buffers: adapt ecdh.c to ssh_buffer_(un)pack()

Reviewed-by: Andreas Schneider <asn@samba.org>

src/ecdh.c

@@ -285,12 +285,6 @@ int ssh_server_ecdh_init(ssh_session session, ssh_buffer packet){
     session->next_crypto->ecdh_privkey = ecdh_key;
     session->next_crypto->ecdh_server_pubkey = q_s_string;
 
-    rc = buffer_add_u8(session->out_buffer, SSH2_MSG_KEXDH_REPLY);
-    if (rc < 0) {
-        ssh_set_error_oom(session);
-        return SSH_ERROR;
-    }
-
     /* build k and session_id */
     rc = ecdh_build_k(session);
     if (rc < 0) {
@@ -310,30 +304,22 @@ int ssh_server_ecdh_init(ssh_session session, ssh_buffer packet){
         return SSH_ERROR;
     }
 
-    /* add host's public key */
-    rc = buffer_add_ssh_string(session->out_buffer,
-                               session->next_crypto->server_pubkey);
-    if (rc < 0) {
-        ssh_set_error_oom(session);
-        return SSH_ERROR;
-    }
-
-    /* add ecdh public key */
-    rc = buffer_add_ssh_string(session->out_buffer, q_s_string);
-    if (rc < 0) {
-        ssh_set_error_oom(session);
-        return SSH_ERROR;
-    }
-    /* add signature blob */
     sig_blob = ssh_srv_pki_do_sign_sessionid(session, privkey);
     if (sig_blob == NULL) {
         ssh_set_error(session, SSH_FATAL, "Could not sign the session id");
         return SSH_ERROR;
     }
 
-    rc = buffer_add_ssh_string(session->out_buffer, sig_blob);
+    rc = ssh_buffer_pack(session->out_buffer,
+                         "bSSS",
+                         SSH2_MSG_KEXDH_REPLY,
+                         session->next_crypto->server_pubkey, /* host's pubkey */
+                         q_s_string, /* ecdh public key */
+                         sig_blob); /* signature blob */
+
     ssh_string_free(sig_blob);
-    if (rc < 0) {
+
+    if (rc != SSH_OK) {
         ssh_set_error_oom(session);
         return SSH_ERROR;
     }