[Pcsclite-muscle] Bug with SCardCancel followed by new requests on the waiting thread

[Maksim Ivanov]

Hello Ludovic,

Thanks for the quick reply.


> Please tell me when you have finished your code review so I can publish a
> new version of pcsc-lite with all the fixes :-)

Actually, this was the only bug that I met.


Thanks,
Maksim


On Fri, Mar 11, 2016 at 11:52 AM, Ludovic Rousseau
<ludovic.rousseau at gmail.com> wrote:
> 2016-03-10 20:01 GMT+01:00 Maksim Ivanov <emaxx at google.com>:
>>
>> Hello all,
>
>
> Hello Maksim,
>
>>
>>
>> Looks like there is a bug related to the management of the blocking
>> requests and of their cancellation.
>>
>> The reproduce steps are the following. Two threads: thread 1 and
>> thread 2. Thread 2 calls SCardGetStatusChange and blocks (with waiting
>> for some event X). Thread 1 calls SCardCancel. Thread 2 unblocks from
>> SCardGetStatusChange due to the cancellation, and starts issuing other
>> PC/SC-Lite API calls. After that, something that triggers the event X
>> happens. After that the PC/SC-Lite API calls that thread 2 is making
>> start to break (they return inconsistent results).
>>
>> The underlying reason is that cancellation in the current
>> implementation of the PC/SC-Lite service does not unsubscribe the
>> client from the list of clients waiting for events. So, when the event
>> finally occurs, the event response is written into the client's
>> socket, even if the cancellation had already happened before. Putting
>> unexpected data into the socket shifts the responses of all further
>> PC/SC-Lite API calls made by that client.
>>
>> If the analysis above is correct, then the correct fix would be
>> probably just adding a "EHTryToUnregisterClientForEvent(fd)" statement
>> into the handler of the SCARD_CANCEL message in function ContextThread
>> (file winscard_svc.c).
>
>
> You are right.
>
> Fixed in 57b0ba5a200bcbf1c489d39261340324392a8e8a
>
> Thanks for the analysis and proposed patch.
>
> Please tell me when you have finished your code review so I can publish a
> new version of pcsc-lite with all the fixes :-)
>
> Bye
>
> --
>  Dr. Ludovic Rousseau
>
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