Re: libccid IFDHControl() / CmdEscape() might truncate reader response

2017-02-17 20:34 GMT+01:00 Maximilian Stein <[email protected]>:

> Hello again,
>

Hello,


>
> one thing I've noticed while analysing the SCardControl() code is, that
> the libccid IFD handler might silently truncate the reader response, if
> the RxBuffer is not large enough. In fact it is the CmdEscape() function
> that does this. But it is used, amongst others, by IFDHControl() in some
> cases (see commands.c:1008):
>
>     /* copy the response */
>     length_out = dw2i(cmd_out, 1);
>     if (length_out > *RxLength)
>         length_out = *RxLength;
>     *RxLength = length_out;
>     memcpy(RxBuffer, &cmd_out[10], length_out);
>
> While other control calls for the reader (e.g. PIN handling) in
> IFDHControl() are handled via CCID_Transmit/CCID_Receive which does
> (commands.c:1567):
>
>     length = dw2i(cmd, 1);
>     if (length <= *rx_length)
>             *rx_length = length;
>     else
>     {
>             DEBUG_CRITICAL2("overrun by %d bytes", length - *rx_length);
>             length = *rx_length;
>             return_value = IFD_ERROR_INSUFFICIENT_BUFFER;
>     }
> [...]
>         memcpy(rx_buffer, cmd+10, length);
>
> Is this intended? If so, the behaviour of IFDHControl() is inconsistent
> regarding the handling of too small return buffers depending on which
> control code is used. Another question is, if it is intended that the
> truncated response is delivered to the client together with the
> INSUFFICIENT_BUFFER error. The code in CCID_Receive looks a bit like it...
>

You are right.
Now IFD_ERROR_INSUFFICIENT_BUFFER is returned. The truncation is no more
silent.

Fixed in
https://github.com/LudovicRousseau/CCID/commit/b15c8f96ca80005c3da024c031e9607051a9fe1a

Thanks

-- 
 Dr. Ludovic Rousseau

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