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 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */

 /* vim: set ts=8 sts=4 et sw=4 tw=99: */

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 #include "WaiveXrayWrapper.h"

 #include "FilteringWrapper.h"

 #include "XrayWrapper.h"

 #include "AccessCheck.h"

 #include "XPCWrapper.h"

 #include "ChromeObjectWrapper.h"

 #include "WrapperFactory.h"

 #include "xpcprivate.h"

 #include "XPCMaps.h"

 #include "mozilla/dom/BindingUtils.h"

 #include "jsfriendapi.h"

 #include "mozilla/Likely.h"

 #include "nsContentUtils.h"

 using namespace JS;

 using namespace js;

 using namespace mozilla;

 namespace xpc {

 // When chrome pulls a naked property across the membrane using

 // .wrappedJSObject, we want it to cross the membrane into the

 // chrome compartment without automatically being wrapped into an

 // X-ray wrapper. We achieve this by wrapping it into a special

 // transparent wrapper in the origin (non-chrome) compartment. When

 // an object with that special wrapper applied crosses into chrome,

 // we know to not apply an X-ray wrapper.

 Wrapper XrayWaiver(WrapperFactory::WAIVE_XRAY_WRAPPER_FLAG);

 // When objects for which we waived the X-ray wrapper cross into

 // chrome, we wrap them into a special cross-compartment wrapper

 // that transitively extends the waiver to all properties we get

 // off it.

 WaiveXrayWrapper WaiveXrayWrapper::singleton(0);

 bool

 WrapperFactory::IsCOW(JSObject *obj)

 {

     return IsWrapper(obj) &&

            Wrapper::wrapperHandler(obj) == &ChromeObjectWrapper::singleton;

 }

 JSObject *

 WrapperFactory::GetXrayWaiver(HandleObject obj)

 {

     // Object should come fully unwrapped but outerized.

     MOZ_ASSERT(obj == UncheckedUnwrap(obj));

     MOZ_ASSERT(!js::GetObjectClass(obj)->ext.outerObject);

     XPCWrappedNativeScope *scope = GetObjectScope(obj);

     MOZ_ASSERT(scope);

     if (!scope->mWaiverWrapperMap)

         return nullptr;

     JSObject* xrayWaiver = scope->mWaiverWrapperMap->Find(obj);

     if (xrayWaiver)

         JS::ExposeObjectToActiveJS(xrayWaiver);

     return xrayWaiver;

 }

 JSObject *

 WrapperFactory::CreateXrayWaiver(JSContext *cx, HandleObject obj)

 {

     // The caller is required to have already done a lookup.

     // NB: This implictly performs the assertions of GetXrayWaiver.

     MOZ_ASSERT(!GetXrayWaiver(obj));

     XPCWrappedNativeScope *scope = GetObjectScope(obj);

     JSAutoCompartment ac(cx, obj);

     JSObject *waiver = Wrapper::New(cx, obj,

                                     JS_GetGlobalForObject(cx, obj),

                                     &XrayWaiver);

     if (!waiver)

         return nullptr;

     // Add the new waiver to the map. It's important that we only ever have

     // one waiver for the lifetime of the target object.

     if (!scope->mWaiverWrapperMap) {

         scope->mWaiverWrapperMap =

           JSObject2JSObjectMap::newMap(XPC_WRAPPER_MAP_SIZE);

         MOZ_ASSERT(scope->mWaiverWrapperMap);

     }

     if (!scope->mWaiverWrapperMap->Add(cx, obj, waiver))

         return nullptr;

     return waiver;

 }

 JSObject *

 WrapperFactory::WaiveXray(JSContext *cx, JSObject *objArg)

 {

     RootedObject obj(cx, objArg);

     obj = UncheckedUnwrap(obj);

     MOZ_ASSERT(!js::IsInnerObject(obj));

     JSObject *waiver = GetXrayWaiver(obj);

     if (waiver)

         return waiver;

     return CreateXrayWaiver(cx, obj);

 }

 // DoubleWrap is called from PrepareForWrapping to maintain the state that

 // we're supposed to waive Xray wrappers for the given on. On entrance, it

 // expects |cx->compartment != obj->compartment()|. The returned object will

 // be in the same compartment as |obj|.

