upstream: make channel_output_poll() return a flag indicating

whether channel data was enqueued. Will be used to improve keystroke timing
obfuscation. Problem spotted by / tested by naddy@

OpenBSD-Commit-ID: f9776c7b0065ba7c3bbe50431fd3b629f44314d0

2 files changed, 24 insertions, 15 deletions

diff --git a/channels.c b/channels.c
index da66b7b3..598ff322 100644
--- a/channels.c
+++ b/channels.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.c,v 1.432 2023/07/04 03:59:21 dlg Exp $ */
+/* $OpenBSD: channels.c,v 1.433 2023/09/04 00:01:46 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -2890,8 +2890,9 @@ channel_after_poll(struct ssh *ssh, struct pollfd *pfd, u_int npfd)
 
 /*
  * Enqueue data for channels with open or draining c->input.
+ * Returns non-zero if a packet was enqueued.
  */
-static void
+static int
 channel_output_poll_input_open(struct ssh *ssh, Channel *c)
 {
 	size_t len, plen;
@@ -2914,7 +2915,7 @@ channel_output_poll_input_open(struct ssh *ssh, Channel *c)
 			else
 				chan_ibuf_empty(ssh, c);
 		}
-		return;
+		return 0;
 	}
 
 	if (!c->have_remote_id)
@@ -2931,7 +2932,7 @@ channel_output_poll_input_open(struct ssh *ssh, Channel *c)
 		 */
 		if (plen > c->remote_window || plen > c->remote_maxpacket) {
 			debug("channel %d: datagram too big", c->self);
-			return;
+			return 0;
 		}
 		/* Enqueue it */
 		if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
@@ -2940,7 +2941,7 @@ channel_output_poll_input_open(struct ssh *ssh, Channel *c)
 		    (r = sshpkt_send(ssh)) != 0)
 			fatal_fr(r, "channel %i: send datagram", c->self);
 		c->remote_window -= plen;
-		return;
+		return 1;
 	}
 
 	/* Enqueue packet for buffered data. */
@@ -2949,7 +2950,7 @@ channel_output_poll_input_open(struct ssh *ssh, Channel *c)
 	if (len > c->remote_maxpacket)
 		len = c->remote_maxpacket;
 	if (len == 0)
-		return;
+		return 0;
 	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
 	    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
 	    (r = sshpkt_put_string(ssh, sshbuf_ptr(c->input), len)) != 0 ||
@@ -2958,19 +2959,21 @@ channel_output_poll_input_open(struct ssh *ssh, Channel *c)
 	if ((r = sshbuf_consume(c->input, len)) != 0)
 		fatal_fr(r, "channel %i: consume", c->self);
 	c->remote_window -= len;
+	return 1;
 }
 
 /*
  * Enqueue data for channels with open c->extended in read mode.
+ * Returns non-zero if a packet was enqueued.
  */
-static void
+static int
 channel_output_poll_extended_read(struct ssh *ssh, Channel *c)
 {
 	size_t len;
 	int r;
 
 	if ((len = sshbuf_len(c->extended)) == 0)
-		return;
+		return 0;
 
 	debug2("channel %d: rwin %u elen %zu euse %d", c->self,
 	    c->remote_window, sshbuf_len(c->extended), c->extended_usage);
@@ -2979,7 +2982,7 @@ channel_output_poll_extended_read(struct ssh *ssh, Channel *c)
 	if (len > c->remote_maxpacket)
 		len = c->remote_maxpacket;
 	if (len == 0)
-		return;
+		return 0;
 	if (!c->have_remote_id)
 		fatal_f("channel %d: no remote id", c->self);
 	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_EXTENDED_DATA)) != 0 ||
@@ -2992,15 +2995,20 @@ channel_output_poll_extended_read(struct ssh *ssh, Channel *c)
 		fatal_fr(r, "channel %i: consume", c->self);
 	c->remote_window -= len;
 	debug2("channel %d: sent ext data %zu", c->self, len);
+	return 1;
 }
 
-/* If there is data to send to the connection, enqueue some of it now. */
-void
+/*
+ * If there is data to send to the connection, enqueue some of it now.
+ * Returns non-zero if data was enqueued.
+ */
+int
 channel_output_poll(struct ssh *ssh)
 {
 	struct ssh_channels *sc = ssh->chanctxt;
 	Channel *c;
 	u_int i;
+	int ret = 0;
 
 	for (i = 0; i < sc->channels_alloc; i++) {
 		c = sc->channels[i];
@@ -3023,12 +3031,13 @@ channel_output_poll(struct ssh *ssh)
 		/* Get the amount of buffered data for this channel. */
 		if (c->istate == CHAN_INPUT_OPEN ||
 		    c->istate == CHAN_INPUT_WAIT_DRAIN)
-			channel_output_poll_input_open(ssh, c);
+			ret |= channel_output_poll_input_open(ssh, c);
 		/* Send extended data, i.e. stderr */
 		if (!(c->flags & CHAN_EOF_SENT) &&
 		    c->extended_usage == CHAN_EXTENDED_READ)
-			channel_output_poll_extended_read(ssh, c);
+			ret |= channel_output_poll_extended_read(ssh, c);
 	}
+	return ret;
 }
 
 /* -- mux proxy support  */
diff --git a/channels.h b/channels.h
index 7afba783..58019a84 100644
--- a/channels.h
+++ b/channels.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.h,v 1.151 2023/07/04 03:59:21 dlg Exp $ */
+/* $OpenBSD: channels.h,v 1.152 2023/09/04 00:01:46 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -335,7 +335,7 @@ struct timespec;
 void	 channel_prepare_poll(struct ssh *, struct pollfd **,
 	    u_int *, u_int *, u_int, struct timespec *);
 void	 channel_after_poll(struct ssh *, struct pollfd *, u_int);
-void     channel_output_poll(struct ssh *);
+int	 channel_output_poll(struct ssh *);
 
 int      channel_not_very_much_buffered_data(struct ssh *);
 void     channel_close_all(struct ssh *);