Check node references during sync DB init

chrome/browser/sync/syncable/syncable.cc

Index: chrome/browser/sync/syncable/syncable.cc
diff --git a/chrome/browser/sync/syncable/syncable.cc b/chrome/browser/sync/syncable/syncable.cc
index b1548f0d8d4611b01650e277d4a5599526033238..c6ae0395c1bdff02c1f970cf9b733344e8f249e5 100644
--- a/chrome/browser/sync/syncable/syncable.cc
+++ b/chrome/browser/sync/syncable/syncable.cc
@@ -14,6 +14,7 @@
 #include <string>
 
 #include "base/compiler_specific.h"
+#include "base/debug/trace_event.h"
 #include "base/file_util.h"
 #include "base/hash_tables.h"
 #include "base/location.h"
@@ -51,6 +52,42 @@ static const InvariantCheckLevel kInvariantCheckLevel = VERIFY_IN_MEMORY;
 
 // Max number of milliseconds to spend checking syncable entry invariants
 static const int kInvariantCheckMaxMs = 50;
+
+// This function checks to see if the given list of Metahandles has any nodes
+// whose PREV_ID, PARENT_ID or NEXT_ID values refer to ID values that do not
+// actually exist.  Returns true on success.
+//
+// This function is "Unsafe" because it does not attempt to acquire any locks
+// that may be protecting this list that gets passed in.  The caller is
+// responsible for ensuring that no one modifies this list while the function is
+// running.
+bool VerifyReferenceIntegrityUnsafe(const syncable::MetahandlesIndex &index) {
+  TRACE_EVENT0("sync", "SyncDatabaseIntegrityCheck");
+  using namespace syncable;
+  typedef base::hash_set<std::string> IdsSet;
+
+  IdsSet ids_set;
+  bool is_ok = true;
+
+  for (MetahandlesIndex::const_iterator it = index.begin();
+       it != index.end(); ++it) {
+    EntryKernel* entry = *it;
+    bool is_duplicate_id = !(ids_set.insert(entry->ref(ID).value()).second);
+    is_ok = is_ok && !is_duplicate_id;
+  }
+
+  IdsSet::iterator end = ids_set.end();
+  for (MetahandlesIndex::const_iterator it = index.begin();
+       it != index.end(); ++it) {
+    EntryKernel* entry = *it;
+    bool prev_exists = (ids_set.find(entry->ref(PREV_ID).value()) != end);
+    bool parent_exists = (ids_set.find(entry->ref(PARENT_ID).value()) != end);
+    bool next_exists = (ids_set.find(entry->ref(NEXT_ID).value()) != end);
+    is_ok = is_ok && prev_exists && parent_exists && next_exists;
+  }
+  return is_ok;
+}
+
 }  // namespace
 
 using std::string;
@@ -477,6 +514,7 @@ DirOpenResult Directory::OpenImpl(
     DirectoryChangeDelegate* delegate,
     const browser_sync::WeakHandle<TransactionObserver>&
         transaction_observer) {
+  TRACE_EVENT0("sync", "SyncDatabaseOpen");
   DCHECK_EQ(static_cast<DirectoryBackingStore*>(NULL), store_);
   FilePath db_path(file_path);
   file_util::AbsolutePath(&db_path);
@@ -490,6 +528,9 @@ DirOpenResult Directory::OpenImpl(
   if (OPENED != result)
     return result;
 
+  if (!VerifyReferenceIntegrityUnsafe(metas_bucket))
+    return FAILED_LOGICAL_CORRUPTION;
+
   kernel_ = new Kernel(db_path, name, info, delegate, transaction_observer);
   kernel_->metahandles_index->swap(metas_bucket);
   InitializeIndices();