File 0025-Fix-bounds-check-in-read_key.patch of Package openvpn.15874

From fce34375295151f548a26c2d0eb30141e427c81a Mon Sep 17 00:00:00 2001
From: Steffan Karger <steffan.karger@fox-it.com>
Date: Tue, 15 Aug 2017 10:04:33 +0200
Subject: [PATCH] Fix bounds check in read_key()

The bounds check in read_key() was performed after using the value, instead
of before.  If 'key-method 1' is used, this allowed an attacker to send a
malformed packet to trigger a stack buffer overflow.

Fix this by moving the input validation to before the writes.

Note that 'key-method 1' has been replaced by 'key method 2' as the default
in OpenVPN 2.0 (released on 2005-04-17), and explicitly deprecated in 2.4
and marked for removal in 2.5.  This should limit the amount of users
impacted by this issue.

CVE: 2017-12166
Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Acked-by: David Sommerseth <davids@openvpn.net>
Message-Id: <80690690-67ac-3320-1891-9fecedc6a1fa@fox-it.com>
URL: https://www.mail-archive.com/search?l=mid&q=80690690-67ac-3320-1891-9fecedc6a1fa@fox-it.com
Signed-off-by: David Sommerseth <davids@openvpn.net>
(backport of git master commit 3b1a61e9fb27213c46f76312f4065816bee8ed01)
---
 src/openvpn/crypto.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/openvpn/crypto.c b/src/openvpn/crypto.c
index 517d9a70..2a59f0ff 100644
--- a/src/openvpn/crypto.c
+++ b/src/openvpn/crypto.c
@@ -1294,13 +1294,14 @@ read_key (struct key *key, const struct key_type *kt, struct buffer *buf)
   if (!buf_read (buf, &hmac_length, 1))
     goto read_err;
 
+  if (cipher_length != kt->cipher_length || hmac_length != kt->hmac_length)
+    goto key_len_err;
+
   if (!buf_read (buf, key->cipher, cipher_length))
     goto read_err;
   if (!buf_read (buf, key->hmac, hmac_length))
     goto read_err;
 
-  if (cipher_length != kt->cipher_length || hmac_length != kt->hmac_length)
-    goto key_len_err;
 
   return 1;
 
-- 
2.13.6