[gnutls-devel] GnuTLS | tls1.3: server returns early on handshake when no cert is provided by client (!711)

[Development of GNU's TLS library]

Daiki Ueno started a new discussion on lib/handshake-tls13.c:

>  		IMED_RET("send finished", ret, 0);
>  		/* fall through */
>  	case STATE107:
> +		/* At this point our sending keys should be the app keys
> +		 * see 4.4.4 at draft-ietf-tls-tls13-28 */
> +		ret =
> +		    generate_ap_traffic_keys(session);
> +		IMED_RET("generate app keys", ret, 0);
> +
> +		/* If the session is unauthenticated, try to optimize the handshake by
> +		 * sending the session ticket early. */
> +		if (!(session->internals.hsk_flags & (HSK_CRT_REQ_SENT|HSK_PSK_SELECTED))) {
> +			STATE = STATE107;

I am a bit confused with the use of STATE here; in the surrounding code it is used like this:
```c
case STATEXXX:
        ret = do_something(session, AGAIN(STATEXXX));
        STATE = STATEXXX;
        IMED_RET("something", ret, 0);
        /* fallthrough */
```
If I understand correctly, this pattern is to allow callers to re-enter if any of the function returns EAGAIN.  However, here, `generate_ap_traffic_keys()` is not reentrant, because it overwrites temp_secret. Wouldn't that be a problem?

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