upstream: When clients get denied by MaxStartups, send a

noification prior to the SSH2 protocol banner according to RFC4253 section
4.2.  ok djm@ deraadt@ markus@

OpenBSD-Commit-ID: e5dabcb722d54dea18eafb336d50b733af4f9c63

1 files changed, 4 insertions, 1 deletions

diff --git a/sshd.c b/sshd.c
index e782a99f2..9d193c9eb 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.539 2019/10/31 21:23:19 djm Exp $ */
+/* $OpenBSD: sshd.c,v 1.540 2019/11/13 11:25:11 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1154,6 +1154,7 @@ server_accept_loop(int *sock_in, int *sock_out, int *newsock, int *config_s)
                         if (drop_connection(startups) == 1) {
                                 char *laddr = get_local_ipaddr(*newsock);
                                 char *raddr = get_peer_ipaddr(*newsock);
+                                char msg[] = "Exceeded MaxStartups\r\n";
 
                                 verbose("drop connection #%d from [%s]:%d "
                                     "on [%s]:%d past MaxStartups", startups,
@@ -1161,6 +1162,8 @@ server_accept_loop(int *sock_in, int *sock_out, int *newsock, int *config_s)
                                     laddr, get_local_port(*newsock));
                                 free(laddr);
                                 free(raddr);
+                                /* best-effort notification to client */
+                                (void)write(*newsock, msg, strlen(msg));
                                 close(*newsock);
                                 continue;
                         }