From: Matt Caswell <matt@openssl.org>
Date: Fri, 9 Sep 2016 09:08:45 +0000 (+0100)
Subject: Fix OCSP Status Request extension unbounded memory growth
X-Git-Tag: OpenSSL_1_0_1u~3
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=2c0d295e26306e15a92eb23a84a1802005c1c137;p=oweals%2Fopenssl.git

Fix OCSP Status Request extension unbounded memory growth

A malicious client can send an excessively large OCSP Status Request
extension. If that client continually requests renegotiation,
sending a large OCSP Status Request extension each time, then there will
be unbounded memory growth on the server. This will eventually lead to a
Denial Of Service attack through memory exhaustion. Servers with a
default configuration are vulnerable even if they do not support OCSP.
Builds using the "no-ocsp" build time option are not affected.

I have also checked other extensions to see if they suffer from a similar
problem but I could not find any other issues.

CVE-2016-6304

Issue reported by Shi Lei.

Reviewed-by: Rich Salz <rsalz@openssl.org>
---

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 7680491340..4bc13ca5ce 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -1284,6 +1284,23 @@ int ssl_parse_clienthello_tlsext(SSL *s, unsigned char **p,
                 size -= 2;
                 if (dsize > size)
                     goto err;
+
+                /*
+                 * We remove any OCSP_RESPIDs from a previous handshake
+                 * to prevent unbounded memory growth - CVE-2016-6304
+                 */
+                sk_OCSP_RESPID_pop_free(s->tlsext_ocsp_ids,
+                                        OCSP_RESPID_free);
+                if (dsize > 0) {
+                    s->tlsext_ocsp_ids = sk_OCSP_RESPID_new_null();
+                    if (s->tlsext_ocsp_ids == NULL) {
+                        *al = SSL_AD_INTERNAL_ERROR;
+                        return 0;
+                    }
+                } else {
+                    s->tlsext_ocsp_ids = NULL;
+                }
+
                 while (dsize > 0) {
                     OCSP_RESPID *id;
                     int idsize;
@@ -1303,13 +1320,6 @@ int ssl_parse_clienthello_tlsext(SSL *s, unsigned char **p,
                         OCSP_RESPID_free(id);
                         goto err;
                     }
-                    if (!s->tlsext_ocsp_ids
-                        && !(s->tlsext_ocsp_ids =
-                             sk_OCSP_RESPID_new_null())) {
-                        OCSP_RESPID_free(id);
-                        *al = SSL_AD_INTERNAL_ERROR;
-                        return 0;
-                    }
                     if (!sk_OCSP_RESPID_push(s->tlsext_ocsp_ids, id)) {
                         OCSP_RESPID_free(id);
                         *al = SSL_AD_INTERNAL_ERROR;