- djm@cvs.openbsd.org 2013/10/29 09:42:11

     [key.c key.h]
     fix potential stack exhaustion caused by nested certificates;
     report by Mateusz Kocielski; ok dtucker@ markus@

1 files changed, 29 insertions, 16 deletions

diff --git a/key.c b/key.c
index 55ee78998..90f0a0173 100644
--- a/key.c
+++ b/key.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: key.c,v 1.104 2013/05/19 02:42:42 djm Exp $ */
+/* $OpenBSD: key.c,v 1.105 2013/10/29 09:42:11 djm Exp $ */
 /*
  * read_bignum():
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -56,6 +56,7 @@
 #include "ssh2.h"
 
 static int to_blob(const Key *, u_char **, u_int *, int);
+static Key *key_from_blob2(const u_char *, u_int, int);
 
 static struct KeyCert *
 cert_new(void)
@@ -1023,6 +1024,18 @@ key_alg_list(void)
         return ret;
 }
 
+int
+key_type_is_cert(int type)
+{
+        const struct keytype *kt;
+
+        for (kt = keytypes; kt->type != -1; kt++) {
+                if (kt->type == type)
+                        return kt->cert;
+        }
+        return 0;
+}
+
 u_int
 key_size(const Key *k)
 {
@@ -1387,8 +1400,8 @@ cert_parse(Buffer *b, Key *key, const u_char *blob, u_int blen)
         }
         buffer_clear(&tmp);
 
-        if ((key->cert->signature_key = key_from_blob(sig_key,
-            sklen)) == NULL) {
+        if ((key->cert->signature_key = key_from_blob2(sig_key, sklen, 0))
+            == NULL) {
                 error("%s: Signature key invalid", __func__);
                 goto out;
         }
@@ -1425,8 +1438,8 @@ cert_parse(Buffer *b, Key *key, const u_char *blob, u_int blen)
         return ret;
 }
 
-Key *
-key_from_blob(const u_char *blob, u_int blen)
+static Key *
+key_from_blob2(const u_char *blob, u_int blen, int allow_cert)
 {
         Buffer b;
         int rlen, type;
@@ -1452,7 +1465,10 @@ key_from_blob(const u_char *blob, u_int blen)
         if (key_type_plain(type) == KEY_ECDSA)
                 nid = key_ecdsa_nid_from_name(ktype);
 #endif
-
+        if (!allow_cert && key_type_is_cert(type)) {
+                error("key_from_blob: certificate not allowed in this context");
+                goto out;
+        }
         switch (type) {
         case KEY_RSA_CERT:
                 (void)buffer_get_string_ptr_ret(&b, NULL); /* Skip nonce */
@@ -1551,6 +1567,12 @@ key_from_blob(const u_char *blob, u_int blen)
         return key;
 }
 
+Key *
+key_from_blob(const u_char *blob, u_int blen)
+{
+        return key_from_blob2(blob, blen, 1);
+}
+
 static int
 to_blob(const Key *key, u_char **blobp, u_int *lenp, int force_plain)
 {
@@ -1747,16 +1769,7 @@ key_is_cert(const Key *k)
 {
         if (k == NULL)
                 return 0;
-        switch (k->type) {
-        case KEY_RSA_CERT_V00:
-        case KEY_DSA_CERT_V00:
-        case KEY_RSA_CERT:
-        case KEY_DSA_CERT:
-        case KEY_ECDSA_CERT:
-                return 1;
-        default:
-                return 0;
-        }
+        return key_type_is_cert(k->type);
 }
 
 /* Return the cert-less equivalent to a certified key type */