CSP should only check host (not including path) when performing frame ancestors checks.

This has been explicitly stated in the CSP-3 spec.

dom/security/nsCSPParser.cpp

@@ -136,6 +136,7 @@ nsCSPParser::nsCSPParser(cspTokens& aTokens,
  , mUnsafeInlineKeywordSrc(nullptr)
  , mChildSrc(nullptr)
  , mFrameSrc(nullptr)
+ , mParsingFrameAncestorsDir(false)
  , mTokens(aTokens)
  , mSelfURI(aSelfURI)
  , mPolicy(nullptr)
@@ -807,6 +808,7 @@ nsCSPParser::sourceExpression()
   if (nsCSPHostSrc *cspHost = hostSource()) {
     // Do not forget to set the parsed scheme.
     cspHost->setScheme(parsedScheme);
+    cspHost->setWithinFrameAncestorsDir(mParsingFrameAncestorsDir);
     return cspHost;
   }
   // Error was reported in hostSource()
@@ -1209,6 +1211,9 @@ nsCSPParser::directive()
   mStrictDynamic = false;
   mUnsafeInlineKeywordSrc = nullptr;
 
+  mParsingFrameAncestorsDir =
+    CSP_IsDirective(mCurDir[0], nsIContentSecurityPolicy::FRAME_ANCESTORS_DIRECTIVE);
+
   // Try to parse all the srcs by handing the array off to directiveValue
   nsTArray<nsCSPBaseSrc*> srcs;
   directiveValue(srcs);

dom/security/nsCSPParser.h

@@ -252,6 +252,10 @@ class nsCSPParser {
     nsCSPChildSrcDirective* mChildSrc;
     nsCSPDirective*         mFrameSrc;
 
+    // cache variable to let nsCSPHostSrc know that it's within
+    // the frame-ancestors directive.
+    bool                    mParsingFrameAncestorsDir;
+
     cspTokens          mTokens;
     nsIURI*            mSelfURI;
     nsCSPPolicy*       mPolicy;

dom/security/nsCSPUtils.cpp

@@ -503,6 +503,7 @@ nsCSPSchemeSrc::toString(nsAString& outStr) const
 
 nsCSPHostSrc::nsCSPHostSrc(const nsAString& aHost)
   : mHost(aHost)
+  , mWithinFrameAncstorsDir(false)
 {
   ToLowerCase(mHost);
 }
@@ -686,6 +687,11 @@ nsCSPHostSrc::permits(nsIURI* aUri, const nsAString& aNonce, bool aWasRedirected
     rv = url->GetFilePath(uriPath);
     NS_ENSURE_SUCCESS(rv, false);
 
+    if (mWithinFrameAncstorsDir) {
+      // no path matching for frame-ancestors to not leak any path information.
+      return true;
+    }
+
     nsString decodedUriPath;
     CSP_PercentDecodeStr(NS_ConvertUTF8toUTF16(uriPath), decodedUriPath);
 

dom/security/nsCSPUtils.h

@@ -256,6 +256,9 @@ class nsCSPHostSrc : public nsCSPBaseSrc {
     void setPort(const nsAString& aPort);
     void appendPath(const nsAString &aPath);
 
+    inline void setWithinFrameAncestorsDir(bool aValue) const
+      { mWithinFrameAncstorsDir = aValue; }
+
     inline void getScheme(nsAString& outStr) const
       { outStr.Assign(mScheme); };
 
@@ -273,6 +276,7 @@ class nsCSPHostSrc : public nsCSPBaseSrc {
     nsString mHost;
     nsString mPort;
     nsString mPath;
+    mutable bool mWithinFrameAncstorsDir;
 };
 
 /* =============== nsCSPKeywordSrc ============ */