gecko-dev/js/ipc/JavaScriptParent.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=4 sw=4 et tw=80:
 *
 * 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 "JavaScriptParent.h"
#include "mozilla/dom/ContentParent.h"
#include "mozilla/dom/ScriptSettings.h"
#include "nsJSUtils.h"
#include "nsIScriptError.h"
#include "jsfriendapi.h"
#include "js/Proxy.h"
#include "js/HeapAPI.h"
#include "js/Wrapper.h"
#include "xpcprivate.h"
#include "mozilla/Casting.h"
#include "mozilla/Telemetry.h"
#include "nsAutoPtr.h"

using namespace js;
using namespace JS;
using namespace mozilla;
using namespace mozilla::jsipc;
using namespace mozilla::dom;

static void
TraceParent(JSTracer* trc, void* data)
{
    static_cast<JavaScriptParent*>(data)->trace(trc);
}

JavaScriptParent::JavaScriptParent()
  : savedNextCPOWNumber_(1)
{
    JS_AddExtraGCRootsTracer(danger::GetJSContext(), TraceParent, this);
}

JavaScriptParent::~JavaScriptParent()
{
    JS_RemoveExtraGCRootsTracer(danger::GetJSContext(), TraceParent, this);
}

static bool
ForbidUnsafeBrowserCPOWs()
{
    static bool result;
    static bool cached = false;
    if (!cached) {
        cached = true;
        Preferences::AddBoolVarCache(&result, "dom.ipc.cpows.forbid-unsafe-from-browser", false);
    }
    return result;
}

bool
JavaScriptParent::allowMessage(JSContext* cx)
{
    MOZ_ASSERT(cx);

    // If we're running browser code while running tests (in automation),
    // then we allow all safe CPOWs and forbid unsafe CPOWs
    // based on a pref (which defaults to forbidden).
    // We also allow CPOWs unconditionally in selected globals (based on
    // Cu.permitCPOWsInScope).
    // A normal (release) browser build will never allow CPOWs,
    // excecpt as a token to pass round.

    if (!xpc::IsInAutomation()) {
        JS_ReportErrorASCII(cx, "CPOW usage forbidden");
        return false;
    }

    MessageChannel* channel = GetIPCChannel();
    bool isSafe = channel->IsInTransaction();

    if (isSafe) {
        return true;
    }

    nsIGlobalObject* global = dom::GetIncumbentGlobal();
    JS::Rooted<JSObject*> jsGlobal(cx, global ? global->GetGlobalJSObject() : nullptr);
    if (jsGlobal) {
        JSAutoRealm ar(cx, jsGlobal);

        if (!xpc::CompartmentPrivate::Get(jsGlobal)->allowCPOWs &&
            ForbidUnsafeBrowserCPOWs())
        {
            Telemetry::Accumulate(Telemetry::BROWSER_SHIM_USAGE_BLOCKED, 1);
            JS_ReportErrorASCII(cx, "unsafe CPOW usage forbidden");
            return false;
        }
    }

    static bool disableUnsafeCPOWWarnings = PR_GetEnv("DISABLE_UNSAFE_CPOW_WARNINGS");
    if (!disableUnsafeCPOWWarnings) {
        nsCOMPtr<nsIConsoleService> console(do_GetService(NS_CONSOLESERVICE_CONTRACTID));
        if (console) {
            nsAutoString filename;
            uint32_t lineno = 0, column = 0;
            nsJSUtils::GetCallingLocation(cx, filename, &lineno, &column);
            nsCOMPtr<nsIScriptError> error(do_CreateInstance(NS_SCRIPTERROR_CONTRACTID));
            error->Init(NS_LITERAL_STRING("unsafe/forbidden CPOW usage"), filename,
                        EmptyString(), lineno, column,
                        nsIScriptError::warningFlag, "chrome javascript",
                        false /* from private window */);
            console->LogMessage(error);
        } else {
            NS_WARNING("Unsafe synchronous IPC message");
        }
    }

    return true;
}

void
JavaScriptParent::trace(JSTracer* trc)
{
    objects_.trace(trc);
    unwaivedObjectIds_.trace(trc);
    waivedObjectIds_.trace(trc);
}

JSObject*
JavaScriptParent::scopeForTargetObjects()
{
    // CPOWs from the child need to point into the parent's unprivileged junk
    // scope so that a compromised child cannot compromise the parent. In
    // practice, this means that a child process can only (a) hold parent
    // objects alive and (b) invoke them if they are callable.
    return xpc::UnprivilegedJunkScope();
}

void
JavaScriptParent::afterProcessTask()
{
    if (savedNextCPOWNumber_ == nextCPOWNumber_) {
        return;
    }

    savedNextCPOWNumber_ = nextCPOWNumber_;

    MOZ_ASSERT(nextCPOWNumber_ > 0);
    if (active()) {
        Unused << SendDropTemporaryStrongReferences(nextCPOWNumber_ - 1);
    }
}

PJavaScriptParent*
mozilla::jsipc::NewJavaScriptParent()
{
    return new JavaScriptParent();
}

void
mozilla::jsipc::ReleaseJavaScriptParent(PJavaScriptParent* parent)
{
    static_cast<JavaScriptParent*>(parent)->decref();
}

void
mozilla::jsipc::AfterProcessTask()
{
    for (auto* cp : ContentParent::AllProcesses(ContentParent::eLive)) {
        if (PJavaScriptParent* p = LoneManagedOrNullAsserts(cp->ManagedPJavaScriptParent())) {
            static_cast<JavaScriptParent*>(p)->afterProcessTask();
        }
    }
}