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apdu-dispatch's Introduction

Apdu Dispatch

This layer accepts APDU (application packet data units) from a contact and/or contactless interface and passes them to a selected app.

It handles parsing APDU's, chaining, T=0, and T=1.

Run tests via cargo test --features std,log-all

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apdu-dispatch's Issues

Tracking: potential incompatibility with Select calls

While I was implementing support for KeepassXC' challenge-response over CCID, I've noticed that the SELECT call used there had not contain the Le byte. This caused the response to SELECT to be 61xx, which needed additional implementation for getting the remaining data. That sprinkled the discussion, why it was not needed before for the other supported there smart card readers. Apparently the SELECT call for them always result with the data in the direct response to the request.

I am documenting this behavior here for the future reference. Perhaps the SELECT command should be exempted from testing the Le byte, and following the usual rules (e.g. to make it work with improper implementations).

Yubikey 4 responds immediately as well AFAICS. Some YK4 traffic excerpt containing the SELECT (00 A4 04 00) calls:

07477498 APDU: 00 A4 04 00 07 A0 00 00 05 27 20 01
00001034 SW: 04 03 05 03 0B 00 06 0F 00 00 90 00
00000136 APDU: 00 A4 04 00 07 A0 00 00 05 27 20 01
00001019 SW: 04 03 05 03 0B 00 06 0F 00 00 90 00
00000062 APDU: 00 03 00 00 06
00000854 SW: 04 03 05 03 0B 00 90 00
00000137 APDU: 00 A4 04 00 07 A0 00 00 05 27 20 01
00001023 SW: 04 03 05 03 0B 00 06 0F 00 00 90 00
00000055 APDU: 00 01 10 00 06
00000849 SW: 00 56 7F B0 90 00
00000130 APDU: 00 A4 04 00 07 A0 00 00 05 27 20 01
00001000 SW: 04 03 05 03 0B 00 06 0F 00 00 90 00

The call used in KeepassXC for SELECT is:

        uint8_t pbSendBuffer_head[5] = {
            CLA_ISO, INS_SELECT, SEL_APP_AID, 0, static_cast<uint8_t>(handle.second.size())};
        auto pbSendBuffer = new uint8_t[5 + handle.second.size()];
        memcpy(pbSendBuffer, pbSendBuffer_head, 5);
        memcpy(pbSendBuffer + 5, handle.second.constData(), handle.second.size());
       // Give it more space in case custom implementations have longer answer to select
        uint8_t pbRecvBuffer[64] = {0}; 
       // 3 bytes version, 1 byte program counter, other stuff for various implementations, 2 bytes status
        SCUINT dwRecvLength = sizeof pbRecvBuffer;
        auto rv = transmit(handle.first, pbSendBuffer, 5 + handle.second.size(), pbRecvBuffer, dwRecvLength);

PR: keepassxreboot/keepassxc#9397

Code in question:

apdu-dispatch/src/dispatch.rs

Lines 280 to 334 in a6f0011

fn handle_reply(&mut self) {
// Consider if we need to reply via chaining method.
// If the reader is using chaining, we will simply
// reply 61XX, and put the response in a buffer.
// It is up to the reader to then send GetResponse
// requests, to which we will return up to `Le` bytes at a time.
let (new_state, response) = match &mut self.buffer.raw {
RawApduBuffer::Request(_) | RawApduBuffer::None => {
info!("Unexpected GetResponse request.");
(RawApduBuffer::None, Status::UnspecifiedCheckingError.into())
}
RawApduBuffer::Response(res) => {
let max_response_len = self.response_len_expected.min(MAX_INTERCHANGE_DATA);
if self.was_request_chained || res.len() > max_response_len {
// Do not send more than the expected bytes
let boundary = max_response_len.min(res.len());
let to_send = &res[..boundary];
let remaining = &res[boundary..];
let mut message = interchanges::Data::from_slice(to_send).unwrap();
let return_code = if remaining.len() > 255 {
// XX = 00 indicates more than 255 bytes of data
0x6100u16
} else if !remaining.is_empty() {
0x6100 + (remaining.len() as u16)
} else {
// Last chunk has success code
0x9000
};
message
.extend_from_slice(&return_code.to_be_bytes())
.expect("Failed add to status bytes");
if return_code == 0x9000 {
(RawApduBuffer::None, message)
} else {
info!("Still {} bytes in response buffer", remaining.len());
(
RawApduBuffer::Response(response::Data::from_slice(remaining).unwrap()),
message,
)
}
} else {
// Add success code
res.extend_from_slice(&[0x90, 00])
.expect("Failed to add the status bytes");
(
RawApduBuffer::None,
interchanges::Data::from_slice(res.as_slice()).unwrap(),
)
}
}
};
self.buffer.raw = new_state;
self.respond(response);
}

Panic on Select command with an invalid Aid.

Hi!

A bit of fuzzing this library found that a panic happens when apdu_dispatch receives a select command with an Aid in the data field that is incorrect. This is because Aid::new panics when the input data is invalid.

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