ChunkSeqNo should not wrap

[steven-bellock]

I believe a reading of the Large SPDM message transfer mechanism implies that ChunkSeqNo should not wrap. Ie, if the message is too large for 65536 chunks then it should not be sent. However libspdm assumes wrapping, for example

libspdm/library/spdm_responder_lib/libspdm_rsp_chunk_get.c

Line 157 in 30014a8

get_info->chunk_seq_no++;

I filed https://github.com/DMTF/SPDM-WG/issues/3703 to increase the size of ChunkSeqNo so that we don't have to think about this for SPDM 1.4 and greater.

[jyao1]

Good finding.

Read the spec, the LargeMessageSize is present when ChunkSeqNo is 0. But it is not considered on wrap case.

I think we should prevent wrap from happening.

[steven-bellock]

The SPDM Working Group confirmed that it does not wrap. This will be made more explicit in the specification.

[Li-Aaron]

I'll take this.

[steven-bellock]

@Li-Aaron if the Responder is sending a message and it's too large for 65536 chunks then it can return ResponseTooLarge.