Bug 1377426 - Set CSP on freshly created nullprincipal when iframe is sandboxed. r=dveditz

dom/base/nsDocument.cpp

@@ -2792,10 +2792,14 @@ nsDocument::InitCSP(nsIChannel* aChannel)
 
   mSandboxFlags |= cspSandboxFlags;
 
-  if (cspSandboxFlags & SANDBOXED_ORIGIN) {
-    // If the new CSP sandbox flags do not have the allow-same-origin flag
-    // reset the document principal to a null principal
-    principal = NullPrincipal::Create();
+  // Probably the iframe sandbox attribute already caused the creation of a
+  // new NullPrincipal. Only create a new NullPrincipal if CSP requires so
+  // and no one has been created yet.
+  bool needNewNullPrincipal =
+    (cspSandboxFlags & SANDBOXED_ORIGIN) && !(mSandboxFlags & SANDBOXED_ORIGIN);
+  if (needNewNullPrincipal) {
+    principal = NullPrincipal::CreateWithInheritedAttributes(principal);
+    principal->SetCsp(csp);
     SetPrincipal(principal);
   }
 

dom/security/test/csp/test_sandbox.html

@@ -106,6 +106,15 @@ var testCases = [
     results: { img12_bad: -1, script12_bad: -1 },
     nrOKmessages: 4 // sends 4 ok message
   },
+  {
+    // Test 13: same as Test 5 and Test 11, but:
+    // * using sandbox flag 'allow-scripts' in CSP and not as iframe attribute
+    // * not using allow-same-origin in CSP (so a new NullPrincipal is created).
+    csp: "default-src 'none'; script-src 'unsafe-inline'; sandbox allow-scripts",
+    file: "file_sandbox_5.html",
+    results: { img13_bad: -1, img13a_bad: -1, script13_bad: -1, script13a_bad: -1 },
+    nrOKmessages: 2 // sends 2 ok message
+  },
 ];
 
 // a postMessage handler that is used by sandboxed iframes without