Use new channel status confirmation callback system to properly deal

with "important" channel requests that fail, in particular command exec,
shell and subsystem requests. Previously we would optimistically assume
that the requests would always succeed, which could cause hangs if they
did not (e.g. when the server runs out of fds) or were unimplemented by
the server (bz #1384)

Also, properly report failing multiplex channel requests via the mux
client stderr (subject to LogLevel in the mux master) - better than
silently failing.

most bits ok markus@ (as part of a larger diff)

3 files changed, 77 insertions, 52 deletions

diff --git a/usr.bin/ssh/clientloop.c b/usr.bin/ssh/clientloop.c
index bebe6f7608b..19bc214dfb0 100644
--- a/usr.bin/ssh/clientloop.c
+++ b/usr.bin/ssh/clientloop.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.189 2008/05/08 12:02:23 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.190 2008/05/08 13:06:10 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -165,6 +165,11 @@ struct confirm_ctx {
 	char **env;
 };
 
+struct channel_reply_ctx {
+	const char *request_type;
+	int id, do_close;
+};
+
 /*XXX*/
 extern Kex *xxx_kex;
 
@@ -637,25 +642,60 @@ client_process_net_input(fd_set *readset)
 }
 
 static void
-client_subsystem_reply(int type, u_int32_t seq, void *ctxt)
+client_status_confirm(int type, Channel *c, void *ctx)
 {
-	int id;
-	Channel *c;
+	struct channel_reply_ctx *cr = (struct channel_reply_ctx *)ctx;
+	char errmsg[256];
+	int tochan;
+
+	/* XXX supress on mux _client_ quietmode */
+	tochan = options.log_level >= SYSLOG_LEVEL_ERROR &&
+	    c->ctl_fd != -1 && c->extended_usage == CHAN_EXTENDED_WRITE;
+
+	if (type == SSH2_MSG_CHANNEL_SUCCESS) {
+		debug2("%s request accepted on channel %d",
+		    cr->request_type, c->self);
+	} else if (type == SSH2_MSG_CHANNEL_FAILURE) {
+		if (tochan) {
+			snprintf(errmsg, sizeof(errmsg),
+			    "%s request failed\r\n", cr->request_type);
+		} else {
+			snprintf(errmsg, sizeof(errmsg),
+			    "%s request failed on channel %d",
+			    cr->request_type, c->self);
+		}
+		/* If error occurred on primary session channel, then exit */
+		if (cr->do_close && c->self == session_ident)
+			fatal("%s", errmsg);
+		/* If error occurred on mux client, append to their stderr */
+		if (tochan)
+			buffer_append(&c->extended, errmsg, strlen(errmsg));
+		else
+			error("%s", errmsg);
+		if (cr->do_close) {
+			chan_read_failed(c);
+			chan_write_failed(c);
+		}
+	}
+	xfree(cr);
+}
 
-	id = packet_get_int();
-	packet_check_eom();
+static void
+client_abandon_status_confirm(Channel *c, void *ctx)
+{
+	xfree(ctx);
+}
 
-	if ((c = channel_lookup(id)) == NULL) {
-		error("%s: no channel for id %d", __func__, id);
-		return;
-	}
+static void
+client_expect_confirm(int id, const char *request, int do_close)
+{
+	struct channel_reply_ctx *cr = xmalloc(sizeof(*cr));
 
-	if (type == SSH2_MSG_CHANNEL_SUCCESS)
-		debug2("Request suceeded on channel %d", id);
-	else if (type == SSH2_MSG_CHANNEL_FAILURE) {
-		error("Request failed on channel %d", id);
-		channel_free(c);
-	}
+	cr->request_type = request;
+	cr->do_close = do_close;
+
+	channel_register_status_confirm(id, client_status_confirm,
+	    client_abandon_status_confirm, cr);
 }
 
 static void
@@ -690,8 +730,7 @@ client_extra_session2_setup(int id, void *arg)
 	}
 
 	client_session2_setup(id, cctx->want_tty, cctx->want_subsys,
-	    cctx->term, &cctx->tio, c->rfd, &cctx->cmd, cctx->env,
-	    client_subsystem_reply);
+	    cctx->term, &cctx->tio, c->rfd, &cctx->cmd, cctx->env);
 
 	c->open_confirm_ctx = NULL;
 	buffer_free(&cctx->cmd);
@@ -1358,7 +1397,9 @@ client_process_buffered_input_packets(void)
 static int
 simple_escape_filter(Channel *c, char *buf, int len)
 {
-	/* XXX we assume c->extended is writeable */
+	if (c->extended_usage != CHAN_EXTENDED_WRITE)
+		return 0;
+
 	return process_escapes(&c->input, &c->output, &c->extended, buf, len);
 }
 
