If we receive an "update_requested" KeyUpdate then respond with a KeyUpdate

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2609)
diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index ced3317..909b2f0 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -439,6 +439,12 @@
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_CR_KEY_UPDATE:
+        if (s->key_update != SSL_KEY_UPDATE_NONE) {
+            st->hand_state = TLS_ST_CW_KEY_UPDATE;
+            return WRITE_TRAN_CONTINUE;
+        }
+        /* Fall through */
+
     case TLS_ST_CW_KEY_UPDATE:
     case TLS_ST_CR_SESSION_TICKET:
     case TLS_ST_CW_FINISHED:
diff --git a/ssl/statem/statem_lib.c b/ssl/statem/statem_lib.c
index 6261804..d65feba 100644
--- a/ssl/statem/statem_lib.c
+++ b/ssl/statem/statem_lib.c
@@ -525,6 +525,14 @@
         return MSG_PROCESS_ERROR;
     }
 
+    /*
+     * If we get a request for us to update our sending keys too then, we need
+     * to additionally send a KeyUpdate message. However that message should
+     * not also request an update (otherwise we get into an infinite loop).
+     */
+    if (updatetype == SSL_KEY_UPDATE_REQUESTED)
+        s->key_update = SSL_KEY_UPDATE_NOT_REQUESTED;
+
     return MSG_PROCESS_FINISHED_READING;
 }
 
diff --git a/ssl/statem/statem_srvr.c b/ssl/statem/statem_srvr.c
index 2a21001..3007088 100644
--- a/ssl/statem/statem_srvr.c
+++ b/ssl/statem/statem_srvr.c
@@ -470,6 +470,12 @@
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_SR_KEY_UPDATE:
+        if (s->key_update != SSL_KEY_UPDATE_NONE) {
+            st->hand_state = TLS_ST_SW_KEY_UPDATE;
+            return WRITE_TRAN_CONTINUE;
+        }
+        /* Fall through */
+
     case TLS_ST_SW_KEY_UPDATE:
     case TLS_ST_SW_SESSION_TICKET:
         st->hand_state = TLS_ST_OK;