Call SSLfatal when the generate_ticket_cb returns 0

Otherwise, the state machine ends up being in a bad state:
```
SSL routines:write_state_machine:missing fatal:ssl/statem/statem.c:XXX:
```

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/15487)

diff --git a/ssl/statem/statem_srvr.c b/ssl/statem/statem_srvr.c
index 386bd983fc49b8fd3ac63a28be1c04e22aad4113..56d4b4591a6df48569bf7970d79784b1e6490732 100644 (file)
--- a/ssl/statem/statem_srvr.c
+++ b/ssl/statem/statem_srvr.c
@@ -3945,9 +3945,10 @@ int tls_construct_new_session_ticket(SSL *s, WPACKET *pkt)
     }
 
     if (tctx->generate_ticket_cb != NULL &&
-        tctx->generate_ticket_cb(s, tctx->ticket_cb_data) == 0)
+        tctx->generate_ticket_cb(s, tctx->ticket_cb_data) == 0) {
+        SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR);
         goto err;
-
+    }
     /*
      * If we are using anti-replay protection then we behave as if
      * SSL_OP_NO_TICKET is set - we are caching tickets anyway so there