thanks. But in Modification Two, I changed object x 's property a in a
different context successfully. is this fulfilled "Access checks are
invoked when trying to access objects" condition?
在 2018年5月30日星期三 UTC+8下午5:32:55，Ben Noordhuis写道：
>
> On Wed, May 30, 2018 at 9:32 AM, <fengx...@gmail.com <javascript:>>
> wrote:
> > I try to understand SetSecurityToken's function. So I modified
> > EvalInAccessCheckedContext test case in test-api.cc which is included in
> v8
> > sourcecode. Follow is my modification.
> >
> > Modification One:
> >
> > TEST(EvalInAccessCheckedContext) {
> > v8::Isolate* isolate = CcTest::isolate();
> > v8::HandleScope scope(isolate);
> >
> > v8::Local<v8::ObjectTemplate> obj_template =
> > v8::ObjectTemplate::New(isolate);
> >
> > //obj_template->SetAccessCheckCallback(AccessAlwaysAllowed); //comment
> > this line to ensure cross access only be controlled by SetSecurityToken
> >
> > v8::Local<Context> context0 = Context::New(isolate, NULL,
> obj_template);
> > v8::Local<Context> context1 = Context::New(isolate, NULL,
> obj_template);
> >
> > Local<Value> foo = v8_str("foo");
> > Local<Value> bar = v8_str("bar");
> >
> > // Set to different domains.
> > context0->SetSecurityToken(foo);
> > context1->SetSecurityToken(bar);
> >
> > // Set up function in context0 that uses eval from context0.
> > context0->Enter();
> > v8::Local<v8::Value> fun = CompileRun(
> > "var x = 42;"
> > "(function() {"
> > " var e = eval;"
> > //" return function(s) { return e(s); }" // this line will fail
> test
> > because SecurityToken is not the same
> > " return function(s) { return eval(s); }" // this line will pass
> > test. but why?
> > "})()");
> > context0->Exit();
> >
> > // Put the function into context1 and call it. Since the access check
> > // callback always returns true, the call succeeds even though the
> tokens
> > // are different.
> > context1->Enter();
> > context1->Global()->Set(context1, v8_str("fun"), fun).FromJust();
> > v8::Local<v8::Value> x_value = CompileRun("fun('x')");
> > CHECK_EQ(42, x_value->Int32Value(context1).FromJust());
> > context1->Exit();
> > }
> >
> >
> > Modification Two:
> >
> > TEST(EvalInAccessCheckedContext) {
> > v8::Isolate* isolate = CcTest::isolate();
> > v8::HandleScope scope(isolate);
> >
> > v8::Local<v8::ObjectTemplate> obj_template =
> > v8::ObjectTemplate::New(isolate);
> >
> > //obj_template->SetAccessCheckCallback(AccessAlwaysAllowed); //comment
> > this line to ensure cross access only be controlled by SetSecurityToken
> >
> > v8::Local<Context> context0 = Context::New(isolate, NULL,
> obj_template);
> > v8::Local<Context> context1 = Context::New(isolate, NULL,
> obj_template);
> >
> > Local<Value> foo = v8_str("foo");
> > Local<Value> bar = v8_str("bar");
> >
> > // Set to different domains.
> > context0->SetSecurityToken(foo);
> > context1->SetSecurityToken(bar);
> >
> > // Set up function in context0 that uses eval from context0.
> > context0->Enter();
> >
> > v8::Local<v8::Value> fun = CompileRun(
> > "var x = {a:42};"
> > "(function() {"
> > " var e = eval;"
> > " return function(s) { return x; }" // just return a object
> that's
> > defined in context0
> > "})()");
> >
> > v8::Local<v8::Value> x_value0 = CompileRun("x.a");
> > CHECK_EQ(42, x_value0->Int32Value(context0).FromJust());
> >
> > Local<v8::Object> obj = context0->Global()->Get(context0,
> > v8_str("x")).ToLocalChecked()->ToObject();
> > obj->Set(context0, v8_str("a"),
> v8::Integer::New(context0->GetIsolate(),
> > 100)).FromJust();
> > context0->Global()->Set(context0, v8_str("fun"), fun).FromJust();
> > v8::Local<v8::Value> x_value00 = CompileRun("fun('x')");
> > CHECK_EQ(100, x_value00->ToObject()->Get(context0,
> > v8_str("a")).ToLocalChecked()->Int32Value(context0).FromJust());
> >
> > context0->Exit();
> >
> > // Put the function into context1 and call it. Since the access check
> > // callback always returns true, the call succeeds even though the
> tokens
> > // are different.
> > context1->Enter();
> >
> > context1->Global()->Set(context1, v8_str("fun"), fun).FromJust();
> > v8::Local<v8::Value> x_value = CompileRun("fun('x')");
> > CHECK_EQ(100, x_value->ToObject()->Get(context1,
> > v8_str("a")).ToLocalChecked()->Int32Value(context1).FromJust());
> >
> > x_value->ToObject()->Set(context1, v8_str("a"),
> > v8::Integer::New(context0->GetIsolate(), 102)).FromJust();// change x
> object
> > of context0 in context1
> > context1->Exit();
> >
> > context0->Enter();
> > {
> > Local<v8::Object> obj = context0->Global()->Get(context0,
> > v8_str("x")).ToLocalChecked()->ToObject();
> > CHECK_EQ(102, obj->Get(context0,
> > v8_str("a")).ToLocalChecked()->Int32Value(context0).FromJust()); // this
> > will pass. so why change is allowed?
> >
> > v8::Local<v8::Value> x_value00 = CompileRun("fun('x')");
> > CHECK_EQ(102, x_value00->ToObject()->Get(context0,
> > v8_str("a")).ToLocalChecked()->Int32Value(context0).FromJust());
> > }
> > context0->Exit();
> > }
>
> Is your question why direct eval() works but indirect eval() doesn't
> with different security tokens?
>
> It's because direct eval() isn't really a function, it's closer to a
> keyword. It has to be because of its runtime semantics of evaluating
> the string in the context of the surrounding code. Indirect eval()
> however is a regular function that is subject to access checks.
>
> Access checks are invoked when trying to access objects. Context A
> can pass on objects from context B as long as it doesn't access it,
> where access = read or write properties, invoke the [[Call]] operation
> of function objects, etc.
>
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