openssh: add openwrt failsafe support

Adds failsafe support to the openssh package.
Roughly based on an earlier patch.

Ref: https://github.com/openwrt/openwrt/pull/865
Signed-off-by: Jeff Kletsky <git-commits@allycomm.com>
Signed-off-by: Kyle Copperfield <kmcopper@danwin1210.me>

net/openssh/files/sshd.failsafe

@@ -0,0 +1,30 @@
+#!/bin/sh
+
+failsafe_sshd () {
+
+	# if dropbear is executable it can handle failsafe
+	[ -x /usr/sbin/dropbear ] && return
+
+	sshd_tmpdir=/tmp/sshd
+	mkdir $sshd_tmpdir
+
+	sed -i 's/^root:.*/root::0:17000:::::/g' /etc/shadow
+
+	for type in ed25519; do
+		key=$sshd_tmpdir/ssh_host_${type}_key
+		ssh-keygen -N '' -t ${type} -f ${key}
+	done
+
+	mkdir -m 0700 -p /var/empty
+
+	cat > $sshd_tmpdir/sshd_config <<EOF
+HostKey $sshd_tmpdir/ssh_host_ed25519_key
+PermitRootLogin	yes
+PermitEmptyPasswords yes
+EOF
+
+	/usr/sbin/sshd -f $sshd_tmpdir/sshd_config -E $sshd_tmpdir/sshd.log
+
+}
+
+boot_hook_add failsafe failsafe_sshd