From e9405983dc1cf9399e560e70f7c681ba62e09131 Mon Sep 17 00:00:00 2001
From: Darren Tucker <dtucker@zip.com.au>
Date: Sun, 20 May 2007 15:09:04 +1000
Subject: [PATCH]    - djm@cvs.openbsd.org 2007/05/17 07:55:29     
 [sftp-server.c]      bz#1286 stop reading and processing commands when input
 or output buffer      is nearly full, otherwise sftp-server would happily try
 to grow the      input/output buffers past the maximum supported by the
 buffer API and      promptly fatal()      based on patch from Thue Janus
 Kristensen; feedback & ok dtucker@

---
 ChangeLog     |  9 ++++++++-
 sftp-server.c | 25 +++++++++++++++++++------
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index c189c7810..2bc077cf7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -15,6 +15,13 @@
    - djm@cvs.openbsd.org 2007/05/17 07:50:31
      [log.c]
      save and restore errno when logging; ok deraadt@
+   - djm@cvs.openbsd.org 2007/05/17 07:55:29
+     [sftp-server.c]
+     bz#1286 stop reading and processing commands when input or output buffer
+     is nearly full, otherwise sftp-server would happily try to grow the
+     input/output buffers past the maximum supported by the buffer API and
+     promptly fatal()
+     based on patch from Thue Janus Kristensen; feedback & ok dtucker@
 
 20070509
  - (tim) [configure.ac] Bug #1287: Add missing test for ucred.h.
@@ -2915,4 +2922,4 @@
    OpenServer 6 and add osr5bigcrypt support so when someone migrates
    passwords between UnixWare and OpenServer they will still work. OK dtucker@
 
-$Id: ChangeLog,v 1.4664 2007/05/20 05:08:15 dtucker Exp $
+$Id: ChangeLog,v 1.4665 2007/05/20 05:09:04 dtucker Exp $
diff --git a/sftp-server.c b/sftp-server.c
index d68584b52..76edebc5a 100644
--- a/sftp-server.c
+++ b/sftp-server.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sftp-server.c,v 1.72 2007/04/18 01:12:43 stevesk Exp $ */
+/* $OpenBSD: sftp-server.c,v 1.73 2007/05/17 07:55:29 djm Exp $ */
 /*
  * Copyright (c) 2000-2004 Markus Friedl.  All rights reserved.
  *
@@ -1214,7 +1214,7 @@ main(int argc, char **argv)
 	int in, out, max, ch, skipargs = 0, log_stderr = 0;
 	ssize_t len, olen, set_size;
 	SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
-	char *cp;
+	char *cp, buf[4*4096];
 
 	extern char *optarg;
 	extern char *__progname;
@@ -1298,7 +1298,15 @@ main(int argc, char **argv)
 		memset(rset, 0, set_size);
 		memset(wset, 0, set_size);
 
-		FD_SET(in, rset);
+		/*
+		 * Ensure that we can read a full buffer and handle
+		 * the worst-case length packet it can generate,
+		 * otherwise apply backpressure by stopping reads.
+		 */
+		if (buffer_check_alloc(&iqueue, sizeof(buf)) &&
+		    buffer_check_alloc(&oqueue, SFTP_MAX_MSG_LENGTH))
+			FD_SET(in, rset);
+
 		olen = buffer_len(&oqueue);
 		if (olen > 0)
 			FD_SET(out, wset);
@@ -1312,7 +1320,6 @@ main(int argc, char **argv)
 
 		/* copy stdin to iqueue */
 		if (FD_ISSET(in, rset)) {
-			char buf[4*4096];
 			len = read(in, buf, sizeof buf);
 			if (len == 0) {
 				debug("read eof");
@@ -1334,7 +1341,13 @@ main(int argc, char **argv)
 				buffer_consume(&oqueue, len);
 			}
 		}
-		/* process requests from client */
-		process();
+
+		/*
+		 * Process requests from client if we can fit the results
+		 * into the output buffer, otherwise stop processing input
+		 * and let the output queue drain.
+		 */
+		if (buffer_check_alloc(&oqueue, SFTP_MAX_MSG_LENGTH))
+			process();
 	}
 }