 JSObject *

 WrapperFactory::DoubleWrap(JSContext *cx, HandleObject obj, unsigned flags)

 {

     if (flags & WrapperFactory::WAIVE_XRAY_WRAPPER_FLAG) {

         JSAutoCompartment ac(cx, obj);

         return WaiveXray(cx, obj);

     }

     return obj;

 }

 JSObject *

 WrapperFactory::PrepareForWrapping(JSContext *cx, HandleObject scope,

                                    HandleObject objArg, unsigned flags)

 {

     RootedObject obj(cx, objArg);

     // Outerize any raw inner objects at the entry point here, so that we don't

     // have to worry about them for the rest of the wrapping code.

     if (js::IsInnerObject(obj)) {

         JSAutoCompartment ac(cx, obj);

         obj = JS_ObjectToOuterObject(cx, obj);

         NS_ENSURE_TRUE(obj, nullptr);

         // The outerization hook wraps, which means that we can end up with a

         // CCW here if |obj| was a navigated-away-from inner. Strip any CCWs.

         obj = js::UncheckedUnwrap(obj);

         MOZ_ASSERT(js::IsOuterObject(obj));

     }

     // If we've got an outer window, there's nothing special that needs to be

     // done here, and we can move on to the next phase of wrapping. We handle

     // this case first to allow us to assert against wrappers below.

     if (js::IsOuterObject(obj))

         return DoubleWrap(cx, obj, flags);

     // Here are the rules for wrapping:

     // We should never get a proxy here (the JS engine unwraps those for us).

     MOZ_ASSERT(!IsWrapper(obj));

     // If the object being wrapped is a prototype for a standard class and the

     // wrapper does not subsumes the wrappee, use the one from the content

     // compartment. This is generally safer all-around, and in the COW case this

     // lets us safely take advantage of things like .forEach() via the

     // ChromeObjectWrapper machinery.

     //

     // If the prototype chain of chrome object |obj| looks like this:

     //

     // obj => foo => bar => chromeWin.StandardClass.prototype

     //

     // The prototype chain of COW(obj) looks lke this:

     //

     // COW(obj) => COW(foo) => COW(bar) => contentWin.StandardClass.prototype

     //

     // NB: We now remap all non-subsuming access of standard prototypes.

     //

     // NB: We need to ignore domain here so that the security relationship we

     // compute here can't change over time. See the comment above the other

     // subsumes call below.

     bool subsumes = AccessCheck::subsumes(js::GetContextCompartment(cx),

                                           js::GetObjectCompartment(obj));

     XrayType xrayType = GetXrayType(obj);

     if (!subsumes && xrayType == NotXray) {

         JSProtoKey key = JSProto_Null;

         {

             JSAutoCompartment ac(cx, obj);

             key = IdentifyStandardPrototype(obj);

         }

         if (key != JSProto_Null) {

             RootedObject homeProto(cx);

             if (!JS_GetClassPrototype(cx, key, &homeProto))

                 return nullptr;

             MOZ_ASSERT(homeProto);

             // No need to double-wrap here. We should never have waivers to

             // COWs.

             return homeProto;

         }

     }

     // Now, our object is ready to be wrapped, but several objects (notably

     // nsJSIIDs) have a wrapper per scope. If we are about to wrap one of

     // those objects in a security wrapper, then we need to hand back the

     // wrapper for the new scope instead. Also, global objects don't move

     // between scopes so for those we also want to return the wrapper. So...

     if (!IS_WN_REFLECTOR(obj) || !js::GetObjectParent(obj))

         return DoubleWrap(cx, obj, flags);

     XPCWrappedNative *wn = XPCWrappedNative::Get(obj);

     JSAutoCompartment ac(cx, obj);

     XPCCallContext ccx(JS_CALLER, cx, obj);

     RootedObject wrapScope(cx, scope);

     {

         if (NATIVE_HAS_FLAG(&ccx, WantPreCreate)) {

             // We have a precreate hook. This object might enforce that we only

             // ever create JS object for it.

             // Note: this penalizes objects that only have one wrapper, but are

             // being accessed across compartments. We would really prefer to

             // replace the above code with a test that says "do you only have one

             // wrapper?"

             nsresult rv = wn->GetScriptableInfo()->GetCallback()->

                 PreCreate(wn->Native(), cx, scope, wrapScope.address());

             NS_ENSURE_SUCCESS(rv, DoubleWrap(cx, obj, flags));

             // If the handed back scope differs from the passed-in scope and is in

             // a separate compartment, then this object is explicitly requesting

             // that we don't create a second JS object for it: create a security

             // wrapper.

