mctpd: check IIDs and opcodes in control protocol responses

Currently we ignore the IID and opcode fields in control protocol
response messages. This means we may get a delayed response from an
endpoint, it may be interpreted incorrectly as a response to the next
message.

Instead, allocate new IIDs for each message, then check the IIDs in
responses. We do this through a new common response validation function,
mctp_ctrl_validate_response.

This requires some additional string building for error messages.

Signed-off-by: Jeremy Kerr <[email protected]>

CHANGELOG.md

@@ -6,10 +6,16 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## Unreleased
 
+
 ### Fixed
 
 1. Fixed build on musl; we were relying on an implicit definition for `AF_MCTP`
 
+### Changed
+
+1. We now enforce IID checks on MCTP control protocol responses; this
+   prevents odd behaviour from delayed or invalid responses.
+
 ## [2.0] - 2024-09-19
 
 ### Added

src/mctp-control-spec.h

@@ -13,6 +13,11 @@ struct mctp_ctrl_msg_hdr {
 	uint8_t command_code;
 } __attribute__((__packed__));
 
+struct mctp_ctrl_resp {
+	struct mctp_ctrl_msg_hdr ctrl_hdr;
+	uint8_t completion_code;
+} __attribute__((packed));
+
 typedef enum {
 	set_eid,
 	force_eid,