From: simon <simon@cda61777-01e9-0310-a592-d414129be87e>
Date: Sun, 4 Aug 2013 19:34:00 +0000 (+0000)
Subject: Avoid trying to take the modular inverse of zero in response to a
X-Git-Url: https://git.distorted.org.uk/~mdw/sgt/putty/commitdiff_plain/919e9a53e43da0082f704b860fa70796c83f3c60

Avoid trying to take the modular inverse of zero in response to a
sufficiently silly DSA signature.


git-svn-id: svn://svn.tartarus.org/sgt/putty@9989 cda61777-01e9-0310-a592-d414129be87e
---

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.
      */