[Vm-dev] VM Maker: VMMaker.oscog-eem.2338.mcz

[Eliot Miranda]

On Sat, Apr 14, 2018 at 10:47 AM, Levente Uzonyi <leves at caesar.elte.hu>
wrote:

>
> Hi Eliot,
>
> On Thu, 12 Apr 2018, Eliot Miranda wrote:
>
> [I'm sorry, I apparently forgot to hit send some weeks ago]
>>
>
> Well, I had started to rewrite the methods myself along with adding tests,
> but you were quicker and pushed the changes.
> I think there are still things that should be fixed. When time allows,
> I'll check my tests and merge them with the existing
> MiscPrimitivePluginTest.


thanks, man!


>
>
> primitiveDecompressFromByteArray
>>> - bm is int*, but it should probably be unsigned int* as the method
>>>
>> stores unsigned ints (data) into it
>
>> - index should be bounds checked (1 .. end)
>>>
>>
>> It gets checked anyway with the comparison against pastEnd
>>
>
> Unfortunately that's not the case. i is compared to end, not pastEnd.
> If index, which is an unnecessary variable btw, is less than or equal to
> 0, then the value of i will be negative, and the input will be processed no
> matter what the value of end is, hence random data from memory will be read
> and processed:
>
> Smalltalk garbageCollect.
> ba := ByteArray new: 256.
> bm := Bitmap new: 1024.
> passes := OrderedCollection new.
> success := true.
> [
>         0 to: -1000000 by: -1 do: [ :start |
>                 success := true.
>                 bm decompress: bm fromByteArray: ba at: start.
>                 success ifTrue: [ passes add: start ] ] ]
>         on: Error
>         do: [ :error |
>                 success := false.
>                 error return: nil ].
> passes
>
> - i, k, end and pastEnd should be unsigned int
>>>
>>
>> That's OK.  In neither V3 nor Spur can objects have more than 1Gb fields
>> so in practice indices can never go negative.
>>
>
> If i's type were unsigned int, the above code wouldn't work, because i <
> end would be false.
>
> Levente
>



-- 
_,,,^..^,,,_
best, Eliot
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