Pause the mux channel while waiting for reply from aynch callbacks.

Prevents misordering of replies if new requests arrive while waiting.

Extend channel open confirm callback to allow signalling failure
conditions as well as success. Use this to 1) fix a memory leak, 2)
start using the above pause mechanism and 3) delay sending a success/
failure message on mux slave session open until we receive a reply from
the server.

motivated by and with feedback from markus@

1 files changed, 37 insertions, 10 deletions

diff --git a/usr.bin/ssh/mux.c b/usr.bin/ssh/mux.c
index e8d14c406ae..84d21ed22ea 100644
--- a/usr.bin/ssh/mux.c
+++ b/usr.bin/ssh/mux.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mux.c,v 1.16 2010/04/23 22:27:38 djm Exp $ */
+/* $OpenBSD: mux.c,v 1.17 2010/05/14 23:29:23 djm Exp $ */
 /*
  * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
  *
@@ -89,6 +89,7 @@ struct mux_session_confirm_ctx {
 	char *term;
 	struct termios tio;
 	char **env;
+	u_int rid;
 };
 
 /* fd to control socket */
@@ -132,7 +133,7 @@ struct mux_master_state {
 #define MUX_FWD_REMOTE  2
 #define MUX_FWD_DYNAMIC 3
 
-static void mux_session_confirm(int, void *);
+static void mux_session_confirm(int, int, void *);
 
 static int process_mux_master_hello(u_int, Channel *, Buffer *, Buffer *);
 static int process_mux_new_session(u_int, Channel *, Buffer *, Buffer *);
@@ -284,6 +285,7 @@ process_mux_new_session(u_int rid, Channel *c, Buffer *m, Buffer *r)
 	/* Reply for SSHMUX_COMMAND_OPEN */
 	cctx = xcalloc(1, sizeof(*cctx));
 	cctx->term = NULL;
+	cctx->rid = rid;
 	cmd = reserved = NULL;
 	if ((reserved = buffer_get_string_ret(m, NULL)) == NULL ||
 	    buffer_get_int_ret(&cctx->want_tty, m) != 0 ||
@@ -437,14 +439,10 @@ process_mux_new_session(u_int rid, Channel *c, Buffer *m, Buffer *r)
 
 	channel_send_open(nc->self);
 	channel_register_open_confirm(nc->self, mux_session_confirm, cctx);
+	c->mux_pause = 1; /* stop handling messages until open_confirm done */
 	channel_register_cleanup(nc->self, mux_master_session_cleanup_cb, 1);
 
-	/* prepare reply */
-	/* XXX defer until mux_session_confirm() fires */
-	buffer_put_int(r, MUX_S_SESSION_OPENED);
-	buffer_put_int(r, rid);
-	buffer_put_int(r, nc->self);
-
+	/* reply is deferred, sent by mux_session_confirm */
 	return 0;
 }
 
@@ -982,17 +980,31 @@ muxserver_listen(void)
 
 /* Callback on open confirmation in mux master for a mux client session. */
 static void
-mux_session_confirm(int id, void *arg)
+mux_session_confirm(int id, int success, void *arg)
 {
 	struct mux_session_confirm_ctx *cctx = arg;
 	const char *display;
-	Channel *c;
+	Channel *c, *cc;
 	int i;
+	Buffer reply;
 
 	if (cctx == NULL)
 		fatal("%s: cctx == NULL", __func__);
 	if ((c = channel_by_id(id)) == NULL)
 		fatal("%s: no channel for id %d", __func__, id);
+	if ((cc = channel_by_id(c->ctl_chan)) == NULL)
+		fatal("%s: channel %d lacks control channel %d", __func__,
+		    id, c->ctl_chan);
+
+	if (!success) {
+		debug3("%s: sending failure reply", __func__);
+		/* prepare reply */
+		buffer_init(&reply);
+		buffer_put_int(&reply, MUX_S_FAILURE);
+		buffer_put_int(&reply, cctx->rid);
+		buffer_put_cstring(&reply, "Session open refused by peer");
+		goto done;
+	}
 
 	display = getenv("DISPLAY");
 	if (cctx->want_x_fwd && options.forward_x11 && display != NULL) {
@@ -1015,6 +1027,21 @@ mux_session_confirm(int id, void *arg)
 	client_session2_setup(id, cctx->want_tty, cctx->want_subsys,
 	    cctx->term, &cctx->tio, c->rfd, &cctx->cmd, cctx->env);
 
+	debug3("%s: sending success reply", __func__);
+	/* prepare reply */
+	buffer_init(&reply);
+	buffer_put_int(&reply, MUX_S_SESSION_OPENED);
+	buffer_put_int(&reply, cctx->rid);
+	buffer_put_int(&reply, c->self);
+
+ done:
+	/* Send reply */
+	buffer_put_string(&cc->output, buffer_ptr(&reply), buffer_len(&reply));
+	buffer_free(&reply);
+
+	if (cc->mux_pause <= 0)
+		fatal("%s: mux_pause %d", __func__, cc->mux_pause);
+	cc->mux_pause = 0; /* start processing messages again */
 	c->open_confirm_ctx = NULL;
 	buffer_free(&cctx->cmd);
 	xfree(cctx->term);