Double-check safe-browsing database validity on update failure.

chrome/browser/safe_browsing/safe_browsing_store_file.cc

Index: chrome/browser/safe_browsing/safe_browsing_store_file.cc
diff --git a/chrome/browser/safe_browsing/safe_browsing_store_file.cc b/chrome/browser/safe_browsing/safe_browsing_store_file.cc
index 7f1924dba3e6d6f3ed8bc672a3bafb76f247d0c6..025ea2fdf6e33705b650b87394cfd1814ec4f542 100644
--- a/chrome/browser/safe_browsing/safe_browsing_store_file.cc
+++ b/chrome/browser/safe_browsing/safe_browsing_store_file.cc
@@ -243,6 +243,59 @@ bool SafeBrowsingStoreFile::Delete() {
   return true;
 }
 
+bool SafeBrowsingStoreFile::CheckValidity() {
+  if (empty_)
+    return true;
+
+  // If the file was not empty, it should be open.
+  DCHECK(file_.get());
+
+  if (!FileRewind(file_.get()))
+    return OnCorruptDatabase();
+
+  int64 size = 0;
+  if (!file_util::GetFileSize(filename_, &size))
+    return OnCorruptDatabase();
+
+  base::MD5Context context;
+  base::MD5Init(&context);
+
+  // Read everything except the final digest.
+  size_t bytes_left = static_cast<size_t>(size);
+  CHECK(size == static_cast<int64>(bytes_left));
+  if (bytes_left < sizeof(base::MD5Digest))
+    return OnCorruptDatabase();
+  bytes_left -= sizeof(base::MD5Digest);
+
+  // Fold the contents of the file into the checksum.
+  while (bytes_left > 0) {
+    char buf[4096];
+    const size_t c = std::min(sizeof(buf), bytes_left);
+    const size_t ret = fread(buf, 1, c, file_.get());
+
+    // The file's size changed while reading, give up.
+    if (ret != c)
+      return OnCorruptDatabase();
+    base::MD5Update(&context, base::StringPiece(buf, c));
+    bytes_left -= c;
+  }
+
+  // Calculate the digest to this point.
+  base::MD5Digest calculated_digest;
+  base::MD5Final(&calculated_digest, &context);
+
+  // Read the stored digest and verify it.
+  base::MD5Digest file_digest;
+  if (!ReadItem(&file_digest, file_.get(), NULL))
+    return OnCorruptDatabase();
+  if (0 != memcmp(&file_digest, &calculated_digest, sizeof(file_digest))) {
+    RecordFormatEvent(FORMAT_EVENT_VALIDITY_CHECKSUM_FAILURE);
+    return OnCorruptDatabase();
+  }
+
+  return true;
+}
+
 void SafeBrowsingStoreFile::Init(
     const FilePath& filename,
     const base::Closure& corruption_callback
@@ -503,8 +556,10 @@ bool SafeBrowsingStoreFile::DoUpdate(
     if (!ReadItem(&file_digest, file_.get(), NULL))
       return OnCorruptDatabase();
 
-    if (0 != memcmp(&file_digest, &calculated_digest, sizeof(file_digest)))
+    if (0 != memcmp(&file_digest, &calculated_digest, sizeof(file_digest))) {
+      RecordFormatEvent(FORMAT_EVENT_UPDATE_CHECKSUM_FAILURE);
       return OnCorruptDatabase();
+    }
 
     // Close the file so we can later rename over it.
     file_.reset();