upstream: Explicitly check for and start time-based rekeying in the

client and server mainloops.

Previously the rekey timeout could expire but rekeying would not start
until a packet was sent or received. This could cause us to spin in
select() on the rekey timeout if the connection was quiet.

ok markus@

OpenBSD-Commit-ID: 4356cf50d7900f3df0a8f2117d9e07c91b9ff987

clientloop.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.366 2021/07/13 23:48:36 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.367 2021/07/16 09:00:23 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1358,6 +1358,10 @@ client_loop(struct ssh *ssh, int have_pty, int escape_char_arg,
 		if (quit_pending)
 			break;
 
+		/* A timeout may have triggered rekeying */
+		if ((r = ssh_packet_check_rekey(ssh)) != 0)
+			fatal_fr(r, "cannot start rekeying");
+
 		/*
 		 * Send as much buffered packet data as possible to the
 		 * sender.

packet.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.c,v 1.300 2021/04/03 06:18:40 djm Exp $ */
+/* $OpenBSD: packet.c,v 1.301 2021/07/16 09:00:23 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1002,6 +1002,15 @@ ssh_packet_need_rekeying(struct ssh *ssh, u_int outbound_packet_len)
 	    (state->p_read.blocks > state->max_blocks_in));
 }
 
+int
+ssh_packet_check_rekey(struct ssh *ssh)
+{
+	if (!ssh_packet_need_rekeying(ssh, 0))
+		return 0;
+	debug3_f("rekex triggered");
+	return kex_start_rekex(ssh);
+}
+
 /*
  * Delayed compression for SSH2 is enabled after authentication:
  * This happens on the server side after a SSH2_MSG_USERAUTH_SUCCESS is sent,
@@ -1695,12 +1704,8 @@ ssh_packet_read_poll2(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p)
 	/* reset for next packet */
 	state->packlen = 0;
 
-	/* do we need to rekey? */
-	if (ssh_packet_need_rekeying(ssh, 0)) {
-		debug3_f("rekex triggered");
-		if ((r = kex_start_rekex(ssh)) != 0)
-			return r;
-	}
+	if ((r = ssh_packet_check_rekey(ssh)) != 0)
+		return r;
  out:
 	return r;
 }

packet.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.h,v 1.92 2020/03/06 18:11:10 markus Exp $ */
+/* $OpenBSD: packet.h,v 1.93 2021/07/16 09:00:23 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -105,6 +105,7 @@ void	 ssh_packet_clear_keys(struct ssh *);
 void	 ssh_clear_newkeys(struct ssh *, int);
 
 int	 ssh_packet_is_rekeying(struct ssh *);
+int	 ssh_packet_check_rekey(struct ssh *);
 void     ssh_packet_set_protocol_flags(struct ssh *, u_int);
 u_int	 ssh_packet_get_protocol_flags(struct ssh *);
 void	 ssh_packet_set_tos(struct ssh *, int);

serverloop.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: serverloop.c,v 1.227 2021/06/25 03:38:17 dtucker Exp $ */
+/* $OpenBSD: serverloop.c,v 1.228 2021/07/16 09:00:23 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -334,7 +334,7 @@ void
 server_loop2(struct ssh *ssh, Authctxt *authctxt)
 {
 	fd_set *readset = NULL, *writeset = NULL;
-	int max_fd;
+	int r, max_fd;
 	u_int nalloc = 0, connection_in, connection_out;
 	u_int64_t rekey_timeout_ms = 0;
 	sigset_t bsigset, osigset;
@@ -396,6 +396,9 @@ server_loop2(struct ssh *ssh, Authctxt *authctxt)
 			channel_after_select(ssh, readset, writeset);
 		if (process_input(ssh, readset, connection_in) < 0)
 			break;
+		/* A timeout may have triggered rekeying */
+		if ((r = ssh_packet_check_rekey(ssh)) != 0)
+			fatal_fr(r, "cannot start rekeying");
 		process_output(ssh, writeset, connection_out);
 	}
 	collect_children(ssh);