             if (js::GetObjectCompartment(scope) != js::GetObjectCompartment(wrapScope))

                 return DoubleWrap(cx, obj, flags);

             RootedObject currentScope(cx, JS_GetGlobalForObject(cx, obj));

             if (MOZ_UNLIKELY(wrapScope != currentScope)) {

                 // The wrapper claims it wants to be in the new scope, but

                 // currently has a reflection that lives in the old scope. This

                 // can mean one of two things, both of which are rare:

                 //

                 // 1 - The object has a PreCreate hook (we checked for it above),

                 // but is deciding to request one-wrapper-per-scope (rather than

                 // one-wrapper-per-native) for some reason. Usually, a PreCreate

                 // hook indicates one-wrapper-per-native. In this case we want to

                 // make a new wrapper in the new scope.

                 //

                 // 2 - We're midway through wrapper reparenting. The document has

                 // moved to a new scope, but |wn| hasn't been moved yet, and

                 // we ended up calling JS_WrapObject() on its JS object. In this

                 // case, we want to return the existing wrapper.

                 //

                 // So we do a trick: call PreCreate _again_, but say that we're

                 // wrapping for the old scope, rather than the new one. If (1) is

                 // the case, then PreCreate will return the scope we pass to it

                 // (the old scope). If (2) is the case, PreCreate will return the

                 // scope of the document (the new scope).

                 RootedObject probe(cx);

                 rv = wn->GetScriptableInfo()->GetCallback()->

                     PreCreate(wn->Native(), cx, currentScope, probe.address());

                 // Check for case (2).

                 if (probe != currentScope) {

                     MOZ_ASSERT(probe == wrapScope);

                     return DoubleWrap(cx, obj, flags);

                 }

                 // Ok, must be case (1). Fall through and create a new wrapper.

             }

             // Nasty hack for late-breaking bug 781476. This will confuse identity checks,

             // but it's probably better than any of our alternatives.

             //

             // Note: We have to ignore domain here. The JS engine assumes that, given a

             // compartment c, if c->wrap(x) returns a cross-compartment wrapper at time t0,

             // it will also return a cross-compartment wrapper for any time t1 > t0 unless

             // an explicit transplant is performed. In particular, wrapper recomputation

             // assumes that recomputing a wrapper will always result in a wrapper.

             //

             // This doesn't actually pose a security issue, because we'll still compute

             // the correct (opaque) wrapper for the object below given the security

             // characteristics of the two compartments.

             if (!AccessCheck::isChrome(js::GetObjectCompartment(wrapScope)) &&

                  AccessCheck::subsumes(js::GetObjectCompartment(wrapScope),

                                        js::GetObjectCompartment(obj)))

             {

                 return DoubleWrap(cx, obj, flags);

             }

         }

     }

     // This public WrapNativeToJSVal API enters the compartment of 'wrapScope'

     // so we don't have to.

     RootedValue v(cx);

     nsresult rv =

         nsXPConnect::XPConnect()->WrapNativeToJSVal(cx, wrapScope, wn->Native(), nullptr,

                                                     &NS_GET_IID(nsISupports), false, &v);

     NS_ENSURE_SUCCESS(rv, nullptr);

     obj.set(&v.toObject());

     MOZ_ASSERT(IS_WN_REFLECTOR(obj), "bad object");

     // Because the underlying native didn't have a PreCreate hook, we had

     // to a new (or possibly pre-existing) XPCWN in our compartment.

     // This could be a problem for chrome code that passes XPCOM objects

     // across compartments, because the effects of QI would disappear across

     // compartments.

     //

     // So whenever we pull an XPCWN across compartments in this manner, we

     // give the destination object the union of the two native sets. We try

     // to do this cleverly in the common case to avoid too much overhead.

     XPCWrappedNative *newwn = XPCWrappedNative::Get(obj);

     XPCNativeSet *unionSet = XPCNativeSet::GetNewOrUsed(newwn->GetSet(),

                                                         wn->GetSet(), false);

     if (!unionSet)

         return nullptr;

     newwn->SetSet(unionSet);

     return DoubleWrap(cx, obj, flags);

 }

 #ifdef DEBUG

 static void

 DEBUG_CheckUnwrapSafety(HandleObject obj, js::Wrapper *handler,

                         JSCompartment *origin, JSCompartment *target)

 {

     if (AccessCheck::isChrome(target) || xpc::IsUniversalXPConnectEnabled(target)) {

         // If the caller is chrome (or effectively so), unwrap should always be allowed.