@@ -1948,8 +1989,7 @@ client_input_global_request(int type, u_int32_t seq, void *ctxt)
 
 void
 client_session2_setup(int id, int want_tty, int want_subsystem,
-    const char *term, struct termios *tiop, int in_fd, Buffer *cmd, char **env,
-    dispatch_fn *subsys_repl)
+    const char *term, struct termios *tiop, int in_fd, Buffer *cmd, char **env)
 {
 	int len;
 	Channel *c = NULL;
@@ -1967,7 +2007,8 @@ client_session2_setup(int id, int want_tty, int want_subsystem,
 		if (ioctl(in_fd, TIOCGWINSZ, &ws) < 0)
 			memset(&ws, 0, sizeof(ws));
 
-		channel_request_start(id, "pty-req", 0);
+		channel_request_start(id, "pty-req", 1);
+		client_expect_confirm(id, "PTY allocation", 0);
 		packet_put_cstring(term != NULL ? term : "");
 		packet_put_int((u_int)ws.ws_col);
 		packet_put_int((u_int)ws.ws_row);
@@ -2022,22 +2063,21 @@ client_session2_setup(int id, int want_tty, int want_subsystem,
 		if (len > 900)
 			len = 900;
 		if (want_subsystem) {
-			debug("Sending subsystem: %.*s", len, (u_char*)buffer_ptr(cmd));
-			channel_request_start(id, "subsystem", subsys_repl != NULL);
-			if (subsys_repl != NULL) {
-				/* register callback for reply */
-				/* XXX we assume that client_loop has already been called */
-				dispatch_set(SSH2_MSG_CHANNEL_FAILURE, subsys_repl);
-				dispatch_set(SSH2_MSG_CHANNEL_SUCCESS, subsys_repl);
-			}
+			debug("Sending subsystem: %.*s",
+			    len, (u_char*)buffer_ptr(cmd));
+			channel_request_start(id, "subsystem", 1);
+			client_expect_confirm(id, "subsystem", 1);
 		} else {
-			debug("Sending command: %.*s", len, (u_char*)buffer_ptr(cmd));
-			channel_request_start(id, "exec", 0);
+			debug("Sending command: %.*s",
+			    len, (u_char*)buffer_ptr(cmd));
+			channel_request_start(id, "exec", 1);
+			client_expect_confirm(id, "exec", 1);
 		}
 		packet_put_string(buffer_ptr(cmd), buffer_len(cmd));
 		packet_send();
 	} else {
-		channel_request_start(id, "shell", 0);
+		channel_request_start(id, "shell", 1);
+		client_expect_confirm(id, "shell", 1);
 		packet_send();
 	}
 }
diff --git a/usr.bin/ssh/clientloop.h b/usr.bin/ssh/clientloop.h
index c7d2233d03a..cb2d7c08949 100644
--- a/usr.bin/ssh/clientloop.h
+++ b/usr.bin/ssh/clientloop.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.h,v 1.17 2007/08/07 07:32:53 djm Exp $ */
+/* $OpenBSD: clientloop.h,v 1.18 2008/05/08 13:06:11 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -43,7 +43,7 @@ void	 client_x11_get_proto(const char *, const char *, u_int,
 	    char **, char **);
 void	 client_global_request_reply_fwd(int, u_int32_t, void *);
 void	 client_session2_setup(int, int, int, const char *, struct termios *,
-	    int, Buffer *, char **, dispatch_fn *);
+	    int, Buffer *, char **);
 int	 client_request_tun_fwd(int, int, int);
 
 /* Multiplexing protocol version */
diff --git a/usr.bin/ssh/ssh.c b/usr.bin/ssh/ssh.c
index 7e110641b61..d6cd504f1af 100644
--- a/usr.bin/ssh/ssh.c
+++ b/usr.bin/ssh/ssh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.310 2008/05/08 12:02:23 djm Exp $ */
+/* $OpenBSD: ssh.c,v 1.311 2008/05/08 13:06:11 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1019,21 +1019,6 @@ ssh_session(void)
 	    options.escape_char : SSH_ESCAPECHAR_NONE, 0);
 }
 
-static void
-ssh_subsystem_reply(int type, u_int32_t seq, void *ctxt)
-{
-	int id, len;
-
-	id = packet_get_int();
-	len = buffer_len(&command);
-	if (len > 900)
-		len = 900;
-	packet_check_eom();
-	if (type == SSH2_MSG_CHANNEL_FAILURE)
-		fatal("Request for subsystem '%.*s' failed on channel %d",
-		    len, (u_char *)buffer_ptr(&command), id);
-}
-
 void
 client_global_request_reply_fwd(int type, u_int32_t seq, void *ctxt)
 {
@@ -1129,7 +1114,7 @@ ssh_session2_setup(int id, void *arg)
 	}
 
 	client_session2_setup(id, tty_flag, subsystem_flag, getenv("TERM"),
-	    NULL, fileno(stdin), &command, environ, &ssh_subsystem_reply);
+	    NULL, fileno(stdin), &command, environ);
 
 	packet_set_interactive(interactive);
 }