4Store::MergeUpdate(const HashPrefixMap& old_prefixes_map,
       next_smallest_prefix_size = next_smallest_prefix_old.size();
 
       // Update the iterator map, which means that we have merged one hash
-      // prefix of size |next_size_for_old| from the old store.
+      // prefix of size |next_smallest_prefix_size| from the old store.
       old_iterator_map[next_smallest_prefix_size] += next_smallest_prefix_size;
 
       if (!raw_removals || removals_iter == raw_removals->end() ||
@@ -559,7 +590,9 @@ ApplyUpdateResult V4Store::MergeUpdate(const HashPrefixMap& old_prefixes_map,
       base::Base64Encode(checksum, &checksum_base64);
       base::Base64Encode(expected_checksum, &expected_checksum_base64);
       DVLOG(1) << "Failure: Checksum mismatch: calculated: " << checksum_base64
-               << " expected: " << expected_checksum_base64;
+               << "; expected: " << expected_checksum_base64
+               << "; store: " << *this;
+      ;
       return CHECKSUM_MISMATCH_FAILURE;
     }
   }
@@ -649,6 +682,7 @@ StoreWriteResult V4Store::WriteToDisk(
 }
 
 HashPrefix V4Store::GetMatchingHashPrefix(const FullHash& full_hash) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   // It should never be the case that more than one hash prefixes match a given
   // full hash. However, if that happens, this method returns any one of them.
   // It does not guarantee which one of those will be returned.
@@ -688,4 +722,48 @@ bool V4Store::HashPrefixMatches(const HashPrefix& hash_prefix,
   }
 }
 
+void V4Store::VerifyChecksumDelayed(const std::string& expected_checksum) {
+  DCHECK(task_runner_->RunsTasksOnCurrentThread());
+
+  IteratorMap iterator_map;
+  HashPrefix next_smallest_prefix;
+  InitializeIteratorMap(hash_prefix_map_, &iterator_map);
+  bool has_unmerged = GetNextSmallestUnmergedPrefix(
+      hash_prefix_map_, iterator_map, &next_smallest_prefix);
+
+  std::unique_ptr<crypto::SecureHash> checksum_ctx(
+      crypto::SecureHash::Create(crypto::SecureHash::SHA256));
+  while (has_unmerged) {
+    PrefixSize next_smallest_prefix_size;
+    next_smallest_prefix_size = next_smallest_prefix.size();
+
+    // Update the iterator map, which means that we have read one hash
+    // prefix of size |next_smallest_prefix_size| from hash_prefix_map_.
+    iterator_map[next_smallest_prefix_size] += next_smallest_prefix_size;
+
+    checksum_ctx->Update(base::string_as_array(&next_smallest_prefix),
+                         next_smallest_prefix_size);
+
+    // Find the next smallest unmerged element in the map.
+    has_unmerged = GetNextSmallestUnmergedPrefix(hash_prefix_map_, iterator_map,
+                                                 &next_smallest_prefix);
+  }
+
+  std::string checksum(crypto::kSHA256Length, 0);
+  checksum_ctx->Finish(base::string_as_array(&checksum), checksum.size());
+  if (checksum == expected_checksum) {
+    return;
+  }
+
+  std::string checksum_base64, expected_checksum_base64;
+  base::Base64Encode(checksum, &checksum_base64);
+  base::Base64Encode(expected_checksum, &expected_checksum_base64);
+  DVLOG(1) << "Failure: Checksum mismatch: calculated: " << checksum_base64
+           << "; expected: " << expected_checksum_base64
+           << "; store: " << *this;
+  RecordApplyUpdateResultWhenReadingFromDisk(CHECKSUM_MISMATCH_FAILURE);
+
+  Reset();
+}
+
 }  // namespace safe_browsing