Avoid trying to take the modular inverse of zero in response to a

[u/mdw/putty] / sshdss.c

diff --git a/sshdss.c b/sshdss.c
index eba03aa..3ea3695 100644 (file)
--- a/sshdss.c
+++ b/sshdss.c
@@ -268,8 +268,19 @@ static int dss_verifysig(void *key, char *sig, int siglen,
     }
     r = get160(&sig, &siglen);
     s = get160(&sig, &siglen);
-    if (!r || !s)
+    if (!r || !s) {
+        if (r)
+            freebn(r);
+        if (s)
+            freebn(s);
        return 0;
+    }
+
+    if (!bignum_cmp(s, Zero)) {
+        freebn(r);
+        freebn(s);
+        return 0;
+    }
 
     /*
      * Step 1. w <- s^-1 mod q.
@@ -624,6 +635,7 @@ static unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen)
     s = modmul(kinv, hxr, dss->q);     /* s = k^-1 * (hash + x*r) mod q */
     freebn(hxr);
     freebn(kinv);
+    freebn(k);
     freebn(hash);
 
     /*