         MOZ_ASSERT(!handler->hasSecurityPolicy());

     } else if (handler == &FilteringWrapper<CrossCompartmentSecurityWrapper, GentlyOpaque>::singleton) {

         // We explicitly use a SecurityWrapper to protect privileged callers from

         // less-privileged objects that they should never see. Skip the check in

         // this case.

     } else {

         // Otherwise, it should depend on whether the target subsumes the origin.

         MOZ_ASSERT(handler->hasSecurityPolicy() == !AccessCheck::subsumesConsideringDomain(target, origin));

     }

 }

 #else

 #define DEBUG_CheckUnwrapSafety(obj, handler, origin, target) {}

 #endif

 static Wrapper *

 SelectWrapper(bool securityWrapper, bool wantXrays, XrayType xrayType,

               bool waiveXrays, bool originIsXBLScope)

 {

     // Waived Xray uses a modified CCW that has transparent behavior but

     // transitively waives Xrays on arguments.

     if (waiveXrays) {

         MOZ_ASSERT(!securityWrapper);

         return &WaiveXrayWrapper::singleton;

     }

     // If we don't want or can't use Xrays, select a wrapper that's either

     // entirely transparent or entirely opaque.

     if (!wantXrays || xrayType == NotXray) {

         if (!securityWrapper)

             return &CrossCompartmentWrapper::singleton;

         // In general, we don't want opaque function wrappers to be callable.

         // But in the case of XBL, we rely on content being able to invoke

         // functions exposed from the XBL scope. We could remove this exception,

         // if needed, by using ExportFunction to generate the content-side

         // representations of XBL methods.

         else if (originIsXBLScope)

             return &FilteringWrapper<CrossCompartmentSecurityWrapper, OpaqueWithCall>::singleton;

         return &FilteringWrapper<CrossCompartmentSecurityWrapper, Opaque>::singleton;

     }

     // Ok, we're using Xray. If this isn't a security wrapper, use the permissive

     // version and skip the filter.

     if (!securityWrapper) {

         if (xrayType == XrayForWrappedNative)

             return &PermissiveXrayXPCWN::singleton;

         else if (xrayType == XrayForDOMObject)

             return &PermissiveXrayDOM::singleton;

         MOZ_ASSERT(xrayType == XrayForJSObject);

         return &PermissiveXrayJS::singleton;

     }

     // This is a security wrapper. Use the security versions and filter.

     if (xrayType == XrayForWrappedNative)

         return &FilteringWrapper<SecurityXrayXPCWN,

                                  CrossOriginAccessiblePropertiesOnly>::singleton;

     else if (xrayType == XrayForDOMObject)

         return &FilteringWrapper<SecurityXrayDOM,

                                  CrossOriginAccessiblePropertiesOnly>::singleton;

     // There's never any reason to expose pure JS objects to non-subsuming actors.

     // Just use an opaque wrapper in this case.

     MOZ_ASSERT(xrayType == XrayForJSObject);

     return &FilteringWrapper<CrossCompartmentSecurityWrapper, Opaque>::singleton;

 }

 JSObject *

 WrapperFactory::Rewrap(JSContext *cx, HandleObject existing, HandleObject obj,

                        HandleObject wrappedProto, HandleObject parent,

                        unsigned flags)

 {

     MOZ_ASSERT(!IsWrapper(obj) ||

                GetProxyHandler(obj) == &XrayWaiver ||

                js::GetObjectClass(obj)->ext.innerObject,

                "wrapped object passed to rewrap");

     MOZ_ASSERT(!XrayUtils::IsXPCWNHolderClass(JS_GetClass(obj)), "trying to wrap a holder");

     MOZ_ASSERT(!js::IsInnerObject(obj));

     // We sometimes end up here after nsContentUtils has been shut down but before

     // XPConnect has been shut down, so check the context stack the roundabout way.

     MOZ_ASSERT(XPCJSRuntime::Get()->GetJSContextStack()->Peek() == cx);

     // Compute the information we need to select the right wrapper.

     JSCompartment *origin = js::GetObjectCompartment(obj);

     JSCompartment *target = js::GetContextCompartment(cx);

     bool originIsChrome = AccessCheck::isChrome(origin);

     bool targetIsChrome = AccessCheck::isChrome(target);

     bool originSubsumesTarget = AccessCheck::subsumesConsideringDomain(origin, target);

     bool targetSubsumesOrigin = AccessCheck::subsumesConsideringDomain(target, origin);

     bool sameOrigin = targetSubsumesOrigin && originSubsumesTarget;

     XrayType xrayType = GetXrayType(obj);

     bool waiveXrayFlag = flags & WAIVE_XRAY_WRAPPER_FLAG;

     Wrapper *wrapper;

     CompartmentPrivate *targetdata = EnsureCompartmentPrivate(target);

     //

     // First, handle the special cases.

