Bug 1084025 - Add telemetry to measure failures due to not falling back. r=keeler

security/manager/ssl/src/nsNSSIOLayer.cpp

@@ -870,18 +870,21 @@ nsSSLIOLayerHelpers::rememberTolerantAtVersion(const nsACString& hostName,
   mTLSIntoleranceInfo.Put(key, entry);
 }
 
-void nsSSLIOLayerHelpers::forgetIntolerance(const nsACString& hostName,
-                                            int16_t port)
+uint16_t
+nsSSLIOLayerHelpers::forgetIntolerance(const nsACString& hostName,
+                                       int16_t port)
 {
   nsCString key;
   getSiteKey(hostName, port, key);
 
   MutexAutoLock lock(mutex);
 
+  uint16_t tolerant = 0;
   IntoleranceEntry entry;
   if (mTLSIntoleranceInfo.Get(key, &entry)) {
     entry.AssertInvariant();
 
+    tolerant = entry.tolerant;
     entry.intolerant = 0;
     entry.intoleranceReason = 0;
     if (entry.strongCipherStatus != StrongCiphersWorked) {
@@ -891,6 +894,8 @@ void nsSSLIOLayerHelpers::forgetIntolerance(const nsACString& hostName,
     entry.AssertInvariant();
     mTLSIntoleranceInfo.Put(key, entry);
   }
+
+  return tolerant;
 }
 
 // returns true if we should retry the handshake
@@ -903,7 +908,47 @@ nsSSLIOLayerHelpers::rememberIntolerantAtVersion(const nsACString& hostName,
 {
   if (intolerant <= minVersion || intolerant <= mVersionFallbackLimit) {
     // We can't fall back any further. Assume that intolerance isn't the issue.
-    forgetIntolerance(hostName, port);
+    uint32_t tolerant = forgetIntolerance(hostName, port);
+    // If we know the server is tolerant at the version, we don't have to
+    // gather the telemetry.
+    if (intolerant <= tolerant) {
+      return false;
+    }
+
+    uint32_t fallbackLimitBucket = 0;
+    // added if the version has reached the min version.
+    if (intolerant <= minVersion) {
+      switch (minVersion) {
+        case SSL_LIBRARY_VERSION_TLS_1_0:
+          fallbackLimitBucket += 1;
+          break;
+        case SSL_LIBRARY_VERSION_TLS_1_1:
+          fallbackLimitBucket += 2;
+          break;
+        case SSL_LIBRARY_VERSION_TLS_1_2:
+          fallbackLimitBucket += 3;
+          break;
+      }
+    }
+    // added if the version has reached the fallback limit.
+    if (intolerant <= mVersionFallbackLimit) {
+      switch (mVersionFallbackLimit) {
+        case SSL_LIBRARY_VERSION_TLS_1_0:
+          fallbackLimitBucket += 4;
+          break;
+        case SSL_LIBRARY_VERSION_TLS_1_1:
+          fallbackLimitBucket += 8;
+          break;
+        case SSL_LIBRARY_VERSION_TLS_1_2:
+          fallbackLimitBucket += 12;
+          break;
+      }
+    }
+    if (fallbackLimitBucket) {
+      Telemetry::Accumulate(Telemetry::SSL_FALLBACK_LIMIT_REACHED,
+                            fallbackLimitBucket);
+    }
+
     return false;
   }
 

security/manager/ssl/src/nsNSSIOLayer.h

@@ -225,7 +225,9 @@ public:
                                    PRErrorCode intoleranceReason);
   bool rememberStrongCiphersFailed(const nsACString& hostName, int16_t port,
                                    PRErrorCode intoleranceReason);
-  void forgetIntolerance(const nsACString& hostname, int16_t port);
+  // returns the known tolerant version
+  // or 0 if there is no known tolerant version
+  uint16_t forgetIntolerance(const nsACString& hostname, int16_t port);
   void adjustForTLSIntolerance(const nsACString& hostname, int16_t port,
                                /*in/out*/ SSLVersionRange& range,
                                /*out*/ StrongCipherStatus& strongCipherStatus);

toolkit/components/telemetry/Histograms.json

@@ -6480,6 +6480,12 @@
     "n_values": 64,
     "description": "TLS/SSL version intolerance was falsely detected, server rejected handshake"
   },
+  "SSL_FALLBACK_LIMIT_REACHED": {
+    "expires_in_version": "default",
+    "kind": "enumerated",
+    "n_values": 16,
+    "description": "TLS/SSL version fallback reached the fallback limit (1=TLS 1.0, 2=TLS 1.1, 3=TLS 1.2) or the minimum version (4=TLS 1.0, 8=TLS 1.1, 12=TLS 1.2), stopped the fallback"
+  },
   "SSL_WEAK_CIPHERS_FALLBACK": {
     "expires_in_version": "never",
     "kind": "enumerated",