Fix CVE-2018-20685:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-20685

Patch copied from upstream source repository:

https://github.com/openssh/openssh-portable/commit/6010c0303a422a9c5fa8860c061bf7105eb7f8b2

From 6010c0303a422a9c5fa8860c061bf7105eb7f8b2 Mon Sep 17 00:00:00 2001
From: "djm@openbsd.org" <djm@openbsd.org>
Date: Fri, 16 Nov 2018 03:03:10 +0000
Subject: [PATCH] upstream: disallow empty incoming filename or ones that refer
 to the

current directory; based on report/patch from Harry Sintonen

OpenBSD-Commit-ID: f27651b30eaee2df49540ab68d030865c04f6de9
---
 scp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/scp.c b/scp.c
index 60682c68..4f3fdcd3 100644
--- a/scp.c
+++ b/scp.c
#@@ -1,4 +1,4 @@
#-/* $OpenBSD: scp.c,v 1.197 2018/06/01 04:31:48 dtucker Exp $ */
#+/* $OpenBSD: scp.c,v 1.198 2018/11/16 03:03:10 djm Exp $ */
# /*
#  * scp - secure remote copy.  This is basically patched BSD rcp which
#  * uses ssh to do the data transfer (instead of using rcmd).
@@ -1106,7 +1106,8 @@ sink(int argc, char **argv)
 			SCREWUP("size out of range");
 		size = (off_t)ull;
 
-		if ((strchr(cp, '/') != NULL) || (strcmp(cp, "..") == 0)) {
+		if (*cp == '\0' || strchr(cp, '/') != NULL ||
+		    strcmp(cp, ".") == 0 || strcmp(cp, "..") == 0) {
 			run_err("error: unexpected filename: %s", cp);
 			exit(1);
 		}
-- 
2.20.1