     //

     // If UniversalXPConnect is enabled, this is just some dumb mochitest. Use

     // a vanilla CCW.

     if (xpc::IsUniversalXPConnectEnabled(target)) {

         wrapper = &CrossCompartmentWrapper::singleton;

     }

     // If this is a chrome object being exposed to content without Xrays, use

     // a COW.

     else if (originIsChrome && !targetIsChrome && xrayType == NotXray) {

         wrapper = &ChromeObjectWrapper::singleton;

     }

     // Normally, a non-xrayable non-waived content object that finds itself in

     // a privileged scope is wrapped with a CrossCompartmentWrapper, even though

     // the lack of a waiver _really_ should give it an opaque wrapper. This is

     // a bit too entrenched to change for content-chrome, but we can at least fix

     // it for XBL scopes.

     //

     // See bug 843829.

     else if (targetSubsumesOrigin && !originSubsumesTarget &&

              !waiveXrayFlag && xrayType == NotXray &&

              IsXBLScope(target))

     {

         wrapper = &FilteringWrapper<CrossCompartmentSecurityWrapper, GentlyOpaque>::singleton;

     }

     //

     // Now, handle the regular cases.

     //

     // These are wrappers we can compute using a rule-based approach. In order

     // to do so, we need to compute some parameters.

     //

     else {

         // The wrapper is a security wrapper (protecting the wrappee) if and

         // only if the target does not subsume the origin.

         bool securityWrapper = !targetSubsumesOrigin;

         // Xrays are warranted if either the target or the origin don't trust

         // each other. This is generally the case, unless the two are same-origin

         // and the caller has not requested same-origin Xrays.

         //

         // Xrays are a bidirectional protection, since it affords clarity to the

         // caller and privacy to the callee.

         bool wantXrays = !(sameOrigin && !targetdata->wantXrays);

         // If Xrays are warranted, the caller may waive them for non-security

         // wrappers.

         bool waiveXrays = wantXrays && !securityWrapper && waiveXrayFlag;

         // We have slightly different behavior for the case when the object

         // being wrapped is in an XBL scope.

         bool originIsXBLScope = IsXBLScope(origin);

         wrapper = SelectWrapper(securityWrapper, wantXrays, xrayType, waiveXrays,

                                 originIsXBLScope);

     }

     if (!targetSubsumesOrigin) {

         // Do a belt-and-suspenders check against exposing eval()/Function() to

         // non-subsuming content.

         JSFunction *fun = JS_GetObjectFunction(obj);

         if (fun) {

             if (JS_IsBuiltinEvalFunction(fun) || JS_IsBuiltinFunctionConstructor(fun)) {

                 JS_ReportError(cx, "Permission denied to expose eval or Function to non-subsuming content");

                 return nullptr;

             }

         }

     }

     DEBUG_CheckUnwrapSafety(obj, wrapper, origin, target);

     if (existing)

         return Wrapper::Renew(cx, existing, obj, wrapper);

     return Wrapper::New(cx, obj, parent, wrapper);

 }

 // Call WaiveXrayAndWrap when you have a JS object that you don't want to be

 // wrapped in an Xray wrapper. cx->compartment is the compartment that will be

 // using the returned object. If the object to be wrapped is already in the

 // correct compartment, then this returns the unwrapped object.

 bool

 WrapperFactory::WaiveXrayAndWrap(JSContext *cx, MutableHandleValue vp)

 {

     if (vp.isPrimitive())

         return JS_WrapValue(cx, vp);

     RootedObject obj(cx, &vp.toObject());

     if (!WaiveXrayAndWrap(cx, &obj))

         return false;

     vp.setObject(*obj);

     return true;

 }

 bool

 WrapperFactory::WaiveXrayAndWrap(JSContext *cx, MutableHandleObject argObj)

 {

     MOZ_ASSERT(argObj);

     RootedObject obj(cx, js::UncheckedUnwrap(argObj));

     MOZ_ASSERT(!js::IsInnerObject(obj));

     if (js::IsObjectInContextCompartment(obj, cx)) {

         argObj.set(obj);

         return true;

     }

     // Even though waivers have no effect on access by scopes that don't subsume

     // the underlying object, good defense-in-depth dictates that we should avoid

     // handing out waivers to callers that can't use them. The transitive waiving

     // machinery unconditionally calls WaiveXrayAndWrap on return values from

     // waived functions, even though the return value might be not be same-origin

     // with the function. So if we find ourselves trying to create a waiver for

     // |cx|, we should check whether the caller has any business with waivers

     // to things in |obj|'s compartment.

