Bug 1148286 - Ensure we don't nullpointer deref if the CDM crashes in MediaKeys and Reader::SetCDMProxy implementations. r=edwin

dom/media/eme/MediaKeys.cpp

@@ -153,6 +153,12 @@ MediaKeys::SetServerCertificate(const ArrayBufferViewOrArrayBuffer& aCert, Error
     return nullptr;
   }
 
+  if (!mProxy) {
+    NS_WARNING("Tried to use a MediaKeys without a CDM");
+    promise->MaybeReject(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return promise.forget();
+  }
+
   nsTArray<uint8_t> data;
   if (!CopyArrayBufferViewOrArrayBufferData(aCert, data)) {
     promise->MaybeReject(NS_ERROR_DOM_INVALID_ACCESS_ERR);
@@ -487,6 +493,12 @@ MediaKeys::CreateSession(JSContext* aCx,
                          SessionType aSessionType,
                          ErrorResult& aRv)
 {
+  if (!mProxy) {
+    NS_WARNING("Tried to use a MediaKeys which lost its CDM");
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return nullptr;
+  }
+
   EME_LOG("MediaKeys[%p] Creating session", this);
 
   nsRefPtr<MediaKeySession> session = new MediaKeySession(aCx,

dom/media/fmp4/MP4Decoder.cpp

@@ -42,7 +42,7 @@ MP4Decoder::SetCDMProxy(CDMProxy* aProxy)
 {
   nsresult rv = MediaDecoder::SetCDMProxy(aProxy);
   NS_ENSURE_SUCCESS(rv, rv);
-  {
+  if (aProxy) {
     // The MP4Reader can't decrypt EME content until it has a CDMProxy,
     // and the CDMProxy knows the capabilities of the CDM. The MP4Reader
     // remains in "waiting for resources" state until then.

dom/media/mediasource/MediaSourceDecoder.cpp

@@ -305,7 +305,7 @@ MediaSourceDecoder::SetCDMProxy(CDMProxy* aProxy)
   rv = mReader->SetCDMProxy(aProxy);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  {
+  if (aProxy) {
     // The sub readers can't decrypt EME content until they have a CDMProxy,
     // and the CDMProxy knows the capabilities of the CDM. The MediaSourceReader
     // remains in "waiting for resources" state until then. We need to kick the