From: simon <simon@cda61777-01e9-0310-a592-d414129be87e>
Date: Sun, 4 Aug 2013 19:33:49 +0000 (+0000)
Subject: Validate newly created DSA keys more carefully. Don't want a structure
X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/commitdiff_plain/36a70e5cb235ac7c3c1e18b535c3b31695785f8c

Validate newly created DSA keys more carefully. Don't want a structure
half-filled with null pointers.


git-svn-id: svn://svn.tartarus.org/sgt/putty@9986 cda61777-01e9-0310-a592-d414129be87e
---

diff --git a/sshdss.c b/sshdss.c
index e634b984..eba03aa8 100644
--- a/sshdss.c
+++ b/sshdss.c
@@ -82,6 +82,8 @@ static Bignum get160(char **data, int *datalen)
     return b;
 }
 
+static void dss_freekey(void *key);    /* forward reference */
+
 static void *dss_newkey(char *data, int len)
 {
     char *p;
@@ -111,6 +113,13 @@ static void *dss_newkey(char *data, int len)
     dss->y = getmp(&data, &len);
     dss->x = NULL;
 
+    if (!dss->p || !dss->q || !dss->g || !dss->y ||
+        !bignum_cmp(dss->q, Zero) || !bignum_cmp(dss->p, Zero)) {
+        /* Invalid key. */
+        dss_freekey(dss);
+        return NULL;
+    }
+
     return dss;
 }
 
@@ -389,7 +398,13 @@ static void *dss_createkey(unsigned char *pub_blob, int pub_len,
     Bignum ytest;
 
     dss = dss_newkey((char *) pub_blob, pub_len);
+    if (!dss)
+        return NULL;
     dss->x = getmp(&pb, &priv_len);
+    if (!dss->x) {
+        dss_freekey(dss);
+        return NULL;
+    }
 
     /*
      * Check the obsolete hash in the old DSS key format.
@@ -435,14 +450,11 @@ static void *dss_openssh_createkey(unsigned char **blob, int *len)
     dss->y = getmp(b, len);
     dss->x = getmp(b, len);
 
-    if (!dss->p || !dss->q || !dss->g || !dss->y || !dss->x) {
-	freebn(dss->p);
-	freebn(dss->q);
-	freebn(dss->g);
-	freebn(dss->y);
-	freebn(dss->x);
-	sfree(dss);
-	return NULL;
+    if (!dss->p || !dss->q || !dss->g || !dss->y || !dss->x ||
+        !bignum_cmp(dss->q, Zero) || !bignum_cmp(dss->p, Zero)) {
+        /* Invalid key. */
+        dss_freekey(dss);
+        return NULL;
     }
 
     return dss;
@@ -482,6 +494,8 @@ static int dss_pubkey_bits(void *blob, int len)
     int ret;
 
     dss = dss_newkey((char *) blob, len);
+    if (!dss)
+        return -1;
     ret = bignum_bitcount(dss->p);
     dss_freekey(dss);