     JSCompartment *target = js::GetContextCompartment(cx);

     JSCompartment *origin = js::GetObjectCompartment(obj);

     obj = AccessCheck::subsumes(target, origin) ? WaiveXray(cx, obj) : obj;

     if (!obj)

         return false;

     if (!JS_WrapObject(cx, &obj))

         return false;

     argObj.set(obj);

     return true;

 }

 bool

 WrapperFactory::XrayWrapperNotShadowing(JSObject *wrapper, jsid id)

 {

     ResolvingId *rid = ResolvingId::getResolvingIdFromWrapper(wrapper);

     return rid->isXrayShadowing(id);

 }

 /*

  * Calls to JS_TransplantObject* should go through these helpers here so that

  * waivers get fixed up properly.

  */

 static bool

 FixWaiverAfterTransplant(JSContext *cx, HandleObject oldWaiver, HandleObject newobj)

 {

     MOZ_ASSERT(Wrapper::wrapperHandler(oldWaiver) == &XrayWaiver);

     MOZ_ASSERT(!js::IsCrossCompartmentWrapper(newobj));

     // Create a waiver in the new compartment. We know there's not one already

     // because we _just_ transplanted, which means that |newobj| was either

     // created from scratch, or was previously cross-compartment wrapper (which

     // should have no waiver). CreateXrayWaiver asserts this.

     JSObject *newWaiver = WrapperFactory::CreateXrayWaiver(cx, newobj);

     if (!newWaiver)

         return false;

     // Update all the cross-compartment references to oldWaiver to point to

     // newWaiver.

     if (!js::RemapAllWrappersForObject(cx, oldWaiver, newWaiver))

         return false;

     // There should be no same-compartment references to oldWaiver, and we

     // just remapped all cross-compartment references. It's dead, so we can

     // remove it from the map.

     XPCWrappedNativeScope *scope = GetObjectScope(oldWaiver);

     JSObject *key = Wrapper::wrappedObject(oldWaiver);

     MOZ_ASSERT(scope->mWaiverWrapperMap->Find(key));

     scope->mWaiverWrapperMap->Remove(key);

     return true;

 }

 JSObject *

 TransplantObject(JSContext *cx, JS::HandleObject origobj, JS::HandleObject target)

 {

     RootedObject oldWaiver(cx, WrapperFactory::GetXrayWaiver(origobj));

     RootedObject newIdentity(cx, JS_TransplantObject(cx, origobj, target));

     if (!newIdentity || !oldWaiver)

        return newIdentity;

     if (!FixWaiverAfterTransplant(cx, oldWaiver, newIdentity))

         return nullptr;

     return newIdentity;

 }

 nsIGlobalObject *

 GetNativeForGlobal(JSObject *obj)

 {

     MOZ_ASSERT(JS_IsGlobalObject(obj));

     if (!MaybeGetObjectScope(obj))

         return nullptr;

     // Every global needs to hold a native as its private or be a

     // WebIDL object with an nsISupports DOM object.

     MOZ_ASSERT((GetObjectClass(obj)->flags & (JSCLASS_PRIVATE_IS_NSISUPPORTS |

                                              JSCLASS_HAS_PRIVATE)) ||

                dom::UnwrapDOMObjectToISupports(obj));

     nsISupports *native = dom::UnwrapDOMObjectToISupports(obj);

     if (!native) {

         native = static_cast<nsISupports *>(js::GetObjectPrivate(obj));

         MOZ_ASSERT(native);

         // In some cases (like for windows) it is a wrapped native,

         // in other cases (sandboxes, backstage passes) it's just

         // a direct pointer to the native. If it's a wrapped native

         // let's unwrap it first.

         if (nsCOMPtr<nsIXPConnectWrappedNative> wn = do_QueryInterface(native)) {

             native = wn->Native();

         }

     }

     nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(native);

     MOZ_ASSERT(global, "Native held by global needs to implement nsIGlobalObject!");

     return global;

 }

 }