From 9c054cf467e357fd9f61cc6217962c3f85635d7a Mon Sep 17 00:00:00 2001
From: Simon Tatham <anakin@pobox.com>
Date: Sun, 4 Aug 2013 19:34:00 +0000
Subject: [PATCH] Avoid trying to take the modular inverse of zero in response
 to a sufficiently silly DSA signature.

[originally from svn r9989]
---
 sshdss.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sshdss.c b/sshdss.c
index bf6c3ba5..3ea36952 100644
--- a/sshdss.c
+++ b/sshdss.c
@@ -276,6 +276,12 @@ static int dss_verifysig(void *key, char *sig, int siglen,
 	return 0;
     }
 
+    if (!bignum_cmp(s, Zero)) {
+        freebn(r);
+        freebn(s);
+        return 0;
+    }
+
     /*
      * Step 1. w <- s^-1 mod q.
      */
-- 
2.45.2