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@

1 files changed, 19 insertions, 6 deletions

diff --git a/usr.bin/ssh/sftp-server.c b/usr.bin/ssh/sftp-server.c
index 6122ed0eabe..632c331d0d2 100644
--- a/usr.bin/ssh/sftp-server.c
+++ b/usr.bin/ssh/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.
  *
@@ -1193,7 +1193,7 @@ 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;
@@ -1271,7 +1271,15 @@ 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);
@@ -1285,7 +1293,6 @@ 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");
@@ -1307,7 +1314,13 @@ 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();
 	}
 }