OOR-CORS: Adjust CORS preflight cache size

To ensure that the cache size can not be too large,
we have the maximum cache entries limit. We change
the limit to 1024, and also introduces the key size
limit since the URL can be too long in some cases.

Bug: 962824
Change-Id: I3252c68a46dfcfc78cdac6d05a3a2481aace7527
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1609727Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659430}

services/network/public/cpp/cors/preflight_cache.cc

@@ -16,7 +16,8 @@ namespace network {
 namespace cors {
 
 namespace {
-constexpr size_t kMaxCacheEntries = 4096;
+constexpr size_t kMaxCacheEntries = 1024u;
+constexpr size_t kMaxKeyLength = 512u;
 
 // These values are persisted to logs. Entries should not be renumbered and
 // numeric values should never be reused.
@@ -44,12 +45,16 @@ void PreflightCache::AppendEntry(
     std::unique_ptr<PreflightResult> preflight_result) {
   DCHECK(preflight_result);
 
+  // Do not cache |preflight_result| if |url| is too long.
+  const std::string& key = url.spec();
+  if (key.length() >= kMaxKeyLength)
+    return;
+
   // Since one new entry is always added below, let's purge one cache entry
   // if cache size is larger than kMaxCacheEntries - 1 so that the size to be
   // kMaxCacheEntries at maximum.
   MayPurge(kMaxCacheEntries - 1);
 
-  const std::string& key = url.spec();
   UMA_HISTOGRAM_COUNTS_1000("Net.Cors.PreflightCacheKeySize", key.length());
   UMA_HISTOGRAM_COUNTS_10000("Net.Cors.PreflightCacheValueSize",
                              preflight_result->EstimateMemoryPressureInBytes());