commit 2341f716198fa90193e040b3fdb16959a47c6c27
Author: Steffan Karger <steffan.karger@fox-it.com>
Date:   Mon Jun 19 11:28:38 2017 +0200

    Fix remote-triggerable memory leaks (CVE-2017-7521)
    
    Several of our OpenSSL-specific certificate-parsing code paths did not
    always clear all allocated memory.  Since a client can cause a few bytes
    of memory to be leaked for each connection attempt, a client can cause a
    server to run out of memory and thereby kill the server.  That makes this
    a (quite inefficient) DoS attack.
    
    When using the --x509-alt-username option on openssl builds with an
    extension (argument prefixed with "ext:", e.g. "ext:subjectAltName"), the
    code would not free all allocated memory.  Fix this by using the proper
    free function.
    
    If ASN1_STRING_to_UTF8() returns 0, it didn't fail and *did* allocate
    memory.  So also free the returned buffer if it returns 0.
    
    These issues were found, analysed and reported to the OpenVPN team by Guido
    Vranken.
    
    CVE: 2017-7521
    Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
    Acked-by: Gert Doering <gert@greenie.muc.de>
    Acked-by: David Sommerseth <davids@openvpn.net>
    Acked-by: Guido Vranken <guidovranken@gmail.com>
    Message-Id: <1497864520-12219-4-git-send-email-steffan.karger@fox-it.com>
    URL: https://www.mail-archive.com/search?l=mid&q=1497864520-12219-4-git-send-email-steffan.karger@fox-it.com
    Signed-off-by: Gert Doering <gert@greenie.muc.de>
    (cherry picked from commit 2d032c7fcdfd692c851ea2fa858b4c2d9ea7d52d)

Index: openvpn-2.4.0/src/openvpn/ssl_verify_openssl.c
===================================================================
--- openvpn-2.4.0.orig/src/openvpn/ssl_verify_openssl.c
+++ openvpn-2.4.0/src/openvpn/ssl_verify_openssl.c
@@ -165,7 +165,7 @@ extract_x509_extension(X509 *cert, char
                     break;
             }
         }
-        sk_GENERAL_NAME_free(extensions);
+        GENERAL_NAMES_free(extensions);
     }
     return retval;
 }
@@ -218,8 +218,7 @@ extract_x509_field_ssl(X509_NAME *x509,
     {
         return FAILURE;
     }
-    tmp = ASN1_STRING_to_UTF8(&buf, asn1);
-    if (tmp <= 0)
+    if (ASN1_STRING_to_UTF8(&buf, asn1) < 0)
     {
         return FAILURE;
     }
@@ -460,7 +459,7 @@ x509_setenv_track(const struct x509_trac
                             ASN1_STRING *val = X509_NAME_ENTRY_get_data(ent);
                             unsigned char *buf;
                             buf = (unsigned char *)1; /* bug in OpenSSL 0.9.6b ASN1_STRING_to_UTF8 requires this workaround */
-                            if (ASN1_STRING_to_UTF8(&buf, val) > 0)
+                            if (ASN1_STRING_to_UTF8(&buf, val) >= 0)
                             {
                                 do_setenv_x509(es, xt->name, (char *)buf, depth);
                                 OPENSSL_free(buf);
@@ -548,7 +547,7 @@ x509_setenv(struct env_set *es, int cert
             continue;
         }
         buf = (unsigned char *)1; /* bug in OpenSSL 0.9.6b ASN1_STRING_to_UTF8 requires this workaround */
-        if (ASN1_STRING_to_UTF8(&buf, val) <= 0)
+        if (ASN1_STRING_to_UTF8(&buf, val) < 0)
         {
             continue;
         }