upstream: cap channel input buffer size at 16MB; avoids high memory use

when peer advertises a large window but is slow to consume the data we send
(e.g. because of a slow network)

reported by Pierre-Yves David

fix with & ok markus@

OpenBSD-Commit-ID: 1452771f5e5e768876d3bfe2544e3866d6ade216

2 files changed, 8 insertions, 2 deletions

diff --git a/channels.c b/channels.c
index 71c94f6cc..e4917f3c9 100644
--- a/channels.c
+++ b/channels.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.c,v 1.401 2020/07/03 07:25:18 djm Exp $ */
+/* $OpenBSD: channels.c,v 1.402 2020/09/20 05:47:25 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -354,6 +354,7 @@ channel_new(struct ssh *ssh, char *ctype, int type, int rfd, int wfd, int efd,
         struct ssh_channels *sc = ssh->chanctxt;
         u_int i, found;
         Channel *c;
+        int r;
 
         /* Try to find a free slot where to put the new channel. */
         for (i = 0; i < sc->channels_alloc; i++) {
@@ -383,6 +384,8 @@ channel_new(struct ssh *ssh, char *ctype, int type, int rfd, int wfd, int efd,
             (c->output = sshbuf_new()) == NULL ||
             (c->extended = sshbuf_new()) == NULL)
                 fatal("%s: sshbuf_new failed", __func__);
+        if ((r = sshbuf_set_max_size(c->input, CHAN_INPUT_MAX)) != 0)
+                fatal("%s: sshbuf_set_max_size: %s", __func__, ssh_err(r));
         c->ostate = CHAN_OUTPUT_OPEN;
         c->istate = CHAN_INPUT_OPEN;
         channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, 0);
diff --git a/channels.h b/channels.h
index ee818880e..74e9b3f87 100644
--- a/channels.h
+++ b/channels.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.h,v 1.134 2020/07/05 23:59:45 djm Exp $ */
+/* $OpenBSD: channels.h,v 1.135 2020/09/20 05:47:25 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -223,6 +223,9 @@ struct Channel {
 /* Read buffer size */
 #define CHAN_RBUF       (16*1024)
 
+/* Maximum channel input buffer size */
+#define CHAN_INPUT_MAX  (16*1024*1024)
+
 /* Hard limit on number of channels */
 #define CHANNELS_MAX_CHANNELS   (16*1024)